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Preliminary

Summary

Published: 2 November 2017

Sequence of events

On the evening of 8 September 2017, an instructor and student were preparing to carry out night circuits at Port Macquarie Airport, Port Macquarie, New South Wales in a Diamond DA40 NG aircraft, registered VH-YPQ. The training flight was being operated by the Australian International Aviation College. As it would be the student’s first time conducting night circuits, the instructor was at the controls for the first take-off, which began at about 1957 EST from runway 21.

The instructor reported noticing a ‘surging’ sound and feel on initial climb towards the end of the runway (Figure 1) and felt as though the engine had lost a significant amount of power. The propeller speed and load instruments were showing oscillations. As there was insufficient time for troubleshooting, and no visible forced landing options in the immediate area, the instructor decided to turn left and attempt to land on the reciprocal of the take-off runway, making an immediate radio call to that effect. The instructor recalled pushing the power lever to ensure that it was fully forward, and possibly experimenting with power settings to see if the issue improved.

Figure 1: Aircraft flight path and key events

Figure 1: Aircraft flight path and key events

Times shown in this image are Universal Coordinated Time (UTC). Local time was UTC + 10.
Source: Google Earth, annotated by the ATSB based on-board recordings (Garmin and ECU), radio recording, and accident site assessment.

The instructor later reported the aircraft would not maintain height through the turn and it collided with trees about 325 m directly abeam the runway 21 departure threshold, coming to rest inverted (Figure 2). Both occupants were seriously injured and the aircraft was destroyed. There was no fire.

Figure 2: Wreckage of VH-YPQ, which was partially disturbed during the rescue

Figure 2: Wreckage of VH-YPQ, which was partially disturbed during the rescue

Source: ATSB

Aircraft information

The DA 40 NG is a four-seat, low-wing, T-tail aircraft. VH-YPQ was manufactured in 2015 and first registered in Australia in January 2016. It was fitted with an Austro Engine AE300 E4-A four-cylinder intercooled turbodiesel engine running on aviation turbine fuel. The engine drove a three-bladed wooden composite variable-pitch MT Propellers MTV-6-R propeller.

The AE300 engine’s fuelling and the propeller pitch are controlled by a single engine control unit (ECU) which has dual-redundant hardware and performs continual self-testing. There is a cockpit switch for selecting ECU channels in case of a fault. The engine is controlled with a single power demand lever with two separate channels into the ECU for fault detection.

The last maintenance carried out on the aircraft was a 50-hourly engine check, landing gear wheel replacement, and coolant relief valve replacement on 28 August 2017. The last major inspection was carried out on 8 August 2017.

The operator’s flight manual for the DA 40 NG, based on that provided by the aircraft manufacturer, had an emergency procedure for a defective propeller RPM regulating system (Figure 3). It stated that in the case of oscillating RPM, pilots should move the power lever to clear the problem.

Figure 3: Operator’s procedure for a defective propeller RPM regulating system

Figure 3: Operator’s procedure for a defective propeller RPM regulating system

Source: Australian International Aviation College

Recorded data

Recorded data was retrieved from the ECU and the Garmin G1000 navigation/display system. The data closely matched between the two ECU channels and the Garmin G1000.

The engine data showed oscillations in propeller speed and engine load that began at a height of around 110 ft and increased over the next 20 seconds (Figure 4). By that time the propeller speed was varying between 2,206 and 2,279 RPM and load was varying by about 2.5 per cent.

Figure 4: Selected engine parameters for take-off showing propeller RPM (dark blue) and engine load (purple) oscillations. Other parameters shown are power lever position (light blue), boost pressure (red), ambient air pressure (dark green), engine oil pressure (light green), and engine status data (orange).

Figure 4: Selected engine parameters for take-off showing propeller RPM (dark blue) and engine load (purple) oscillations. Other parameters shown are power lever position (light blue), boost pressure (red), ambient air pressure (dark green), engine oil pressure (light green), and engine status data (orange).

Image shows increasing oscillations in propeller RPM and engine load, followed by a sequence of power lever movements. RPM and load vary with power lever movement.

Source: Austro Engine

The data presented in Figure 4 shows variations in power lever position following oscillations in propeller RPM and engine load. The movements were accompanied by a reduction in engine load and propeller speed. Full power was then applied and maintained until at least the end of the recording 4 seconds later. It was not clear whether any oscillations occurred after the initial power reduction. The last few seconds of engine data, below about 100 ft height, were lost due to the impact affecting the recording.

No ECU faults were recorded. The engine manufacturer reported that, other than the oscillations in propeller speed and engine load, which were not the result of power lever movement, no signs of engine problems were recorded throughout the flight.

The Garmin G1000 GPS data showed the aircraft banked left at about the same time as the power was reduced, with airspeed then decreasing to about 59 kt. The aircraft reached a height of about 431 ft above ground level before descending in a left turn, with the last recorded bank angle at 30°. Based on alignment between the accident site location, direction of travel, and the recorded data, the left turn and steep descent continued to impact. About 12 seconds of data were lost as a result of the impact.

Accident site examination

Examination of the aircraft wreckage found no pre-existing airframe issues. The aircraft impacted terrain in a northerly direction at a relatively slow speed and steep (about 20°) angle of descent. The cockpit was partially collapsed with the airframe resting on the instrument panel and seat backs. Both wings and the tail were structurally detached during the impact sequence.  

The flap actuator was found in the take-off flap position. The aircraft’s fuel tanks were breached and there was evidence of spillage, although the fuel quantity could not be determined. A small quantity of fuel was drained from the tanks, and matched the characteristics of aviation turbine fuel. It tested negative to water content. Previous fuel records and the engine data both indicated that there was sufficient fuel on board the aircraft.

Weather and environmental information

The weather was fine with light winds and little to no cloud. The time of the occurrence was past astronomical twilight and the moon, although nearly full, was on the horizon and would not have provided any significant light.

The departure end of runway 21 was surrounded by scrub and swamp. The township of Port Macquarie provided some light and a horizon reference to the east but the ground near the airport was dark apart from a few scattered dwellings.

Related occurrences

The engine manufacturer reported it was aware of 16 other events on aircraft fitted with the AE300 engine worldwide involving oscillations in propeller speed and load, none of which resulted in an accident. The engine manufacturer reported that in all cases, oscillations ceased with a change in power lever position.

Fifteen of these occurrences were later found to be the result of a fuel pressure issue, propeller imbalance, or faulty electrical connection in the propeller governor. Limited data from one occurrence of each type were provided by the engine manufacturer and exhibited different data signatures than that seen in the VH-YPQ accident.

The other occurrence involved a Diamond DA42, a twin-engine aircraft with a similar engine type to VH-YPQ. The reasons for that oscillation could not be determined from post-event examinations.

ATSB publications

The ATSB research report Avoidable Accidents No. 3 – Managing partial power loss after take-off in single-engine aircraft provides information to assist pilots handling both partial and complete engine power loss after take-off. It states:

While acknowledging the difficulty of attempting to train pilots for a partial power loss event which has an almost infinite variability of residual power and reliability, analysis of the occurrences supports the need to raise greater awareness of the hazards associated with partial power loss and to better train pilots for this eventuality… Partial power loss occurrences have a very broad range of characteristics by nature. The most effective risk control method for managing these occurrences may be significantly different between pilots of varying experience and training, aircraft models and the environmental conditions.

Pilots and operators can significantly reduce risk following a partial or complete engine power loss using the following strategies:

  • Pre-flight decision making and planning for emergencies specific to the current location and conditions, taking into account the runway direction and the best direction of any turn, the local wind strength and direction on a particular day, terrain and obstacles, decision points (taking into account aircraft height and performance) where different landing options will be taken.
  • Taking positive action and maintaining aircraft control when turning back to the aerodrome or conducting a forced landing.

Safety actions

After the accident, the Australian International Aviation College:

  • introduced partial engine failure after take-off training into the syllabi for instructors and students, comprising pre-flight planning and self-briefing, ground training, and flight training
  • performed flight simulator tests for partial engine failure after take-off conditions in each single engine aircraft model operated by the flying school
  • amended procedures to ensure that pilots keep a hand on the power lever throughout the take-off
  • investigated the potential to introduce specific single engine escape procedures for partial and complete power loss situations for each runway regularly used by the flying school.

Continuing investigation

The investigation is continuing and will include further examination and analysis of the:

  • recorded data
  • propeller hub, governor, and engine control unit
  • aircraft maintenance documentation
  • weather conditions
  • pilot qualifications and experience
  • coordination and planning of the training flight
  • aircraft and flying school operational procedures
  • related occurrences.

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The information contained in this web update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB's understanding of the accident as outlined in this web update. As such, no analysis or findings are included in this update.

 
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