On 26 September 2009, a privately operated Piper PA28-140 with only the pilot on board was about to touch down on Runway 26 at Humberside Airport, after a day Visual Meteorological Conditions (VMC) approach when the aircraft rolled uncontrollably to the right in the flare and struck the ground. The aircraft came to rest inverted beside the runway and suffered significant damage but there was no fire. The pilot sustained serious injuries.
The pilot advised that the final approach had been normal but that after crossing the runway threshold, in the flare, the aircraft had rolled uncontrollably to the right. The right wing had contacted with the runway surface and failed so that the aircraft had become inverted. The cockpit door was jammed by the remains of the right wing, but, after use of considerable force, the pilot had been able to open the door and escape from the aircraft unaided. After a considerable delay due their not being promptly advised of the accident location, the AFRS arrived at the scene.
It was estimated that the accident aircraft had been about 1nm behind a Sikorsky S76 helicopter which had crossed the same landing threshold ahead of it and that the prevailing surface wind had been equivalent to an 8 kts head wind component and a 1.5 knot crosswind component.
The Investigation noted that there is evidence that “the vortices generated by helicopters are more powerful than that generated by a fixed wing aircraft of equivalent weight and speed, particularly during the final decelerating flare to a hover during landing” and noted a previous UK fatal accident which had occurred in similar circumstances at Oxford in July 1992 to the same aircraft type in the presence of the same helicopter type (see the UK AAIB Accident Report: Aircraft Accident Report No.: 1/93 EW/C92/7/2).
The Investigation also noted extant guidance material for both pilots and air traffic controllers indicating that when light aircraft are following, or in the vicinity of, a helicopter in flight or hover taxiing, caution is required. One official source was found advising that, for wake vortex separation purposes, pilots of light aircraft should treat a helicopter as being in one weight category higher than that formally listed in the UK wake vortex separation procedures.
It was found that aircraft movements continued at the airport despite the AFRS deployment to the accident and that there had been a delay in notifying the downgrading of the airport fire category following the AFRS deployment.
It was also found that the position of the airport fire training facility close to the threshold of Runway 26 was found to have obstructed the view of the runway from the TWR for a section immediately beyond the threshold where the accident occurred. This prevented the ATCO from directly observing the accident site and the accident aircraft was not located (by another aircraft) until an estimated three minutes after the accident had occurred.
The formal Conclusion of the Investigation was that:
“The uncontrollable right roll experienced by the pilot of (the accident aircraft) was probably the result of the aircraft flying through the wake turbulence generated by the preceding Sikorsky S76.”
Typical helicopter wake vortices Source: AAIB Bulletin: 7/2010 EW/C2009/09/07
Safety Action implemented by the airport operator as a result of their review of the findings from this accident were considered to ”have addressed the airport-related issues highlighted in this investigation.”
One Safety Recommendation was made:
- that the Civil Aviation Authority review CAP 493 Section 1, Chapter 3 and AIC P64/2009 and provide clear advice regarding the potential hazards to fixed wing aircraft when following a helicopter in the same wake turbulence weight category.
The Final Report of the investigation was published on 8 July 2010.