What happened
On 10 August 2017, an HPH Glasflugel 304 eS sailplane, registration G-GSGS, was involved in a battery fire during its landing at Parham Airfield, West Sussex. The aircraft, which utilizes a Front Electric Sustender (FES) system, was being operated on a private flight.
Prior to the flight, the pilot had prepared the electric propulsion system by charging and installing the batteries. During the flight, the pilot utilized the electric motor for approximately four minutes. Following the use of the motor, the pilot noted that the propeller failed to realign correctly against the aircraft nose, a known issue the pilot had encountered previously.
Upon touchdown on the grass runway, the pilot heard an unusual noise. As the aircraft decelerated during the landing roll, smoke and a burning smell entered the cockpit. The pilot observed that the battery compartment cover was missing and flames were emerging from the compartment. While an initial attempt to extinguish the fire with a CO2 extinguisher failed, the fire was eventually suppressed using aqueous film-forming foam (AFFF). No injuries were reported.
The investigation
The AAIB investigation examined the damage to the FES battery compartment and the electrical components. The investigation found that the forward FES battery box had been ruptured at the rear left corner, with the battery assembly suffering heavy fire damage. The investigation also noted that the battery compartment cover's rear carbon fibre catch had fractured, which was consistent with a vertical load being applied to the inside of the cover.
Investigators also reviewed the functionality of the FES Control Unit (FCU). It was noted that the FCU does not currently provide any specific indication of a fire occurring within the battery compartment. Furthermore, the investigation considered the possibility of a previous impact, noting the pilot had reported a battery pack falling from a vehicle earlier in the year, though it could not be confirmed if that specific pack was involved.
Findings
- The fire originated in the forward FES battery pack, resulting in significant damage to the battery box and the composite material of the compartment.
- The FES battery compartment lacks a warning system to alert the pilot to a fire or other hazardous conditions.
- The pilot was unable to visually monitor the battery compartment during flight as it is located behind the pilot within the fuselage.
- The fractured catch on the battery compartment cover was consistent with a vertical load acting on the inside of the cover.