What happened
On July 18, 2012, a Boeing 757-223 operating a passenger service from Reykjavik-Keflavik, Iceland, to Frankfurt, Germany, experienced a cabin air disturbance. Approximately one hour into the flight at FL390, the purser notified the flight crew that several cabin crew members were suffering from headaches, dizziness, and sweating. In an attempt to increase fresh air, the pilots deactivated the right recirculation fan. After consulting with the airline's maintenance control center, the fan was reactivated, and the crew initiated a descent to lower the cabin pressure altitude from 7,000 ft to approximately 4,000 ft (descending through FL350 to FL310).
Despite these measures, the situation worsened during the descent. As the aircraft leveled off at FL200 and engine power was increased, the cabin crew reported severe symptoms, including intense dizziness, numbness in the legs, and cyanosis (blue lips and fingers). The pilot requested priority handling from Air Traffic Control and requested a shortened approach to Frankfurt. During the descent, the pilot also experienced a brief moment of dizziness while interacting with the crew in the galley. The aircraft landed in Frankfurt at 12:55 local time without further incident, and the crew members subsequently sought medical evaluation.
The investigation
The BFU examined the aircraft's systems and flight data. Tests performed on the cabin pressure controllers and the air conditioning packs showed no malfunctions in the left pack, though the right pack failed to regulate to "High Flow" during a specific test. Engine inspections using an Aerotracer showed no evidence of smoke, odor, or oil leaks. While the cockpit voice recorder (CVR) confirmed the timeline of the crew's distress, post-flight measurements of the cabin air revealed no chemical contaminants.
Findings
- The cabin crew experienced symptoms consistent with hypoxia (oxygen deficiency).
- The symptoms were localized to the cabin crew, while the pilots and 132 passengers remained unaffected; investigators noted that the physical activity of the crew might have resulted in a higher oxygen demand compared to the seated passengers and pilots.
- A potential contributing factor is restricted airflow within the cabin, specifically in the rear sections. Boeing had previously noted similar issues on this aircraft type caused by foreign objects obstructing the air conditioning system.
- There were no injuries to passengers or crew, and no damage to the aircraft.