What happened
On November 12, 1976, a Piper PA-31T Cheyenne, registration HB-LHT, operated by Aeroleasing S.A., was preparing for a flight from Shannon, Ireland, to London-Gatwick. The flight was scheduled for late afternoon, but heavy fog had significantly reduced visibility at the airport.
During the takeoff roll on runway 06, the aircraft initially remained on the centerline. However, shortly after lifting off, the aircraft deviated to the left. At a distance of approximately 1,690 meters from the start of the runway, the propellers struck the ground. The aircraft then veered off the airfield, breached the perimeter fence, and collided with a stone wall. A violent fire broke out upon impact, destroying the aircraft. The pilot and four passengers were killed in the accident.
The investigation
The investigation examined the meteorological conditions, the pilot's experience, and the aircraft's mechanical state. It was determined that the pilot had consulted meteorological services earlier in the day and was aware of deteriorating conditions. Despite the thick fog, the pilot proceeded with the takeoff, having previously stated a personal minimum visibility of 100 meters.
Investigators also reviewed the Runway Visual Range (RVR) measurement process. It was found that the fire service driver had measured the RVR from an incorrect location, though the actual visibility was slightly higher than the value reported to the pilot. Furthermore, the use of anti-collision strobe lights was noted, as their reflections in heavy fog can contribute to spatial disorientation.
Findings
- The primary cause of the accident was the pilot's inability to maintain a positive rate of climb while flying under instrument conditions in visibility that was below the company's established operational minima.
- The pilot had relatively low experience on the Piper PA-31T, with only approximately 30 flight hours on this specific type.
- The aircraft's flight characteristics required a high degree of pilot attention, which was further complicated by the use of strobe lights in low-visibility conditions.
- The aircraft was operating near its maximum allowable weight, and while the mechanical condition of the aircraft was sound, the stability augmentation system (SAS) and its associated control spring characteristics were noted as factors affecting handling.
Safety action
Following the investigation, recommendations were made for Swiss authorities to review operational requirements regarding pilot experience and minimum weather requirements, particularly for single-pilot operations. Additionally, a recommendation was made to US authorities to re-examine the use of heavy control springs in light aircraft to ensure certification standards do not inadvertently degrade handling characteristics.