ASN Wikibase Occurrence # 254076
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| Date: | Thursday 29 April 2021 |
| Time: | c. 15:28 |
| Type: |  Piper PA-46-350P Malibu Mirage |
| Owner/operator: | ZeroAvia Ltd |
| Registration: | G-HYZA |
| MSN: | 4636130 |
| Year of manufacture: | 1997 |
| Engine model: | YASA electric motors (common shaft) |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | near Cranfield Airport (EGTC), Bedfordshire -
 United Kingdom
|
| Phase: | Approach |
| Nature: | Test |
| Departure airport: | Cranfield Airport (EGTC) |
| Cranfield Airport (EGTC) | |
| Investigating agency: | AAIB |
| Confidence Rating: |  Accident investigation report completed and information captured |
An electric engine and hydrogen fuel cell powered Piper PA-46-350P Malibu Mirage force landed near Cranfield Airport (EGTC), Bedfordshire, UK. The airplane sustained substantial damage. The crew were uninjured.
On the morning of the accident flight, G-HYZA was flown for approximately 16 minutes on test flight 85. The flight test team debriefed the results and prepared the aircraft for flight 86.
The plan for this flight was for the high voltage lithium (HV) battery to be switched off at the end of the downwind leg then, if able, to fly three or more circuits at 1,000 ft aal using the hydrogen fuel cell (HFC) only to provide electrical power. The flight test team discussed experimenting with combinations of higher airspeeds and propeller rpm that would reduce the aircraft angle of attack and improve the mass flow of air through the radiator which provided cooling for the HFC. This was considered as a potential strategy to manage a slow rise in temperature in the HFC which they had observed in previous flights when flying on that power source alone. The test card for flight 86 was not amended to reflect this intention.
After takeoff, the pilot turned onto the crosswind leg and climbed to the circuit height of 1,000 ft agl. During the downwind leg of the right-hand circuit, the pilot stated the power was set to 95 kW, the propeller to 2,500 rpm and the airspeed to 100 kt. Once stabilised at these parameters, which were at variance with the flight test card conditions, the observer confirmed that the HFC operating temperatures were within limits. He then instructed the pilot to reduce power to 90 kW to assess the effect on the airspeed, which reduced to approximately 95 kt. The pilot increased the power to 95 kW to regain the target speed.
The pilot set the power by reference to his display unit which was located below the throttle quadrant. When he looked up from this task, he recognised that the aircraft was in a late downwind position. He turned onto base leg and commented that they were losing speed in the turn. The observer suggested that they could increase power to 120 kW to regain the lost airspeed, then reduce power before turning off the HV battery to re-establish the test conditions. He also suggested a reduction in propeller rpm. The pilot increased power to 120 kW but did not reduce the propeller rpm. As he started to turn onto final, the pilot briefed that once he had established straight and level flight he would reduce the power slightly and turn off the HV battery leaving the electrical motors powered by the HFC. He called final on the radio and was cleared by ATC to fly through at circuit height.
Approaching the runway threshold at approximately 940 ft agl, the pilot reduced power to 90 kW, set the airspeed to 90 kt then selected the HV battery to off. Immediately, all electrical drive to the propeller was lost. The pilot and observer made several unsuccessful attempts to reset the system to restore power from the HFC with the observer stating the action to be taken and the pilot making the switch selection. The observer instructed the pilot to select the HV battery to on to reconnect the alternative power source. HV power was not restored so the observer instructed the pilot to attempt a system reset with the HFC in the off position. Electrical power was still not restored and at 440 ft agl the observer declared “the voltage is too high”, to which the pilot replied, “we’ve got to do something quick”.
The observer called for a further reset attempt and adjusted the power lever. The aircraft had now travelled the length of the runway and was at approximately 320 ft aal when the observer reported that power could not be restored.
The pilot transmitted a MAYDAY call and initiated a turn to the left to position for a landing on Runway 21. Almost immediately he recognised that he did not have sufficient height to complete the manoeuvre so lowered the landing gear and selected full flap for a forced landing in a field that was now directly ahead on a north-westerly heading. The aircraft touched down at approximately 87 kt ground speed on a level grass field. The pilot applied the brakes, and the aircraft continued its movement until it struck, and passed through, a hedge during which the left wing broke away. The nosewheel and left main wheel entered a ditch and the aircraft came to an abrupt stop. The pilot and observer were uninjured and exited the aircraft through the upper half of the cabin door.
The airport fire service arrived quickly at the scene. The observer returned to the aircraft and vented the hydrogen tank to atmosphere and disconnected the HV battery to make the aircraft safe.
AAIB Conclusions
The accident occurred when electrical power was lost to both motors as the power source was changed, and the inverters locked out, at a position in the circuit where the aircraft could not safely glide to the runway. A number of factors contributed to the accident:
● Sufficient ground testing had not been carried out to determine the effect of the back voltage from a windmilling propellor on the inverter protection system.
● The emergency procedure to clear an inverter lock out after the protection system operated was ineffective.
● An investigation had not been carried out into a previous loss of power resulting from an inverter lock out, which occurred three flights prior to the accident flight.
● The risk assessment had not been reviewed following the loss of propulsion on two previous flights.
● Ad hoc changes were made to the flight test plan, including the position where the electrical power source was switched, without the knowledge of the competent person.
G-HYZA met all the requirements to be flown under E Conditions and a comprehensive dossier was produced by the competent person. However, this was a complex project, and the competent person was unable to completely fulfil his responsibilities as detailed in CAP1220. The competent person’s involvement was restricted in a number of areas due to issues within the organisational relationships, the fast tempo of the project, other work commitments and restrictions from the COVID-19 pandemic. The operator’s chief executive and the flight test director took on the day-to-day management responsibility for much of the programme. However neither individual had the necessary safety and flight test experience for that role and their focus was primarily on meeting key project targets.
Accident investigation:
 |
|
Sources:
1, https://www.buckinghamshirelive.com/news/buckinghamshire-news/cranfield-plane-crash-milton-keynes-5358566
2. https://www.bedfordshirelive.co.uk/news/bedfordshire-news/two-people-escape-serious-injury-5358592
3. https://www.bedfordindependent.co.uk/hydrogen-powered-plane-crashes-during-test-flight-at-cranfield/
4. https://www.zeroavia.com/offairportlanding
5. https://fuelcellsworks.com/news/zeroavia-issues-statement-as-test-flight-ends-in-wreckage-of-piper-aircraft/
6. https://www.australianflying.com.au/latest/zeroavia-flies-hydrogen-electric-piper-m-series
7. https://ychef.files.bbci.co.uk/976x549/p09cywzj.jpg (photo)
8. AAIB Final Report: https://assets.publishing.service.gov.uk/media/62a20c39d3bf7f037097be7b/Piper_PS-46-350P__Modified__G-HYZA_08-22.pdf
History of this aircraft
Other occurrences involving this aircraft
| 28 September 1999 | N666LP | Southern Aircraft Conslutancy Inc Trustee | 0 | Eastleigh Airport, Southampton, Hampshire | |
sub |
Media:
During an experimental flight near Cranfield Airport, Bedfordshire, a modified electrically powered Piper PA-46-350P (G-HYZA) experienced a loss of power from the hydrogen fuel cells to the electrical motors.
— AAIB (@aaibgovuk) July 8, 2022
Read the report: https://t.co/TNKOe7OtTM#aviationsafety pic.twitter.com/DeO1luNWSa
The aircraft crash landed in a field and the 2 people on board self extricated prior to arrival of our crew. The tower contacted fire control to report the incident at 15:29 and crews from Kempston, Bedford, Biggleswade, Leighton Buzzard, Woburn (pt2.)
— Bedfordshire Fire Control (@Beds_FireCtrl) April 29, 2021
On April 29th, our R&D aircraft made a safe, off-airport landing in a field just outside the Bedfordshire airport. Aircraft has sustained some damage, but everybody involved is safe, and without injury. As we analyze the flight data, we will provide updates as we learn more.
— ZeroAvia (@ZeroAvia) April 29, 2021
Hydrogen-powered plane crashes during test flight at Cranfield https://t.co/kMZQMdEaXe via @BedfordIndy
— Aerossurance (@Aerossurance) May 1, 2021
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 29-Apr-2021 16:24 | gerard57 | Added |
| 29-Apr-2021 17:22 | RobertMB | Updated [Time, Aircraft type, Registration, Cn, Operator, Location, Destination airport, Source, Damage, Narrative] |
| 29-Apr-2021 19:46 | aaronwk | Updated [Narrative] |
| 29-Apr-2021 19:49 | Captain Adam | Updated [Aircraft type, Narrative] |
| 30-Apr-2021 01:53 | Dr. John Smith | Updated [Cn, Departure airport, Source, Embed code, Narrative] |
| 30-Apr-2021 04:01 | RobertMB | Updated [Cn, Embed code, Narrative] |
| 30-Apr-2021 11:59 | Aerossurance | Updated [Nature] |
| 30-Apr-2021 19:03 | Aerossurance | Updated [Phase, Source] |
| 01-May-2021 09:15 | Aerossurance | Updated [Source, Embed code, Narrative] |
| 02-May-2021 07:13 | Aerossurance | Updated [Source, Embed code] |
| 02-May-2021 14:12 | harro | Updated [Source, Narrative] |
| 28-Jul-2021 14:51 | Dr. John Smith | Updated [Category] |
| 28-Jul-2021 14:52 | Dr. John Smith | Updated [Source] |
| 08-Jul-2022 16:58 | harro | Updated [Narrative, Accident report] |
| 08-Jul-2022 18:36 | Dr. John Smith | Updated [Source, Narrative] |
| 08-Jul-2022 19:36 | Dr. John Smith | Updated [Embed code] |
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