Cessna 402C, VH-NMQ

History of the flight

The pilot of a Cessna 402C aircraft, VH-NMQ, was conducting a scheduled passenger service from Tindal to Darwin, with 4 passengers.

During the climb to the planned cruise altitude of 8,000 ft, the fuel quantity gauges indicated that fuel was being consumed from the left tank only. At the top of climb, the fuel gauges indicated 100 lb in the left tank and 200 lb in the right tank. Once established in the cruise the pilot tried to balance the fuel load by positioning the left fuel selector to allow the left engine to be supplied with fuel from the right tank.

Approaching the midway point between Tindal and Darwin, the fuel gauges confirmed that the imbalance remained. The pilot assessed that sufficient fuel was available to continue to Darwin. As the flight approached the last suitable alternate aerodrome, the pilot calculated that 13 lb of fuel was needed to reach Darwin from that point, based on the current consumption rate. The left fuel tank gauge showed 40-lb remaining.

The pilot requested and was given a direct approach to runway 29. During the landing roll the left engine stopped, and the right engine stopped soon after the aircraft cleared the runway. The fuel quantity gauges showed 20 lb for the left tank and 200 lb for the right tank.

The operator's ground support staff then towed the aircraft to the terminal area where the passengers disembarked normally.

The aircraft had flown from Darwin for Tindal the previous day with 650 lb of fuel on board. The pilot's navigation log showed that 365 lb was required for the flight from Tindal to Darwin. This comprised 230 lb flight fuel (59 minutes), 100 lb fixed reserve (30 minutes), 25 lb variable reserve fuel, and 10 lb taxi fuel. The navigation log also showed the total fuel on-board at Tindal before departure for Darwin was 385 lb. The pilot reported that before departure from Tindal, the aircraft fuel quantity gauges showed 185 lb in the left tank and 200 lb in the right. The pre-flight check of the fuel cross-feed was normal.

A landing at an alternate aerodrome was not considered necessary, as the pilot had calculated sufficient fuel was available to continue to Darwin, and was conscious of the operating schedule for the aircraft. However, company management stated that there was no instruction or pressure on pilots in this regard.

The pilot held a current commercial pilot licence, a command multi-engine instrument rating a valid medical certificate, and had logged 2,454 hours aeronautical experience. This included 150 hours on Cessna 402C aircraft. The pilot's last proficiency check was on 8 March 2000.

On the day of the occurrence, 5 May 2000, the pilot did submit an incident report to the operator. However, due to a breakdown in the operator's reporting procedures following staff changes, the ATSB was not notified of the occurrence until 15 May. As a result, it was unable to conduct an examination of the fuel selector system fitted to NMQ before the aircraft was returned to service.

Background

The then Civil Aviation Authority of Australia issued Civil Aviation Advisory Publication No: 234-1 (0) in March 1991. It provided advice about the quantity of fixed reserve fuel to be carried, and noted the use of fixed reserve fuel was limited to unplanned manoeuvring in the vicinity of the destination aerodrome. It further noted that fixed reserve fuel would normally be retained in the aircraft until the final landing.

The operator's fuel policy stated that in all foreseeable circumstances an aircraft should complete a flight with at least the fixed reserve fuel intact. The standard fixed reserve for the operator's Cessna 402C fleet was 100 lb of fuel for 30 minutes of flight.

Cessna 402C Fuel Selector System

The two fuel selector controls are attached to the cabin floor between the pilot and co-pilot seats. The selectors enable the fuel selector valves, located behind the engine firewalls, to be positioned to the corresponding tank, crossfeed, or off. The arrow-shaped ends of the selector control handle points to the position on the selector placard that corresponds to the control valve position. Each handle connects directly to a gearbox located under the floor. Cables connect each gearbox to their respective fuel selector valve.

An inspection by the maintenance provider in Darwin confirmed that the pilot had positioned the right fuel selector handle to the right tank. However, the cable connecting the gearbox to the fuel selector valve did not position the valve to the right tank.

The right fuel selector gearbox was removed, the selector gearing adjusted and the selector cable re-rigged. The aircraft was returned to service after the fuel selector system was ground tested.

The Pilot's Operating Handbook for the aircraft contained a description of the fuel system and it's operation. In the Normal Procedures section of the handbook, pilots were cautioned that they should "Feel for (the) detent" when placing the fuel selector at the desired position.

Maintenance action

The operator's maintenance controller was located at Alice Springs. A sub-contract maintenance provider conducted maintenance at Darwin. The operator's maintenance controller was not advised of the occurrence until 23 May, and was therefore unable to specify extra inspection procedures for the operator's Cessna 402C fleet until that time. The maintenance controller issued maintenance alert MA/C400/2 on 25 May. It was applicable to all Cessna 402C aircraft used by the operator and its associate company, and required a detailed inspection of the fuel selector system. These checks were to be conducted at each scheduled inspection until the requirements were included in the operator's System of Maintenance.

During one such check of the fuel selector system on another of the company aircraft, VH-TZH, the screws securing the selector cable lever arm/travel stop to the sector gear were found to be loose. This allowed the travel stop to slide under the base-plate and the sector gear to move beyond the end of its travel, resulting in loss of synchronisation between the selector handle and the selector valve.

The operator immediately issued an amendment to maintenance alert MA/C400/2 that included photographs of the defective fuel selector on TZH. The alert specified that the selector gearbox was to be checked if the fuel selector valve was found not synchronised with the selector indicator. During the investigation the fuel selectors of two other of the operator's Cessna 402C aircraft were found to lack an effective detent.

At the time of the occurrence, the maintenance release for NMQ contained an annotation arising from a previous report of uneven fuel consumption from the left tank. Examination of the fuel system related maintenance documentation for the aircraft revealed 17 events since December 1999. Seven involved reports of the aircraft using more fuel from the left tank than the right when the fuel selectors were correctly positioned. There was one report of greater fuel usage from the right tank. The rectification section for four of the entries stated that the fuel selector system was re-rigged. The reported defect for three of the entries was annotated "not major defect" and transferred to the deferred defects list. The fuel related defect entry for the 18 April 2000 stated "fuel not feeding correctly. Fuel noted to be crossfeeding some fuel in level flight - report further".

The last reference to fuel transfer problems, prior to the incident, was on 20 April. The endorsement on the trip record stated "both engines draw fuel from the left tank only". The rectification section of the record noted the fuel selector valve was removed, lubricated, refitted and pressure tested. The selector cable was re-rigged, and the system operated satisfactorily during ground testing.

Fuel system pre-flight checks

The fuel system pre-flight checks specified in the operator's Cessna 402C Operations Manual differed from the procedures specified in the manufacturer's Pilot's Operating Handbook.

The operator's standard operating procedures required pilots to operate the fuel supply cross feed for 60 seconds to verify normal operation. Also, pilots were to ensure normal operation of the fuel valves by positioning the fuel selectors to the off position to observe a decrease in fuel flow. Following these checks, pilots were to position the fuel selectors to the main tanks.

The manufacturer's Pilot's Operating Handbook did not specify checks for crossfeed operation or positioning the fuel selectors to the off position to observe a decrease in fuel flow.

The pilot did not move the fuel selectors to the off position as part of the pre-flight checks. This was because the Fleet Manager had advised his intention to amend the pre-flight check to delete the requirement. The pilot reported awareness of the need to feel for the detent when moving the fuel selectors, and was confident the detent was achieved during the pre-flight check.

On 16 May the operator issued a memo on the occurrence to its Cessna 402 pilots, and included new instructions for pre-flight operation of the fuel selector. The memo cancelled the previous requirement for pilots to position the fuel selectors to the off position to confirm a decrease in fuel flow.

The fuel selector system defect need not have led to a situation in which the safety of the flight was not assured.

The problem was recognised by the pilot early in the flight, and, despite attempts to resolve it, was confirmed when about mid-way. Consequently, without fuel from the right tank, there was insufficient fuel available for the planned flight fuel requirement, let alone the required reserve fuel. The pilot considered that a landing at an alternate aerodrome may have been necessary. However, the need to maintain adequate reserve fuel to ensure safety of the flight was apparently not recognised. As the flight progressed, the quantity of fuel required was assessed only in the context of a direct approach and landing at Darwin.

After landing, the fuel gauge indicated that the left tank contained about 20 lb of unusable fuel. The pilot had therefore made the decision to overfly an alternate aerodrome when in reality, only about 20 lb (or about 6 minutes) of fuel was available.

Maintenance oversight of the aircraft was inadequate. This is evidenced by:

the number of reported occurrences of fuel system problems; and
the deferral of rectification of 3 such problems because they were regarded as "not major defect".

The repetition of reports and the request entered on the maintenance release to "please report further", suggest that the focus of maintenance rectification action was deficient.

The late reporting of the occurrence to the ATSB and to the operator's maintenance controller arose through breakdowns in the operator's reporting procedures following staff changes.

Several safety deficiencies were identified during the initial phase of the investigation. Local safety action was agreed to and addressed by the operator prior to publication of the final report. Those safety actions were as follows:

Issue of company Maintenance Alert MA/C400/2, which required a detailed inspection and functional check of the fuel selector system of all the operator's Cessna 402C aircraft.

A second Alert MA/C400/2 amendment 1, was issued a short time later after the initial fleet inspection found that the fuel selector valves for a second aircraft were out of synchronisation with the selector indicator. This alert detailed further inspection and rectification instructions.

The operator has undertaken to re-examine the company operations manual with a view to improving the guidance information on fuel planning and reserves.

The operator has agreed to re-examine the need for the cross-feed and shut-off checks. If they are considered necessary, then a procedure to ensure that the desired outcome is achieved will be devised and introduced.

The operator's maintenance controller has introduced procedures to ensure that all trip records are now vetted daily. Any endorsement item considered to have the potential to affect the safety of flight will now be subject to immediate maintenance rectification.

The operator has amended and amplified the incident and accident reporting section of the company Policy and Procedures Manual to better reflect the correct reporting procedures.

The Operator has introduced the Daniel System Australia, Integrated Aviation Software (IAS) in the company's electronic maintenance control system. This software has the ability to monitor and identify repetitive defects. The company Maintenance Control manual Vol 1, section 9 has been changed to reflect the changed procedures.