The Incident
On 18 August 2022, a Cessna 310R (registration VH-JQK) operated by Aircraft Australia was conducting a training flight from Redcliffe, Queensland. After completing asymmetric training sequences east of Brisbane, the crew proceeded toward Sunshine Coast Airport for instrument training. While establishing a practice instrument approach, both engines began surging alternately. The instructor declared a MAYDAY. During descent, the crew switched from the auxiliary fuel tanks to the main tanks, which resolved the engine issues, and the aircraft landed without further incident.
ATSB Investigation Findings
The Australian Transport Safety Bureau (ATSB) investigated the occurrence and identified several contributing factors related to fuel management.
The crew did not fully adhere to the operator's pre-flight and in-flight fuel management procedures, which required cross-checking fuel quantity before flight with visual confirmation or a fuel log, and monitoring fuel levels and tank selection every 30 minutes during flight. The aircraft journey log was not located, and fuel on board at departure could not be determined. Post-flight inspection revealed the main tanks were completely full while the auxiliary tanks were empty, indicating the engines had been starved of fuel from the auxiliary tanks.
Further, the instructor was unaware of the actual fuel system configuration of VH-JQK, believing the aircraft was equipped with larger auxiliary tanks than it had. The trainee instructor relied on the instructor's experience and had limited familiarity with the specific aircraft's fuel system.
The operator had inconsistent and incomplete documentation for the aircraft. The fuel selector plaques contained contradictory information about the size of the auxiliary tanks, and the operations manual provided generic fuel flow rates without specific data for the Cessna 310R variant being operated.
Fuel System Analysis
The engine surging was consistent with fuel starvation from the auxiliary tanks. The crew operated on main tanks for about 30 minutes after departure before switching to auxiliary tanks. At a fuel flow of 120 L/hour, approximately 120 L would have been consumed by the time surging began, but the auxiliary tanks held about 140 L. However, unused fuel from the fuel pumps recirculated from the auxiliary tanks to the main tanks, depleting the auxiliary tanks faster than engine consumption alone. This caused the auxiliary tanks to empty while selected, leading to fuel starvation and surging. The main tanks, which were full, vented excess fuel overboard.
Operator Remedial Actions
Aircraft Australia implemented a new fuel log specific to the Cessna 310R and issued an internal memo outlining changes to the aircraft's data sheet to ensure all pilots and students are aware of its complex fuel configuration. The operator also requested replacement of the fuel selector plaques with correct data labels.
Probable Cause
The ATSB determined the cause to be the crew's failure to completely follow the operator's pre-flight and in-flight fuel management procedures, resulting in continued selection of fuel from the auxiliary tanks after they were empty, which led to fuel starvation of both engines.