Engine malfunction and collision with terrain involving a Piper PA-23, VH-BIQ, near Mareeba, Queensland, on 5 March 2016

What happened

The owner and maintainer of a Piper PA-23 aeroplane, registered VH-BIQ, who was also a pilot, had received a special flight permit (from a person authorised by the Civil Aviation Safety Authority to issue such permits) to ferry the aircraft from Mareeba, Queensland, to Darwin, Northern Territory, for a 100-hourly inspection.

On the morning of 5 March 2016, the pilot conducted a local flight from Mareeba Airport, to check everything was functioning normally on the aircraft, in preparation for the planned flight to Darwin. The pilot reported that the aircraft performed normally during the take-off and climb to about 2,500 ft above mean sea level (AMSL). However, witnesses reported that at least one engine was running roughly during taxi and take-off, and that the aircraft appeared to climb poorly after take-off. After departing the airport, the pilot reported performing a number of in-flight checks of the aircraft, including retracting and extending the landing gear.

At about 1200 Eastern Standard Time (EST), the aircraft was returning to the airport when the pilot observed the left engine revolutions per minute (RPM) decrease from about 2,300 RPM to 2,000 RPM, which was still above idle power. The pilot conducted a series of actions to try to rectify the power loss, including checking the fuel mixture and full range of the throttle, but the aircraft descended rapidly. As the aircraft continued to descend, the pilot set the aircraft attitude to maintain an airspeed of 70 kt, which was the nominated glide speed for the aircraft.

As the aircraft descended to about 200 ft above ground level, the pilot realised that the landing gear was extended. The pilot reduced the power to idle and conducted a forced landing. The aircraft collided with cane fields, crossed a road and collided with a tree, resulting in substantial damage (Figure 1). The pilot, who was the only occupant of the aircraft, initially exited the aircraft without injury. A small quantity of fuel in the cross-feed line ignited briefly, but the flame quickly extinguished. After assessing that there was then minimal risk of a fire, the pilot returned to the aircraft and in the process sustained a minor injury.

Pilot comments

The pilot provided the following comments:

• The temperature was 33 °C, with light rain falling, and the aerodrome was at an elevation of 1,560 ft AMSL. These conditions may have contributed to the aircraft being unable to maintain altitude even while the right engine continued to produce normal power. The pilot also elected not to feather the left propeller as the engine was still producing some power. The extended landing gear created substantial drag and further reduced the aircraft’s ability to maintain altitude.
• Some debris may have been present in the fuel that blocked the injectors, resulting in partial loss of power. It was possible that fuel had dried out in the distributor valve, creating a gum, which was then loosened and picked up in the fuel.

Figure 1: Accident site showing damage to VH-BIQ

Source: Aircraft owner

Safety message

The partial or complete failure of one engine in a light twin-engine aircraft can present a number of issues for a pilot to manage. Immediate actions include maintaining control of the aircraft, while assessing the aircraft’s ability to climb or maintain altitude, and configuring the aircraft for maximum available performance.

Reducing the drag by retracting landing gear and flaps, and by feathering the propeller of the failed engine, need to be considered as they may assist in maintaining altitude, but may be extended for approach and landing.

The aircraft’s ability to maintain altitude depends on the pilot’s timely and correct actions, as well as factors that affect aircraft performance such as heat, high humidity and altitude. The local conditions and aircraft configuration may reduce the capability of the aircraft such that a forced landing is the only option available. In this situation, good decision making such as selecting a suitable landing site as soon as possible, which way to turn and avoiding manoeuvring at low level, is essential.

Pilots need to be situationally aware at all times, and be able to impose good judgement and well developed skills to accomplish the flight objectives. Pilot actions or inactions may reduce perceived safety margins and increase the probability of adverse operational events. The CASA training resource Safety Behaviours: Human Factors for Pilots includes guidance for pilots in situational awareness, decision making, threat and error management and airmanship.

Aviation Short Investigations Bulletin - Issue 49