The Australian Transport Safety Bureau (ATSB) investigated this
occurrence in accordance with the Transport Safety Investigation
Act 2003, for the sole purpose of improving transport safety. It is
not the object of an ATSB investigation to determine blame, provide
a means of determining liability, or to assist in court proceedings
between parties.
FACTUAL INFORMATION
Sequence of events
On 10 August 2004, the pilot of a Piper Aircraft Corporation
PA-31-350 (Chieftain) aircraft, registered VH-MZV, was conducting a
visual flight rules charter flight from Darwin to Bathurst
Island1 and return. The pilot was the
only person onboard for the return to Darwin.
As the aircraft approached Darwin, air traffic control cleared
the pilot to make a visual approach to runway 11. Recorded radar
data indicated that at 5 NM the pilot turned onto the left base leg
of the circuit at an altitude of about 1,000 ft. At about that time
the pilot broadcast a Mayday2,
indicating that both engines had failed. He landed on tidal
mudflats to the west of the airport.
Damage was sustained to the propellers and lower fuselage skins
and bulkheads. The pilot was not injured.
The pilot recalled that the flight from Bathurst Island had been
normal and that he had leaned the engines during the cruise at
3,500 ft. Turning onto the base leg, he reduced airspeed, extended
the first stage of flap, lowered the landing gear and completed the
pre-landing checklist. As the aircraft's speed reduced, the pilot
moved the throttle controls forward, but neither engine responded.
There was no significant yawing or rolling associated with the
power loss. The pilot considered that both engines lost power
simultaneously without any surging, misfiring, rough running or
abnormal vibrations. He checked the position of the fuel tank
selectors, confirmed that the mixture controls were positioned to
full rich, and that the fuel boost pumps and magnetos were on. When
those actions did not restore engine power, the pilot retracted the
landing gear and concentrated on landing on the mudflats.
Aircraft examination
In accordance with normal procedures, the Australian Transport
Safety Bureau (ATSB) placed a protection order3 on the aircraft to preserve the physical
evidence while investigators travelled to Darwin. Staff from the
Darwin office of the Civil Aviation Safety Authority attended the
site and supervised, on behalf of the ATSB, the relocation of the
aircraft from the tidal mudflats to dry land. That necessitated
removal of the engines from the airframe and each was separately
lifted out by helicopter. The aircraft and its engines were
cordoned off at a vacant block of land and a security guard was in
attendance until investigators examined the aircraft.
The propellers had continued to windmill after the engines
failed, operating the engine-driven hydraulic pumps, which provided
hydraulic pressure to enable retraction of the landing gear.
Both propellers exhibited damage consistent with little or no
power being produced by the engines during the wheels-up landing.
Neither propeller had been feathered. The wing flaps were not
extended.
The quantity of fuel contained in each inboard tank was not
sufficient to enable the tank contents to be visually assessed
through the filler neck. Fuel from the inboard tanks would not flow
under gravity from the engine firewall fuel line fitting when the
fuel line was disconnected. A check of another Chieftain fuelled to
a similar quantity confirmed that this was a normal characteristic
of the fuel system design.
A total of approximately 236 L of fuel was recovered from the
aircraft's fuel tanks, which comprised 101 L from the left inboard
tank (main), 105 L from the right inboard tank (main) and about 15
L from each outboard tank. Each inboard tank had a capacity of 212
L, including about 11 L unusable. The capacity of each outboard
tank was 152 L, including about 8 L unusable.
Inspection of the fuel system confirmed the correct operation of
the fuel selector controls, the fuel filters were clear of
contaminants and the tank venting system functioned normally. No
water or other contaminant was recovered from the fuel system
drains and collector points. There was no evidence to indicate that
fuel had been lost from the aircraft during flight.
Inspection of the engines and their systems did not identify any
defect that may have influenced the circumstances of the
occurrence. The engines and their accessories operated normally in
an engine test stand.
Fuelling records
Trip and fuelling records indicated that the inboard fuel tanks
were fully fuelled (capacity 402 L usable fuel) during the morning
of 9 August 2004. Fuel consumption of 180 L was recorded during a
subsequent two-sector return flight of 1.1 hours duration and 222 L
of fuel remained in the inboard tanks. That pilot reported that he
did not use the outboard tanks during those flights.
The occurrence pilot requested that the aircraft be refuelled
with 80 L on the morning of the occurrence. Fuelling records
indicated that this fuel was delivered to the aircraft. The pilot
estimated that after refuelling, the inboard tanks contained about
300 L, sufficient fuel to complete the return flight to Bathurst
Island.
The aircraft had flown 0.6 hours since departing Darwin and was
completing the second sector at the time of the occurrence. Based
on the trip records and the calculated fuel consumption, the
aircraft main tanks should have contained about 160 L.
The pilot reported that on the day of the occurrence he did not
operate either tank on 'crossfeed'4,
nor did he select the outboard tanks.
Fuel testing
Laboratory analysis of fuel samples from the aircraft's fuel
tanks confirmed that the fuel complied with the relevant
specifications for AVGAS 100. Although minor traces of water and
fine particulates were detected, that sample was obtained from a
fuel line disconnected during recovery of the aircraft. The
quantity of those contaminants was not significant.
Descent profile
Analysis of the radar data indicated that the aircraft's descent
profile was normal until reaching left base for runway 11. Soon
after the turn onto the base leg, the aircraft's groundspeed
reduced significantly and the rate of descent increased. The final
descent to the emergency landing area took about 1 minute.
Data from the aircraft manufacturer indicated that the
aircraft's glide ratio was approximately 12.5:1 and accordingly,
from a height of 1,000 ft, the aircraft could glide about 2
NM.5 The investigation concluded that
the aircraft was not within gliding range of the airport when the
engines failed.
Operational information
The pilot had logged approximately 1,000 hours on PA-31 type
aircraft. The pilot also regularly operated the company's Embraer
E110-P1 Bandeirante aircraft in single pilot operations. The
pilot's practice was to select the Bandeirante's engine fuel
condition levers to LO IDLE during his pre-landing checks. The
configuration of those engine controls was similar to that of the
Chieftain's fuel mixture controls. Moving the Chieftain's mixture
controls to a position consistent with LO IDLE for a Bandeirante
would stop the flow of fuel to both engines and result in a sudden
and complete loss of engine power.
- Bathurst Island is located approximately 40 NM
north-west of Darwin.
- Mayday
is an internationally recognised call for urgent assistance.
- A
protection order is issued under the provisions of section 45 of
the Transport Safety Investigation Act 2003 for the purpose of
protecting evidence that might be relevant to an
investigation.
- Crossfeed describes an abnormal operating
configuration, where fuel from tanks on one side of the aircraft is
provided to the opposite engine, therefore operating both engines
from the same tank of fuel.
- In nil
wind, at the airspeed for best glide, wheels and flap retracted and
propellers of both inoperative engines feathered.
