The pilot had planned to conduct a charter flight, with three passengers, from Essendon to Latrobe Valley, Vic. in a twin engine Beech Duchess aircraft. The pilot reported that he arrived at the Essendon airport about 90 minutes prior to the scheduled departure, carried out the daily inspection on the aircraft and submitted an instrument flight rules flight notification. He checked the aircraft maintenance release and the company fuel log that included the aircraft's last flight four days earlier. The pilot reported that he checked the two fuel quantity gauge readings which indicated a half-full tank and a slightly less than half full tank. He then visually checked the contents of the tanks relative to the '30 US gallon' metal tabs that are visible through the filler opening. He estimated that the fuel tanks contained a total of about 200 litres, but did not confirm this, as a fuel tank dipstick was not provided for that aircraft. The pilot's flight plan indicated that 128 litres of fuel, including reserves, would be required for the flight.
During the climb to the planned altitude of 7,000 ft, the right engine's power reduced. The pilot concluded that, from the engine tachometer reading of 1,500 revolutions per minute, and the manifold pressure indications, the right engine had partially failed. He carried out engine failure confirmation checks, but as the propeller pitch lever was very stiff, was unable to place it in the feather position. The pilot later reported that, during manipulation of the pitch lever, the aircraft had yawed significantly. Therefore, he decided to reset the right engine controls to a cruise setting because partial power was preferable to no power.
The aircraft was unable to maintain altitude so the pilot decided to return to Essendon. He requested an air traffic clearance from the Melbourne Approach air traffic controller (ATC) when the aircraft was about 50 NM east of Essendon. After receiving a clearance, and as he turned onto a westerly heading, the aircraft descended into cloud. At the pilot's request, ATC provided headings for the pilot to track further to the south to avoid the higher terrain on the direct track to Essendon. Lowest safe altitude (LSALT) is a published or pilot calculated minimum altitude that ensures terrain clearance during flight in instrument flight conditions. Flight below an LSALT altitude is only permissible during visual meteorological conditions or while conducting a published instrument approach. When the aircraft descended below the LSALT, ATC advised that a diversion to the closer Moorabbin airport, which was to the south east of Essendon and to the south of the aircraft, was available. That option would have allowed the aircraft to track over lower terrain and would have minimised the track distance over the Melbourne suburbs. However, the pilot decided to return to Essendon, where the operator's maintenance facilities were located and the passengers could be transferred to another company aircraft. After descending through the next LSALT step while in cloud, the aircraft descended into visual conditions about 21 NM east of Essendon at about 2,500 ft. The aircraft continued to descend until it stabilised in almost level flight at about 1,500 ft. The pilot then tracked direct to Essendon and carried out a visual approach and landing.
The pilot had bypassed two other suitable airfields, Lilydale and Coldstream, approximately 10-15 NM to the right of his track. The Civil Aviation Safety Authority (CASA) Civil Aviation Orders (CAO) 20.6 permitted the pilot of an aircraft with a failed engine to fly past a suitable aerodrome if another suitable aerodrome was available nearby and the pilot assessed that the aircraft could be flown safely to that aerodrome.
Company engineering inspection of the aircraft found that the right fuel tank, that was supplying the right engine when it lost power, contained no fuel. The right fuel quantity gauge transmitter unit was corroded and seized in a position that resulted in the gauge always indicating half-full. It was possible to feather the right propeller, although the pitch control was stiff.
The control cable and the fuel tank sender unit were subsequently replaced. The pilot commented that he had conducted a feather check as part of the pre-takeoff checks and although the right pitch lever was stiff to operate, he was satisfied that the propeller feathering mechanism was operating satisfactorily. The pilot later commented that the engine had failed due to fuel starvation and that he had not recognised the symptoms of a piston engine failure. He reported that he did not notice the reduced fuel pressure to the right engine until after the aircraft descended into visual conditions.
The aircraft's pilots operating handbook cautioned pilots against attempting to determine the inoperative engine by reference to the tachometers or the manifold pressure gauges and stated that those instruments often indicated near normal readings after an in-flight engine failure.
The pilot had recently resumed employment with the operator. He began his career with the operator and had flown as a first officer on F-27 turboprop aircraft for four years. He then obtained employment with a regional airline for two years as a first officer on turboprop aircraft, and had just completed line training as first officer on a jet aircraft when that airline suspended operations.
The day before the incident, the pilot had completed a 12-hour tour of duty, including 8.1 hours of flight time completing a co-pilot endorsement on a business jet. The two days prior to that had been spent on ground duties. He had 6-8 hours rest overnight at home and had risen early on the day of the occurrence. The pilot reported that he was tired on the day of the occurrence and that he had felt similarly for some time. He had been on duty for 16 consecutive days or a total of 159.4 hours duty time, primarily in a capacity unrelated to his employment as a pilot. Those additional duties were reflected in the pilot's recorded duty times.
The pilot had logged about 3,600 hours total flight time, including 600 hours in command on piston-engine aircraft. Those command hours consisted of about 200 hours twin-engine, of which 25 were in Duchess aircraft. All his other flying had been in turboprop and jet aircraft. During the three months preceding the incident, the pilot had flown approximately 70 hours, but had only flown the Duchess for three hours during that time.
The pilot's work/rest history for the four weeks prior to the incident was examined using a computerised fatigue algorithm developed by the Centre for Sleep Research, University of South Australia. The results indicated that the pilot was probably experiencing moderate levels of fatigue in the week leading up to, and on the day of the incident.