What happened
On March 19, 2007, at 15:10 UTC, a Dornier DO-228, registration CS-TGG, was preparing for a passenger flight from Vila Real (LPVR) to Lisbon (LPPT). During the engine start sequence, the crew had already started the number two engine at low RPM. Upon attempting to start the number one engine using the onboard batteries, the engine experienced an extremely slow acceleration, which triggered a fire within the turbine area and the exhaust cone.
Ground personnel responded immediately with a portable fire extinguisher to suppress the flames. The crew successfully evacuated all 15 passengers from the aircraft. Following a visual inspection of the engine, the crew utilized a Ground Power Unit (GPU) to perform a ventilation of the engine and successfully completed a normal start-up.
The investigation
The GPIAAF investigation focused on the electrical state of the aircraft and the mechanical behavior of the engine during the start sequence. The investigators reviewed the Aircraft Operating Manual, which specifies a minimum battery voltage of 24V for start-up and notes that lower voltages are associated with hot starts. While the crew reported that the battery voltage was within the recommended range, the investigation identified that the batteries had a low charging capacity, providing normal voltage but insufficient amperage.
Findings
- The onboard batteries, while showing a normal voltage, suffered from low charging capacity, failing to provide the required 800A necessary for a proper start.
- This insufficient electrical power likely caused the fuel cutoff valve to malfunction; the valve had not closed completely after the previous engine shutdown and only closed via the movement of the speed lever.
- When the speed lever was moved to the "LOW" position, the valve opened, allowing fuel to enter the engine.
- The low battery amperage prevented the engine from accelerating sufficiently to establish adequate airflow. Consequently, the engine reached the 10% RPM threshold required for ignition, but the resulting excess of fuel and low airflow caused the flame to propagate into the turbine and exhaust nozzle.
- The successful subsequent start using a GPU and new batteries confirmed that the issue was isolated to the depleted capacity of the installed batteries.