On the morning of 15 August 2003, the pilot hired a Victa Ltd
Airtourer, registered VH-MVP, to practice basic aerobatics. Prior
to flying to the training area, the pilot was conducting a number
of touch and go circuits. Following the fourth takeoff and while
climbing through about 200 ft, witnesses described hearing the
aircraft engine surge then stop. Shortly after, witnesses saw the
aircraft turn left. The turn steepened as witnesses lost sight of
the aircraft behind trees and houses and a short time later they
heard the aircraft impact the ground. The pilot was fatally injured
in the accident.
The pilot was appropriately licensed and was reported by a
family member to be fit and well and looking forward to the flight.
The family member believed that the pilot was going to conduct
circuits in another aircraft, not aerobatics in the Victa. However,
the company flight details log sheet contained an entry for
`aerobatics' and the pilot had discussed the aerobatic component of
the flight with an instructor.
The Australian built, two seat, aerobatic rated, single-engine,
low-wing aircraft was originally fitted with a 100 hp engine
driving a fixed pitch propeller. However, the aircraft was later
fitted with a 180 hp engine with a constant speed propeller.
Examination of the aircraft fuselage, flight controls, fuel
system and engine including magnetos and spark plugs, by the
Australian Transport Safety Bureau (ATSB) investigation team,
provided no explanation for the sudden loss of power observed by
witnesses. During the onsite phase, approximately 6.8L of fuel was
removed from the aircraft fuel tank, which was still securely
attached and not deformed. This included approximately 1L that
drained from the tank as it was removed from the wreckage. The fuel
was free of visible contaminants and was the correct colour. No
other fuel was recovered from the site, nor was fuel staining or
odour evident on the fuselage or the ground immediately below the
wreckage. There was no evidence of excessive fuel consumption.
Emergency workers and witnesses, who arrived at the accident site
within minutes of the accident, could not recall a fuel smell. The
ATSB did not receive any fuel related incident reports from other
aircraft that had refuelled from the same source following the
accident.
The fuel system consisted of a 130L (total capacity) rubber
bladder fuel tank located in the fuselage. Fuel addition and manual
contents checking was via an angled filler tube into the bladder
tank through the side of the fuselage. Fuel was supplied to the
engine via an engine-driven fuel pump and carburettor, with an
electric boost pump as backup. Fuel quantity is checked via an
electric fuel gauge and a flexible dipstick graduated in imperial
gallons. The dipstick is made up of a number of five imperial
gallon graduated segments, held taut by a chord under tension.
Dipping of the fuel contents required a pilot to depress the button
on the top of the dipstick to relax the tension on the segments and
allow the flexible dipstick to travel down the angled fuel filler
tube. After traversing the angled section of the filler tube,
pressure on the button was required to be relaxed, thereby
re-tensioning the segments prior to the end of the dipstick
contacting the bottom of the tank. The procedure required the
dipstick to be under tension prior to contacting the bottom of the
tank and that the dipstick did not rest on a fold or ripple in the
bladder. Failure to do this may result in an erroneous reading of
the tank's content.
The approved aircraft flight manual stated that 1.3L of fuel was
unusable. Although not stated, this is assumed to be for level
flight. Calculations by the investigation indicated that about 6.2L
of fuel would be unusable while the aircraft had a 5 degree nose up
attitude in a climb. This would increase to about 12.4L at 10
degrees of nose up attitude.
Examination of the tank sender unit, a wire-wound wiper type,
showed wiper shaft bearing surface wear. This would have allowed
lateral movement of the wiper arm resulting in intermittent contact
with the wire wound former and is likely to have caused the fuel
gauge to display intermittent readings to the pilot. However, due
to impact damage of the sender unit, it was impossible to determine
the extent of the intermittent readings.
Three small pin size holes were located in the rubber bladder. A
test indicated that 250 ml could have leaked from the tank from the
time of the last refuelling to the time of the accident. The holes
were not collocated and were not in the vicinity of the dipstick.
It could not be determined if the holes were due to impact
damage.
The tank had been filled on the day before the accident, prior
to completing a 2.2 hour cross country flight. On the day of the
accident, the pilot checked the tank contents and informed an
instructor who assisted her to push the aircraft from the hangar
that it held 15 imperial gallons (68L). However, presumably in
error, the pilot entered 75L (16.5 imperial gallons) in the company
flight details log sheet. The instructor did not see the pilot dip
the tank or check the fuel gauge.
The investigation examined the aircraft engine manufacturer's
fuel consumption tables and company flight details log sheet to
establish the fuel consumption rate. Based on the record of total
hours and fuel consumed, for the previous two weeks, the aircraft
had consumed about 37.6L per hour for all modes of flying.
Therefore the tank should have held about 47.3L after the previous
day's cross country flight. If the tank contained 75L prior to the
accident flight, as entered in the log by the pilot, the aircraft
consumption rate would have been about 25L per hour. That fuel
consumption rate was unlikely to be achieved during the cross
country flight. The chief flying instructor commented that the
company instructed students to plan using a fuel consumption rate
of 40L per hour.
An instructor reported that the aircraft had completed three
circuits prior to the accident, which would equate to roughly 35
minutes of taxi and flying time. Allowing for an average fuel burn
of 37.6L per hour, there should have been about 25L remaining at
the time of the accident. The ATSB fuel consumption calculations
for some individual flights ranged from 35L to 50L for circuits,
aerobatics and cross country flights. However, the log was
incomplete, so it was not possible to derive a fuel consumption per
flight for some of the previous flights. The reason for the
discrepancy between what should have been in the tank and what was
recovered at the accident site could not be determined.
The investigation examined a similar model aircraft and its fuel
system. It was found that it is relatively easy to have the bottom
(five imperial gallon) segment of the dipstick bend sideways, when
the dipstick contacts the bottom of the tank. This will occur if
the segments are not tensioned by releasing pressure on the tension
button prior to the dipstick contacting the bottom of the tank.
This results in the dipstick over-reading by about 4 to 5 imperial
gallons (18.2L to 22.7L) and could have led the pilot to believe
that there was adequate fuel for the flight.
Based on the examination of the recovered engine components, the
witness reports of engine surging just prior to the engine failure,
the lack of fuel odour at the accident site and the company fuel
details log sheet, it is probable that there was insufficient fuel
to complete the flight, either due to fuel exhaustion or
starvation. It is possible that the pilot's operation of the
dipstick provided an erroneous reading, which led her to believe
that the aircraft's tank contained more fuel than it actually did.
Additionally, the intermittent fuel gauge reading may have meant
that she was not able to check the fuel quantity by a secondary
means, other than the log entry for the previous day's flying.
In a take-off climb attitude of between 5 to 10 degrees, the
fuel pickup point in the tank was probably unported, interrupting
the fuel flow to the engine thus causing it to lose power. The
flight path of the aircraft after the loss of engine power
indicates that the pilot may have been attempting to turn the
aircraft back to the runway at a low height and lost control with
insufficient height to effect recovery.