On 2 March 2018, a single-pilot Cessna 441 (VH-LBY) being operated by Skippers Aviation on a scheduled domestic passenger flight from Fitzroy Crossing to Broome in day VMC successively lost power on both engines due to fuel exhaustion. A MAYDAY was declared and since it was impossible to reach the destination or any other aerodrome, a forced landing was completed on the main highway in the area with no damage to the aircraft or injury to the 10 occupants.
The aircraft secured in its final stopping position. [Reproduced from the Official Report]
An Investigation into the accident was carried out by the Australian Transport Safety Bureau (ATSB).
It was noted that the pilot was one of four employed by Skippers Aviation and based at Broome to operate the C441 aircraft there. After being employed by the operator, he had qualified on type 9 months prior to the investigated event and had a total of 2,403 hours flight time, of which 402 hours were on type. His training records for conversion to the C441, line check and most recent instrument proficiency were found “not to contain any major issues or concerns regarding his performance or capability”.
The pilot was operating the aircraft involved on a return scheduled passenger flight from Broome to Halls Creek via Fitzroy Crossing on an IFR flight plan. The first and last sectors were expected to take around 45 minutes and the second and third about half an hour. No significant weather was forecast for the Broome area although there was a possibility of afternoon thunderstorms whilst away from Broome. The same pilot had flown the aircraft the previous day and had recorded the fuel on board at the end of the day’s flying read from the fuel gauges as 1,300 lb. Prior to departing for the following day’s flights, fuel to make a total of 2,350 lb was uploaded which would be sufficient to complete the planned four sectors.
After arriving at Halls Creek, the pilot recorded the fuel quantity on board from the gauges as 1,430 lb and stated that the difference in indicated fuel quantity after the first two sectors was consistent with the expected use. On arrival at Fitzroy Crossing after the third sector, he recorded the fuel quantity on board from the gauges as 1,300 lb which indicated an apparent fuel burn of 130 lb (although he erroneously recorded 230 lb on the flight log) whereas the expected fuel burn was 357 lb which would have led to an indicated fuel quantity of about 1,110 lb.
The OFP (Operational Flight Plan) showed that an estimated 977 lb would be used on the final sector including required reserves and the pilot subsequently stated that having noted that the indicated fuel quantity was above that required, he had not considered the difference between the expected and indicated fuel quantity any further. He reported that when taxiing for departure from Fitzroy Crossing, the right fuel transfer pump ‘fail’ indication had “illuminated momentarily” which he had attributed to “fuel movement within the tank during the left turn onto the runway from a downward sloping taxiway”. Having also noticed an imbalance between the indicted fuel quantity in the left tank and right tanks (left higher) he had then selected the right engine crossfeed (both engines supplied from the left tank) until the indicated quantity in each tank was similar before taking off.
The subsequent takeoff and the 18 minute climb to FL 260 were reported as normal. However, shortly after levelling off, the left main fuel boost pump CB tripped and the corresponding auxiliary boost pump on annunciator illuminated. After waiting a short time for the main fuel pump to cool, the pilot reset its CB but it tripped again, so he actioned the QRH Checklist for “Main and Auxiliary fuel boost pump failure”. Six minutes after reaching the top of climb, the pilot contacted Brome TWR and reported maintaining FL 260 with approximately 90 nm to run to Broome and was cleared when ready to descend to 7,000 feet.
Almost immediately this clearance had been received, descent was commenced from a position approximately 27 nm south of Curtin Airport and 42 nm south of Derby Airport (see the illustration below). At about the same time, the pilot reported having again observed a fuel imbalance, this time with the right tank contents higher than left) and that the total indicated fuel quantity “was not consistent with the fuel quantity indications on departure and the fuel flow observed during climb”. He stated that he had then selected left engine crossfeed (both engines supplied from the right tank), but had seen that the right auxiliary boost pump annunciator did not illuminate as expected for this crossfeed selection. He reported that when the left tank quantity began to show the expected increase, he had “assessed” that the absence of an indication that the auxiliary booster pump was working was an indication fault.
He added that during the crossfeed, an intermittent annunciation that the right fuel transfer pump had failed occurred (as seen prior to the earlier cross feeding prior to takeoff) and this had prompted him to stop the crossfeed. The right tank fuel low level indication was then annunciated but having checked the total fuel remaining based on the indications on both fuel gauges, he had concluded that there was sufficient fuel to continue to Broome as planned. However, shortly after this, the right fuel transfer pump fail annunciation became continuous and the right ‘FUEL PRESS LOW’ indication was illuminated, with corresponding left fuel system indications then following a few minutes later.
The annotated ground track of the aircraft from just before top of climb until the forced landing. [Reproduced from the Official Report]
The right engine then began surging and whilst the pilot was actioning the partial / intermittent engine power checklist, the left engine also started to surge. The right engine then failed and the pilot contacted the Broome TWR controller and declared a MAYDAY with the aircraft at FL155 and approximately 47 NM east of Broome and at around the same distance from both Derby and Curtin. A few minutes later, with the aircraft descending through 10,800 feet and now approximately 38 nm from Broome, the TWR controller asked if the aircraft would still be able to reach Broome and was advised that the left engine was still operating and they would be able to reach Broome.
However, shortly after this, the left engine also lost all power with an attempted restart only briefly successful before it again failed. Having recognised that it was now impossible to reach Broome, the pilot turned south towards the only main road in the area and advised TWR of a dual engine failure and the intention to make a forced landing on the road south of Broome. A successful emergency landing gear extension and passenger briefing followed but the latter did not include an instruction to brace for the landing.
The forced landing was subsequently accomplished on the main road approximately 21 nm east-south-east of Broome without any occupant injuries or damage to the aircraft. After bringing the aircraft to a stop, the pilot contacted another aircraft in the area who was able to relay their situation to Broome TWR. The passengers were all subsequently taken to Broome by road and the aircraft was towed to a nearby truck stop and secured. A photo of the fuel quantity gauges taken approximately an hour after the landing showed that their combined indications were about 1,120 lb whilst subsequent inspection found that there was “little or no usable fuel on board”.
Why it Happened
On the day following the forced landing, the fuel drains were operated and “a significant but unquantified amount of water” was collected. Fuel from sealed drums was then placed in the tanks and when drained was found not to contain any significant quantity of water. Engine ground runs did not result in any fuel leaks being detected and the fuel pump pressure low and fuel level low annunciators were checked and found to be operating normally. Based on this action and findings, and a preliminary assessment that both engines had probably lost power due to fuel exhaustion, the CASA issued Skippers Aviation with a special flight permit to allow the aircraft to be flown to Broome.
Once at Broome, all usable fuel was drained from the aircraft by diverting boost pump output into drums. After allowing for the quantity of fuel added at the roadside and used during the ferry flight, it was confirmed that there was little or no usable fuel on board the aircraft at the time of the forced landing whilst the fuel quantity gauges both indicated 370 lb. To allow inspection of the fuel tanks and their internal components, the fuel drains were opened and the underwing access panels removed. Inspection of the interior of both tanks was found to show “significant water beading on the surfaces and on the fuel quantity probes and a grey substance, subsequently identified as a fungus, was found in the tanks (although not on the probes)". The probes were tested and found to be outwith the required capacitance specifications but when cleaned, dried and retested, functioned normally so that the zero fuel state was correctly indicated on the fuel quantity gauges.
Potential opportunities for abnormal levels of fuel system contamination to have occurred after the last time the absence of such contamination had been routinely checked as a maintenance action during a scheduled check two months earlier were examined. The only such opportunity was after the aircraft was parked outside during a period of particularly heavy rainfall during a period when it was out of service awaiting a repair to the right wingtip damaged during a towing accident. However these circumstances could not be confirmed to have resulted in water ingress to the right wing fuel tank.
An explanation as to why the routinely required daily checks for water in drained fuel samples and the responses to such findings in the event that abnormal water contamination was found was sought. It was noted that the operators OM Part 1 included a requirement that pilots must conduct a fuel drain prior to the first flight of the day and following each refuel. This fuel sample must be visually checked for water and other contaminants and in the event any water is evident, further drains must be conducted until water was no longer visually evident. Once this point is reached during any required fuel drain process, the procedure requires that a further sample must be chemically tested for water using a water detection capsule. Should this water test result in a positive detection of water, a corresponding defect was to be recorded and this would ground the aircraft until the defect was cleared by qualified maintenance personnel.
It was found that the operator did not provide guidance as to what amount of water should be considered excessive nor did it require any reporting or recording (in the aircraft flight log or alternative maintenance documentation) of any water drained from fuel tanks. It appeared to the Investigation that the assessment of excessive water in the fuel relied on the judgement of individual pilots as supported by any knowledge gained from instructor pilots during training. It was also found that the operator’s water drain procedure did not include guidance on allowing a fuel sample to stagnate for a period to enable any water in suspension to settle, or to remind pilots that water may be in areas not immediately accessible via drain points.
In the case of the series of flights by the aircraft involved on the day of the forced landing, the pilot stated that he had carried out a fuel drain check during his first pre-flight external check of the day whilst the aircraft was still in the hangar and did not recollect any concerns about the findings. He did perform a second water drain test after refuelling had taken place and on neither occasion did he carry out the second stage of required testing using the water detection capsule, a lack of compliance which he was unable to offer any explanation for.
On the subject of fuel management during and between flights, relevant guidance in the General and Type-Specific sections of the OM stated that the PIC must use the indicated against calculated cross check to ensure sufficient fuel is on board for an intended flight before departure. It noted that “when a series of flights is undertaken by the same crew and refuelling is not carried out at intermediate stops, cross checks, other than prior to the first flight of the day, may be made by checking the fuel quantity gauge readings against the calculated fuel on board".
The operator’s practice for recording fuel burn and fuel on board before each flight relied on the flight log forms used by each pilot which, in terms of fuel, allowed them to compare fuel actually used per sector based on the fuel gauge differences with the planned fuel burn. An examination of the flight log figures for fuel actually burned on the previous days two sectors flown by the same pilot and aircraft found that after the first sector the fuel recorded as burnt was 201 lb compared to a 664 lb planned burn and for the second sector the fuel recorded as burnt was122 lb compared to a 730 lb planned burn. On the four sectors the following day which ended in the forced landing, it was noted that whilst the planned and actual fuel burns for the first two sectors were similar, the fuel recorded as burned was significantly lower than planned (130 lb compared to a planned 357 lb) and had resulted in the recorded departure fuel for the final sector being artificially inflated. It was noted that the OM Part 1 stated that the definition of the recorded fuel quantity on departure “shall be the fuel total as described in the aircraft type specific operations manual” but no such information was provided.
It was noted that the fuel flow gauges on all the operator’s Cessna 441 aircraft received their information from fuel flow transducers and that this information was also fed to the Garmin GNS 530 GPS/navigation system which had a fuel totaliser function. This required that a departure fuel figure was manually entered prior to each flight and/or after refuelling after which the residual fuel was continuously calculated. Senior pilots told the Investigation that the fuel burn figures produced by the Garmin 530 totaliser function were accurate. However, although there was a stated requirement that the Garmin GNS 530 totaliser function should be used as a means to cross check the fuel quantity indications after each fight, it was found that this requirement was widely ignored and that this fact was widely known. It was observed by the Investigation that “if the pilot of the occurrence flight had used the procedure, then it would have identified a significant discrepancy after the third sector on the day of the occurrence (and was) also likely to have detected the discrepancies on the two sectors they had flown on the previous day".
The other concern was that the pilot took no account of the illumination of the fuel low level annunciators, which were independent of the fuel quantity indication system, when deciding whether to continue the planned fight. Had he done so, he would have been able to safely complete a diversion.
Five Contributing Factors, one of which was defined as a ‘Safety Issue’, were identified as follows:
- Due to water contamination in the fuel tanks, the aircraft’s fuel quantity gauges were significantly over reading on the day of the occurrence and on previous days. This ultimately resulted in the aircraft departing for a flight without sufficient fuel to reach its destination.
- [Safety Issue] Although the operator had specified multiple methods of cross-checking fuel quantity gauge indications for its C441 fleet, there were limitations in the design, definition and/or application of these methods. These included:
- The primary method used (indicated versus calculated fuel) was self-referencing in nature, and not able to detect gradual changes in the reliability of fuel quantity gauge indications.
- Pilots did not record (and were not required to record) sufficient information on flight logs to enable trends or patterns in fuel quantity gauge indications to be effectively identified.
- Pilots did not routinely cross-check information from fuel quantity gauge indications with information from the independent fuel totaliser.
- Although the pilot routinely compared indicated versus calculated fuel quantities, and indicated versus flight-planned fuel quantities, the pilot did not routinely conduct two other methods stated in the operator’s procedures for cross-checking fuel quantity gauge indications.
- The recorded fuel burn for the previous (third) sector based on fuel quantity gauge indications was substantially lower than the expected fuel burn based on the flight plan. However, in the absence of relevant information from other sources, the pilot did not regard this as being an indication of a fuel quantity indicating system problem.
- The pilot disregarded the L/R FUEL LEVEL LOW annunciators, which likely illuminated approximately 30 minutes before the fuel was exhausted in each tank and when the aircraft was still within range of suitable alternative airports. The pilot relied on the (erroneous) fuel quantity indications and continued to Broome until the engines lost power, at which point a forced landing on a highway was the only remaining option.
Two Other Factors that increased risk, were also identified:
- Although the pilot stated that they conducted a fuel quality check prior to the first flight of the day, they did not conduct another check after refuelling (as required by the operator’s procedures), increasing the risk of undetected fuel contamination.
- The pilot did not instruct the passengers to brace for impact prior to the emergency landing.
Safety Action taken as a result of this event and known to the Investigation was reported as having included:
- Skippers Aviation strengthened company management surveillance of its Broome base and enhanced its pilot line training procedures.
- The CASA increased its surveillance of Skippers Aviation through a series of visits, interviews and observation flights over a period of 18 months and, after concluding that the operator had effected necessary operational safety improvements at its Broome base, made no ongoing findings on completion of the surveillance.
The Final Report was released on 27 May 2021. No Safety Recommendations were made.