What happened
On January 18, 2007, a BAe 146 operating from Basel was instructed to enter a holding pattern near the Spessart radio beacon due to stormy weather while approaching Frankfurt/Main. During the hold, the flight crew noticed an unusual, unidentified odor within the cockpit.
As the pilot non-flying (PNF) attempted to adjust the air conditioning temperature, she began to feel unwell and experienced hand tremors. The training captain, who had assumed the role of pilot flying (PF) following the detection of the odor, noted that the PNF appeared confused. In response to the deteriorating situation, the crew donned oxygen masks. The captain declared a medical emergency and requested medical assistance upon landing.
Despite the PNF's physical impairment, she was able to assist the captain with checklists and the extension of the landing gear and flaps. The aircraft landed safely on runway 25R, and a medical team attended to the pilot once the aircraft reached the parking position. There were no injuries reported among the passengers or crew, and no damage was sustained by the aircraft.
The investigation
The BFU examined the aircraft's systems and the crew's physiological responses. The investigation focused on the source of the cockpit odor and the subsequent impairment of the pilot. While the flight crew's medical and toxicological examinations yielded no specific cause for the pilot's symptoms, the technical inspection of the aircraft revealed a specific mechanical failure.
Findings
Technical analysis determined that an oil leak at the APU impeller inlet had contaminated the air conditioning system. This leak allowed oil to enter the air supply used for temperature regulation in the cockpit and cabin.
Following the discovery, the airline performed inspections and maintenance as mandated by the manufacturer and the German Federal Aviation Office. The APU was replaced to rectify the leak. The investigation also noted that the airline had already begun an air quality modification campaign in December 2006 to address similar odor issues across its fleet.