What happened
On 24 April 2026, a Skyranger Swift 912S(1) registered as G-MLZZ was destroyed by fire at Balado Airfield in Kinross. The single-engine aircraft was on a private flight from Laurencekirk to Strathaven with one crew member and one passenger on board.
Approximately 40 minutes into the flight, south-west of Dundee, the pilot received an audible alert from an active carbon monoxide detector. The digital display indicated a concentration of 465 ppm, significantly above the normal background range of 0–9 ppm. Despite the alarm, the engine performance remained stable, and there were no visible, olfactory, or gustatory signs of fault in the cabin.
The pilot decided to divert to the nearest airfield, Balado. To mitigate the gas exposure, he opened both windows and sideslipped the aircraft to increase ventilation, which reduced the detector reading to 190 ppm. During the approach, the engine power began to fluctuate, resulting in a hard landing. The engine stopped completely as the aircraft vacated the runway onto the taxiway.
After several unsuccessful attempts to restart the engine, smoke emerged from under the cowls. When the pilot exited the aircraft to investigate, flames were visible. Although extinguishers were available, the fire had taken hold too aggressively for safe approach. The local fire service arrived later to extinguish the remaining blaze, but the airframe was already destroyed. The pilot sustained 1 minor injury, while the passenger was not injured.
The investigation
The AAIB examined the sequence of events and the role of the carbon monoxide exposure. Carbon monoxide is a colourless, odourless gas produced by incomplete combustion that binds to haemoglobin, reducing oxygen transport. In light aircraft, common sources include exhaust leakage into cabin heating systems.
The pilot had previously experienced a similar leak in another aircraft and credited his active detector with allowing him to recognise the issue before symptoms appeared. He noted that while the alarm was clear, he was uncertain about specific danger thresholds. The CAA’s Safety Sense Leaflet suggests 50 ppm as an appropriate threshold for action, recommending immediate ventilation and landing.
The investigation highlighted that without the detector, the pilot might not have been aware of the abnormality until the engine failed. At that point, with CO levels at 465 ppm, it is possible the pilot was already suffering from early symptoms such as dizziness or confusion, which could have compromised his ability to manage the emergency.
Findings
The primary causal factor was an unexplained source of high carbon monoxide in the cabin, detected only by the active monitor. The subsequent engine failure and fire were not causally linked to the CO leak in the available evidence; the cause of both the gas emission and the post-landing fire remained not established. The pilot’s immediate response to ventilate the cabin was effective in reducing exposure levels but did not prevent the mechanical failure.