What happened
On July 13, 2015, at approximately 10:00 LT, a Fokker 50, registration OO-VLM, operated by VLM Airlines, was taxiing from parking position 127 toward the runway 23 hold short point at Geneva Airport (LSGG). The aircraft was carrying two crew members, a cabin crew member, and 11 passengers.
As the aircraft approached taxiway exit Charlie, the cabin crew notified the flight deck of high temperatures within the cabin and a noticeable burning odor. Shortly thereafter, the "smoke in the toilet" alarm was activated. The pilot in command immediately halted the aircraft and instructed the first officer to declare a "MAYDAY" on the tower frequency. Following the emergency declaration, the pilot ordered an evacuation. All 11 passengers and the cabin crew exited the aircraft via the rear right door (2R) without injury. Airport security services (SSA) responded promptly, assisting passengers and inspecting the aircraft. While white smoke was visible upon opening the lavatory door, thermal imaging conducted by firefighters showed a maximum temperature of 44 °C, which ruled out an active fire.
The investigation
The investigation focused on the mechanical failure within the aircraft's environmental control systems. The aircraft was equipped with two air conditioning packs located in the unpressurized tail cone area. Investigators examined the right-side pack and discovered that a ball bearing within the rotor had failed, leading to a rotor blockage. This failure caused the rotor blades to strike the stator, resulting in structural damage to the blades and damage to a nearby carbon seal. This mechanical breakdown allowed crankcase oil to leak into the turbine section of the pack, where it ignited or vaporized, creating the smoke. The smoke then traveled through the air conditioning distribution ducts, eventually triggering the smoke detector in the lavatory.
Findings
- The primary cause of the smoke was oil leaking into the turbine section of the right air conditioning pack following a mechanical failure.
- A broken ball bearing caused the rotor to seize and damaged the rotor blades and the carbon seal.
- The smoke detection system functioned as intended, alerting the crew to the issue.
- The investigation noted that similar bearing failures have been documented in maintenance facilities, often caused by rotor imbalance stemming from manufacturing defects or ice buildup on the blades during high demand for cold air.
- The evacuation was executed successfully, and all occupants remained uninjured.