What happened
On 7 July 2002, a Piper PA-28-181, registration G-KAIR, was performing a private flight from Cumbernauld Airport to Aldergrove for scheduled maintenance. Shortly after departure, the pilot noted that the engine was running roughly. The pilot decided to return to the departure airfield, but while approximately six miles from Cumbernauld, smoke began to fill the cockpit.
To mitigate the effects of the smoke, which was causing physical discomfort and obscuring vision, the pilot opened the cockpit door and requested that all circuit traffic be cleared. The intention was to perform a direct downwind approach to land on Runway 08 as quickly as possible. Upon touchdown, the pilot applied heavy braking, which caused the aircraft to oscillate laterally and resulted in the right main wheel tyre burst. After taxiing to the apron and shutting down the engine, ground crews used CO2 and powder extinguishers on the smoking engine compartment. The pilot was subsequently treated at a local hospital for smoke inhalation.
The investigation
An investigation involving a maintenance engineer and a CAA surveyor examined the aircraft's engine compartment. Investigators discovered that a bead of black RTV sealant, used to protect the edges of the front cylinder baffles from erosion, had detached from the baffle near the No.2 cylinder. This specific area was located near the air intake for the cabin heater's exhaust heat exchanger.
Fragments of the detached sealant were recovered and found to smouldering when subjected to heat, matching the odour of the fumes reported by the pilot. The investigation established that pieces of the sealant had entered the cabin air heat exchanger, and because the cabin heat control was not fully closed, the fumes entered the cockpit.