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P28A / S76, Humberside UK 2009

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Summary
On 26 September 2009, a Piper PA28-140 flown by an experienced pilot was about to touch down after a day VMC approach about a mile behind an S76 helicopter which was also categorised as 'Light' for Wake Vortex purposes rolled uncontrollably to the right in the flare and struck the ground inverted seriously injuring the pilot. The Investigation noted existing informal National Regulatory Authority guidance material already suggested that light aircraft pilots might treat 'Light' helicopters as one category higher when on approach and recommended that this advice be more widely promulgated.
Event Details
When September 2009
Actual or Potential
Event Type
Loss of Control, Wake Vortex Turbulence
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft PIPER Cherokee (PA-28-140/150/160/180)
Operator Not Recorded
Type of Flight Private
Intended Destination Humberside Airport
Take off Commenced Yes
Flight Airborne Yes
Flight Completed No
Flight Phase Landing
LDG
Flight Details
Aircraft SIKORSKY S-76
Operator Not Recorded
Type of Flight Not Recorded
Intended Destination Humberside Airport
Take off Commenced Yes
Flight Airborne Yes
Flight Completed Yes
Flight Phase Landing
LDG
Location - Airport
Airport Humberside Airport
General
Tag(s) Ineffective Regulatory Oversight
LOC
Tag(s) Extreme Bank
WAKE
Tag(s) ICAO Standard Wake Separation prevailed,
Own separation,
In trail event
EPR
Tag(s) RFFS Procedures
Outcome
Damage or injury Yes
Aircraft damage Hull loss
Injuries Most or all occupants
Causal Factor Group(s)
Group(s) Aircraft Operation
Safety Recommendation(s)
Group(s) Aircraft Operation,
Air Traffic Management
Investigation Type
Type Independent

Description

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.

Investigation

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 kts14.816 km/h
4.112 m/s
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.

[2010-026]

The Final Report of the investigation was published on 8 July 2010.

Further Reading