The student pilot hired a Cessna 150L aircraft to undertake a local training flight with an instructor. The aircraft departed Canberra airport at approximately 1705 Eastern Summer Time and proceeded directly to the training area. The aircraft entered the circuit area for a landing at Canberra about 1.2 hours later. At that time, the pilot was instructed by air traffic control to track the aircraft in order to position it on a left downwind leg for a landing on runway 12. However, the controller observed the aircraft positioning for a right downwind leg. The controller instructed the pilot to turn left onto a heading of 090 degrees to reposition for a left circuit. Following the turn, the student pilot and instructor observed a decrease in engine power. The instructor resumed control of the aircraft and attempted to diagnose the loss of power. The engine surged a number of times and then lost power entirely, including stoppage of the propeller. The instructor transmitted a mayday message, and was cleared by the controller to track for the closest runway. When it became apparent that the aircraft would not reach the runway, the instructor changed heading and was manoeuvring to land in a field when the aircraft struck a tree and impacted the ground.
Both occupants were injured in the accident, but vacated the aircraft through the left door. There was no post-impact fire. The instructor died seven days later as a result of complications associated with injuries suffered in the accident.
Before the flight, the instructor had dipped the fuel tanks and ascertained that the aircraft contained 40 L of useable fuel, with 4 L more in the right tank than the left tank. The fuel tanks are interconnected and are intended to allow fuel to self-level. It is not possible to select fuel from individual tanks during flight.
Examination of the wreckage indicated that the aircraft had impacted the ground in a nose-down attitude. The engine was not operating at the time of the impact and the propeller was stationary. The aircraft was considered to have been capable of normal operation before impact.
The fuel tanks were found to be intact. However, the fuel and cross-vent plumbing on the right tank was disrupted during the impact sequence. That disruption would have prevented fuel from transferring between tanks following the accident. There was no indication of a fuel spill at the accident site. The left fuel tank was found to contain no fuel, and the right tank was found to contain 12 L. Advice from the manufacturer and the owner's manual indicated that the unusable fuel for that aircraft was 11.4 L, which is spread throughout the fuel system (including the two tanks). No defect was found in the fuel system that would have caused a difference in the quantity in the fuel tanks or the engine power loss. Nor were any defects found in the fuel gauges or their respective sender units.
At the time of the engine failure, the aircraft had been airborne for about 1.2 hours. During the exercise, the instructor and student engaged in steep turning exercises at 45 and 60 degrees bank angle, and in spiral dive and incipient spin recovery. The instructor also demonstrated how to configure the aircraft to commence a loop, which was conducted at 5,500-6,000ft. Much of the lesson would have required the use of full power to achieve the desired performance.
The owner's manual indicated the fuel consumption for a 75% power setting to be 22 L/h. Company policy was to plan for 22 L/h. An engine manufacturer's representative indicated that a fuel consumption of 33.4 L/h could be expected when operating the aircraft at the full-power setting.
An aircraft manufacturer publication titled "Pilot Safety and Warning Supplements" cautions pilots regarding uncoordinated flight for longer than 30 seconds when the fuel tanks are less than one-quarter full. The publication indicates that the aircraft is considered to be in uncoordinated flight when the balance "ball" on the turn coordinator instrument is displaced more than one quarter from its centre position. Uncoordinated flight may result in an interruption of the fuel supply to the engine.
The instructor held a commercial pilot licence and a valid medical certificate. The instructor's licence was endorsed with a Grade 3 instructor rating. The student pilot held a student pilot licence. ANALYSIS The investigation could not determine the reason for the engine failure, although the circumstances were consistent with fuel starvation. The aircraft departed Canberra with 40 L of useable fuel. The instructor and student had planned for a fuel consumption of 22 L/h, consistent with operations at 75% power and equating to an endurance of 1.8 hours flight time. However, much of the lesson would have required using full power with a fuel consumption rate of about 33 L/h. The aircraft had been operating for 1.2 hours when the engine lost power. It is possible that training manoeuvres resulted in fuel transferring from the left to the right tank, and may explain the fuel quantity imbalance noted during the post-accident examination of the fuel system. While the aircraft may have had sufficient fuel to complete the flight, an uncoordinated turn to position the aircraft for the correct approach may have resulted in the remaining fuel in the right fuel tank being displaced away from the fuel pick-up pipe, disrupting the fuel supply to the engine.