What happened
On 21 October 2015, a Gippsland Aeronautics GA-8 aircraft, registered VH-FGN (FGN), was conducting parachute operations at Busselton Airport, Western Australia (Figure 1). Prior to commencing the day’s operations, a company pilot conducted a pre-flight inspection of the aircraft, with no defects found.
Figure 1: VH-FGN
Source: Aircraft operator
At about 1500 Western Standard Time (WST), FGN took off from Busselton Airport with a pilot and seven parachutists on board. As the aircraft climbed through about 2,000 ft, the pilot observed a decrease in the engine manifold pressure. The manifold pressure was still in the green arc, or normal operating range, but indicating about 30 inches. The normal manifold pressure during the climb was about 38 inches. The fuel flow also increased from about 120 L/hr to 154 L/hr. As the aircraft was tracking south towards forested terrain, the pilot elected to turn back towards the aerodrome, and continue the climb, in case the engine issue worsened. The pilot conducted the standard engine checks, but the engine continued to produce only partial power. The pilot broadcast a Mayday[1] on the Melbourne Centre air traffic control (ATC) frequency.
The pilot advised the parachutists that they would establish the aircraft in the drop run overhead the aerodrome at about 4,000 ft (instead of the planned FL 140[2]) to allow the parachutists to exit the aircraft. As the pilot subsequently reduced engine power to allow the parachutists to exit the aircraft, the engine ran roughly. Six of the parachutists exited normally and landed safely at the drop zone, while the seventh, who was also a company pilot and seated in the front passenger seat, remained in the aircraft with the pilot in command.
The pilot then increased the aircraft’s power until the engine ran smoothly, although only producing partial power, while continuing the descent to the aerodrome. The pilot also advised ATC that they did not require immediate assistance and downgraded to a PAN[3], as the engine continued to produce some power. The aircraft landed safely at Busselton at about 1514.
After shutting down the engine, the pilot consulted with the maintainer, and found that the intake tube on the No. 4 cylinder was loose.
Aircraft maintenance and engineering inspection
On 10 October 2015, a licensed aircraft maintenance engineer had completed a 100-hourly inspection on the aircraft, including a ‘top overhaul’ of the engine.
After the incident, the engineer completed the following:
- removed the bolts and inspected the wire thread (Helicoil) inserts, and found no damage
- fitted a new intake gasket and o-ring to the intake tube, and resecured the tube to the No. 4 cylinder with new spring washers
- checked the torque of all other intake tube bolts, and found none loose.
Safety message
This incident highlights the importance of having thoroughly rehearsed emergency procedures, particularly for parachute operations. The parachutists had, in accordance with standard procedures, removed the single point restraints during the climb, and were prepared to exit the aircraft quickly.
For pilots, this provides a reminder that constant monitoring of the engine instruments can provide early indication of a problem. Acting quickly on this information may reduce the impact of partial or total power loss on flight safety.
The ATSB publication Avoidable Accidents No. 3 – Managing partial power loss after take-off in single-engine aircraft, provides information also relevant to partial losses of power in flight as well as after take-off. Following a complete engine failure, a forced landing is inevitable. For a partial power loss, pilots are faced with deciding whether to continue the flight or land immediately.
Aviation Short Investigations Bulletin Issue 46
Purpose of safety investigationsThe objective of a safety investigation is to enhance transport safety. This is done through:
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- Mayday is an internationally recognised radio call for urgent assistance.
- At altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 140 equates to 14,000 ft.
- An internationally recognised radio call announcing an urgency condition which concerns the safety of an aircraft or its occupants but where the flight crew does not require immediate assistance.