What happened
On 18 December 2014, an Airbus A320-232, registration G-TTOB, was performing a scheduled passenger flight from London Heathrow to Paris Charles de Gaulle. The aircraft was carrying 137 passengers and 6 crew members. Shortly after departing Heathrow at 20:15 UTC, the flight crew detected a musty odor while climbing through 5,000 ft. As the flight progressed, the smell intensified.
The situation escalated when the purser notified the commander that cabin crew members in both the forward and aft sections of the aircraft were experiencing symptoms of nausea and light-headedness. In response to the potential presence of fumes, the flight crew followed established procedures from the Quick Reference Handbook, which included donning oxygen masks. The commander declared a PAN-PAN call to Air Traffic Control and requested an immediate return to London Heathrow.
Upon landing, the aircraft stopped on a taxiway to allow emergency services to perform an external inspection. While the odor had diminished by the time the aircraft reached the stand, the crew remained masked during the approach. There were no injuries reported among the passengers or crew, and the aircraft sustained no damage.
The investigation
The investigation focused on identifying the source of the unusual odor and the cause of the crew and passenger symptoms. Technical examinations conducted by the aircraft operator revealed that hydraulic fluid had leaked from a yaw damper actuator. This leaking fluid was subsequently sucked into the air inlet of the Auxiliary Power Unit (APU). Because the APU provides bleed air to the aircraft's air conditioning system, the contaminated fluid was distributed throughout the cabin air supply.
Findings
- The primary cause of the incident was the ingestion of hydraulic fluid into the air conditioning system via the APU air inlet.
- The leak originated from a faulty yaw damper actuator.
- The presence of the fluid in the cabin air supply resulted in the reported symptoms of nausea and light-headedness among the cabin crew.