What happened
On November 28, 2001, an Embraer EMB-145LU, registration HB-JAH, was operating a flight from Krakow to Zurich when the crew detected a burning odor in the cabin. During the descent, the flight attendant reported that certain floor coverings near the wing area felt hot, and a distinct smell of burnt material was present throughout the aircraft.
As the aircraft approached Zurich, the crew observed light smoke within the cockpit. In response, the pilots donned their oxygen masks. The flight subsequently requested landing priority and requested that emergency services be on standby. Despite the developing situation, the aircraft landed safely on runway 16 at Zurich Airport, and passengers were able to disembark at the gate without injury.
The investigation
Investigators examined the aircraft's engines and the condition of the cockpit emergency equipment. The investigation focused on the source of the odor and the subsequent breakdown in crew coordination during the approach phase. Technical inspections of the right engine revealed carbon deposits on three fuel injectors.
Furthermore, the investigation scrutinized the functionality of the cockpit oxygen masks. It was found that the masks were difficult to remove from their stowage containers. Additionally, the investigation identified issues with the microphones integrated into the masks and the clarity of the mask visors.
Findings
- The primary cause of the smoke and odor was the contamination of bleed air used for the air conditioning packs, resulting from the carbonization of three fuel injectors in the right engine.
- Crew coordination during the approach nearly collapsed due to several critical equipment failures:
- The oxygen masks were improperly installed, making them difficult to deploy quickly.
- The visor of the co-pilot's mask was heavily contaminated, which created a false perception that the smoke density was increasing.
- The microphones within the oxygen masks functioned intermittently due to a faulty reed-switch mechanism, severely hindering communication between the pilots and with Air Traffic Control.
Safety action
Following the incident, the following safety measures were implemented:
- The maintenance interval for inspecting oxygen masks was significantly reduced from 4,000 flight hours to 400 flight hours.
- The operator implemented a modified mask liner to ensure easier, quick-donning capability.
- The faulty reed-switch mechanism in the microphones was removed to stabilize communication.
- New quality guidelines were established for the replacement of mask visors to prevent obscuration.