Introduction
On 13 September 2020 at 1742 UTC, a Piper PA-28-161, registration G-BZDA, was conducting a training flight from White Waltham Airfield, Berkshire. The aircraft was climbing through 100 ft after takeoff from Runway 29R when its engine abruptly lost power. The instructor took control, lowered the nose, and briefly transmitted a MAYDAY call. The engine then recovered to full power, but after the instructor raised the nose to continue the climb, the engine failed again and stopped. The instructor turned left towards open ground and carried out a forced landing. The nosewheel collapsed during the landing, but both the instructor and student were uninjured and vacated the aircraft without assistance.
History of the Flight
The flight was the fourth instructional flight of the day for the instructor, who also served as pilot-in-command. During pre-flight checks, he conducted a Transit Check per the PA-28 checklist, which included sampling fuel from both wing tank drains and the gascolator. After engine start, the fuel pressure dropped when the fuel pump was turned off but remained within the green range. Engine parameters were normal during the before-takeoff power check. The takeoff roll proceeded normally until the loss of power during climb. The airfield fire service observed fuel leaking from the gascolator drain upon arrival.
Gascolator Drain Valve Background
The gascolator is a combined fuel filter and sump located upstream of the engine fuel inlet. It traps water and debris and is typically fitted with a drain valve to allow fuel sampling. Lockable drain valves have a plunger mechanism that can be held open by rotating a cross bar into a locking detent. When left open, fuel can leak and air can be drawn into the gascolator, leading to engine fuel starvation, especially at high power settings such as during climb.
Previous Incidents
The AAIB investigated a similar accident in December 1988 involving a PA-28, G-BPBM, which led to a recommendation to remove the locking feature. Another accident in November 1989 (G-BHFL) also involved a lockable gascolator drain. In 1990, the CAA issued Emergency Airworthiness Directive EAD 001-02-90 requiring placards alerting pilots to check the drain was closed. G-BZDA was placarded accordingly. Despite this, the locking feature remained on G-BZDA.
Investigation Findings
Examination of G-BZDA after the accident revealed that the gascolator drain was a lockable variant, although the aircraft was built to a later standard that specified a non-locking valve. How the non-locking original was replaced with the lockable type could not be determined. The open drain allowed partial fuel starvation, causing the engine power loss. The investigation noted that wing tank drains, if left open, would not cause starvation, making the gascolator drain critical.
Regulatory Action
In response to this accident, the UK CAA released Safety Notice SN-2021/005, reminding owners and operators of the hazard posed by lockable gascolator drains and recommending replacement with non-locking alternatives. The CAA also undertook to review the risk against current Airworthiness Directive criteria. The aircraft manufacturer had changed its design to non-locking gascolator drains in 1989, but G-BZDA had been fitted with an incorrect part during its service life.