Fuel starvation

SYNOPSIS

The aircraft was operating a freight charter flight, cruising normally at an altitude of 20,000 ft (FL200), when, about 150 km south-east of Mackay, the left engine lost power and could not be restarted. During the subsequent landing on runway 14 at Mackay, the pilot attempted a single engine go-around when he suddenly had the (mistaken) impression that the landing gear was not down. He temporarily lost control of the aircraft but recovered to touch down on the flight strip to the left of the runway, some 500 m before the runway end. During the landing roll, the landing gear collapsed, and the aircraft sustained substantial damage.

The report concludes that the engine power loss was caused by failure of the fuel pump high pressure relief valve.

The pilot, believing that the landing gear was still retracted, initiated action to avoid a wheels-up landing. This action was initiated too late in the landing approach for a successful outcome.

1. FACTUAL INFORMATION

1.1 History of flight

The aircraft was operating a freight charter flight from Archerfield to Mackay. The flight proceeded normally until about 150 km south-east of Mackay when, while cruising at FL200, the left engine lost power. The pilot feathered the propeller and made three unsuccessful attempts to restart the engine. At each attempt, the indicated fuel flow remained at zero. The pilot then directed his attention to conducting a single engine landing at Mackay.

The pilot reported that he positioned the aircraft to arrive abeam the upwind end of runway 14 at 2,000 ft at an airspeed of 180 kt. The descent was continued on the downwind leg, with the aircraft abeam the threshold at 1,500 ft, indicating 150-160 kt. Early in the base turn, and at an airspeed of 130-140 kt, the landing gear was selected down (with three green indicator lights illuminated) and flaps set to one quarter. The pilot recalled that the Visual Approach Slope Indicator (VASI) was indicating two to three dots high at this stage. Half flap was selected after two-thirds of the base turn had been completed. The aircraft was rolled out on final at 120-130 kt, with the VASI indicating 2-3 dots high. Three quarter flap was then selected. The pilot selected full flap when he judged that touchdown on the runway was assured and confirmed that the landing gear indicator was still showing three green lights. He noted that the airspeed was reducing towards Vref (the pilot had earlier calculated Vref to be 111 kt). The aircraft was still high on the approach, so the pilot lowered the nose and pointed the aircraft at the threshold. He recalled the airspeed indicating 118 kt as the aircraft crossed the end of the runway.

The pilot flared the aircraft for landing and believed that it was settling normally as he reduced power on the right engine. As the aircraft floated, however, he felt the aircraft sinking and suddenly experienced a very strong perception that the landing gear was not down and that the propellers were about to contact the runway surface. The pilot reacted to this sensation by immediately applying full power to the right engine in an attempt to go-around. However, the aircraft pitched up and began rolling uncontrollably to the left. When he realised, he could not control the aircraft, the pilot reduced power on the right engine and stabilised the aircraft which, by this stage, was above the flight strip to the left of the runway. He landed the aircraft on the flight strip, touching down about 500 m from the far end of the runway. During the landing roll, the landing gear collapsed, and the aircraft skidded on its under-belly through the airport boundary fence, coming to rest at the edge of an area of mangroves about 200 m beyond the end of the runway.

1.2 Injuries to persons

The pilot, the only occupant of the aircraft, received minor injuries in the accident.

1.3 Damage to aircraft

All three landing gears had failed rearwards. The nose landing gear became wedged beneath the cockpit, causing distortion to the lower fuselage around the nose landing gear attachment point and at the rear cockpit bulkhead. There was substantial damage to the engine nacelles, propellers, and engine mounts.

1.4 Personnel information

The pilot in command was 29 years old. He held a current First-Class Airline Transport Pilots Licence and was appropriately endorsed on Swearingen SA226 aircraft. His total flying experience at the time of the accident was 2,670 hours, of which 181 were on type. The pilot had 2,350 hours flying experience on multi-engined aircraft and 1,500 hours experience on turbine engined aircraft.

1.5 Aircraft information

The aircraft was a Swearingen Aviation Corporation SA226-TC, Serial Number TC-330, manufactured in the USA in 1979. It was powered by two Garrett Airesearch TPE-331-10 turboprop engines.

1.6 Meteorological information

The weather at Mackay at the time of the accident was reported to have been fine with a light south-easterly wind. The beginning of daylight on the day of the accident was 0550 hours EST.

1.7 Communications

Satisfactory radio communications existed between the aircraft and Brisbane Flight Service. The pilot did not declare an emergency or advise Flight Service of the engine failure.

1.8 Aerodrome information

Runway 14/32 at Mackay is 1981 m in length. It is 45 m wide and has a surface of grooved asphalt. The runway is equipped with T-VASIS approach slope indicator system, set for a 3 degree glide slope.

1.9 Flight recorders

The aircraft was equipped with a Collins 642C-1 cockpit voice recorder. The unit was removed from the aircraft and replayed following the accident. The quality of the recording was satisfactory, and the contents of the tape supported the pilot's account of the sequence of events.

1.10 Wreckage information

The aircraft's weight and centre of gravity at the time of the accident were within limits.

Examination of the left engine revealed a failure of the threaded section of the fuel pump assembly high pressure relief valve body. When the part was disassembled, the packing washer that fits between the threaded section and the hexagon portion of the valve body was missing. The face of the hexagon portion of the valve body contained marks consistent with the cap having been tightened against this face. The fracture surface was indicative of overload failure.

No reason could be determined for the packing washer not being fitted, nor could it be determined who might have tightened the valve cap.

1.11 Survival aspects

The aircraft was equipped with full safety harnesses for both cockpit seats. The pilot reported that his habit was to fly with the lap strap secured and the shoulder straps undone during the cruise. On this occasion, he forgot to reconnect the shoulder straps before landing. He recalled that, during the impact sequence, he braced himself with his hands against the instrument panel coaming.

The pilot did not advise any air traffic services agency of the emergency. Mackay Tower was not manned at the time of the accident, nor were any emergency services in attendance at the airport.

1.12 Human performance aspects

1.12.1 Pilot's recent history

The accident flight was the pilot's first duty period following a three-day break. He had worked on three of the four days before the break, commencing duty not earlier than 0500 hours and finishing not later than 2300 hours on each occasion.

On the night of the accident, the pilot rested from about 2300 hours to 0200 hours. This was his normal practice. The pilot said that he routinely felt tired during early morning flights and this occasion was no different.

1.12.2 Stress

In unexpected and unusual situations, an individual's stress level increases. In high stress situations, performance can degrade as the individual tends to restrict or focus attention on that which is perceived to be the primary demand (an effect often termed narrowing of attention).

1.12.3 Workload

The ability of the human to process information is limited. Influences such as stress and fatigue can increase the perception of the demands of the task and therefore increase workload. In work overload conditions, the human responds in one of the following ways:

1. Omission - Ignoring some aspect of or responsibility associated with the task.
2. Error - Information is processed incorrectly.
3. Queueing - Responses are delayed until lulls occur in workload.
4. Filtering - Certain categories of information are omitted according to some priority scheme.
5. Approximation - Responses become less precise.
6. Regression - Responses are in accordance with previous overlearned behaviour.
7. Escape - Giving up.

1.12.4 Information processing

When making decisions, an individual will search the environment for critical cues. Evidence is available which suggests that the decision maker's cue seeking behaviour is heavily influenced by any hypothesis which may have already been chosen. Information which is consistent with the hypothesis is used in the decision-making process while information which is inconsistent is ignored. Such a scenario is particularly relevant in high stress situations. Equally, when there is pressure to make a decision quickly, the chance of making an error increases - a phenomenon which is known as the speed-accuracy trade-off. This trade-off often occurs when the consequences of making an error are most unforgiving, such as when landing an aircraft.

1.13 Additional information

1.13.1 Asymmetric flight training

The pilot had completed the required training for his endorsement on the

SA226-TC aircraft. This training included asymmetric flight training and involved circuits and landings with an engine set at zero thrust. The accepted standard technique for asymmetric circuit training is for the pilot to fly as close to a normal circuit as possible, using power as required on the live engine to achieve the required performance.

The pilot indicated that the conversion training he undertook on the aircraft included a number of practice asymmetric circuits and landings with the failed engine set at zero thrust, not shut down. These circuits were flown using the height and speed parameters for a normal circuit with the aircraft carrying no load other than the pilot and check pilot.

CAO 40.1.0 Appendix III specifies the flying training syllabus applicable for a type conversion on to SA226-TC aircraft. Paragraph 1(d) of the CAO refers to asymmetric flight and lists, as one requirement, approach and landing with one or more engines inoperative (at least twice).  The CAA advised that there was no requirement for landings to be conducted with one propeller feathered and it was acceptable for an engine to be set at zero thrust for landing.

1.13.2 Single engine operations aspects

The pilot said that, for the arrival at Mackay, his aim was to maintain aircraft speed close to, but not below, normal and to remain slightly high compared to a normal powered approach. He was very conscious of the need not to let the aircraft get too low or slow and felt that, in flying the type of circuit described, he had achieved his aim.

The pilot provided a comparison between the parameters he used for a normal powered circuit and those flown for the single engine approach into Mackay.

When abeam the upwind end of the runway, the aircraft should be at 1,000 ft, 210 kt and with 1/4 flap lowered. The pilot reported that his aircraft was at 2,000 ft and 180 kt, with the flap still up.

By mid-downwind, the aircraft should be maintaining 1,000 ft, airspeed 180 kt with 1/2 flap lowered. The pilot stated that the descent was still continuing at this point.

By abeam the runway threshold the aircraft should still be at 1,000 ft with the speed reduced to 170 kt and the gear down. Abeam the threshold, the aircraft was passing 1,500 ft at 150 to 160 kt.

One third of the way around base, the aircraft should be at 140 to 150 kt. The pilot reported that it was at 130 to 140 kt with the gear down, 1/4 flap lowered and three dots high on the VASI.

Two thirds of the way around base, the aircraft should have been at 130 kt. At this point the pilot lowered half flap.

The aircraft should be lined up on final approach not below 500 ft when full flap can be selected. The pilot reported that the aircraft was at 120 to 130 kt when lined up on final approach with 3/4 flap selected and two to three dots high on the VASI.

Mid to late final approach, the pilot should have been flying to achieve a Vref airspeed of 111 kt at 50 ft. At this stage, the aircraft was configured with full flap, airspeed decreasing towards Vref and still above the desired glide slope. The pilot then lowered the nose and "aimed the aircraft" at the threshold.

2. ANALYSIS

The Specialist Report details the cause of the failure of the fuel pump assembly high pressure relief valve. Failure of this valve interrupted the flow of fuel to the engine. This not only caused the engine failure, but also prevented a restart.

A key issue in this accident was the pilot's decision to fly a non-standard approach. The aircraft was carrying about 650 kg of freight at the time of the occurrence. Thus, the pilot was operating the aircraft at a considerably higher weight than that at which he had conducted asymmetric training. The pilot was also conscious of not allowing the aircraft to get too low or too slow at any stage of the approach. It is probable that these two aspects led him to adopt a continuously descending approach from 2,000 ft abeam the upwind end of the runway instead of flying a standard 1,000 ft circuit.

The effect of flying the modified circuit was to place the pilot in a situation involving judgements and assessments with which he was not familiar as he had not previously flown such an approach. The aircraft was higher than normal for the complete circuit and, according to the pilot, crossed the end of the runway at an airspeed of 118 kt. The calculated Vref was 111 kt. The less than normal propeller drag (due to the left propeller being feathered) would have reduced the rate of deceleration of the aircraft after the pilot closed the throttles and flared the aircraft for landing. The pilot had not previously conducted a landing in the aircraft type with one propeller feathered. He therefore had no reference upon which to base his expectations concerning the rate of deceleration in this configuration. The pilot also indicated that after flaring the aircraft for landing, he held it off the runway rather than flying it on. These three elements - the high speed, the lower drag, and the pilots landing technique - would all have contributed to prolonging the float before the wheels contacted the runway.

The pilot described experiencing a sinking feeling which led him to believe that the landing gear was not down. This feeling most probably resulted from the float during the flare. Although he indicated otherwise during interview, the pilot's stress level was probably elevated during the arrival at Mackay. The higher the stress level, the less likely it would have been for the pilot to recall the "three greens" landing gear check he had completed on base and final approach and to assess this against the sinking feeling.

In most situations in which an aircraft is close to the ground and uncertainty arises as to whether a safe landing can be made, the familiar pattern of behaviour would be for the pilot to remove the aircraft from the immediate threat by increasing power and climbing away.  In this instance, the pilot seems to have done this almost as an unconscious automatic reaction to the sudden (misconceived) impression that the landing gear was not extended. It is perhaps indicative of the level of stress he was under at that instant, that he reacted in the manner he did.

As soon as the aircraft began rolling left after power had been increased on the right engine (the airspeed would almost certainly have been below Vmca by this time), the pilot quickly recognised the situation and reacted correctly by closing the throttle and landing the aircraft.

The pilot was fortunate that the deceleration forces experienced during the off-runway landing were relatively low, as he had not secured his shoulder harness (this omission may be another indication of his stress level). The pilot was also fortunate that assistance after the landing was not required from any of the emergency services. The aerodrome was unmanned at the time of the accident and no emergency services had been activated because the pilot had not advised any agency (other than his company) of the abnormal situation.

3. CONCLUSIONS

3.1 Findings

1. The pilot was appropriately licensed and qualified, and medically fit, to undertake the flight.
2. The aircraft weight and centre of gravity were within limits.
3. The left engine failed, and could not be restarted, following failure of the fuel pump high pressure relief valve for that engine.
4. The pilot did not notify any agency, other than his company, of the emergency situation prior to the approach.
5. The pilot conducted a non-standard, single-engine approach into Mackay.
6. The pilot had not previously conducted a landing in the aircraft with one propeller feathered.
7. The pilot was probably experiencing some stress during the approach and landing.
8. The aircraft speed across the threshold was about 7 kt above the reference threshold speed.
9. A combination of reduced propeller drag, high threshold speed, and the landing technique of the pilot resulted in the aircraft floating for a substantial distance along the runway.
10. The pilot formed a false hypothesis that the landing gear was not extended.
11. The pilot initiated and then discontinued a single-engine go-around at a speed below Vmca.
12. The aircraft subsequently landed on unsuitable terrain adjacent to the runway.
13. The pilot did not have his shoulder harness secure for the landing.

3.2 Significant Factors

1. Failure of the fuel pump high pressure relief valve interrupted fuel flow to the engine.
2. During the subsequent single-engine landing, a combination of reduced propeller drag, high threshold speed, and the landing technique of the pilot resulted in the aircraft floating for a substantial distance along the runway.
3. The pilot perceived that the landing gear was not extended and attempted a single-engine go-around at a speed below Vmca.

The pilot had been authorised to conduct a solo navigational exercise as part of a commercial pilot licence course. The authorisation did not include the three passengers, two of whom were trainees from the same training facility as the pilot. The flight was planned to track from Cessnock to Tamworth for a landing, then Gunnedah to refuel before returning to Cessnock.

The flight progressed as planned to Tamworth where the fuel quantity was visually confirmed adequate for the next leg to Gunnedah. At Tamworth, the pilot discussed with the front seat passenger the possibility of performing a simulated engine failure in cruise using the fuel selector to fail the engine. The passenger stated that, as he considered this to be unsafe, he would simulate an engine failure by retarding the throttle only.

The pilot reported that during cruise at 6,500 ft, after departing Tamworth, the front seat passenger retarded the right engine throttle to simulate an engine failure. The engine failure procedure was performed by stating the actions and touching, but not manipulating, the appropriate controls. Power was then restored to a normal cruise setting.

Later, whilst passing through 5,000 ft on descent into Gunnedah, the right engine began to run roughly, and the aircraft yawed to the right. The pilot carried out system checks, including repositioning the throttle to achieve the smoothest operation. He did not shut down the engine, as he considered it to be capable of producing some power. The descent continued to the circuit area, which was entered on the crosswind leg for runway 11. A strong southerly wind was noted. The landing gear was extended at about mid-base leg. A normal circuit was flown until the turn onto final at about 400 feet AGL when the aircraft encountered turbulence and overshot the runway extended centreline. The pilot applied power to go around. However, the aircraft yawed to the right and continued to descend. The landing gear was retracted but the aircraft performance did not improve. Both engines were shut down and an emergency landing was carried out off the aerodrome. The occupants evacuated the aircraft through a shattered side window.

Investigation revealed that the right engine carburettor bowl and its supply line contained no fuel, but there was ample fuel in the right tank. As there was no physical damage to the bowl or line which could have allowed the fuel to leak away, it was concluded that the right engine fuel supply had been selected off some time prior to the accident.

The front seat passenger later stated that he had failed the right engine by selecting the fuel off some time prior to the aircraft entering the circuit. It was determined that the aircraft, as configured, was not capable of maintaining height and that the pilot had misjudged the circuit and approach. It is likely that the aircraft was positioned low and too far from the runway threshold as it overshot the turn onto final. The subsequent attempt to go around was unsuccessful because, with the landing gear extended and the right propeller windmilling, the aircraft had no climb capability. The pilot stated that he had continued with the approach as he believed that the right engine was capable of delivering some power if required.

Significant Factors

1. An engine failure was simulated by turning off the fuel to the right engine.

2. The right propeller was not feathered.

3. The pilot misjudged the circuit and approach to land and attempted to conduct a go-around.

4. The aircraft, as configured, was not capable of maintaining height.

What happened

On 3 May 2015, at about 0230 Central Standard Time (CST), a Cessna 210 aircraft, registered VH-BKD (BKD), departed from Alice Springs Airport, Northern Territory for a ferry flight to Broome, Western Australia. The pilot was the sole person on board.

At about 70 NM from Broome, the pilot obtained a weather report from the automated aerodrome weather information service (AWIS) located at Broome Airport. The AWIS indicated a dewpoint^[1] of 22 °C and an ambient temperature of 22° C, which indicated conditions suitable for the development of fog.

The pilot reported that the AWIS information prompted them to start considering alternatives should fog prevent a landing. The pilot had planned and flown BKD at the optimum endurance profile of 45% power^[2] and changed tanks^[3] on a regular time-based pattern. The pilot reviewed the fuel log and determined they had sufficient fuel for a 30-minute search for a suitable break in the fog. If unsuccessful, the pilot planned to turn back inland on a reciprocal to the inbound track and land on the highway.

At about 15 NM from Broome, the pilot observed the start of a thick layer of fog below the aircraft. Arriving overhead Broome Airport at about 0622 Western Standard Time (WST), with the right fuel tank selected, the pilot initially surveyed the area from about 1,000 ft above ground level. However, as there were no breaks in the fog, the pilot descended the aircraft to about 650 ft. The pilot kept the aircraft in visual conditions while circling the airport and Cable Beach areas (Figure 1) occasionally flying at a lower level to take a closer look for possible breaks. With the right fuel tank still selected, the pilot’s search continued for about forty-five minutes.

Figure 1: Broome Airport and accident site

Source: Google earth annotated by the ATSB

Deciding that landing was not possible until the fog lifted, the pilot sought assistance from the person waiting on the ground for the aircraft. As this person was local and understood the likely extent of the fog, they were able to offer the pilot two alternate airports, as options. The first option, Beagle Bay was about 62 NM to the north, and the second option Eco Beach, about 23 NM to the south. The pilot considered these options, but reasoned that with such widespread fog, these options may also be fog bound. With limited choices and now limited fuel, the pilot turned BKD for one last low-level check along runway 10. The pilot then initiated a climb with the intent of heading back to the highway to land.

Shortly after applying full power to initiate the climb, the aircraft’s engine surged and spluttered. The pilot instantly realised that the right tank had been selected for over an hour, and quickly changed the fuel selector to the left tank. However, the engine did not respond. The pilot then attempted to restart the engine with the ignition key, but reported hearing a crunching noise as the starter motor engaged. The propeller was still windmilling.

With the aircraft only at about 500 ft and descending into the thick layer of fog, the pilot levelled the aircraft’s wings and prepared for a forced landing. Electing to leave the undercarriage retracted, the pilot descended through the fog and noted the outline of a dirt track. The pilot attempted to land on the track, but the aircraft collided with the sandy terrain just prior to reaching it. The aircraft momentum allowed it to skid across the track, coming to rest in the mangroves a few metres on the other side (Figure 2 and 3). The accident site was located within the mangrove area of the Dampier Creek.

The pilot was not injured; however, the aircraft propeller and engine sustained substantial damage.

Figure 2: Initial contact point

Source: WA Police 

Figure 3: VH-BKD in the mangroves

Source: WA Police

Pilot experience and comments

The pilot had around 3,850 flying hours, with around 830 of those on Cessna 210 aircraft.

Pre-flight planning

The pilot elected to conduct the flight at night to increase their night command hours. The evening before the flight, the pilot checked the weather forecast and completed the flight plan. They noted a 30% probability of fog on the terminal area forecast (TAF) for Broome during the planned arrival time. However, the pilot reported that, in their experience, 30% probability of fog would mean non-existent or minimal impact on operations, so they did not consider or plan for any alternates

The pilot pre-flighted the aircraft in the morning prior to the 0230 departure.

The pilot had personal commitments in Broome that morning and back in Alice Springs the next day. Hence, they needed to deliver the aircraft in time to catch the lunchtime jet flight back from Broome to Darwin and eventually be back in Alice Springs the next morning.

The flight

The pilot made the following comments about the flight:

• the cruise level was 8,500 ft
• there was smooth conditions enroute but with a stronger headwind than forecast
• the flight time between Alice Springs and Broome was about 5 hours.

Fuel management

The pilot maintained a fuel log during the flight. They initially used fuel from the left tank for 30 minutes, then 60 minutes on the right, back to the left. The pilot continued using this pattern until they arrived overhead Broome.

Although the pilot had calculated there was sufficient fuel to search for a break in the fog for 30 minutes, once pressured and distracted looking for an expected opening to be able to land, the pilot reported flying in excess of 60 minutes with the right fuel tank selected.

The aircraft fuel tanks were dipped post- accident. The right tank had no fuel remaining while there was 45 L remaining in the left tank.

Aviation weather forecasts and alternate aerodrome requirements

The Aeronautical Information Publication Australia (AIP) ENR 1.1 87 details the following requirements concerning planning for alternate aerodromes:

A pilot in command must make provision for flight to an alternate aerodrome, when required, in accordance with the following paragraphs:

…Except when operating an aircraft under the VFR by Day within 50NM of the point of departure, the pilot in command must provide for a suitable alternate aerodrome, when arrival at the destination will be during the currency of, or up to 30 minutes prior to the forecast commencement of, the following weather conditions:

Cloud – more than SCT below the alternate minimum

Visibility – less than the alternate minimum

Visibility – greater than the alternate minimum, but the forecast is endorsed with a percentage probability of fog, mist, dust or any other phenomenon restricting visibility below the alternate minimum….

Note: When weather conditions at the destination are forecast to be as above, but are expected to improve at a specific time, provision for an alternate aerodrome need not be made if sufficient fuel is carried to allow the aircraft to hold until that specified time plus 30 minutes.

AIP GEN 3.5-7 explains that:

PROB% is used in terminal area forecasts (TAF) to indicate an expected 30 or 40% probability of occurrence. If greater than or equal to 50% probability is forecast, reference is made to the phenomenon in the forecast itself not by the addition of a PROB statement

Safety message

The pilot had planned the flight using maximum endurance performance figures and kept a fuel log. The pilot’s fuel management used a time-based system up until arriving overhead the destination. Due to the unexpected distraction and increased workload of arriving at the destination airport covered in thick fog, with no planned alternates, the pilot lost situational awareness of the aircraft’s fuel state.

Issue number 5 in the ATSB’s Avoidable Accident Series – Starved and exhausted: Fuel management aviation accidents looks in more detail at such scenarios. The report notes that fuel exhaustion is more likely to occur on flights when there is little flight fuel margin.

The Avoidable Accidents series is available on the ATSB website under the Safety Awareness tab.

The ATSB published a research report titled Dangerous Distraction, an examination of aviation accidents and incidents involving pilot distraction in Australia between 1997 and 2004, covers in detail the role of pilot distraction in a number of aircraft accidents.

The research looked closely at 325 occurrences involving some measure of pilot distraction. The researchers were able to develop a taxonomy of three major causes of distraction. They were ‘flight management tasks’, ‘external objects’, and ‘people on board the aircraft’. The report concludes with a number of tentative suggestions for minimising the risk of pilot distraction. Further reading is available on the ATSB website.

Information regarding alternate aerodrome requirements is available in the Air Information Publication (AIP), ENR 1.1-87. This is available on the Airservices Australia website.

The Civil Aviation Safety Authority flight planning kit covers issues such as planning for alternates, obtaining local knowledge when flying to an unfamiliar destination and the importance of considering all aspects of the weather forecast.

This Flight Planning Kit is available from the online shop on the CASA website.

Aviation Short Investigations Bulletin - Issue 43

About this report Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2015 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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1. Dewpoint is the temperature at which water vapour in the air starts to condense as the air cools. It is used among other things to monitor the risk of aircraft carburettor icing or likelihood of fog at an aerodrome.
2. Endurance power setting allows for the longest time in the air.

The Cessna 206 floatplane was on a charter flight taking passengers from Kimberley Coastal Camp to Lake Kununurra. During descent 25 NM from Lake Kununurra, the aircraft's engine lost power. The pilot reported that he immediately switched the fuel selection from the left to the right fuel tank. He also selected full throttle, full rich fuel mixture, boost pump to low prime and full fine on the propeller pitch control. The engine did not respond so he elected to conduct an emergency landing on the Ord River. The pilot reported that the descent took about five minutes, during which he selected high prime on the boost pump for several seconds.

The engine did not recover power throughout the descent. The landing was conducted without further incident. The aircraft was undamaged, and the passengers were uninjured. The pilot reported that he filled the tanks before leaving Lake Kununurra for the Camp. Because of the amount of fuel he thought was in the left tank, the pilot had intended to select the right tank at 15 NM from Lake Kununurra. However, the engine lost power before he could do so. After the landing, the aircraft's left fuel tank was found to have about 8 L of fuel remaining, approximately 20 L less than the pilot had planned. The right tank had about 60 L. The operator reported that the only fuel system fault was three clips that secured the left fuel tank bladder to the wing were found undone. No fault could be found with the engine.

The pilot had planned a solo training flight from Canberra to Scone, returning to Canberra via Goulburn the next day. The aircraft departed Canberra with full fuel tanks and continued to Scone without incident, where it remained overnight. The pilot reported that on the return flight the main fuel tanks were used for take-off, and the auxiliary tanks were selected after the aircraft was established on the departure route. Approximately 50 minutes later, when the right auxiliary tank indicated almost empty, the right main tank was selected. However, as the left auxiliary tank still indicated some 10 to 12 gallons, feed to the left engine from that tank was continued.

A short time later, just prior to commencing descent from 9,000 ft into Goulburn, the left engine lost power. The throttles on both engines were retarded for descent and the left main tank was selected to supply fuel to the left engine. The left throttle was advanced some time later but there was no response from the engine. The pilot reported that his troubleshooting checks consisted of checking that the fuel selectors were on the main tanks, the mixtures were full rich, the ignition was on and that the auxiliary fuel pumps were selected to LOW. The left throttle was again advanced but there was still no response from the engine. The checks were then repeated, but with the auxiliary fuel pumps selected to HIGH. Again, there was no response from the engine.

The same checks were performed on both engines but neither engine responded when the throttles were advanced. Both mixture controls were moved to idle cut-off for about 30 seconds. Full rich mixture was then selected, but the engines still failed to respond. As the aircraft was now at a low height, the pilot concentrated on finding a suitable forced-landing site. Just prior to landing on an open field, he had to manoeuvre the aircraft to avoid a wire and a ditch which lay across the intended approach path. The aircraft subsequently landed heavily, sustaining substantial damage. The pilot evacuated the aircraft without injury.

The investigation determined that although the main tanks had been ruptured in the accident, sufficient fuel would have been available for continued operation of the engines. However, an inspection of the aircraft found there was no HIGH auxiliary fuel pump switch position, as reported by the pilot. The three switch positions available were LOW, which runs the auxiliary fuel pump continuously at low pressure, a centre OFF position, and an up position, placarded ON. In the ON position, the pump runs continuously at low pressure until low fuel pressure is sensed by the engine fuel pressure switch. This could occur due to an engine-driven fuel pump failure, or running a fuel tank empty. The pump then automatically runs at high pressure, and is retained in that mode by a latching relay.

If a fuel tank is allowed to run dry, and fuel supply to the engine is restored by selecting an alternate tank, the engine will then be supplied with an excessive amount of fuel, resulting in a loss of engine power due to over-fuelling. To correct that condition, the auxiliary fuel pump switch must be moved to OFF to unlock the latching relay. The flight manual instructions for the fuel system are to select the auxiliary fuel pumps to ON for takeoff and landing, and to use full rich mixture and auxiliary fuel pumps on LOW when changing fuel tanks. Further investigation determined that the right engine fuel pressure switch had a very high electrical resistance after activation.

Consequently, electrical current was able to flow in the latching circuit and lock the system to high flow mode when selected to the ON position. The left engine initially lost power due to fuel exhaustion of the left auxiliary tank. When the main tank was selected, and the auxiliary fuel pump switch was moved to ON, the pump mode changed to HIGH and the latching relay engaged. The consequent over-fuelling condition prevented the left engine from being restarted the right engine stopped from a similar over-fuelling condition when the right auxiliary fuel pump was selected to ON during troubleshooting.

In 1988, the aircraft manufacturer issued Service Bulletin MEB 88-3, which modified the auxiliary fuel pump system and operation because of reported failures of engine fuel pressure switches. The modification included changing the auxiliary fuel pump ON placard to read HIGH. The service bulletin was applicable to all 300/400 series aircraft. However, the modification was not mandatory in Australia and resulted in aircraft in the Australian fleet having differing operational specifications. Service Bulletin MEB 88-3 had not been incorporated on this aircraft.

Modified aircraft have appropriate cockpit placarding and flight manual instructions, but the pilot's operating handbooks do not include the amended instructions. This leads to a misunderstanding of systems operation between different aircraft. The pilot's response to the engine failure was not in accordance with the manufacturer's checklist.

SAFETY ACTION

The Bureau of Air Safety Investigation is currently investigating a perceived safety deficiency identified as a result of this occurrence. The deficiency relates to a misunderstanding of operational procedures on Cessna 300/400 series aircraft as a result of the optional modification state of the auxiliary fuel system (incorporation of Cessna Service Bulletin MEB 88-3).

Any recommendation issued as a result of this investigation will be published in the Bureau's Quarterly Safety Deficiency Report.

The aircraft was being used to muster cattle at Tallering Station. The pilot reported that the aircraft's fuel tanks had been filled the night before the accident. On the morning of the accident, the pilot again checked that the fuel tanks were full.

Having been airborne for approximately 4.75 hours, the pilot flew the aircraft towards the station homestead to refuel. The pilot estimated that there was sufficient fuel to remain airborne for at least a further 45 minutes. However, almost immediately, the aircraft's engine began surging and misfiring. The pilot reported that he completed the appropriate checks and when he pumped the throttle, the engine gave some response for approximately 5 to 10 seconds before it finally stopped.

The pilot reported that he attempted to find a suitable forced landing area but the aircraft impacted trees at approximately 40 kts late on final approach. The pilot was uninjured. Later, approximately 22 L of fuel was drained from the aircraft's left fuel tank but none was found in the right tank.

The aircraft's left and right fuel tanks were vented through a vent line connected to the left fuel tank. The vent line is fitted with a vent valve. However, the right fuel tank also had a vented cap. The subsequent engineering inspection found that the vent line valve had deteriorated and was sticking closed. It is likely that the vent valve had stuck closed at some point during the flight. The right tank probably fed quicker than the left tank due to it venting correctly through the vented cap. When the right tank contents had been exhausted, the low air pressure in the left tank probably created an insufficient head of fuel to feed the engine.

A defect report has been submitted to CASA by the operator's engineering organisation, recommending that both fuel tanks be fitted with vented fuel caps.

FACTUAL INFORMATION

Circumstances

The company's primary source of revenue was from scenic flights over the Great Barrier Reef. The flights were usually conducted in single-engine aircraft and at an altitude of 1,500 ft AMSL.

The planned one hour scenic flight was the third in a series of similar flights undertaken by the pilot in the aircraft that day. The pilot reported that, after a normal take-off, he was instructed by air traffic control to make a left turn, maintain 1,000ft, and track to a position abeam the control tower before proceeding to Green Island. When the aircraft was approximately abeam the control tower, the engine began to run roughly. This was followed by a significant power loss. The pilot immediately transmitted a mayday broadcast on the Cairns Approach frequency, advising that the engine had failed and that he would be returning to the runway. However, a short time later, the pilot assessed that the aircraft did not have sufficient altitude to reach the runway and he decided to land in a cleared area a short distance inland from the coast.

The pilot reported that he changed the position of the fuel selector soon after the engine lost power. He did this without looking down at the selector which was positioned on the floor of the aircraft. A short time later, when there was no apparent response from the engine, he moved the selector back to its original position, again without looking at the selector.

In the subsequent forced landing, the aircraft landed heavily in a left wing low, nose down attitude. It slewed left and hit a road sign before crossing a narrow sealed road and coming to rest against the gutter. There was no fire.

Communications

The pilot's distress call was his first transmission after changing to the Cairns Approach frequency. The approach controller acknowledged the call and then asked the pilot to report his altitude and confirm the aircraft's registration. Later, the controller requested that the pilot change to the tower frequency. The pilot subsequently advised that these requests increased his workload and distracted him from the primary task of flying the aircraft.

The Manual of Air Traffic Services, page 17-2-1, stated in part; `Distress or urgency communications should be maintained on the frequency on which it was initiated until it is considered that better assistance can be provided by transferring to another frequency'. It also stated that `Staff shall be conscious of the distracting effect that information requests may have on the aircrew'. The investigation could not determine whether, or to what extent, the pilot's performance was affected by the requests from the approach controller.

Wreckage examination

The impact marks and the nature of the damage indicated that the aircraft struck the ground at low forward speed, but with a high descent rate. The aircraft sustained major structural damage to the forward fuselage area. The main spar of the left wing was broken at about the mid-span position and the nose and left main landing gear assembly had separated from the airframe. The engine/cockpit firewall and cockpit floor on the pilot's side was compressed rearward and upward into the cockpit area. The flaps were up.

The right-wing fuel tank, the fuel filter, and the carburettor bowl were empty. The left-wing tank contained approximately 60 lt of fuel. Distortion of the cockpit floor had locked the cockpit fuel selector control in the right tank position, confirming that it was in this position at impact. All fuel lines were clear of obstructions. The nature of the damage to the propeller indicated that it was either stationary or rotating slowly at impact. The magnetos and carburettor were undamaged. These were retained and the engine was removed from the wreckage and test run. It started and operated normally.

The aircraft fuel system

Two integral tanks, one in each wing supplied fuel to the engine. Fuel from these tanks flowed through the fuel selector to a reservoir tank under the cockpit floor, then through a fuel shutoff valve and fuel strainer to the engine driven fuel pump. The fuel selector had three positions - LEFT, RIGHT and BOTH. Useable fuel in each wing tank was 91 lt. The aircraft was refuelled to approximately 60 lt per tank (120 lt total) prior to the first flight on the day of the accident. Recent fuel consumption tests conducted by the operator confirmed a usage rate of about 30 lt per hour.

The pilot advised that he normally operated the aircraft with the fuel selector in the BOTH position, as it was his experience that the tanks emptied at about the same rate during normal operations. Another company pilot advised that, because of an earlier indication of fuel imbalance, he had returned from the last flight on the previous day with the right tank selected. He did not move the selector from that position at the conclusion of the flight.

The aircraft operating handbook called for the fuel selector to be in the BOTH position for engine start and for it to be selected to BOTH during the pre-landing checks. A note in the handbook stated that the purpose of this check was to prevent engine failure due to one tank running empty.

Survival aspects

Whilst the outcome of this occurrence was not a ditching event, it was considered relevant to investigate aspects of survivability given that the majority of flights conducted by the company were overwater scenic flights at an altitude of 1,500 ft AMSL. The single-engine land aircraft used by the company to conduct these flights were therefore operated beyond gliding distance of a suitable landing area in the event of an engine failure for a significant proportion of each flight.

The company provided waist pack type life jackets for passengers and pilots. The normal procedure was for passengers to wear the waist packs, but to not undo the pack or don the jacket. Pilots usually stowed their life jackets under the cockpit seat. The expectation was that, in the event of an emergency occurring while the aircraft was over water, there would be sufficient time for the passengers and the pilot to don their life jackets before the aircraft ditched. The pilot of DZJ reported that, when the emergency situation developed, he had insufficient time to consider the passengers, or to instruct them on the use of life jackets, had that been necessary. A similar situation existed concerning his life jacket.

Recorded radar information

The recorded radar data showed that the aircraft's groundspeed for the last 20 seconds of flight was 49 kts. The aircraft handbook stated that the power off, flaps up stalling speed of the aircraft was 54 kts.

ANALYSIS

The evidence indicated that the engine failed because of fuel starvation that occurred when the right tank contents were exhausted. Given the reported contents of each tank at the start of flying on the day of the accident, and the contents of the left tank when the aircraft impacted the ground, it is likely that the fuel selector was not moved from the RIGHT position after the aircraft was refuelled the day before the accident. This conclusion is supported by the evidence that, in the two-hour period the aircraft had operated that day, the engine would have used about 60 lt fuel.

The reserve fuel tank below the cockpit floor would have emptied after the right tank ran dry, causing the engine power loss. When the pilot moved the fuel selector during the emergency (probably to either BOTH or LEFT), fuel would have begun to flow to the reserve tank. However, it is probable that pilot reselected the empty right tank before there was sufficient fuel in the reserve tank to restore engine power.

The recorded radar data indicated that the aircraft speed in the latter stages of the flight was close to, if not below, the stalling speed. The aircraft impact attitude, and the extent and nature of the damage, supports this conclusion. This evidence, along with the fact that the flaps were in the UP position at impact, indicates that the pilot had mismanaged the aircraft during the forced landing.

SIGNIFICANT FACTORS

1. The pilot did not select the fuel system to the BOTH position prior to take-off.

2. The engine ceased operation due to fuel starvation.

3. The pilot did not configure the aircraft appropriately for the forced landing.

4. The pilot did not maintain proper control of the aircraft.

SAFETY ACTION

While it was determined not to be a contributing factor in this occurrence, the Bureau believed that the safety implications of overwater operations in single-engine land aircraft carrying fare-paying passengers, required further investigation.

The Bureau considers that overwater operations in single-engine land aircraft carrying fare-paying passengers, at altitudes that will not allow the aircraft to glide to land (suitable for an emergency landing) in the event of an engine failure, is a high-risk practice. In particular, the outcome of a ditching event in a high-wing aircraft similar to the accident type presents obvious exit problems. The fact that this aircraft was equipped with fixed landing gear further reduces the survivability of a ditching event.

As a result, the Bureau of Air Safety Investigation issued the following interim recommendation to the Civil Aviation Safety Authority on 28 Jan 1998:

R970176

The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority reconsider the conditions of the current exemption to CAR 258 as it applies to passenger-carrying charter operations in single-engine land aircraft with a view to:

(a) minimising the likelihood of a ditching event; and

(b) minimising the risks associated with the outcome of a ditching event.

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Previous safety action

A previous fatal accident highlighted the safety implications of the practice of not correctly "donning" waist pack type life jackets during operations at or below 2,000 ft AMSL.

As a result of the investigation of that occurrence, the Bureau issued the following interim investigation to the Civil Aviation Safety Authority on 9 December 1997 (only the relevant parts of the interim recommendation have been reported below):

"IR960138

The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority:

(i) review the current orders and regulations to ensure that the intention of Civil Aviation Order 20.11 part 5, governing the wearing of a life jacket is clear and unambiguous, and that jackets worn in accordance with the order afford the wearer the maximum safety benefit; and

(ii) educate the industry on the need to have life jackets worn in such a manner that they afford the wearer the maximum safety benefits."

The following response was received from the Civil Aviation Safety Authority on 21 May 1996 (only the relevant part of the response has been reproduced below):

"Interim recommendation(i)

It is CASA's opinion that the current provisions of CAO 20.11.5 are essentially adequate. However, this issue will be referred to the relevant Technical Committee under the Regulatory Review Program for its review.

Interim recommendation (ii)

CASA supports this proposal and is considering the best means to give effect on this recommendation."

Ongoing safety action

As a result of this and other similar occurrences, the Bureau of Air Safety Investigation intends to conduct a review of Australian aviation occurrences involving fuel starvation and exhaustion. This study is due to be completed prior to July 1999. Any recommendations issued as a result of this safety study will be published in the Bureau's Quarterly Safety Deficiency Report.

Factual information

The pilot had planned to fly from Moorabbin direct to Ocean Grove, then on to Warrnambool. Prior to departure he was advised that there was 40 litres of fuel in the left main tank and the right main tank was full at 91 litres. Both tip tanks were also full at 63 litres each.  Records held by the operator showed that the aircraft was consuming an average of 61 litres per hour. Accordingly, the pilot was advised to use the right main tank for one hour, then use the tip tanks, and go back to the fullest main tank for the landing.

The pilot loaded his five passengers, selected the right main fuel tank, started the engine, conducted engine runs and taxied for take-off. These actions took approximately 20 minutes. After take-off the pilot flew coastal from Moorabbin to Ocean Grove rather than direct as planned, then tracked direct for Warrnambool. Due to weather constraints, he cruised between 2,000 feet and 2,500 feet above mean sea level and also deviated from his track to avoid rain showers. He used a high-power setting of 24 inches of manifold pressure and 2,400 rpm, and did not lean the fuel mixture. Approximately 65 minutes after take-off, at a position about 15 minutes from Warrnambool, the engine suddenly failed. At low altitude over hilly terrain the pilot said he did not have time to conduct a proper assessment of the cause of the power loss, nor did he have time to carry out a successful restart procedure. The pilot forced landed the aircraft onto a sloping field, colliding with a fence before bringing the aircraft to a stop. The aircraft suffered substantial damage, however the six persons on board were uninjured.

Investigation disclosed that the right main fuel tank contained unusable fuel only, and the fuel feed system to the engine was empty. When the system was supplied with fuel the engine was started and ran satisfactorily. Tests indicated that the fuel quantity measuring system was serviceable.

The pilot advised that during the flight he did not maintain a flight log and did not monitor the right main tank fuel quantity. His planning had indicated that the flight would take about one hour and he had intended to change to the fullest tank prior to landing.

The recommended power charts contained in the pilots operating handbook, which was available to the pilot, did not cover the combination of parameters under which this flight was conducted.

Analysis

While the contents of the right main tank prior to departure could not be definitely established it was most probably full at 91 litres. The coastal track taken by the pilot could have added up to an extra ten minutes flying and his deviations from track to avoid showers would also have added to his flight time. While the flying school's flight sheets indicated that the average fuel usage was 61 litres per hour, this was attained by using recommended power settings and correct leaning procedures. It was calculated that the aircraft could use up to 88 litres of fuel per hour while flying at low altitude with high power and a rich mixture. This, coupled with the taxiing, take-off and climb fuel flows would have depleted the 91 litre contents of the tank after approximately one hour in flight, as occurred.

By operating the aircraft as he did, the pilot chose to fly outside of the recommendations contained in the pilots operating handbook. However, even flying in this manner had the pilot maintained a flight time log and a fuel usage log, and monitored the fuel quantity gauges, he would have become aware of the contents of the right main fuel tank before the fuel was depleted.

Significant factors

1. The pilot did not use effective fuel management techniques.
2. Engine power was lost when the fuel tank in use was allowed to run dry.

The pilot reported that while spraying a crop in a scrubby paddock, the engine lost power during a pull-up manoeuvre over a scrub line. There was no suitable landing area ahead, so the pilot turned left through 100 deg in an attempt to reach a suitable clear area. He dumped the load to clear a fence but the angle of approach into the clearing was encroaching on another fence line running in approximately the same direction as the intended landing direction. This required a shallow right turn which was still being completed at touchdown. This resulted in the right-wing spray boom catching in the crop which in turn resulted in a ground loop and left main landing gear collapse.

The maintenance engineer who recovered the aircraft, advised that the engine operated normally when test run. The aircraft is fitted with two fuel tanks, one in each wing. The tanks feed into a common sump and the fuel selector only has two positions - ON or OFF. One tank contained 28 lts of fuel and the other one was empty. The tank vent line for the tank containing fuel was found to be blocked by a wasp's nest. Normally the two tanks would feed evenly to the common sump, but the blocked vent line probably prevented this from occurring and in turn starved the engine of fuel.

FACTUAL INFORMATION

Sequence of events

The flight was to conduct photographic work around the Kununurra area. The crew consisted of the pilot in command and a second pilot in the right front seat to assist with look-out, radio communications and communicating with the photographer. The photographer operated from the rear seat without a headset.

After the crew had completed part of the task, the pilot started to climb the aircraft to a higher altitude. As the aircraft passed about 600 ft above ground level, the engine stopped suddenly without warning. The pilot transmitted a Mayday message and carried out a forced landing into 30-foot trees. During the impact, the aircraft turned over and the stitching of the harness of both pilots came undone, releasing the shoulder harnesses.

The pilot in command and the photographer suffered minor injuries. The right-seat pilot was seriously injured.

Wreckage

The aircraft came to rest inverted with the left wing torn off. The propeller blades were broken but showed no signs of rotation during impact. The Bureau was advised that, four days after the accident, an inspection of the fuel tanks indicated that the right tank was about three-quarters full, while the left tank contained only about 20 litres. Fuel was leaking from the impact-damaged left tank-to-engine feed lines. Consequently, the fuel quantity remaining in the aircraft at the time of the engine failure could not be accurately determined. Subsequent specialist inspection of the fuel-system components found that the engine-driven fuel pump outlet port was blocked by grit wrapped in fibrous material. The system filters were also contaminated.

The aircraft was normally refuelled at Kununurra, but had been refuelled from drums when operating from another strip in the area.

Aircraft maintenance

Further inspection of the engine found that the mixture control was excessively worn and that three spark plugs could be unscrewed by hand. The time at which contamination of the fuel system occurred was determined. The last periodic inspection was conducted 94 hours prior to the accident.

Emergency locator transmitter

A portable Pointer 3000 emergency locator transmitter (ELT) was carried in the baggage compartment. The ELT was turned on by the pilot after the accident and its signal was detected by the Brisbane Search and Rescue Co-ordination Centre.

ANALYSIS

The reported blockage of the engine-driven fuel pump outlet port is consistent with the circumstances of the engine failure. Contamination could have been introduced to the system if appropriate filtration was not used during refuelling from drums. Although there were indications that the aircraft maintenance was deficient, there was insufficient evidence to suggest that inadequate maintenance was implicated in the circumstances of the accident.

SIGNIFICANT FACTOR

It is likely that engine power was lost due to fuel starvation caused by system contamination.