Incident Description
On 19 March 2007, at approximately 15:10 UTC, a Dornier DO-228 (registration CS-TGG) was preparing for a passenger flight from Vila Real (LPVR) to Lisbon (LPPT). The aircraft had two crew members and fifteen passengers on board. During rotation on the ground, engine #2 remained at low revolutions per minute (rpm). After the completion of boarding and loading, the crew initiated a start of engine #1 using the onboard batteries. During the start, the engine accelerated very slowly, and a fire ignited inside the exhaust cone and turbine area. Ground personnel immediately responded with a portable fire extinguisher and extinguished the fire. The crew evacuated the passengers. No injuries or damage were reported.
Post-Incident Actions
After the fire, a visual inspection of the engine was conducted. Subsequently, a ground power unit (GPU) was connected, the engine was ventilated, and a normal start was performed without issues. Following the incident, the onboard batteries were found to be discharged and were replaced. All subsequent starts were normal.
Analysis
According to the Aircraft Flight Manual, the minimum battery voltage required for engine start is 24V, as noted in the 'BEFORE STARTING' checklist. The crew reported verifying the battery voltage within the recommended range (greater than 24V). However, investigators suspected a deficient charging capacity, meaning the batteries exhibited normal voltage but low amperage. This low charge state may have caused improper operation of the fuel shut-off valve, which might not have closed completely during normal engine shutdown, closing only through the action of the speed lever. When the speed lever was moved to 'LOW' before starting, the fuel shut-off valve likely opened, allowing fuel to enter. The crew reported a small amount of fuel exiting the purge tubes. The low battery charge hindered engine acceleration; the engine rotated very little but reached 10% rpm, activating the ignition. The combination of low airflow and excessive fuel led to a fire inside the engine exhaust nozzle.
Conclusions
The investigation concluded that, despite indicating normal voltage, the batteries had low capacity and did not supply the required amperage (800A) for engine start. The engine reached the minimum rpm for fuel introduction and ignition but could not accelerate sufficiently to ensure proper airflow. Consequently, the flame propagated beyond the combustion chamber into the turbine and exhaust nozzle area. The use of a GPU and battery replacement resolved the issue, confirming that the root cause was the inadequate battery charge state.