The pilot was conducting a series of scenic charter flights in a
Kawasaki KH4 helicopter and had already completed several flights
during the morning. The pilot reported that he departed on a
30-minute scenic flight and had been airborne for about 25 minutes
when the engine suddenly failed. At the time the of the engine
failure the helicopter was flying 500 ft above ground level, about
2 NM north-west of the planned landing area. The pilot immediately
lowered the collective control for the main rotor and entered an
auto-rotative descent.
During the descent the pilot assessed that the helicopter could
not safely reach a clearing to the south-west and manoeuvred to
land in lightly timbered terrain. During the landing flare the tail
rotor was reported to have struck the branches of a tree and the
helicopter tipped forward before landing in a slight nose-down
attitude. Damage to the tail rotor blades, main rotor mast, right
front landing skid, VHF radio aerial and landing light was
reported. The pilot and the two passengers did not report being
injured.
The helicopter operator reported there was no mechanical reason
for the loss of engine power and that fuel exhaustion may have
contributed to the engine's loss of power. Approximately half a
litre of AVGAS was recovered from the fuel tanks at the accident
site and there was no obvious damage to the fuel system. Standard
company policy required the pilot to ensure the helicopter carried
enough fuel to complete the planned flight, plus an extra 20-minute
fixed fuel reserve.
The pilot was a part-time employee of the helicopter operator
and would relieve the full-time pilot, usually one day a week. He
had been employed on this basis for approximately three months. The
operator reported the recent replacement of the calibrated dip
stick used to measure the fuel tank contents had contributed to the
circumstances of the fuel exhaustion.
The original dip stick was a hollow calibrated hard-plastic tube
and was the dip stick supplied by the helicopter manufacturer for
dipping the fuel tanks. The tank contents were measured by
inserting the dip stick diagonally into the tank, passing it
through a hole in the tank baffle and then placing a finger over a
small hole at the top of the dip stick. This would cause fuel to be
trapped inside the tube, allowing the dip stick to be removed from
the tank and reading of the tank contents against a graduated
scale.
To ensure the plastic dip stick was inserted at the correct
angle, two metal pins protruded from either side, near the top of
the dip stick. These pins would rest on the fuel filler neck and
ensured the fuel quantity could be measured consistently. Cracks in
the plastic tube had made the dip stick ineffective for measuring
the tank contents and the helicopter operator had recently replaced
it with a wooden dip stick.
The new wooden dip stick had been calibrated to measure the fuel
quantity when inserted almost vertically into the tank, without
passing through the hole in the tank baffle. Using this technique
had the advantage of restricting the angle at which the dip stick
could be inserted into the tank and when correctly applied, would
not cause large errors in measuring fuel quantity.
On the day of the accident, the pilot reported that he had used
the new wooden dip stick for the first time. He had used the same
technique to dip the fuel as he had been instructed to use with the
original plastic dip stick. He was not aware that this method for
measuring the fuel quantity was only valid when using the original
manufacturer's supplied dip stick.
This had resulted in the pilot inserting the wooden dip stick
into the tank at an oblique angle, passing through the tank baffle
and resting on the tank bottom. This technique could result in a
significant over estimation of tank contents. The pilot reported
that he had not been advised of the change in method for dipping
the tanks using the new dip stick, although he previously had used
similar dip sticks on other models of helicopter.
The pilot reported that on the day of the accident, he had first
dipped the fuel tanks during the daily inspection conducted prior
to the first flight of the day. During this inspection, he detected
a discrepancy with the helicopter's fuel log, where the closing
figure from the previous days flying did not appear to match the
reading he obtained from the tank dip. In trying to resolve this
discrepancy, the pilot reviewed other entries in the fuel log and
noticed what he believed was another similar discrepancy from the
day before. With this discrepancy in mind, he elected to proceed on
the basis that his dip of the tank was accurate. The pilot
continued to over estimate the quantity of fuel contained in the
tanks during subsequent dips of the tank.
The operator subsequently reported the pilot had misread the
fuel log and there was no discrepancy. The investigation reviewed
the calculations of the aircraft's hourly fuel consumption, which
supported the accident pilot's interpretation of the entry in the
fuel log for the day before the accident. It was not possible to
further address this ambiguity or to determine positively what
figure had been entered in the fuel log.
The operator did not have a policy for resolving discrepancies
with fuel log entries and relied on the pilot using the dip stick
to check the fuel quantity before confirming this reading with a
visual check of the tank contents. The operator reported that all
pilots were trained to verify dip stick readings using this method
and that the tank contents could be seen through the opening of the
filler neck. This figure would then be verified against the
indications of the fuel gauge and the information contained in the
aircraft fuel log. The pilot reported that he was not in the
practice of making a visual check of the tank contents and he
relied on the reading he obtained from the fuel dipstick as being
the quantity contained in the tanks. He could not recall being
instructed in the technique of comparing dipstick readings with a
visual assessment of the tank contents during his training. The
pilot did not detect any discrepancy between the fuel quantity
measured using the dip stick and the readings from the cockpit fuel
gauge. The investigation was unable to verify the apparent training
discrepancy.
The pilot fuelled the helicopter twice on the day of the
accident. Before the first flight of the day, 40 litres had been
added and another 105 litres was added later that morning. The
pilot estimated that when the engine failed, the helicopter had
flown about 1-hour 25-minutes since the last refuelling. Based on
information supplied to the investigation, it was likely the fuel
tanks contained between 30 and 50 litres before the first flight of
the day and between 25 and 35 litres before departing on the
accident flight.
The pilot reported that he had been monitoring the fuel
consumption by crosschecking the fuel gauge indications with
readings obtained from the dip stick. However, he did not detect
the critically low fuel level before he departed on the accident
flight. It was also likely the fuel level was critically low on
completion of the first flight of the day.
Contributing to the circumstances of the fuel exhaustion was the
ambiguity with the fuel log entry from the previous day's flying.
The pilot's relatively low-level of experience on this helicopter
type and his employment status as a part-time relieving pilot had
possibly contributed to his reliance on a dip stick reading to
resolve the discrepancy with the helicopter's refuelling log.
