Flight Details
The aircraft, a 1961 Piper PA-24 (N7456P) powered by a single Lycoming 250 piston engine, departed Leeds East Airport for Retford (Gamston) Airport, Nottinghamshire, at 1055 UTC on 21 July 2017. The pilot, aged 59, held a US Federal Aviation Administration Private Pilot's Licence and had 1,257 hours of flying experience, of which 388 were on type. He had flown only one hour in the preceding 90 days. A passenger, a qualified FAA Flight Instructor, occupied the front right seat to observe the pilot for a Flight Review.
Accident Sequence
Prior to departure, the pilot obtained a forecast surface wind for Retford of 180° at 14 kt. The flight proceeded southward at heights between 1,000 ft and 2,000 ft agl, experiencing light to moderate turbulence. On arrival, the reported wind was 160° at 10 kt with no warnings of turbulence or windshear. The pilot set up for Runway 21 using intermediate flap and increased airspeed to compensate for the crosswind. The instructor described the approach as “fairly stable” until about 100 ft agl, when the airspeed temporarily dropped by approximately 10 kt. The pilot recalled increased turbulence and a sink, which he corrected. At about 20 ft agl, another sink occurred. He added power, but the stall warner sounded and he pushed the control column forward. The aircraft struck the runway “fairly hard” nose first. The nose landing gear collapsed on impact, the propeller struck the surface, and the engine stopped. The main landing gear then collapsed as the aircraft skidded. The pilot switched off the master switches and fuel, while the passenger opened the door and moved the mixture to cut-off. Both occupants evacuated without injury before airport rescue services arrived.
Pilot Observations
The pilot, who had operated at Retford for 24 years, acknowledged that he was not mentally prepared for the downdraughts because earlier conditions did not seem severe. He noted that the accident occurred in the lee of a line of airport buildings and tall trees, which may have caused a rotor effect. He also considered that the wind report was received while still three miles from the airfield; in hindsight, a closer report might have been beneficial. After the accident, the airport rescue service recorded surface wind as 150° at 17 kt.
AAIB Comment
The AAIB referenced the International Civil Aviation Organisation's 'Manual on Low-level Windshear' (Doc 9817), which states that structures such as hangars and fuel storage tanks commonly cause low-level windshear, especially at smaller aerodromes. These buildings can present a wide, solid barrier to the prevailing wind, forcing flow around and over them, resulting in localized, shallow, turbulent horizontal wind shear that can affect light aircraft.