What happened
On September 2, 1999, a Saab 2000, registration HB-IZC, was completing a scheduled flight from Basel to Geneva. As the aircraft landed on runway 05 at 23:26 local time, the crew observed an "L GEN FAULT" message on the Engine Indicating and Crew Alerting System (EICAS), accompanied by a strong smell of burning oil. During the braking phase, a "L ENG OIL PRESS LOW" alert appeared, and smoke began to fill the cockpit and the forward section of the cabin. The crew brought the aircraft to a stop on a taxiway and immediately initiated the checklist for an emergency evacuation. All 12 passengers and the crew were evacuated safely and met by airport security services.
The investigation
Investigators examined the mechanical failure of the left engine generator and the subsequent smoke production. The investigation established that the generator casing and its drive shaft had ruptured, allowing oil to leak into the engine air intake. This oil leak contaminated the air entering the cabin' and cockpit ventilation systems.
Following the incident, a replacement generator was installed. However, during a subsequent ground run, the new generator suffered an identical failure of the drive shaft. This led to a deeper technical analysis of the engine's oil system.
Findings
- The primary cause of the smoke was the leakage of oil into the turbine air intake.
- The failure was triggered by a malfunctioning pressure relief valve located between the air-oil and fuel-oil heat exchangers.
- This faulty valve allowed operating pressures within the oil system to reach excessively high levels.
- The generator's drive shaft acted as the weakest link in the system, failing under the excessive pressure.
- The aircraft's weight and balance were within limits, and the pilots were properly licensed.