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.