History of the Flight
On 24 April 2024, an Airbus A320-214 (registration EI-DEJ) was conducting a positioning flight from Madrid-Barajas Airport (LEMD) to Dublin Airport (EIDW) with two pilots on board and no passengers or cabin crew. The aircraft had undergone landing gear maintenance in Madrid. After take-off at approximately 10:25 UTC, the Commander, who was the Pilot Flying, detected a slight chemical-type odor similar to "when a hot iron burns clothes." The First Officer did not notice it initially, and the odor dissipated in the flight deck during cruise but remained detectable in the aft galley.
During the subsequent descent into Dublin, while passing approximately 6,500 ft, a very strong chemical odor was encountered in the flight deck. Due to its severity, the Commander immediately ordered the donning of flight crew oxygen masks. Both pilots donned their masks. The aircraft was already turning onto the localiser for Runway 28L, so no ATC assistance was sought. The oxygen masks were removed at approximately 600 ft to aid visibility and communication; at that stage the odor had diminished but was still noticeable. The aircraft landed normally on Runway 28L at about 12:35 UTC and taxied to the parking stand. During taxi, cockpit windows were opened for ventilation, and the odor was no longer apparent after engine shutdown. The Auxiliary Power Unit (APU) had been running on the ground in Madrid and was shut down after engine start; it was not used again until arrival in Dublin.
Crew Actions and Medical Checks
Following the flight, both crew members traveled to a hospital for medical evaluation. Physical examinations, blood tests, X-rays, and ECGs were conducted, and no abnormalities were detected. Both were discharged a number of hours later. The Commander later reported tingling in his left arm and fatigue that continued for several weeks; he returned to work approximately one month later. The First Officer reported a headache and throat pain lasting several days; he returned to work on 28 April 2024 after three rostered rest days. No injuries were reported to the investigation, and there was no damage to the aircraft.
Aircraft and APU Details
The aircraft, an Airbus A320-214 (serial number 2364), was manufactured in 2005 and had a valid Certificate of Airworthiness issued in 2008, with an Airworthiness Review Certificate valid until February 2025. The Honeywell 131-9A APU, installed in the tail compartment, supplies electrical power and bleed air primarily during ground operations. It has a lubrication system with an oil sump in the lower gearbox. The APU includes a load compressor that supplies air to the air conditioning system through a bleed valve, with exit air temperatures between 150 and 185 degrees Celsius. The APU air intake, fitted with a motorized flap, is located at the base of the APU compartment. A drain mast aft of the intake can expel fuel or oil from internal leaks. In this event, an external oil leak at the APU led to oil being ingested by the load compressor, contaminating the air conditioning system.
Probable Cause
The AAIU determined that the probable cause of the fumes was contamination of the aircraft’s air conditioning system due to oil from an external oil leak at the Auxiliary Power Unit being ingested by the APU’s load compressor.