The glider had been prepared for its first flight of the day and found airworthy. The pilot was considered to be competent and had been trained in all emergency procedures pertaining to winch launches.

Witnesses reported that although the take-off appeared normal, the glider climbed at a steep angle and slow forward speed.  At about 200 ft above ground level the winch tow cable failed. The pilot lowered the nose to about the level flight attitude before commencing a turn to the right and releasing the broken tow cable. As he had not lower the nose sufficiently for the glider to gain flying speed, it stalled, entered a spin and impacted the ground.

Winch tow cable are known to break regularly, and glider pilots are trained to cope with this situation.  It could not be determined why the pilot failed to apply the correct recovery procedures.

Synopsis

1. FACTUAL INFORMATION

1.1 History of the flight

The aircraft was engaged in aero-magnetic survey operations in an area which extended from approximately 40–130 km south of Cloncurry. The task involved flying a series of north-south tie lines spaced 2 km apart at a height above ground of 80 m and a speed of 140 kts. At this speed, each tie line occupied about 20 minutes of flight time. The flight was planned to depart Cloncurry at 0700–0730 EST and was to return by 1230 to prepare data collected during the flight for transfer to the company’s head office.

An employee of the operating company saw the crew (pilot and equipment operator) preparing to depart the motel for the airport at about 0500. No person has been found who saw the crew at the aerodrome or who saw or heard the aircraft depart.

At about 1000, three witnesses at a mining site in the southern section of the survey area saw a twin-engine aircraft at low level heading in a northerly direction. One of these witnesses, about 1.5 hours later, saw what he believed was the same aircraft flying in an easterly direction about 1 km from his position. Between 1000 and 1030, two witnesses at a mine site some 9 km north of the survey area (and about 5 km west of the accident site) heard an aircraft flying in a north-south direction, apparently at low level.

On becoming aware that the aircraft had not returned to Cloncurry by 1230, a company employee at Cloncurry initiated various checks at Cloncurry and other aerodromes in the area, with Brisbane Flight Service, and with the company’s head office later in the afternoon. At about 2030, the employee advised the company chief pilot that the aircraft was overdue. The chief pilot contacted the Civil Aviation Authority Search and Rescue organisation at about 2045, and search-and-rescue action was initiated. The burnt-out wreckage of the aircraft was found early the following morning approximately 9 km north of the survey area.

1.2 Injuries to persons

1.3 Damage to aircraft

The aircraft was destroyed by impact forces and post-impact fire.

1.4 Other damage

No other damage was reported.

1.5 Personnel information

                                                                                 Pilot                                   Equipment operator

Note. As far as could be ascertained, all 710 hours on type were flown in 500 Series Aero Commander aircraft. No record was found of the pilot having flown a 680F model Aero Commander until he flew SPP for about 2 hours on the day before the accident.

Two of the 500 Series aircraft the pilot had flown (VH-KAC and VH-FGS) were 500S models which had been modified by the fitment of long-range (outboard) tanks. Operation of the fuel systems in these aircraft was similar to that in SPP (see 1.17.4).

Pilot’s recent flying experience

Company records showed that, between 7 July and 7 October 1994, the pilot flew approximately 113 hours on overwater low-level survey tasks in a Ted Smith 601-P aircraft.

There was evidence that the pilot next flew on 4 November 1994 when he conducted endorsement training on an Aero Commander 500S aircraft for a pilot from another survey company. According to this pilot, the endorsing pilot said that he was not very practised in asymmetric flight or in asymmetric operations and that he would leave all the flying to the pilot undergoing the endorsement. Notwithstanding this information, the pilot had extensive check-and-training experience in Aero Commander aircraft. 

During the flight, aircraft speed was reduced towards V_MCA but not to V_MCA.

Pilot’s previous 72-hour history

The pilot travelled from Perth to Cloncurry on 7 November arriving at approximately 2100. On the afternoon of 8 November he conducted a survey flight in SPP which was restricted to approximately 2 hours because of problems with the on-board sensor equipment. After dining at about 2000 and retiring to his motel room at about 2200 on 8 November, the pilot, along with the equipment operator, was observed preparing to depart the motel at about 0500 on 9 November. Neither crew member was supplied any breakfast by the motel.

1.6 Aircraft information

1.6.1 Significant particulars

No outstanding maintenance requirements were identified concerning the aircraft.

1.6.2 Weight and balance

1.6.3 Single-engine rate of climb

The aircraft flight manual lists single-engine rate of climb figures for the aircraft using maximum continuous power on the operating engine, landing gear and flaps up, and the inoperative engine feathered. In this configuration, at an aircraft gross weight of 3,630 kg, a pressure altitude of 2,000 ft and an outside air temperature of 37 degrees C, a rate of climb of 160 ft/min should be achieved at a best climb speed of 102 kts.

1.6.4 Cabin environmental control 

The operator advised that cockpit/cabin cooling in the aircraft was via ram air only. The aircraft was not equipped with air-conditioning or blower fans as electrical motors interfered with the survey equipment. Fresh (ram) air was available through the normal aircraft system which included vents in the cockpit. Additional ram air ducts had been installed to provide supplementary outside air to both the cockpit and the survey equipment rack.

1.6.5 Fuel load for the flight 

Information from the operator indicated that the aircraft fuel load for the flight was approximately 956 L, including a full centre tank, full outboard tanks, and 90 L useable fuel in the boot tank. This estimate was based on the flight time for the previous day’s flight.

1.6.6 Fuel usage rate

The aircraft flight manual indicated that, at sea level, 24 degrees C, 21 inches MAP, 2,100 RPM and 137 KIAS, the aircraft would have been using 112 L fuel per hour. Fuel consumption at rated power was 256 L/h. According to the operator, based on actual fuel usage, SPP had been using 112 L fuel per hour on low-level survey at 140 KIAS.

1.7 Meteorological information

The following information was recorded at Mt Isa on 9 November 1994:

The sky was clear throughout the period and the relative humidity was around 10%. The low-level winds were from the south-east at about 10 kts. There was moderate thermal and mechanical turbulence at low level.

No weather observations were taken at Cloncurry, which is situated approximately 104 km east of Mt Isa. It is likely, however, that weather conditions at Cloncurry were similar to those at Mt Isa.

1.8 Aids to navigation

Not relevant.

1.9 Communications

No record was found of any communications from the aircraft to any Air Traffic Services agency. See also 1.15.2 (‘SAR activities’).

1.10 Flight recorders

The aircraft was not equipped with a flight data recorder or a cockpit voice recorder, nor were these required by regulation.

1.11 Wreckage and impact information

The aircraft struck the eastern slope of a 200-ft high ridge running approximately northsouth. At impact, the aircraft was heading in a westerly direction, was banked left in excess of 120 degrees, and was in a nose-down attitude of about 35 degrees. Initial impact occurred when the left engine and forward fuselage struck embedded rocks, causing severe airframe disruption. The aircraft then bounced up the hill a short distance, coming to rest right way up and pointing east. Most of the aircraft was destroyed by the subsequent fire, although some components, including the engines and propellers, were recovered for later examination.

1.11.1 Left engine

A strip examination of the left engine did not reveal any fault which might have precluded normal operation. Examination of a section of damaged exhaust pipe from the engine confirmed that the damage occurred when the pipe was cold.

1.11.2 Right engine

A strip examination of the right engine did not reveal any fault which might have precluded normal operation. Examination of a section of damaged exhaust pipe from the engine confirmed that the damage occurred when the pipe was hot.

1.11.3 Propellers 

Both propellers were dismantled. Inspection confirmed that the left propeller was in the feathered position and the right propeller in or near the fine pitch position. There was no pre-existing fault evident in either propeller mechanism.

1.11.4 Fuel tank selector valves

Inspection of the fuel tank selector valves (see 1.17.2) at the accident site revealed the following:

1. For the left engine, both the centre and outboard tank selector valves were in the closed position.
2. For the right engine, the centre tank selector valve was in the open position while the outboard tank selector valve was in the closed position.

1.12 Medical and pathological information

Post-mortem examination was unable to confirm the medical condition of the pilot at the time of the accident. However, the pilot held a current Class 1 medical certificate issued by the CAA.

1.13 Fire

The impact caused the fuel tanks to be disrupted, releasing a substantial quantity of

aviation gasoline. Ignition probably resulted from electrical arcing and/or contact with high-temperature engine components.

1.14 Survival aspects

The accident was not survivable due to both impact forces and fire.

1.15 Search and rescue

1.15.1 Company procedures

The company operations manual stated that all operational flights were to be the subject of prior flight plan notification on the minimum basis of a SARTIME for the end of the last flight of the day. The manual also stated that, when an operation from any temporary base was likely to continue for more than a few days, application might be made to the appropriate airways operations unit for the acceptance of a standard plan to cover daily flying activities.

No flight plan had been submitted for the flight. Another company pilot participating in the survey indicated that no plan was submitted because the operation was only scheduled for a few days and local company SAR was being maintained by the other company personnel at Cloncurry.

1.15.2 SAR activities

No information was held by the CAA concerning the flight prior to the initial telephone call from a company employee at Cloncurry at about 1640. During the progress of this conversation, attempts were made by Brisbane Flight Service to contact SPP through another aircraft in the Cloncurry area. At 1641, the pilot of this aircraft advised Flight Service that he was in contact with SPP. He was asked by Flight Service to request an estimate for when SPP would return to Cloncurry. A short time later, the pilot of the other aircraft advised that he was no longer in contact with SPP. (The pilot later advised that radio communications on the day of the accident were very scratchy.) Flight Service advised the company employee that contact with SPP had been lost, at which stage he terminated the call. At 1826, the company employee again called Brisbane Flight Service, asking if there was any contact with SPP. Flight Service advised that there had been no contact with the aircraft. At 2043, the company chief pilot called Flight Service and advised that SPP was overdue. He was then transferred to SAR, whereupon search action was initiated.

1.16 Human performance aspects

1.16.1 Heat stress

Heat stress, or hyperthermia, occurs when the body’s temperature regulation mechanisms fail. In extreme conditions, heat stress can lead to an inability to control body temperature and result in mental impairment and collapse. Individual responses to heat stress are influenced by factors such as age, lack of sleep, the amount and rate of work being performed, and acclimatisation to environmental conditions.

Heat stress not only causes physiological changes but also results in performance impairment. Even a slight increase in body temperature can impair an individual’s ability to perform complex tasks such as those required to operate an aircraft safely. Some of the known effects of heat stress on individuals are that:

1. error rate increases; 
2. short-term memory becomes less reliable; and (c) perceptual motor skills slow.

Importantly, the affected individual may not recognise a decrease in efficiency but may feel perfectly normal and able to continue operations.

1.16.2 Time zone change

When the pilot travelled from Perth to Cloncurry two days before the accident, he moved into the Eastern Standard Time zone, which is 2 hours ahead of Western Standard Time. In other words, 0500 EST is equivalent to 0300 WST.

1.16.3 Food and water

The operator advised that two flasks containing 7–8 L water were on board the aircraft for the flight. Food was generally not carried on survey flights. Whether any food was carried on this flight could not be determined but the crew did not request that the motel provide any food for the flight.

1.17 Aircraft fuel systems 

Among the various Aero Commander models that have been produced, aircraft fuel systems have differed. Long-range models of the aircraft were fitted with integral wing tanks (called outboard tanks), and in some cases boot tanks in the rear fuselage, in addition to the main, or centre tank. In some aircraft, additional tanks were incorporated during manufacture, while in others, they were fitted as a modification after manufacture.

1.17.1 Fuel system Aero Commander 680F Series aircraft 

The Aero Commander 680F fuel system comprises four tanks: the centre tank, the boot tank, and two outboard tanks. The centre tank consists of five interconnected cells having a total capacity of 601 L (592 useable). This tank supplies fuel to both engines. Tank contents are indicated on a cockpit gauge. The boot tank has a capacity of 439 L (419 L useable). Fuel is transferred from this tank to the centre tank by the activation of a switch on the cockpit instrument panel. This is normally conducted in cruise, in stages, when the centre tank level has reduced to 90 US gallons indicated (340 L) or below. The left and right outboard tanks each have a capacity of 127 L (254 L total useable). The contents of these tanks are indicated on gauges in the cockpit. The total fuel capacity of the aircraft is 1,294 L (1,265 useable).

Rotary fuel selector switches located on the cockpit overhead switch panel control the flow of fuel to the engines from either the centre tank or the outboard tanks by way of electrically operated shut-off valves located in each main landing-gear wheel well. Rotating the switches to the right and left OUTBOARD positions (three o’clock and nine o’clock positions respectively) allows fuel from the outboard tanks to flow to the respective engine. At the same time, fuel flow from the centre tank is shut off. Fuel vapour return from the fuel injector pumps is fed to the centre tank.

Switching the selector switches to the CENTRE position (half-past ten o’clock position on the left switch and half-past one o’clock position on the right switch) allows fuel to flow from the centre tank to the respective engine and shuts off flow from the outboard tanks. Selecting the switch to OFF (twelve o’clock position on both switches) closes both shut-off valves and cuts off fuel flow to the engines. A sketch of the right fuel control selector panel is shown below.

The aircraft flight manual, section 4 (‘Normal Procedures’) contained a caution note which stated (emphasis theirs):

CAUTION. Burn centre tank first. When 100 gallons is shown on centre tank gauge, switch to outboard tanks. Do not allow engine to be starved of fuel when outboard tanks run dry. Select centre tank at first indication of fuel pressure loss. Fuel boost pumps must be on when switching tanks.

Anecdotal evidence obtained during the investigation indicated that, should a tank run dry and air enter the fuel lines, up to 2–3 minutes were required to restore normal engine operation following selection to another tank. It was not uncommon for there to be substantial engine power surges during this period.

1.17.2 Fuel selector valves 

The centre and outboard tank fuel systems each have their own electrically operated shutoff valve. Electrical power is required to both open and close the valves. Placing the fuel selector switch in the OFF position closes both shut-off valves controlled by that selector.

Control of the valves is lost in the event of a total loss of electrical power in the aircraft.

1.17.3 VH-SPP fuel system and modification

According to the aircraft logbook, in October 1963 the six-cylinder IO-540 engines which were standard fitment for the aircraft were replaced with eight-cylinder Lycoming IO-720 engines. As part of this conversion, bypassed fuel from the engine-driven pump was returned to the pump inlet instead of being fed to the centre tank. The engines were later fitted with turbochargers.

In 1981, apparently to overcome fuel pump cavitation problems, the fuel system was modified to incorporate a pressure relief return line. According to the aircraft logbook, the modification was completed on 25 May 1981 to approved Engineering Order DFS-AC-08. No reference could be found in the (then) CAA Aircraft History File concerning the modification. Further, the approved flight manual for the aircraft contained no flight manual supplement or other reference to the modification However, a copy of the engineering order cover sheet was obtained from the operator. This indicated that the order had been approved by the then Department of Transport on 11 May 1981. The delegate of the Secretary, Department of Transport, who approved the modification, was unable to recall, other than in a very broad sense, the events surrounding approval of the modification. In particular, he was unable to recall what consideration might have been given to including detail of the modification as an approved supplement to the approved flight manual for the aircraft. (The then ANO (now CAO) 100.6 addresses ‘Administration and Procedure – Design Approval of Modifications, Repairs and Replacement Components’. The order indicates, among other things, that the Secretary may require the (approved) flight manual to be amended upon an approved modification being installed in an aircraft.)

The operator advised that the modification fed bypassed fuel to the centre tank. Advice from pilots who had flown SPP was that, during typical low-level survey operations, outboard tank transfer was complete in about 20 minutes. In other words, in excess of 5 L of fuel per minute was bypassed from each outboard tank to the centre tank. These pilots also indicated that the left outboard tank fed at a slightly higher rate than the right outboard tank so that, during typical low-level survey flight, it emptied 3–5 minutes quicker than the right tank.

1.17.4 VH-SPP fuel system management 

Information from the operator indicated that its fuel system management procedures, and those probably followed by the pilot of SPP, were as follows:

1. Start, taxi, and take-off with centre tank selected.
2. After approximately 1 hour, when centre tank contents indication falls to about 80 US gallons, transfer boot tank fuel to centre tank.
3. When centre tank contents again indicates about 80 US gallons, select both outboard tanks.
4. Re-select centre tank as each outboard tank indication approaches empty.

During survey operations, tank changes were only made during turns between line runs because operation of the boost pumps (which was part of the tank change procedure) caused electrical interference in the survey equipment.

1.17.5 VH-SPP briefing 

Another company pilot at Cloncurry, who was experienced on SPP, briefed the accident pilot on the operation of the aircraft prior to the 2-hour flight he conducted on 8 November 1994. The briefing was conducted in a motel room. Matters covered included the aircraft fuel system. The briefing pilot indicated that he told the accident pilot that the outboard tanks were normally selected when the centre tank contents were indicating about 80 gallons and that they emptied in 15–20 minutes. He recalled some discussion on the latter point as the accident pilot had thought it would take about 60 minutes for the outboard tanks to empty. (This belief was probably based on his experience in 500S Series Aero Commander aircraft in which outboard tank transfer during low-level survey flight took approximately 60 minutes.) During this discussion, the accident pilot indicated that his habit was to select the left and right outboard tanks so that both were feeding at the same time.

1.17.6 Alternative outboard tank transfer procedure

Discussions with other Aero Commander pilots during the investigation revealed an alternative outboard tank transfer procedure. This involved selecting the outboard tank for one engine and leaving the other engine to continue to receive fuel from the centre tank. When the outboard tank neared empty, the procedure was reversed. The advantage of this procedure was that it ensured centre tank fuel was always available to at least one engine, thus providing a safeguard against failure of the aircraft electrical system (which rendered the fuel selector valves inoperative).

1.17.7 Flight in VH-SPP by pilot on 8 November 1994

The flight in SPP conducted by the pilot on the day before the accident was limited to 2 hours due to survey equipment malfunction. According to the operator, the aircraft fuel load on departure was 844 L, this being a full centre tank (590 L) and full outboard tanks (254 L). The boot tank was empty. Approximately 290 L fuel was used during the flight, all from the centre tank. The outboard tank fuel was reported not to have been used.

1.17.8 Fuel system 500S Models VH-KAC and VH-FGS

500S Model Aero Commander aircraft KAC (Aircraft Serial No. 3185) and FGS (Aircraft Serial No. 3315) were fitted with long-range (outboard) tanks shortly after leaving the factory. According to the relevant documentation, KAC was modified in July 1974 in accordance with STC SA 973SW, and FGS was modified in August 1978 in accordance with STC SA-2826-SW. A check revealed that the STCs were identical except that, in SA-2826-SW, figures 24 and 24.1 (‘Overhead Switch Panel Cover Rework’) contained the following: ‘NOTE: 500 B, U, S, thru s/n 3075 only’.

The modification involved the fitment of outboard wing tanks and associated system work. The capacity of the outboard tanks was 254 L, the same as in SPP. Part of the modification involved the installation of rotary fuel selector switches to the cockpit overhead switch panel.

A physical check of the fuel selector panels on KAC and FGS revealed that, in these aircraft, the CENTRE tank selections were at the 12 o’clock position. In turn, this meant that the left and right OFF positions were at half-past one/half-past ten o’clock, while the OUTBOARD positions were at half-past ten/half-past one o’clock. In other words, the orientation of the selector switches was different to that in SPP. The holder for STC SA-2826-SW advised that to maintain the selector switch OFF position at twelve o’clock would have required considerable rework.

A sketch comparison of the fuel control panels for SPP and KAC/FGS is shown below.

1.18 Class endorsement

CAO part 40, section 40.1.0, subsection 4, para. 4.1 states:

A class endorsement specified in Part 1, Part 2 or Part 3 of Appendix IA authorises the holder of the endorsement to fly an aeroplane included in that class as pilot in command.

The notes to this sub-section state:

NOTE 1: The holder of a class endorsement should not act as pilot in command of any aeroplane included in the class on any flight unless he or she is familiar with the systems, the normal and emergency flight manoeuvres and aircraft performance, the flight planning procedures, the weight and balance requirements and the practical application of take-off and landing performance charts of the aeroplane to be flown and has sufficient recent experience or training in the aeroplane type, or in a comparable type, to safely complete the proposed flight.

NOTE 2: The owner and the operator of a type of aeroplane included in a class of aeroplane should ensure that any person who proposes to fly as pilot in command of the aeroplane complies with the requirements set out in Note I and should, where necessary, require the pilot to provide evidence of recent experience or training in the aeroplane type, or in a comparable aeroplane type.

Part 2 of appendix IA (‘Class Endorsements’) includes Aero Commander as a class.

Appendix IB (‘Classes of Aeroplanes’) includes, among other things, Aero Commander 680F and various Aero Commander 500 models (including Aero Commander 500S) in the Aero Commander class.

1.19 Time/event information

The operator provided information concerning pre-flight preparation and in-flight activities, which enabled the following time/event sequence to be developed. This information was based on the experience of other company pilots and was, therefore, an estimate only.

The estimated amount of fuel used from engine start to commencement of survey at 0750 was 160 L.

2. ANALYSIS

2.1 Impact and wreckage information

The factual information obtained from examination of the accident site and the wreckage enabled a number of deductions to be made concerning the accident sequence.

Fire damage to the wreckage indicated that there was substantial fuel on board the aircraft at impact.

The extreme, unusual attitude of the aircraft at impact indicated that the pilot lost control of the aircraft prior to impact. The respective propeller positions and engine operating conditions at impact imply that, with the right engine operating and the left propeller feathered, such an impact attitude could have resulted from the aircraft developing an uncontrollable roll left as a result of aircraft speed reducing below V_MCA.

No mechanical fault was identified in the left engine which might have been reason for the left propeller to have been feathered. The closed position of both selector valves implied deliberate movement of the fuel selector in the cockpit to the OFF position.

The right engine was operating at impact and the aircraft performance charts indicated that the aircraft had sufficient single-engine performance at its estimated operating weight to climb from the survey operating height and return to Cloncurry. This leaves the following questions:

1. Why was the (serviceable) left engine shut down?
2. Why did the pilot apparently lose control of the aircraft?

2.2 Hypothesis

In the absence of any recorded or witness information, the answers to these questions are necessarily speculative. However, after consideration of the factual evidence, the following hypothesis is considered a plausible explanation of the accident sequence.

Background relevant to the hypothesis centres on the accident flight being only the second time the pilot had flown SPP but the first time he had cause to feed fuel from the outboard tanks. Significant differences between SPP and other Aero Commander aircraft the pilot had flown involved the orientation of cockpit fuel tank selector switches and outboard tank fuel transfer time.

With respect to the fuel selectors, in the 500 Series aircraft the centre tank selection was at the twelve o’clock position. This compared with SPP where the twelve o’clock position was OFF. Fuel transfer from the outboard tanks took approximately 1 hour in the 500 Series aircraft, while it took some 20 minutes in SPP. Also, the left outboard tank emptied 3–5 minutes more quickly than the right outboard tank.

Assuming that the aircraft commenced survey at about 0750 (see 1 .17.2) and had, at that time, used 160 L fuel, the following time/event sequence is hypothesised (based on a fuel usage rate of 112 L/h on survey):

If the pilot followed his normal habit of selecting both outboard tanks at about the same time but forgot that the tanks emptied in about 20 minutes in SPP instead of at least 60 minutes as he was accustomed to from his experience in other Aero Commander aircraft, then at about 1007, the left engine would have ceased operating as the tank ran dry. The expected reaction to such an event would be for the pilot to reselect the centre tank and switch the boost pump on. However, in the stress of the moment, he may have regressed to previously learned behaviour and placed the cockpit selector in the twelve o’clock position, forgetting that this was OFF in SPP, even though this involved passing the centre tank detent and greater angular rotation of the knob than from the OUTBOARD to CENTRE position. When normal left engine operation was not restored, it would have been reasonable for the pilot to have increased power on the right engine, feathered the left propeller, and commenced a climb from survey height. Within a short time, however, the right engine would have begun to run roughly as the right outboard tank became empty. The resultant power loss would have caused the aircraft to lose performance rapidly. Now with similar malfunctions in both engines, the pilot might have realised that he had made an incorrect fuel selection for the left engine and positioned the right selector correctly at the centre tank (half-past one o’clock) position. Given that these events would take time and could have resulted in air entering the right engine fuel line, the aircraft could have lost both performance and altitude by the time the fuel supply to the engine was restored. The sudden power increase as fuel flow was restored could have been sufficient to yaw and roll the aircraft uncontrollably to the left and result in the impact attitude found at the accident site.

The location of the wreckage north of the survey area could mean that the aircraft was heading towards Cloncurry at the time of the accident. It could also indicate that the pilot selected outboard tanks prior to commencing a south-north survey run, and that those tanks emptied around the time that run was completed (20 minutes later).

Apart from the possible sighting of the aircraft by one witness at about 1130, there is consistency between the time of the accident deduced above (1002–1007 EST) and the other witness sightings. That the 1130 sighting was a possible sighting could be reason enough to discount this report.

There is a disparity between the deduced time of the accident and the reported radio contact established with SPP by the other aircraft at 1641. However, as the aircraft endurance was only some 7 hours, fuel exhaustion would have occurred before 1500. It would appear, therefore, that, perhaps due to the poor radio conditions existing at the time, the pilot of the other aircraft may have misidentified the transmission from another aircraft as being from SPP. The possibility that SPP had landed at a remote strip for some reason and later taken off again to continue the survey task was considered. However, as the crew were aware of the requirement to return to Cloncurry by 1230, it would be reasonable to expect that they would have contacted the company if this requirement could not be met. No such contact was made.

2.3 Aircraft single-engine climb performance

Assuming the aircraft weight at take-off was 3,735 kg, then 105 kg (153 L) of fuel had to be used before weight reduced to maximum take-off weight (3,630 kg). Given that approximately 160 L fuel was used by 0750 EST when the survey proper was estimated to have begun, it follows that, at any later time, the aircraft should have been able to achieve a single-engine rate of climb of at least 160 ft/min (see 1.6.2).

2.4 Fuel system modification

It is arguable that the fuel system modification to SPP (1.17.3) did warrant inclusion in the approved flight manual because of its effect on outboard tank transfer time, not only with respect to SPP, but also in comparison to other Aero Commander models with similar fuel systems. However, given that the pilot was briefed on the operation of the SPP fuel system the day before the accident (including specific reference to the outboard tank transfer time), it is debatable whether flight manual reference to the fuel system modification could be considered a factor in the accident.

2.5 Fuel system briefing

CAO part 40 places responsibility on the operator and the pilot for ensuring that the pilot is familiar with the aircraft systems. It seems clear that a briefing took place and that the unique features of the SPP fuel system were discussed with the pilot. However, the briefing may have been more effective had it been conducted in the aircraft.

2.6 Human performance

There are a number of human performance aspects which could have affected the pilot’s ability to operate the aircraft safely. These include:

1. The high ambient temperatures and the non-airconditioned cockpit could have resulted in the pilot experiencing some degree of heat stress. The longer the flight continued, the more serious this would have become.
2. There was no evidence of the pilot having consumed any food before or during the flight. Thus, the pilot had probably not eaten for up to 14 hours before the accident.
3. Low-level survey flying is both physically and mentally demanding on the pilot. High temperatures and turbulence increase these demands.
4. The pilot had been at Cloncurry for less than 40 hours at the time of the accident.  He therefore had only limited opportunity to adjust to the local weather conditions and the 2-hour time change from Perth.
5. The pilot’s ability to cope with the above influences could have been limited by his age.

2.7 Other aspects

In analysing this accident, other possibilities such as pilot incapacitation and bird strike were considered. However, given the engine, propeller, and fuel selector valve configurations at aircraft impact, and the deliberate actions by the pilot these configurations imply, neither of these possibilities was considered realistic.

3. CONCLUSIONS

3.1 Findings

1. The pilot held a valid ATPL, was appropriately endorsed, and held a current medical certificate at the time of the accident.
2. The pilot had substantial experience on 500-S Series Aero Commander aircraft but minimal experience on VH-SPP.
3. A modification to the fuel system of VH-SPP reduced the time taken for the outboard tanks to empty to approximately 20 minutes compared to about 60 minutes in some 500 Series Aero Commander models.
4. The approved flight manual for the aircraft contained no reference to the fuel system modification.
5. The pilot’s fuel system management technique involved feeding fuel from the left and right outboard tanks simultaneously.
6. An alternative fuel system management technique, as used by some other pilots, was to feed fuel from one outboard tank at a time.
7. On the day before the accident, the pilot was briefed by another company pilot on the aircraft fuel system and its operation, including reference to the outboard tank transfer time. The briefing was not conducted in the aircraft.
8. The aircraft maintenance release was valid and no outstanding maintenance requirements were identified.
9. The aircraft departed Cloncurry at a weight which exceeded the MTOW by about 125 kg; however, this was not considered to have been a factor in the accident.
10. There was no indication that either engine or either propeller had suffered any mechanical failure.
11. The aircraft impacted the ground inverted, in a steep nose-down attitude.
12. Both fuel selector valves for the left engine were closed and the left engine was not operating at impact.
13. The left propeller was in the feathered position at impact.
14. The outboard tank selector valve for the right engine was closed, while the centre tank selector valve was open.
15. The right engine was operating at impact.
16. Water, but no food, was carried on the aircraft.
17. The pilot had been in the Cloncurry area for less than 40 hours at the time of the accident.
18. The flight was conducted in very hot, dry, conditions with moderate thermal turbulence.
19. During the 2-hour flight on the day before the accident, the pilot did not operate the outboard tank fuel-feed system.

3.2 Significant factors

1. For reason(s) which could not be conclusively established, the pilot shut off the fuel supply to the left engine and feathered the left propeller.
2. For reason(s) which could not be conclusively established, the pilot lost control of the aircraft.

FACTUAL INFORMATION

History of the Flight

The pilot had carried out a local flight with his wife, and a number of circuits and landings were made at the property airstrip. His wife then alighted from the aircraft and went inside the residence which was adjacent to the runway. The pilot had said he intended to do a few more circuits and landings. The aircraft was heard taking off a few minutes later, and witnesses located to the south of the strip saw it making what appeared to be a "flat" left turn onto a northerly heading. The witnesses said the aircraft was about 100 m above ground level and that the engine noise level was low. The aircraft then went out of their field of view. A short time later, the crashed aircraft was discovered by a neighbour who was driving towards the property. The weather was fine and there was a light southerly wind at the time.

Impact Information

The aircraft impacted flat ground whilst upright, descending, and slightly left-wing low. It then bounced beneath powerlines which were approximately 11 m high, and across a road in a direction of 315 degrees. The canopy, ailerons, and various small pieces of aircraft separated before the aircraft came to rest upright, 52 m from the initial impact point. There was no fire. The point of impact was about 300 m to the north of the airstrip which is aligned northeast-southwest.

Wreckage Examination

Detailed technical examination of the aircraft was carried out. Specialist examination of a portion of the exhaust pipe confirmed that the engine had been operating at the time of the accident, albeit at low power, as evidenced by the nature of damage to the propeller and the spinner. There were no mechanical defects found that would have prevented the engine from operating normally.

The structure of the aircraft was examined, and no pre-existing structural defects were found. However, a fibreglass fairing from the base of the tailfin had become detached in such a way that it could have restricted the movement of the elevator control surface. Two small screws had pulled out of the lower rear edge of the fairing. A white paint witness mark on the fairing matched the top inboard edge of the left elevator and showed that the two surfaces had at some stage been in contact. When the fairing was placed against the elevator with the witness marks aligned, it was evident that the detached section of fairing could restrict the upward movement of the elevator. In addition, the elevator trim tab was found in the fully down position.

ANALYSIS

The available evidence does not support pilot incapacitation being a factor in this accident.

Examination of the aircraft indicated that it was capable of operating normally at the time of impact. However, there is a possibility that a fibreglass fairing had detached in flight and restricted up movement of the elevators. The elevator trim tab appears to have been fully down at the time of impact, as it had punctured the rudder surface in that position. This trim-tab position is that which normally gives full nose-up trim. However, if the elevator were restricted in upwards movement and only the tab was movable, then downwards movement of the tab would result in a nose-down effect, the reverse of that expected by the pilot.

A control working in the opposite sense to that expected would be extremely confusing to the pilot. A pilot placed in this situation might reduce the power, because the effect of controls is influenced by power and airspeed. The witnesses who saw the aircraft said it seemed to be making very little noise and was flying slow and at a low altitude. The effect of reducing power, however, would be for the aircraft to adopt a nose-down attitude, compounding the difficulty faced by the pilot.

The pilot was possibly attempting to fly the aircraft back onto the airstrip. From the position of the aircraft before ground impact, and in relation to the airstrip, the pilot would have had to make a left descending turn to align the aircraft with the strip. At this point it would have also been necessary to make a power reduction. This would have further compounded the nose-down tendency of the aircraft which the pilot would have instinctively tried to overcome with the use of nose up trim, further exacerbating the nose-down tendency.

While the above hypothesis offers an explanation for the circumstances of the accident, it relies on an assumption that the fibreglass fairing became detached before impact. However, it has not been possible to determine conclusively whether the fairing became detached before or after impact.

CONCLUSIONS

Findings

1. There was no evidence to support pilot incapacitation being a factor in this accident.
2. The aircraft was operating normally on the flight preceding the accident flight.
3. The weather was fine.
4. The aircraft was seen operating at a low altitude with low power setting immediately before the time of the accident.
5. The engine was capable of normal operation but was delivering low power at the time of impact.
6. The nature of the ground impact indicates that the pilot lost control of the aircraft.
7. The elevator trim tab was in the fully down position at the time of impact.
8. The tailfin fairing was detached and showed evidence of having been in contact with the left elevator control.
9. It could not be determined if the fairing became detached before or as a result of the impact.

Significant Factors

1. Control of the aircraft was lost at low altitude for reasons which could not be determined.
2. The pilot was unable to prevent ground impact.

The pilot was scheduled to spray 50 acres of rice with Londax. The paddock was level and open with no significant obstructions.

The aircraft departed Wakool with a fuel quantity of 200 L (144 kg) of AVGAS and approximately 510 kg of a mixture of Londax and water in the spray hopper.

About five minutes before arriving overhead the treatment area, the pilot established radio contact with the farmer, who was to act as the swath marker. After completing the first spray run in a northerly direction, a second run was completed in a southerly direction. During this run the marker observed that the spray equipment was operating. The aircraft departed the area, heading approximately towards Wakool, however, the pilot did not advise the marker of any reason for departing. When unable to re-establish radio contact, the marker arranged for the operator at Wakool to be advised.

The operator's chief pilot commenced an airborne search from Wakool to the paddock where the aircraft had been spraying.  Finding nothing, he returned to Wakool and arranged for the police to be advised that the aircraft was missing, before re-commencing the air search.  He found the wreckage near the base of trees about 2 km south-east of the spray site, close to a private airstrip.  This strip, aligned 080/260 degrees, was about 850 m long and suitable for a Pawnee Brave landing.

The accident site was in trees about 100 m east and about 50 m south of the unmarked 260 degree strip threshold.

At the time of the accident, the temperature was about 20 degrees Celsius.  The weather was fine with a north-north-easterly wind of 5 to 10 kts.  There were no significant gusts, no significant cloud and visibility was excellent.

The aircraft was within its approved centre of gravity and gross weight limits at the time of the accident and the fuel on board was adequate for the flight.

The pilot was appropriately endorsed on the Pawnee Brave, however, he was relatively inexperienced in agricultural operations.  His Grade 2 Agricultural Rating was issued on 5 July 1994, and he completed 10 hours under direct supervision on 28 October 1994, and then a further 8 hours unsupervised prior to accident.

There were no known witnesses to the accident.  Examination of the impact marks on the trees, fence and the ground indicated that the aircraft had struck the trees while tracking 230 degrees, displaced to the south of the extended strip centreline, with an angle of bank of about 110 degrees to the right and an attitude of 30 degrees nose down.  The short distance of about 20 m from the initial impact point to the final resting position of the wreckage was indicative of a relatively slow horizontal velocity.  Damage to the propeller was consistent with the engine producing power at impact. Flaps were ascertained to have been at 15 degrees which was the recommended landing setting for a heavily loaded Pawnee Brave. There was no fire.

The wreckage was examined by engineers at the accident site and the engine and propeller assemblies were later subjected to more detailed inspection.  No pre-existing faults were found with the aircraft which may have contributed to the accident.

The aircraft was not equipped with a survival beacon.

It is possible that the pilot was intending to land into the west on the airstrip near which he crashed.  The approach path for a landing to the west was over open, flat, dry pasture clear of obstacles.  However, on the southern side of the approach path a tree line converged towards the airfield's southern boundary.

Given the impact position in relation to the airstrip, it is possible that the pilot conducted a low-level right turn onto final for a downwind landing into the west and that the aircraft stalled at a height from which recovery was not possible before ground impact.

Significant Factors

The following factor was considered relevant to the development of the accident:

1.   The pilot probably underestimated the effect of the tailwind component during the turn onto final. 

The flight was an international regular public transport operation between Sydney, Australia and Osaka, Japan on 19 October 1994. The technical crew consisted of a very experienced (B747) pilot in command who was also acting as a training pilot, an experienced co-pilot who had not yet completed his line training on the B747, and an experienced but newly B747-rated flight engineer who was on his first revenue flight as a qualified B747 flight engineer.

Approximately one hour after departure the crew shut down the number one engine because of an oil leak. They returned the aircraft to Sydney where the approach proceeded normally until the landing gear was selected. With selection of the landing gear and selection of the flap beyond a setting of flaps 20, the landing gear warning horn began to sound because the nose landing gear had not extended. The flight crew unsuccessfully attempted to establish the reason for the warning. Believing the gear to be down, the crew elected to complete the landing, with the result that the aircraft was landed with the nose gear retracted. There was no fire and the pilot in command decided not to initiate an emergency evacuation.

The investigation found that the oil loss was caused by the failure of a threaded insert used to retain the engine angle gearbox housing cover. The cover came loose, allowing oil to escape. An opportunity to action service bulletin SB JT9D-7R4-72-410, which would have prevented the oil leak had not been taken. Although the same engine is used on a number of aircraft approved for extended range operations over water, the manufacturer had not made the incorporation of this service bulletin mandatory. The owners of an aircraft can elect not to action a manufacturer's recommendation to incorporate a service bulletin.

An unexplained reduction in air-driven hydraulic pump output caused slower than expected operation of the number one hydraulic system. The system may still have been capable of extending all the landing gear, given adequate time. However, the aircraft landed before the system could complete the landing gear extension.

The flight crew had the opportunity to recognise and correct the landing gear problem prior to landing. The pilot in command attempted to determine the actual landing gear situation from the flight engineer. Although the flight engineer's panel indicated the nose gear was not down and locked, the flight engineer did not recognise this and subsequent communication and co-ordination between the flight crew failed to detect this error.

During the latter part of the flight, the crew did not adequately manage the operation of the aircraft. The crew's performance reflected a lack of effective crew resource management, the crew's lack of knowledge about some of the company's procedures for B747 operations, the flight engineer's and the co-pilot's lack of experience in the B747 and perceived pressure.

A review of events associated with the introduction of the B747 indicated that organisational factors involving both Ansett and the Civil Aviation Authority led to a situation where there was increased potential for an accident of this nature to occur. These factors included deficiencies in the planning and implementation of the introduction program for the new aircraft, particularly with respect to manuals, procedures and line training. In addition, all regulatory requirements were not observed, nor were they enforced.

The flight crew's performance combined with the organisational factors to breach defences that had been put in place to ensure the safety of regular public transport operations in high-capacity aircraft.

A number of recommendations were made as a result of the investigation.

Ansett Australia has advised the Bureau that it has taken a number of significant actions in response to this occurrence. Details of the actions taken can be found in Section 4 of this report.

Summary

The flight was planned as a regular public transport flight from Williamtown to Lord Howe Island. After departure, the pilot reported to Sydney Flight Service that he intended climbing to flight level 230. However, as the aircraft passed flight level 200 the pilot advised flight service that he was now climbing to flight level 210.

The pilot did not report at the first scheduled position code named 'Shark' on time but subsequently advised that he was descending to flight level 130. Shortly afterwards, the pilot reported having crossed 'Shark' and provided an estimate for the next scheduled position, 'Shrimp'. He also stated at this time that the aircraft was maintaining flight level 160. No further communications were recorded by Air Traffic Services from the aircraft. However, during the above period the pilot was in radio communication with two other company aircraft, both bound for Lord Howe Island. One aircraft was crewed by the company managing director and the company chief pilot.

When Sydney Flight Service did not receive the 'Shrimp' position report communications checks were commenced, and following the failure of these checks to establish contact with the aircraft, a search-and-rescue uncertainty phase was declared.

After the managing director arrived at Lord Howe Island, he contacted Melbourne Rescue Co-ordination Centre in response to a request from that centre and inquired about the aircraft. The crews of both other company aircraft subsequently reported hearing a radio transmission from the pilot of VH-SVQ stating that he had 'lost it'.

An extensive air and sea search failed to locate the aircraft or its occupants. Only a small number of pieces of the aircraft were found floating on the sea surface.

The investigation determined that the flight was not a regular public transport flight as the company did not hold the required approval from the New South Wales Air Transport Council to operate such flights over the Williamtown to Lord Howe Island route.

The factors that directly related to the loss of the aircraft could not be determined. However, a number of factors relating to the operation this flight, the operation of the company and the oversight of that operation by the regulator were identified.

The report concludes with a number of safety recommendations.

1. FACTUAL INFORMATION

History of the Flight

The aircraft had returned to Walgett late on the afternoon of the day before the accident, having completed a five-day charter to the Gulf of Carpentaria.

On the day of the accident the Walgett Aero Club held a barbecue and flying competition. The pilot of the Cessna 337 indicated that he did not intend to take part in this competition. Later in the day, he advised the flying instructor who was supervising the flying competition that he wished to carry out a low pass over the aerodrome. The instructor had no objection to this request.

At approximately 1550 hours the pilot took off from runway 18 with three passengers. After what appeared to be a normal circuit and approach, the aircraft made a high-speed pass, with the landing gear retracted, parallel to runway 18 at approximately 20-30 ft above ground level (AGL).

At 100-150 m from the runway intersection, witnesses observed the aircraft enter a steep climb. Witness estimates of the attitude adopted by the aircraft ranged from 40 to 70 degrees nose-up. The aircraft remained in this high nose attitude for 6-10 seconds until an altitude of approximately 700-1,000 ft AGL was reached.

At this point the aircraft's left wing dropped, the nose lowered steeply, and witnesses noted that the engine noise reduced significantly. The instructor supervising the competition stated that after the aircraft appeared to stall, he saw the rudder surface on the tailplane fully deflect in a direction opposite to the observed rotation. The aircraft rotated slowly to the left in an extreme low-nose attitude. Another witness commented that when the aircraft had descended to approximately 200-300 ft AGL, it appeared to adopt a slightly higher nose attitude. This change of attitude was transitory. The nose attitude lowered again quickly, and the aircraft impacted the ground in a very steep nose-down attitude.

Wreckage Examination

The wreckage was located on the Walgett aerodrome, 42 m to the south of the runway strip markers of runway 36.

The aircraft had impacted the ground in a steep nose-down attitude, wings level, with negligible rotation after impact. It did not slide along the ground after impact. The structural deformation was related to the onset of impact loads.

All aircraft extremities, including doors and all control surfaces, were present in the wreckage.

Technical examination of the engines and propellers showed them to be capable of normal operation prior to the impact. No indication was found of any aircraft system malfunction which may have contributed to the accident. However, destruction of the cockpit and the instruments precluded the individual systems' pre-impact status being determined.

The accident was not survivable.

Pilot Information

The pilot was the holder of a commercial pilot licence (aeroplanes). He held a valid medical certificate with a requirement to wear glasses. He was also the aircraft owner. He held an air operator's certificate, re-issued by the Civil Aviation Authority on 30 June 1994, which allowed him to carry out charter operations in VH-DRI.

The last entry in the pilot's logbook was made on 23 August 1994. At this time, he had accumulated approximately 3,200 hours total flight time (3,100 hours in single-engine aircraft and 3,050 hours as pilot in command).

The pilot had completed his endorsement training on the C337A on 11 June 1994. This was his first multi-engine endorsement. At the time of the last logbook entry, he had accumulated 102 hours in the aircraft type, most of which was in VH-DRI.

On 27 June 1994 the pilot undertook a flight check with a Civil Aviation Authority flying operations inspector in order to complete his chief pilot requirements and to include the C337A on his air operator's certificate.  On this occasion it was considered that the pilot met requirements but was to complete further training in the handling of emergency procedures. The CAA pilot file notes that an approved air test officer completed this training and advised that the pilot's handling of emergency procedures was satisfactory. The variation on the air operator's certificate was issued on 30 June 1994.

Post-mortem examination of the pilot revealed the presence of marked atherosclerosis of the coronary artery but there was no evidence of a coronary occlusion. Some alcohol was detected in liver and muscle fluid which was used for testing as sampling of blood or vitreous humour was not possible.

Weather

The weather on the day of the accident was mild with a temperature of 23 degrees C. A high-pressure system was located over south-east Australia.  The sky was clear and there was a gentle breeze from the south-west of up to 5 kts. The visibility was good.

2. ANALYSIS

Aircraft Handling Characteristics

Cessna aircraft are generally docile in most areas of handling. A number of pilots who had extensive experience on the C337, including flight instructors, agreed that placing the aircraft in the attitude that was witnessed on the day of the accident would have resulted in a much more aggravated stall than would be experienced as a result of a stall from straight and level flight. Witness statements agree that the aircraft was being operated at or near full power during the manoeuvre. It could not be ascertained whether the pilot reduced power before or after the point of the stall.

As the aircraft was seen to adopt and maintain a very high nose attitude, the stall that resulted would have occurred quickly due to the rapid loss of airspeed. The height required to recover from such a stall would have been significant and probably greater than that which was available.

The observed full deflection of the rudder surfaces was consistent with the actions of a pilot who may have been attempting to counter an incipient spin.

The C337A was certified under the United States Civil Aviation Regulations Part 3 which preceded the Federal Aviation Regulations Part 23.  As this aircraft was considered a multi-engine aircraft, it was not required to undergo spin testing as part of its type certification. Consequently, no data is available to indicate the typical height loss expected as the result of a spin.

VH-DRI was certified for operations in the normal category. The flight manual stated that operation shall be limited to normal flying manoeuvres but may include straight and steady stalls and turns in which the angle of bank to the horizontal is 60 degrees or less. Other acrobatic manoeuvres shall not be performed.

The Australian Civil Aviation Regulations define aerobatics as "manoeuvres intentionally performed by an aircraft involving an abrupt change in its attitude, an abnormal attitude, or an abnormal variation in speed". A glossary of aeronautical terms used for accident investigation by the US Department of Transportation Safety Institute, Oklahoma, defines an aerobatic manoeuvre as "a pre-planned flight manoeuvre in which the aircraft exceeds either 60 degrees of bank or 30 degrees of pitch".

The observed manoeuvre is consistent with the pilot's probable intention to attempt a wingover or possibly a stall turn. By any of the above definitions, wingovers and stall turns are aerobatic manoeuvres and are outside the normal flight envelope for this aircraft type.

Fuel System

VH-DRI was equipped with a main fuel tank of 174 litres usable fuel capacity in each outboard wing panel and a sump tank of 2.7 litres fuel capacity in the lower portion of each tail boom. Fuel flows to the sump tanks via two outlets in each main tank, one at the bottom forward edge and one at the bottom rear edge of each tank. Fuel then flows from the sump tanks through a bypass in each electric auxiliary fuel pump (when the pump is not operating) to selector valves located at the wing roots.

The inclusion of sump tanks reduces the risk of interruption of the fuel flow when the aircraft is placed in a range of flight attitudes including those that were witnessed during the accident. Had fuel been unable to drain from the main cells to the sump tanks due to the observed manoeuvre, it would have taken approximately two minutes and thirty seconds to unport the fuel lines in the sump tanks with the aircraft operating at full power, assuming that the sump tanks were full at the time the aircraft entered the nose-high attitude. As witnesses reported that the elapsed time between the aircraft entering the pull-up and the nose lowering at the top of the manoeuvre did not exceed 10 seconds, it is unlikely that engine failure would have occurred as a result of interruption to the fuel flow due to unporting of the fuel outlets from the main fuel cells.

VH-DRI was also equipped with an optional auxiliary fuel tank (68 litres usable capacity) in each wing between the cabin and the tail boom. The auxiliary tanks feed directly through the engine-driven fuel pump to the engine. The fuel from each auxiliary tank drains via a single outlet near the bottom of the tank approximately halfway between its forward and aft edges.

If the auxiliary tanks were selected it might be possible, at very low fuel levels, to unport the outlet to the tanks if the aircraft were in a very nose-high attitude for a considerable length of time.

The C337A engine is fuel injected. The fuel injection system delivers fuel, under pressure, to the inlet manifolds of the engine and is unlikely to be affected by the placement of the aircraft in unusual attitudes.

It was not possible, due to the severity of the damage, to accurately determine the position of the fuel selectors in the cockpit prior to impact. The flight manual stated that main fuel tanks should be selected for take-off, landing and the first 60 minutes of flight. It is therefore most likely that the main tanks were selected for this flight. Calculations have determined that there was approximately 150 litres of fuel on board the aircraft prior to its last flight. It was also not possible to accurately determine the quantities of fuel in each tank as every fuel cell was ruptured on impact with little or no fuel being observed in each cell. Nonetheless, it is unlikely that either engine failed due to fuel starvation.

Weight and Balance

Calculations of the weight and balance of the aircraft were based on the following:

1. The pilot was in the front left pilot seat while the three passengers occupied the right front seat and the two centre seats directly behind.
2. According to fuel agent records, the pilot purchased fuel at Birdsville but did not purchase fuel after return to Walgett. The aircraft flew direct from Birdsville to Walgett, a flight time of four hours. Assuming full tanks at Birdsville and a fuel consumption of 85 litres per hour (based on the pilot's operating handbook), fuel remaining at Walgett was calculated at 154 litres. After return to Walgett the pilot told the passengers that the aircraft had consumed 90 litres per hour. The pilot also informed the instructor supervising the flying competition that the aircraft had approximately 150 litres of fuel on board.
3. A bag of flour was found in the cabin area of the aircraft.  It was estimated to have weighed 20 kg.

Using these figures, it was determined that the aircraft was within weight limits but that the centre of gravity (c.g.) was outside limits, marginally forward of the c.g. envelope.

Having more or less fuel on board would not have significantly affected this result, with the c.g. close to or just forward of the c.g. envelope.  The only factor that would have made a significant difference to the position of the

c.g. would have been the seating position of the passengers. Had they been seated in the rear row of seats or some combination of centre and rear seats, the position of the c.g. would have moved to within the envelope.

Despite this finding, discussions with C337 pilots indicate that it is unlikely that the forward position of the c.g. had a significant effect on the handling characteristics of the aircraft.

Seat Mechanism

There have been documented occasions when control seats have dislodged from their previously locked position and moved backwards when loads have been imposed by rotation for take-off, or by g-loads in aerobatic manoeuvres or in turbulence. This has been attributed to excessive wear in the seat adjustment mechanism.

A sudden rearward movement of the seat could make it difficult for the pilot to reach the control column. There is also the possibility that the pilot could instinctively grab at the control column in an attempt to counter the seat movement, causing an abrupt nose-up change in attitude.

The Civil Aviation Authority issued an Airworthiness Directive (AD) in relation to the seat adjustment mechanism in September 1988 (AD/CESSNA 337/27 Amt. 1 Seat Adjustment Mechanism). This AD was required as a periodic inspection every 100 hours or 12 months, whichever occurred earlier.

The aircraft logbook indicated that the AD had been complied with. The most recent inspection was carried out on 5 July 1994, approximately three months prior to the accident.

Due to the severity of the damage to the cockpit area, it was not possible to determine if the seat had dislodged, in flight, from the desired position.

Pilot Performance

Estimates of any degree of pilot performance degradation due to the presence of alcohol in liver and muscle tissue should be treated with caution. It was therefore not possible to accurately determine the blood alcohol level.

There was no evidence to suggest that the pilot had consumed alcohol on the day of the accident.

There was no evidence that pilot incapacitation was a factor in the accident.

Weather

The weather was not considered to be a contributing factor to this accident.

Summary

As the aircraft was observed to adopt a very nose-high attitude and to sustain it, airspeed would have reduced significantly. As the pilot attempted to turn out of the nose-high attitude, the observed subsequent flight path of the aircraft was consistent with a stall and spin. The altitude of the highest point in the flight path was insufficient to permit the pilot to effect a recovery from a spin.

Loss of engine power at or near the highest point in the flight path would have reduced the power available during the manoeuvre intended to bring the aircraft out of the nose-high attitude. This could have increased the rate of airspeed loss and may have slightly advanced the time at which control was lost. It is doubtful, however, that an engine failure would have precipitated the loss of control.

3. CONCLUSIONS

Findings

1. The pilot held a valid licence and was endorsed on the aircraft type.
2. The pilot carried out a manoeuvre for which the aircraft was not certified.
3. The aircraft appeared to stall at the highest point in its flight path.
4. The aircraft descended in a steep nose-low attitude and impacted the ground shortly after.
5. The aircraft was within maximum weight limits.
6. The centre of gravity of the aircraft was marginally forward of the forward limit of the c.g. envelope.
7. The engines and propellers were capable of delivering power prior to impact.
8. No other pre-existing airframe or system malfunction that could have directly affected the flight was found.
9. There was no evidence of a medical condition that could have affected the pilot's ability to control the aircraft.

Significant factors

The pilot lost control of the aircraft at an altitude which was insufficient to permit a recovery before the aircraft impacted the ground.

The purpose of the flight, which had departed from Moorabbin earlier in the week, was to enable the pilot to achieve the required hours for the issue of a commercial pilot licence.

On the day of the accident the pilot had submitted a visual flight rules (VFR) flight plan before departing from Ayers Rock at about 1000 CST, accompanied by one passenger.  The aircraft tracked via Nullabor to Ceduna, where a stop was made for fuel and lunch, then departed at about 1625 for Adelaide.

At 1754, in the vicinity of Cowell, the pilot contacted Adelaide Flight Service Unit requesting clearance to climb from 3,000 ft to 6,000 ft above mean sea level (AMSL). The Flight Service Officer (FSO) queried the request as 6,000 ft was non-hemispherical, and an IFR altitude, although no instrument flight rules (IFR) flight plan was held for the aircraft. After further discussions with the pilot, the FSO established that the flight was operating under VFR, and the pilot amended the requested altitude to 5,500 ft.

The pilot was instructed to contact Adelaide Approach, and, as the aircraft approached 50 km from Adelaide, it was cleared to descend to 1,000 ft. The pilot advised commencing descent immediately. Several minutes later the aircraft was observed on radar, about 46 km north-west of Adelaide over St Vincent Gulf, passing through 2,600 ft on descent.  The radar return then disappeared and attempted radio contact with the aircraft was unsuccessful. A distress phase was initiated.

An IFR aircraft, departing Adelaide to the north, was diverted to the area in an effort to locate the missing aircraft. The pilot reported that the cloud base was 1,000 ft with patches to 600 ft.  It was dark, and rain showers were in the area. The Bureau of Meteorology advised that isolated thunderstorms were also in the area.

An air and sea search found pieces of floating wreckage and other debris. Later searching discovered the wreckage on the seabed in the vicinity of the point where the aircraft was last seen on radar.

Underwater photography showed that the aircraft had sustained extensive damage, indicating a high-speed impact with the water.  All extremities of the aircraft could be accounted for.  The instrument panel was recovered from the wreckage for further analysis which revealed that all instruments had been serviceable, and that vacuum pressure was available for the gyro instruments.  During inspection of the attitude indicator, witness marks indicated that the aircraft was probably in a wings level, 60 degree nose down attitude at impact.

No evidence has been found to suggest that the aircraft was other than serviceable prior to impact.

The recorded radar data was examined in detail and showed the aircraft descending to, then levelling at about 1,000 ft before commencing a steepening left turn with a very high rate of descent.  The radar return was lost at about 300 ft.  The radar data does not take the current QNH into consideration and indicated altitudes may not coincide with AMSL altitudes.

Approaching Adelaide, the pilot probably commenced an early descent in order to remain beneath the cloud base. The left turn observed on radar is consistent with an attempt by the pilot to regain visual reference following inadvertent entry to cloud.

The pilot may have been suffering from fatigue, having been on duty since early that morning and having flown for more than 6 hours, particularly as the latter part of the flight was in marginal VFR weather conditions.

Significant factors

1. It is likely that the pilot inadvertently entered instrument meteorological conditions.
2. While attempting to regain visual reference, control of the aircraft was lost at a height insufficient to effect recovery.

The aircraft was operating from a 400 m grass airstrip orientated approximately 080 degrees M. The strip was on a property where the aircraft had been in storage for some six months prior to the accident. However, the pilot flew the aircraft for about 1.5 hours a few days before the accident. This activity included a flight to Mareeba Airport where the aircraft landed and the pilot borrowed some tools, including a soldering iron, to work on the aircraft. No information about the work done was available. However, the aircraft later departed Mareeba and apparently functioned normally during the return flight to the property.

On the day of the accident, the pilot secured two jerry cans of fuel in the right seat of the aircraft and placed two carry bags on the shelf behind the seat. The pilot indicated to witnesses that he intended to fly one circuit and land, bid farewell to those at the strip, and then depart for Innisfail, his first intended landing point.

A witness reported that the pilot started the engine and allowed it to idle for between 3 and 5 minutes before commencing the take-off. As the aircraft accelerated for take-off, it drifted towards the left side of the strip, but the pilot corrected this, and the aircraft became airborne. The witness, who had observed the aircraft take off from the strip a number of times, considered that the length of strip the aircraft used to become airborne was greater than he had observed on previous occasions. He believed, also, that the aircraft did not climb as well as usual and was making little headway against the wind. At an estimated height of 20 m above ground level, the aircraft entered a left turn at about 30 degrees angle of bank. When heading approximately north-west, it suddenly rolled further left and spiralled to the ground.

The Bureau of Meteorology advised that, based on observations taken at Mareeba Airport on the day of the accident, the estimated weather conditions around the time of the accident were: wind, south-easterly at 5-10 kt, temperature 19-20 degrees C, and relative humidity 80 percent.

Reports from Mareeba Airport indicated that the wind was gusty at times during the day, making the conditions unsuitable for circuit flying. Witnesses at the accident site reported the weather conditions as a light south-easterly breeze with occasional drizzle, although the sun was shining when the aircraft took off. This information appears to be supported by a photograph taken of the aircraft shortly before take-off. However, other photographs taken shortly after the aircraft took off, and looking towards the south-east, show a darkened sky and low cloud.

Examination of the aircraft wreckage did not reveal any abnormality which might have contributed to the accident. Metallurgical examination of a section of the exhaust pipe confirmed that the engine was developing power at impact.

The aircraft engine was fitted with a carburettor heat control. This was found in the off position during the wreckage examination. The atmospheric conditions which existed at the time of the accident were such that serious carburettor icing was likely at idle engine power. It is possible, therefore, that there was a buildup of carburettor ice in the period the engine was idling before take-off. However, any such buildup would cause a decrease in engine performance by lowering the available maximum RPM, an effect which would be evident to the pilot via the cockpit engine instruments. The photographs referred to above show that the aircraft became airborne well before the end of the strip. The presence of carburettor icing cannot, therefore, be confirmed. However, any reduction in engine power would have reduced aircraft performance, particularly during a climbing turn.

The described behaviour of the aircraft in spiralling to the ground is typical of loss of aircraft control following wing stall. The height at which the event occurred would have precluded recovery to normal flight.

A further possibility is that the aircraft was affected by a change in wind conditions or turbulence and that the pilot lost control of the aircraft in these changing conditions.

Factors

The following factors are considered relevant to the development of this occurrence:

1. For reason(s) which could not be positively determined, the pilot lost control of the aircraft during a climbing turn after take-off.
2. The height at which the loss of control occurred precluded the pilot recovering the aircraft to normal flight.

FACTUAL INFORMATION

The aircraft was being flown on a night navigation training exercise from Canberra to Bankstown, then returning via Bathurst, in accordance with the night visual flight rules (NGT VFR). The crew included an instructor, a licensed private pilot undergoing NGT VFR training, and a licensed student pilot who was observing the flight from a rear seat. The exercise was to include a diversion during the return leg. The planned cruising altitude for the return leg was 7,500 ft, remaining outside controlled airspace. The flight plan submitted included the lowest safe altitude (LSALT) for each of the planned legs. The flight was conducted entirely at night.

The pilot-in-command held valid instructor and command instrument ratings. The pilot under instruction was undertaking NGT VFR training as a qualification towards obtaining a commercial licence. He had previously completed some basic instrument flight training.

The aircraft departed Canberra at 1745, arriving at Bankstown at 1853 after an apparently uneventful flight. It subsequently departed Bankstown at 1945 for the return flight. Recorded radar data indicated that, in accordance with its flight plan, the aircraft initially tracked towards Katoomba and climbed to 2,000 ft. After passing 22 NM from Sydney the aircraft commenced a further climb, reaching 4,300 ft by 33 NM, having infringed controlled airspace without a clearance. The aircraft then turned left onto a reciprocal track and descended to 2,300 ft. After travelling about 9 NM along the reciprocal track the aircraft turned right and tracked south towards Camden, descending to 2,100 ft. The pilot under instruction advised Flight Information Service that he was amending his flight plan and was now tracking to Canberra via Camden and the Shellys non-directional beacon (NDB).

After passing Camden, the aircraft turned onto a south-westerly track, towards the Shellys NDB, and gradually climbed to an altitude of 3,100 ft. The climb rate was erratic and included periods where the aircraft descended at up to 300 ft/min. The altitude flown did not conform with the enroute LSALT of 3,900 ft. At 2017, a minute after reaching its maximum altitude the aircraft commenced a gradual descent at rates of up to 350 ft/min. Passing 2,500 ft, the aircraft turned left through 110 degrees onto an easterly track before colliding with terrain in the Hilltop area, at an elevation of about 1,820 ft, some 2 km south of the last recorded radar position. The calculated groundspeed just prior to impact was more than 150 knots.

An examination of the wreckage found no defects which were likely to have contributed to the accident. The aircraft had initially collided with the crown of a tree about 18 m above the ground, descending at an angle of about 15 degrees, in a wings level attitude. Both wingtips had been detached on impact with the tree, and their relative positions suggested the aircraft had been inverted at that point. An emergency locator transmitter (ELT) fitted to the aircraft had activated on impact. Another activated ELT was also found in the wreckage. This unit was the personal property of one of the occupants. The ELT signals assisted the crew of a search helicopter to subsequently locate the accident site.

Post-mortem examinations indicated that neither the instructor or rear seat observer had any pre-existing physical condition likely to have contributed to the accident. The student was found to have severe coronary artery disease, but there was insufficient evidence to indicate that he had suffered some form of inflight incapacitation. Toxicological analysis indicated the three crew members, despite being non-smokers, had carbon monoxide saturation levels ranging between 7% and 8%. The reason(s) for the elevated carbon monoxide levels was not established, however, values of up to 10% at sea level are considered to be within the normal range.

A specialist analysis of the weather conditions in the vicinity of the crash site indicated there was fog in the area, with five to eight octas of stratus or cumulus cloud ranging from 2,000 ft to 8,000 ft. The wind was light and variable. The temperature was eight degrees Celsius.

ANALYSIS

After departing Bankstown, the aircraft had conducted a step climb, apparently attempting to remain outside controlled airspace whilst achieving LSALT requirements. However, just prior to commencing the diversion, the aircraft had briefly penetrated controlled airspace. It then tracked towards Camden, descending to 2,300 ft. After passing Camden the aircraft remained below the enroute LSALT, failing to climb to 3,900 ft, although the aircraft did climb somewhat erratically to 3,100 ft, remaining there for only a short time before gradually descending into the ground. The vertical profile flown prior to the accident would appear to indicate that the instructor was not adequately monitoring the performance of the student and consequent flight progress. It could not be determined if the student's heart disease contributed to the accident, however, if he had become disabled then it would be expected that the instructor could have regained control of the aircraft with the assistance of the passenger.

The reason why the aircraft had climbed somewhat erratically after passing Camden, and then descended, may have been due to an attempt to remain clear of cloud. The radical alteration of track, and increase in groundspeed just before impact, may have been indicative of the student becoming spatially disoriented whilst attempting to either remain clear of instrument meteorological conditions (IMC), or having unintentionally entered IMC. Why the instructor, who was qualified to fly in IMC, did not, or could not intervene, was not able to be established. The carbon monoxide levels, although slightly elevated, are not considered to have been sufficient to have caused any significant impairment of the performance of the flight crew.

SIGNIFICANT FACTORS

The investigation was unable to determine with any certainty the significant factors associated with this occurrence.