Circumstances

VH-OJJ was cleared to track inbound via the 229 VOR radial, while maintaining 6,000 ft. The Approach South radar control sector controller (APP S) was processing the aircraft for landing on runway 16R. Due to operational requirements, the APP S controller delayed turning the aircraft onto a right downwind for that runway.

VH-TCH had departed runway 16R, cleared initially to climb to 5,000 ft. The Departures South radar control sector controller (DEP S) cleared the aircraft for an early right turn and unrestricted climb to its planned cruising level. The aircraft was then to be vectored left to intercept the 207 VOR radial.

A short time later, as the APP S controller was about to instruct the crew of VH-OJJ to turn downwind and VH-TCH was turning left to intercept the 207 VOR radial, the crew of VH-OJJ advised that they had received a TCAS Resolution Advisory (RA) alert.

Recorded radar information indicated that each aircraft had penetrated its respective airspace boundary buffer, and closed to within 2.5 NM while both were at 6,000 ft.

The runway 16 airspace agreement has a narrow corridor in the APP S airspace to the west of the airport. This airspace design limits the flexibility available to APP S controllers when vectoring aircraft to downwind for runway 16. The latitude that the DEP S controller may apply when turning departing aircraft onto south-westerly tracks, and providing climb, is also restricted.

Separation was not ensured before VH-TCH was cleared for an unrestricted climb. The situation was possibly worsened by the southerly wind which would have drifted VH-TCH closer to the APP S airspace boundary.

Findings

1. The unrestricted climb instruction provided to VH-TCH by the DEP S controller was premature.
2. The vectoring of VH-OJJ onto downwind for runway 16 by the APP S controller was initiated late.
3. The airspace agreement boundary for runway 16 operations did not afford adequate separation assurance.

Factors

1. The radar surveillance techniques used by both controllers were inadequate to prevent the loss of the prescribed separation standards.

Safety action

As a result of the investigation, the Bureau of Air Safety Investigation made the following interim recommendation.

IR950212

The Bureau of Air Safety Investigation recommends that Airservices Australia amend the runway 16 airspace agreement boundaries to ensure that arriving and departing aircraft cannot be on, or near, reciprocal tracks. The amendment should address excursions into either buffer area.

Airservices Australia responded to this recommendation as follows:

"A Standard Instrument Departure (SID) has been developed for non-jet southern departures which will provide greater separation assurance and reduce controller workload. At this stage we expect the new SID to be included in DAP EAST Amendment List 52.

I should, however, point out that there remains a requirement for air traffic control to apply vertical separation between departing aircraft and arriving aircraft until the departing aircraft is clear of approach airspace. Vertical separation is applied at the clearance delivery phase of flight. Jet aircraft are required to maintain 5,000' and propeller driven aircraft are required to maintain 3,000'. The need for crossovers between arriving and departing aircraft within the Sydney TMA is unavoidable."

VH-EAA was processed into the Sydney Terminal Area by the Approach south radar control sector, and was tracking via the 094 VOR radial, on descent to 6,000 ft in visual conditions. At 9 DME, the flight crew, in response to a TCAS RA alert, climbed the aircraft approximately 300 ft. They did not advise ATC of the alert.

VH-NEK had departed runway 16L, on initial climb to 5,000 ft, and was being processed to depart the Sydney Terminal Area by the Departures south radar control sector. The aircraft was vectored onto a north-easterly track from a left turn after take-off.

Recorded radar information indicated that VH-EAA had continued descent to a pressure altitude of 5,700 ft and VH-NEK had climbed to a pressure altitude of 4,900 ft. When their flight paths crossed, VH-EAA was 800 ft above, and 1.86 NM to the right of VH-NEK.

The traffic management plan, techniques and procedures, for processing both aircraft were adequate to maintain prescribed separation standards and tolerances in accordance with the runway 16 airspace agreement. However, neither controller had recognised the incident, probably due to the short duration of the encounter, and the lack of advice from either flight crew.

Findings

1. The traffic management procedures adopted by the controllers for processing the aircraft were adequate.

2. VH-EAA descended below the assigned altitude.

3. In response to the TCAS RA alert, the flight crew returned the aircraft to the assigned altitude.

Significant factors

1. The required separation standard was infringed when the flight crew permitted VH-EAA to descend below their assigned altitude.

As VH-NJR was approaching Perth from the east APP (E) was responsible for initial radar vectoring. To improve aircraft handling APP (W) agreed that APP (E) would maintain vectoring after the aircraft crossed into APP (W)'s airspace. APP (W) also indicated that he would keep all his other traffic clear of VH-NJR.

The pilot of VH-MPZ was cleared to depart Jandakot’s runway 06 in a left turn with a climb to 2,000 ft. He read back his allocated transponder code as 4503 instead of 4502 and the error was not detected despite a request to repeat his read-back. VH-MPZ's clearance for a departure from Jandakot meant that separation between VH-NJR (initially cleared to descend to 2,500 ft) and VH-MPZ (cleared to climb to 2,000 ft) was not assured. APP (W) did not realise this error, nor did he coordinate VH-MPZ's departure with APP (E) and as a result APP (E) was not warned there might be a traffic conflict. APP (W) had placed VH-MPZ's flight strip in the bay between the two controllers and had intended drawing APP (E)'s attention to it. APP (E) was busy, and APP (W) decided to leave it until later. He was then distracted by communications with another aircraft and forgot about it.

When VH-MPZ departed Jandakot its transponder code was set at 4503. A code of 4502 had been programmed into the radar's computer; consequently, when the return appeared on both APP (W) and APP (E)'s screens it did not have a label indicating the aircraft's callsign. It appears both controllers initially assumed that the un-labled return was circuit traffic at Jandakot and paid little attention to it. VH-MPZ exited the Jandakot control zone at the same time as APP (E) was giving further directions to VH-NJR to turn right and continue on a visual descent. Because APP (E) had the quick-look facility selected on her radar she observed that the traffic, which was now heading towards VH-NJR, was at 2,000 ft and would be in conflict. She immediately turned VH-NJR further right and assigned the aircraft 2,500 ft.  This was to provide emergency separation of 500 ft between the aircraft. VH-NJR descended to 2,300 ft before returning to 2,500 ft.

Analysis

The factors leading to the occurrence started when APP (W) cleared the pilot of VH-MPZ to depart Jandakot at 2,000 ft on a track that would take the aircraft towards the flight path of VH-NJR which had been cleared to descend to 2,500 ft. The separation requirement were not assured by this instruction. APP (W) should have cleared VH-MPZ via a different route or restricted its climb to 1,500 ft. APP (W) could also have coordinated a descent limit of 3,000 ft for VH-NJR with APP (E), to provide the required assurance. A lack of commitment to the principal of separation assurance was identified as a possible factor in APP (W)'s under-performance.

Having started the process APP (W) did not ensure that APP (E) was aware of the possible traffic by drawing her attention to the flight progress strip located in the bay between the controllers. Distraction probably played a part in this failure. APP (E) was operating on the assumption that APP (W) was going to keep all other traffic clear and was not expecting any conflicting traffic and therefore, was not looking for it.

All the visual cues that may have been provided to both APP (W) and APP (E) by their radar screens were not there because VH-MPZ's pilot did not have the correct transponder code set. In addition, APP (W) did not have the quick-look facility selected and was therefore, not aware, at least, of the un-labled returns altitude. It was APP (E)'s use of the quick-look facility which alerted her to the approaching confliction. Use of the quick-look facility is not mandated because of the radar return clutter that results from the circuit traffic at Jandakot, when it is selected.

Safety Action

Airservices Australia's Western Australian office is reviewing the airspace layout around Perth and Jandakot, Jandakot departure procedures and coordination requirements, the use of the radar quick-look facility and methods of reducing radar clutter in the Jandakot area. They will also continue to emphasise, to their staff, the mandatory use of defensive control techniques that are designed to provide separation assurance in all appropriate circumstances.

FACTUAL INFORMATION

History of the flight

While the aircraft was in cruise at FL350, approaching waypoint MILUV, the flight crew was cleared by Brisbane sector control to track inbound to Sydney via the CHEZA 2 Standard Arrival Route (STAR). The controller advised the crew that the aircraft was radar identified and to expect runway 34R (right) for landing. Both pilots reviewed the approach information, which was then programmed, including reference to runway 34R, into the aircraft's flight management computer.

The aircraft was subsequently cleared to descend to 8,000 ft and at about 35 NM east of Sydney the crew was instructed to contact Sydney Approach (north) on 124.4 MHz. On initial contact with Approach the crew was cleared to descend to 5,000 ft and was advised, “runway 34 left, localiser frequency 110.1, independent approach". In accordance with current procedures the crew acknowledged "5,000". Soon after, the controller cancelled the requirement to approach via the Cheza STAR and issued a vector for the approach.

When establishing communications with the Director on 125.3, the crew advised that they were visual with the runway in sight. They were issued further descent instructions and a vector to intercept the localiser final approach. At 12 NM from touchdown, they were instructed to join the centreline for runway left, make a visual approach and contact Sydney Tower on 120.5. The tower frequency was then confirmed at the request of the crew. Shortly after, the Director advised the tower that the aircraft had intercepted the final approach for runway 34R. The controllers resolved that, as there was no potential conflict with other aircraft, VH-TAI could continue its approach to runway right.

On initial contact with the tower the crew reported that they were on a six-mile final approach for runway 34R and were subsequently cleared to land on that runway.

Flight crew information

The pilot in command was experienced in domestic airline operations into Sydney. This was the return leg of his first international flight. Both pilots had reviewed the required pre-flight briefing material, including audio-visual and printed route and terminal area information. The co-pilot was experienced, both in operations into Sydney and on international operations.

When informed that they had conducted an approach for the wrong runway, neither crew could recall being advised that they were to land on runway 34L. Both pilots were aware that the advice to "expect" runway 34R could be subject to change.

Communications

There were no identified technical deficiencies in any communications with the aircraft, nor was there evidence of over-transmitting or other interference with the broadcast or reception of critical information.

Parallel runway operations at Sydney

With the introduction of parallel runway operations, an agreement was established between Sydney and Brisbane Air Traffic Services to provide early advice of the landing runway at Sydney to all international arrivals from the north and the east. This agreement required that Brisbane Control advise aircraft of B767/A300 size and smaller to expect to land on runway 16L/34R and for larger aircraft to expect to land on runway 16R/34L.

The advice to flight crews of a landing runway, different from that for which an expectation had been provided, was not seen by the management of the Sydney district office of Airservices Australia to constitute a change of runway.

The processing of VH-TAI for runway 34L reflected the requirement for the aircraft to taxi to the international terminal and the lack of potential traffic conflictions.

When they were advised of runway 34L at both 35 NM and 12 NM, there was no requirement for the flight crew to read back the runway identifier. Current parallel runway operational procedures required only that pilots confirm "visual" and/or runway "left/right in sight" on first contact with the Director, or as soon as each is the case. When the crew of VH-TAI first contacted the Director at about 28 NM from touchdown, they reported visual, with the runway sighted. They did not identify the runway on which they were intending to land, nor did the Director request runway identification.

The investigation of this occurrence identified safety deficiencies in procedures relating to the operation of parallel runways at Sydney. Current operational documentation contain areas of ambiguity between standard operating procedures and instructions published in the AIP, AIP supplement H36/95, the Manual of Air Traffic Services and the Sydney Terminal Area Temporary Local Instructions. These ambiguities include the use in the various documents of the terms "expected", "nominated" and "specified" in reference to landing runways.

ANALYSIS

The published standard operational procedures and instructions did not address the implications of providing a runway expectation, which was subject to change, without the provision of either change alert or read back requirements. Consequently, the significance of the change to the runway expectation was apparently not recognised by those involved. To contend that the advice of 34L as the landing runway did not constitute a runway change is to discount the effect of the provided expectation. It would then be reasonable to question the value of providing an early expectation of the landing runway beyond the orientation of either runway 16 or 34.

The Director and the tower controller were unaware until late in the approach that the crew was not intending to land on runway 34L. This was due, in part, to the lack of a requirement for the crew to read back the runway identifier when first advised by approach control. The omission by the crew and the Director to confirm the runway identifier when the crew reported having the runway in sight also delayed recognition of the error.

Neither pilot recognised the advice of the nomination of runway 34L for their arrival, although it had been given twice and included confirmation of the localiser and tower frequencies. This is probably a consequence of the lack of a specific alert of the change to the runway expectation without a requirement for the flight crew to read back the runway designator. The inclusion of the runway designator when the crew entered the arrival information in the flight management computer preceded the confirmation of the landing runway. This action and the crew's experience that B737 aircraft generally use runway 16L/34R would have served to reinforce to them that they were being processed to land on runway 34R.

The ambiguities in the Sydney parallel runway procedures terminology have the potential to lead to misunderstandings between controllers and pilots. This is due to the apparent interchangeability of terms used in the various documents to describe runway application.

CONCLUSIONS

Findings

1. The flight crew was familiar with parallel runway operations at Sydney.
2. Brisbane Control, in accordance with normal procedures, provided the flight crew with an expectation to land on runway 34R.
3. Current procedures did not require that controllers alert flight crews to any change to a landing runway expectation.
4. Sydney approach, and later the Director, advised the flight crew of runway 34L for their landing.
5. Current procedures did not require that flight crews read back runway information to confirm recognition of the correct runway.
6. On initial contact with the Director, the flight crew did not advise, and the Director did not confirm, their landing runway intention.
7. The flight crew intercepted the final approach for runway 34R and was subsequently cleared to land.
8. There was no breakdown in separation standards.
9. Instructions, concerning some aspects of parallel runway operations at Sydney, are inconsistent and ambiguous.

Significant factors

1. The flight crew did not recognise the change of runway advice.
2. The controllers were unaware, until late in the approach, that the flight crew intended to land on runway 34R.

Safety Action

As a result of the investigation into this occurrence, the Bureau of Air Safety Investigation issued the following interim recommendations:

IR950213 issued 3 January 1996

That the Civil Aviation Safety Authority and Airservices Australia jointly:

1. remove from all published standard operating procedures, publications and instructions any ambiguities concerning the meanings of the terms "expected", "nominated" and "specified" in relation to landing runways.
2. amend the published standard operating procedures, publications and instructions to include advice to flight crew that the approach will involve a cross-over manoeuvre if their aircraft is required to cross a parallel approach path;
3. rectify the ambiguity in the present requirement for flight crew to report "visual" for independent visual approaches to parallel runways;
4. include a requirement for flight crews to read back the runway in aeromobile communications phraseology; and
5. amend standard operating procedures to ensure that flight progress strip notations include verification of complete runway information transfer.

CASA response dated 12 March 1996.

I refer to your Interim Recommendation number IR950213 concerning the accident involving Boeing 737, VH-TAI at Sydney Airport on 0 October 1995. The Authority wishes to forward the following response.

Summary

1. Agreed. CASA and Airservices will review all documentation.
2. Agreed. CASA will pursue with Airservices to provide necessary phraseology.
3. CASA does not concur with BASI' s concern.
4. CASA and Airservices are working to implement new phraseologies.
5. This is an issue for Airservices to address.

Background to response

1. CASA agrees that terminology used by ATC to identify the landing runway must be unambiguous. CASA will, with Airservices, review all documentation to satisfy this requirement.
2. In the case of a crossover to final, CASA agrees that ATC phraseology should positively alert a pilot to the situation. CASA will pursue this issue with Airservices to provide the necessary phraseology.
3. CASA is unable to understand BASI's concern with regard to the use of the phrase 'VISUAL'. It is only used by a pilot to indicate to a controller that the aircraft can proceed to destination in accordance with the visual approach requirements. When localizer tracking is required and the aircraft is established, pilots report

'ESTABLISHED' and when tracking visually to the runway pilots must report 'RUNWAY....LEFT/RIGHT IN SIGHT' when the appropriate runway is sighted. As each situation has a separate and district phrase, there is no ambiguity.

4. CASA and Airservices are working to implement ICAO phraseology in Australia.  As runway readback is included in ICAO procedures, this recommendation will be satisfied when the new phraseologies are introduced.
5. Amending standard operating procedures to ensure that flight progress strip notations include verification of complete runway information transfer is an issue for Airservices to address.

Response status: Closed-Accepted.

Airservices Australia response dated 22 July 1996

I refer to your letter dated 3 January 1996, concerning interim recommendation IR950213, and relating to an incident involving parallel runway operations at Sydney airport. The particular circumstances relating to this incident were discussed at a special meeting of the Sydney Parallel Runway Operations Group, held on Tuesday 28th November 1995. This group comprises representatives from Airservices operational and policy areas, CASA and industry, and is charged with the development of standards and procedures for parallel runway operations.

Several recommendations were made at that meeting, proposing changes to AIP SUP H36/95, AIP, and Sydney Local Instructions, to preclude the possibility of a recurrence of this incident. It was felt, however, that major changes in reaction to a single incident should be considered carefully and take into consideration the amount of pilot and controller training material in circulation, and the potential risks of changing procedures so soon after implementation of independent visual approaches.

In relation to your recommendation (i), references to runway expectation are being removed from approach and director phraseology. Instead, the runway will be specified without the word "expect", and any subsequent change will only take place with the concurrence of the pilot in command.

In relation to recommendation (ii), a controller awareness program will be initiated, with guidance material being published in an information circular, highlighting the need for caution and advice to pilots when crossing centrelines. It was felt, however, that pilots should normally be aware of centreline crossover through the controller advice of runway and circuit direction.

In relation to recommendation (iii), it is difficult to see that there is any ambiguity in the pilot report requirements. During conduct of any approaches, pilots established on a LLZ should report established. The LLZ established call confirms to the controller the track guidance being used, and the report of "visual" is required to enable the application of the standard. When a pilot is not tracking on the LLZ, the track guidance is confirmed by pilot report of "runway in sight".

In relation to recommendation (iv), consultations are continuing separately on a proposed completely revised AIP and MATS phraseology package. This review is intended to bring Australian phraseologies into line with ICAO, as far as is practicable. One of the items being considered as part of this process, is the ICAO recommended practice of runway readback. It was considered prudent to wait for the results of this project, instead of a unilateral implementation at Sydney.

In relation to recommendation (v), any outcome from the revision of phraseologies that requires a pilot readback will be recorded on the flight progress strip as currently specified in MATS page 10-2-2 paragraph 32g.

It is proposed to review and re issue the AIP SUP relating to parallel runway operations in the near future, and account will be taken of the recommendations contained in BASI interim recommendation IR950213.

Response status: Closed Accepted

At 1139 the Canberra approach controller cleared Hawk 02 to track to Canberra from the east-south-east at an altitude of 3,500 feet. Just after this VH-GJZ departed from runway 12, tracking via Bindook. The pilot had been told to turn left onto a heading of 070 degrees and climb to 4,500 feet. A short time later the approach controller passed the responsibility for Hawk 02 to Canberra tower, saying this aircraft was to track for a left base on runway 17. The pilot of Hawk 02 was given a visual approach and commenced descent.

At 1142 the pilot of VH-GJZ advised approach control he was climbing to 4500 feet and turning left onto a heading of 070 degrees. The approach controller realised that separation would be lost between VH-GJZ and Hawk 02. The controller told the pilot of VH-GJZ to stop the turn on a heading of 110 degrees. Horizontal separation reduced to about one mile before vertical separation was established. The pilot of VH-GJZ reported sighting Hawk 02 and was told to pass behind this aircraft, then turn left onto a heading of 040 degrees.

A third aircraft, callsign Squirrel 005, had been cleared direct to Canberra from the north-east at an altitude of 4500 feet. As a result of the controller's instructions to VH-GJZ this aircraft and Squirrel 005 were now on conflicting tracks. The pilot of Squirrel 005 was told to turn 30 degrees to the right and the pilot of VH-GJZ was told to climb to 7,000 feet. Horizontal separation between VH-GJZ and Squirrel 005 reduced below the minimum standard before vertical separation was established.

Significant Factors

The following factors were considered relevant to the development of the incident:

1 The approach controller did not satisfactorily plan the handling of the sequence.

2 The approach controller did not take timely steps to avoid potential traffic conflicts.

The pilot stated that during the take-off run with both engines at full power, the aircraft veered to the left. At 40 kts the aircraft did not respond to full right rudder, so the pilot aborted the take-off. The aircraft came to rest in an adjoining cultivated paddock with the nosewheel broken off and both propellers damaged.

The pilot had recently passed his General Flying Progress Test (GFPT), and on the day of the accident had completed a dual check on VH-PXB. He had subsequently made three local passenger carrying flights. During the fourth flight the pilot stated that, as the aircraft approached Archerfield circuit area, and shortly after he had changed the fuel selector from the right tank to the left tank, the engine lost power. The pilot decided to conduct an emergency landing on a road. During the landing roll, the left wing struck a signpost.

Both fuel tanks were drained after the accident and the left fuel tank yielded 18.5 litres and the right fuel tank 9 litres. The published unusable quantity for each tank is 1 litre. This implies that adequate fuel was available for continued engine operation. However, the pilot reported that the flying conditions were turbulent at about the time he changed tanks, and it is possible that air may have entered the fuel system while the right tank was selected. The engine was ground run after the aircraft had been recovered and functioned normally.

The reason for the loss of engine power was not determined.

The pilot was tasked to fly parachutists to altitude where they would exit for a display at the Melbourne Masters Games.

Prior to any jumps, the pilot had held a safety briefing for about 50 parachutists involved in the event. According to the Safety Support Officer of the Australian Parachuting Safety Council, the safety briefing stipulated that every jumper would climb out onto the helicopter's landing gear skids and then leave one at a time at five second intervals without pushing off.

On about the eighth jump run, four parachutists climbed out onto the skids of VH-JGE. This placed two parachutists on the left skid and two on the right. The pilot flew from the right front seat, which is normal practice in a Bell 206.

When the helicopter was at 3,500 ft and 50 kts over Olympic Park, the target area, one parachutist from the left rear position departed the skid, immediately followed by the second parachutist from the left side. With the two remaining parachutists still standing on the right skid, plus the pilot in the right front, the helicopter's lateral centre of gravity limits were exceeded. According to the pilot, he was unable to prevent the helicopter from rolling to the right. At some point during the roll, the two parachutists standing on the right skid also departed. In the opinion of the pilot, the right side parachutists pushed off rather than stepping off and that the push aggravated the rate of roll. The roll continued through 360 degrees. The helicopter recovered at 70 kts after a height loss of six or seven hundred feet. The pilot advised that torque and rotor RPM limits were not exceeded during the incident.

After the incident the pilot landed and inspected the aircraft. He discovered evidence of a slight mast bump. He then flew the helicopter to Essendon where further inspections were performed by engineers. The main rotor mast was removed and checked for ovality and runout. The manufacturer was consulted during the inspections. When no fault was found with the helicopter, it was returned to service.

Just prior to the incident there had been some reorganisation of jump loads due to a six place helicopter arriving. The parachutists involved in the incident had, in rapid succession, been assigned to a four place load, then a six place load and finally to a different four place load. The Safety Support Officer subsequently determined that the two parachutists on the left side thought that all four parachutists were going to exit simultaneously on an exit count of `ready set go' given by the parachutist on the front left. The parachutists on the right side had previously briefed with a different group which had planned to exit alternatively left and right at five second intervals; they believed this was the standard briefing and had not discussed it with the left side jumpers after being reassigned to the Bell 206.

Since the incident, the Australian Parachute Federation, via a News Sheet and News Letter, has reinforced the importance of the pre-jump safety briefings, and the exit practice. Also, parachutists have been reminded of the need for extra care at special events where normal exit procedures may be varied due to operational requirements.

The following factors were considered relevant to the development of the incident:

1. The pre-jump safety briefing was probably inadequate.

FACTUAL INFORMATION

A short local test flight was planned to verify scientific equipment installed in the aircraft before it embarked on an atmospheric research flight.

The take-off was normal from runway 03, and after climbing through 500 ft the pilot reduced the manifold pressure and RPM settings of both engines from take-off to climb power. Sometime after this he turned the auxiliary fuel pump switches from low to off. At 1,500 ft a vibration, which appeared to have originated in the left wing, was noticed by both the pilot and the data systems operator, who also held a private pilot licence endorsed on the aircraft type. They said that the left tip tank seemed to move through 10 - 15 mm, and the equipment pod, mounted on the underside of the left wing moved in the same plane and frequency. The right alternator warning light then illuminated.

Both pilots decided that it would be more prudent to return than continue the flight. The data systems operator suggested that because of the vibration a slow airspeed should be maintained during the descent. The pilot noticed that the airspeed indication was 115 kts, and believed he carried out the descent without any change to the power settings. He notified the control tower of his intention to return, but without advising the actual reason.

Approaching base leg for runway 03 the pilot reported that he selected 10 - 15 degrees of flap, and that the data systems operator extended the landing gear without consulting him. The data systems operator stated that it was after the aircraft had turned onto final approach, he noticed the landing gear selector lever was between the retract and extend positions and moved it to the extend position. He also attracted the pilot's attention to the airspeed, which had dropped to 82 kts, this being only several knots above the stall speed for the aircraft in its present configuration. The pilot advanced both throttles to reduce the high sink rate which had developed due to the slow forward speed, but neither engine appeared to respond. The throttles, pitch levers and mixture controls were then fully advanced, but still without any apparent response from either engine.

The pilot then realised it would be impossible to land the aircraft on the aerodrome, and a forced landing was inevitable. He thought he noticed the data systems operator selecting the flaps up at about this time, although the data systems operator could not recall doing this. As the data systems operator had more flying experience on the aircraft, and also being a glider pilot familiar without landings, the pilot considered him better qualified to carry out the forced landing, so gave him control. The data systems operator then had just enough time to ensure that the wings were level and initiate a flare, which failed to arrest the high rate of descent.

The aircraft impacted the ground heavily on a golf course adjacent to the runway threshold. Both main gear legs failed and separated, the nose gear leg remaining in situ still extended. The aircraft continued along a fairway for 230 m in a direction of 023 degrees, colliding with an automatic sprinkler system control unit, which buried deep into the left-wing root area. The aircraft then struck two small trees. This turned the aircraft to the right before it came to a stop on a heading of 090 degrees. The pilot and data systems operator sustained minor injuries.

The landing gear was found to be extended, with its selector in the corresponding down position, and the flaps retracted with its selector in the up position.

Ground slash marks, and damage to all propeller blades indicated that the engines were operating at impact. The right propeller had all blades bent back, one blade severely bent, with lesser bending on the other two, indicating that each blade had contacted the ground before the engine stopped. Two of the blades also had forward bending tendencies, but marks on the blades indicated they had been buried in the ground when stationary, and this bending occurred as a result of the aircraft turning at the end of the ground run. All blades on the left propeller were bent back in a gradual curve, the bending again corresponding with each blade contacting the ground before the engine stopped.

Witnesses who observed the aircraft on its final approach reported hearing engine noise. Black smoke was also noticed coming from the right engine, and several backfiring sounds were heard.

After the accident, when the pilot was securing the cockpit and turning off electric power, switches, and fuel, he noticed that an auxiliary fuel pump switch was in the high position. He could not recall this pump being turned on at any time during the flight. An inspection revealed that the right engine exhaust pipes had deposits of soot, but none at the outlet or along the underside of the nacelle. There was no soot in the left engine exhaust pipes.

All fuel filters were found to be clear of contamination, there were no obstructions in the fuel lines from the tanks to engines, and normal quantities of fuel were found at the engines in the fuel control units and distributor valves. Laboratory testing found no problems with the fuel.

No faults were found with the ignition systems which may have caused both engines to fail.

All external pods and probes were correctly attached, and no damage or defects could be found which may have contributed to the reported inflight vibration.

Both engines were inspected and no defects found which could have affected their operation. They were then installed in an engine test stand and ran normally at all power settings, responding correctly to all throttle movements.

The aircraft had been operated in the private category. The flight manual states that pilots required to operate the aircraft must be trained and approved to fly this particular aircraft when configured for atmospheric research with external pods, pylons and probes fitted. The pilot had undergone several hours of familiarisation training 12 months previously but had not flown the aircraft since. The operator did not conduct recency checks or give continuation training for pilots.

ANALYSIS

An inspection of the aircraft and its ancillary pods, pylons and probes failed to find any looseness, faults or any other airframe problems which may have caused the inflight vibration. It is possible that slight turbulence may have produced the effect. Illumination of the right alternator light was not considered as having contributed to the accident.

Both engines were found to be serviceable and capable of delivering full power. The propeller slash marks in the ground and damage suffered by the propeller blades before the engines stopped indicated that they were developing power at impact.

It is possible that the right auxiliary fuel pump was accidentally turned on as the pilot turned the pump switches from low to off during the climb. This would have produced a rich mixture in the right engine with associated rough running and vibration. It would also account for the deposits of soot in the right engine exhaust pipes, and the smoke seen by the witness.

While returning to the aerodrome the pilot stated that he did not adjust the engine power settings for the descent to circuit height. Due to possible task saturation, he probably reduced the power without realising it, otherwise, with its engines operating normally, the aircraft would have accelerated. During this time however, the airspeed deteriorated from 115 kts to 82 kts.

The pilot selected 15 degrees of flap on base leg, and then after turning final was warned of the slow airspeed by the data systems operator, who had extended the landing gear, causing more drag. The aircraft would have been near its stall speed, with a subsequent high rate of descent. This would have been exacerbated if the data systems operator had raised the flaps, which he could not recall doing.

When the pilot opened the throttles, he may have gained the impression that the engines were not developing power as the aircraft would have continued its rapid descent. With all the unusual activity going on it is possible that the pilot failed to register an increase in engine noise. The application of power probably prevented a stall developing, with subsequent loss of control.

There was no evidence found to indicate that both engines had suffered failures simultaneously and were not capable of responding to throttle movement.

SIGNIFICANT FACTORS

1. A possible rich mixture on the right engine may have caused an inflight vibration.
2. The pilot and data systems operator became worried about a vibration, and did not monitor the aircraft's progress adequately.
3. The pilot was not current on the aircraft and allowed the airspeed to deteriorate with the aircraft developing a high rate of descent.

The glider was on an aero tow take off. On the ground roll the right wing contacted the ground and the glider veered to the right of the tug. Corrective control inputs were applied and the glider moved to the left side of the tug. The glider pilot pulled the release. The glider went through a cartwheel manouver and the nose struck the ground heavily.

Significant Factors

The following factors were considered relevant to the development of the accident:

1 Probable inappropriate control inputs by the glider pilot.