What happened
On 23 March 2020, a Scheibe Super Falke SF25E, registration G-KDEY, was performing visual circuits at Aston Down Airfield in Gloucestershire. The pilot had recently refuelled the aircraft using Mogas. During the flight, the pilot experienced a period of unconsciousness, only regaining awareness at a very low altitude, which was too late to recover the aircraft. The aircraft struck the ground in a field west of the airfield boundary, impacting a parked vehicle and a treeline. The impact resulted in the destruction of the aircraft and caused serious injuries to the pilot.
The investigation
Investigators examined the engine, exhaust system, and cockpit environment. The examination of the Limbach engine revealed that the exhaust system had experienced leaks. Specifically, the down pipe from the number one cylinder was found to be severely corroded and had failed prior to the accident. Furthermore, the tail pipe was not an approved design and featured cuts that allowed exhaust gases to escape. The investigation also looked into the engine firewall, finding that the seals and grommets used to protect the cockpit from engine bay gases had deteriorated and perished, creating a pathway for gases to enter the cabin.
Regarding the fuel, the aircraft was using Mogas, and investigators considered the potential for carburettor icing due to the ethanol content and weather conditions. However, the primary focus remained on the presence of exhaust gases. The investigation also evaluated the effectiveness of the CO spot detector installed in the cockpit, noting that such passive devices may not provide timely or noticeable warnings at low concentrations.
Findings
- Evidence indicated that carbon monoxide leakage from the exhaust system likely reached the cockpit through degraded firewall seals.
- The pilot was likely incapacitated by carbon monoxide poisoning before the impact.
- The exhaust system featured a non-approved tail pipe design and significant corrosion on the number one cylinder down pipe.
- The engine bay seals and grommets were in a deteriorated state, allowing engine bay gases to enter the cabin.
- While carburettor icing due to the use of Mogas could not be entirely ruled out, the primary cause was identified as gas leakage.