What happened
On 24 August 2016, a HAV Airlander 10, registration G-PHRG, was conducting a flight test at Cardington Airfield. During the initial approach to the mooring mast, the ground crew encountered a mechanical issue where a diesel engine powering the winch hydraulics failed to start due to a drained starter battery. To avoid a prolonged period of loitering, the pilot elected to take the aircraft back into the air while the ground equipment was addressed.
During this second flight, the mooring line, which had been temporarily stowed through a cabin access panel, fell free and hung at its full length beneath the aircraft. The pilot was misinformed by the ground team regarding the actual length of the trailing line. To prevent the line from snagging on perimeter fences or trees, a steeper and higher approach was required. During this approach, the line became entangled in wires outside the airfield boundary.
As the aircraft arrived over the landing site at an altitude of approximately 180 ft, the pilot attempted to manage the aircraft's centre of gravity to induce a nose-down trim, aiming to bring the mooring line within reach of the ground crew. During this manoeuvre, the aircraft unexpectedly transitioned from a 10-degree nose-down pitch to an 18-degree pitch and began a rapid descent. Despite efforts to recover, the aircraft struck the ground, resulting in no injuries to the two crew members but causing structural damage to the cabin flight deck area.
The investigation
The investigation examined the sequence of events leading to the loss of control and the mechanical failures on the ground. It established that the aircraft was operating outside its normal flight regime due to the necessity of a controlled vertical landing in light winds. The investigation also looked into the failure of the winch's diesel engine and the lack of a secure stowage method for the mooring line once it had been extracted from the interface.
Findings
- The primary cause of the impact was the unexpectedly exaggerated nose-down pitch during a manual attempt to adjust the aircraft's attitude.
- The necessity for a high-altitude approach was driven by the need to clear obstacles with the trailing mooring line.
- The mooring line became a hazard because there was no dedicated stowage facility for the line once it was removed from the mast interface.
- An electrical fault had rendered the winch inoperative by draining the starter battery of the diesel engine.
- The pilot received inaccurate information regarding the length of the trailing line from the ground crew.