What happened
On 8 December 2022, an Ikarus C42 FB80 Bravo, registration G-CICF, was conducting a local flight for currency at Headcorn Aerodrome. The aircraft was occupied by the pilot and a passenger acting as an instructor. Shortly after departing Runway 28 Left and climbing to 1,300 ft, the occupants noticed heavy smoke filling the cabin.
Although the pilot switched the battery master to the OFF position, the smoke persisted. To mitigate the danger, the passenger opened the upward-opening cabin door, holding it slightly ajar to allow smoke to escape. This action enabled the pilot to perform a successful downwind landing. Upon stopping, the airfield rescue and fire service arrived to find the main battery still burning. They used CO2 extinguishers to suppress the flames and removed the damaged battery pack.
The investigation
Investigators examined the aircraft's electrical system and the damaged battery. The G-CICF was equipped with a LiFePO4 lithium-ion battery, which had replaced a heavier lead-acid unit in 2016. The battery was housed in a box between the seats, but the box lacked any mechanism to contain heat or vent gases externally.
Testing with a datalogging voltmeter during a subsequent flight revealed that the charging voltage occasionally reached 14.7 V, slightly exceeding the manufacturer's 14.6 V limit. However, these spikes were very brief and unlikely to be the primary cause. The investigation also noted that the aircraft's UK approval holder had not implemented a manufacturer service bulletin that recommended installing an over-voltage protection device.
Findings
- The specific cause of the thermal runaway in the lithium-ion battery could not be determined due to the extent of the fire damage.
- The battery's location within the cabin area meant that smoke and toxic gases directly threatened the occupants.
- The battery box provided no containment for combustion products or heat.
- A similar battery fire involving the same aircraft type and battery model had previously resulted in the total loss of an aircraft in Germany.
Safety action
Following the incident, the manufacturer of the C42 has ceased installing lithium-ion main batteries in new aircraft, reverting to lead-acid batteries. A safety recommendation has been issued to the CAA to review installation requirements for lithium-ion batteries in the cabin areas of Non-Part 21 aircraft.