| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
On 21 October 2018, an experimental Jabiru J170-D departed Launceston Airport, Tasmania for a local flight. In cruise between 1,500 ft and 2,500 ft above ground level (AGL), a fire began in the cockpit. The pilot, who was the sole occupant on board, conducted an emergency landing into a paddock. The aircraft struck a fence and fire destroyed the aircraft. The pilot sustained serious injuries and received first aid from the landowners until emergency services arrived.
On the morning of the accident, the aircraft was difficult to start. The pilot reported that the aircraft was started using an external portable power supply. This power supply remained connected from inside the cockpit for the duration of the flight, and the pilot reported switching this off after the start. During the flight, the pilot observed the electrical overvoltage alarm both visually and audibly activate on a Dynon D10 engine management system.
It indicated that the electrical system was charging the battery above normal capacity and possibly greater than 15 volts (normal range is 13-13.5v). The pilot had never encountered this problem previously and dismissed the alarm. However, about 5-10 minutes later the fire was observed entering the cockpit.
The pilot began an emergency descent into a paddock as fire began to engulf the cockpit. He opened his door to provide some outside visibility given cockpit windows were no longer transparent, which also assisted with cooling the flames. However, the pilot’s clothes had caught alight. During a high-speed landing, the aircraft bounced and the pilot exited the aircraft prior to the aircraft touching down again. The aircraft collided with a fence and was consumed by fire. (Figure 1).
The pilot found a cattle trough, immersed himself and called for help to a nearby farmhouse. The residents rendered first aid until emergency services arrived.
Figure 1: J170-D consumed by fire
Source: Tasmanian Fire Service, Fire investigation Report Aircraft Fire TFS Incident Number 18033397- Photograph 2, annotated by the ATSB
The Tasmanian Fire Service, Fire Investigation Report[1] established the area of fire origin on the engine side of the aircraft firewall[2] in front of the passenger’s feet position and within 400 mm radius of the battery (Figure 2).
Figure 2: J 170-D area of fire origin
Source: Tasmanian Fire Service, Fire investigation Report Aircraft Fire TFS Incident Number 18033397- Photograph 23, annotated by the ATSB, indicating fire origin.
The pilot reported that the engine did not exhibit any abnormal vibration and continued to run until impact with the fence. The pilot stated that the spread of the flames in the cockpit was sustained by a fuel source. This hastened the rapid spread of flames into the cockpit.
The aircraft had about 760 hours total time and had a Deltran 330 Lithium-iron Phosphate battery installed in September 2016, which had recently developed problems. The pilot recalled accidentally flattening the battery a month or two prior by leaving the master switch on. He had experienced problems with the battery since that time. The pilot reported that he used a Deltran trickle charger when the aircraft was not in use. However, the battery was not holding sufficient charge to start the engine consistently. The aircraft then required elevated RPM[3] in order to get sufficient voltage for the radios to be serviceable during taxi.
The J170-D Pilot’s Operating Handbook indicates that below 2000 RPM the alternator cannot supply sufficient power output to run ancillaries. This power then comes from the battery. Jabiru Service Letter JSL021 further identifies charging system limitations and risks of overvoltage situations. Operating the aircraft with a low voltage battery or one that will not accept electrical system charge may increase this risk.
Thermal runaway in a Lithium-ion battery is a dynamic chemical reaction accompanied by the release of heat. The temperature of the affected cell increases exponentially, triggering nearby cells to also increase their temperature and continue the reaction.
Lithium-ion battery thermal runaway is a known aviation safety hazard and can be initiated by mechanical, thermal of electrical abuse. Over discharge and overcharging of battery cells are two factors that can lead to an electrically induced thermal runaway and subsequent fire.
Safety message
In retrofitting Lithium-ion batteries to experimental aircraft, operators should consider the risks and to be aware of the appropriate charge and discharge requirements for the battery. They may not be suitable for the existing aircraft electrical systems.
Operators should also be aware of the potential risk of damage to Lithium-ion batteries should they be discharged below their minimum cell voltage.
Should a pilot notice any performance change in a fitted Lithium-ion battery, they should take action immediately to remove and replace the battery. This may prevent irreversible damage that may instigate a thermal runaway situation while in use.
In-depth knowledge of individual aircraft systems and regular emergency procedures practice is essential to ensure that pilots provide the most appropriate responses to uncharacteristic warnings or emergencies in flight.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
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