Lingus A320 at Madrid and Dublin on Apr 24th 2024, chemical odour on board

Last Update: August 14, 2025 / 10:26:43 GMT/Zulu time

Bookmark this article
Incident Facts

Date of incident
Apr 24, 2024

Classification
Incident

Airline
Aer Lingus

Departure
Madrid, Spain

Destination
Dublin, Ireland

Aircraft Registration
EI-DEJ

Aircraft Type
Airbus A320

ICAO Type Designator
A320

An Aer Lingus Airbus A320-200, registration EI-DEJ performing positioning flight EI-593 from Madrid,SP (Spain) to Dublin (Ireland) with 2 crew on board, was climbing out of Madrid's runway 36L when the captain noticed a faint chemical odour similiar to a hot iron burning clothes, the first officer did not detect any odour. The odour dissipated in cruise but returned very strongly during the approach to Dublin while descending through about 6500 feet prompting the captain to order donning of the oxygen masks. Both crew donned their oxygen masks and continued the approach without reporting the odour to ATC, at 600 feet AGL both crew removed their oxygen masks to improve vision and landed the aircraft on runway 28L without further incident.

Ireland's AAIB rated the occurrence a serious incident and open an investigation. The AAIB reported the aircraft had been in Madrid for maintenance on the landing gear. Although the odour had dissipated in cruise, it was still detectable in the aft galley. After donning their oxygen masks at 6500 feet due to the strong odour the crew removed the oxygen masks at 600 feet to improve vision and detected that the odour had reduced even though was still detectable by both crew.

On Aug 14th 2025 the AAIU released their final report concluding the probable cause of the serious incident was:

Contamination of the aircraft’s air conditioning system due to oil from an APU external oil leak being ingested by the APU’s load compressor.

Contributory Cause(s)

Maintenance actions following previous reports of odours/fumes did not identify the source of the odours/fumes.

The AAIU analysed:

After take-off on a positioning flight to EIDW, the Commander, who was the PF, detected a ‘slight chemical-type’ odour. At this stage, it was not detected by the First Officer, who was the PM. However, during the descent into EIDW, when passing approximately 6,500 ft, both Flight Crew members detected a ‘very strong chemical odour’. Consequently, the Commander ordered the donning of the flight crew oxygen masks. The masks were subsequently removed at approximately 600 ft to improve visibility and communication. The odour was reported to have diminished but that it was still noticeable. The aircraft landed normally on RWY 28L at EIDW and taxied to its parking stand.

Reaction to Odours

If oil enters an APU’s load compressor, it can become mixed with the hot, high-pressure air being generated by the load compressor and cause odour, smoke or fumes in the aircraft cabin and/or cockpit.

As outlined in the Aircraft Manufacturer’s In-Service Information Bulletin on the subject of odours in the cabin, ‘a smell does not necessarily indicate a high concentration of contaminants’ and ‘is not an objective criteria [sic] for air pollution’. The bulletin also notes that a smell can ‘influence our belief about risk and health and can trigger conscious and subconscious physiological reactions’. Nevertheless, odours or fumes in an aircraft cabin (and/or cockpit) have the potential to cause adverse symptoms. To minimise the possibility of any adverse consequences, flight crews are directed by the QRH checklist for ‘SMOKE/FUMES/AVNCS [avionics] SMOKE’ to don the crew oxygen masks if required.

In this case, following the flight, the Flight Crew immediately attended a hospital, where physical examination, blood tests, X-rays, and ECGs were conducted. No abnormalities were detected and both crew members were discharged a number of hours later, although they continued to report symptoms for a period of time. However, in the absence of any detected medical abnormalities, it is not possible to attribute the reported symptoms to a specific cause.

A UK National Health Service (NHS) ‘Care Pathway’ flowchart for ‘patients exposed to fumes onboard commercial aircraft’ was reportedly used by medical personnel during their examination of the Flight Crew. However, other bespoke medical examination protocols or specialist testing techniques could further assist in identifying levels of exposure to airborne contaminants, such as the laboratory analysis of hair samples obtained from affected persons. The Operator informed the Investigation that it is working on the development of a bespoke protocol to be used following fume events.

Previous Reports of Odours/Fumes

In the weeks preceding the occurrence, there were several reports of odours/fumes on the aircraft, followed by extensive troubleshooting by maintenance personnel, during which instances of contamination and oil leaks were identified, maintenance actions were carried out, and decontamination runs were performed. Troubleshooting resulted in the APU being replaced on 28 March 2024. This APU (S/N 2788) had been installed on the aircraft since 23 December 2021.

The removed APU was sent to the Manufacturer’s workshop, where it was found that the external condition was ‘severely dirt contaminated’. It was also noted that the inlet plenum was ‘found heavily contaminated [with oil]’ but that there was ‘no oil indication at load compressor side’. The workshop report recorded that there was an ‘ingestion of oil’, i.e. that oil leaking externally had been ingested into the APU.

The replacement of the APU would be expected to prevent further occurrences. However, two weeks later, on 11 April 2024, following a flight from Dublin, the flight crew reported a ‘strong smelly socks’ odour during the descent and that the cabin crew reported a ‘chemical smell’ in the aircraft cabin. Maintenance personnel performed troubleshooting and a Level A decontamination run, noting that there was ‘No smoke or smell found’. Maintenance personnel also rendered the APU inoperative.

When the aircraft returned to EIDW, the flight crew recorded that the ‘Cabin Crew reported smell again during descent circa 5-6 mins prior to landing. Cleared more quickly than previous flight. Nothing in FD [Flight Deck]’. The fact that a smell was reported while the APU was inoperative and a Level A decontamination run had been carried out, indicates that the decontamination run was ineffective and that it is likely some contamination remained in the ECS at that time. During subsequent troubleshooting carried out the following day (12 April 2024), oil was found on the ‘APU load compressor and inlet plenum’ and a further decontamination run was carried out. The aircraft was returned to service on 13 April 2024 with the APU remaining inoperative.

During further troubleshooting performed on the night of 16/17 April 2024, maintenance personnel noted an ‘oil weep’ at the APU chip detector. An external oil leak, such as a leak at the APU chip detector could result in oil leaking onto the APU cowlings, entering the APU air intake and contaminating the inlet plenum and load compressor. The chip detector o-rings were replaced, and the APU was ‘cleaned and ran for 1 hr with no further leaks or smells […]’.

The aircraft was released to service with the APU operative. The following flight was to a maintenance base later that day (17 April 2024) for landing gear maintenance. The next flight was the occurrence flight, which was the return flight from the maintenance base, one week later.

The APU had been running on the morning of the occurrence flight until the engines were started. It is therefore possible that an APU oil leak remained from before the week-long maintenance visit, and that when the APU was running prior to engine start-up, it contaminated the air conditioning system and caused the odour on the subject flight.

Maintenance Actions following Occurrence Flight

Initially, following the subject occurrence, maintenance personnel performed a ‘Decontamination of [the] Environmental Control System with both engines supplying air’. The aircraft was returned to service the following day with the APU inoperative (25 April 2024).

On 26 April 2024, during subsequent troubleshooting, maintenance personnel found evidence of oil in the APU’s inlet plenum. Then, on 30 April 2024, the APU cooling fan, and cooling fan outlet duct were found to be ‘contaminated with oil’. On 2 May 2024, maintenance personnel removed the ‘load compressor cavity plug’ and oil-contaminated fluid ‘poured’ from the cavity drain. In addition, the load compressor’s inlet lip was ‘found to be heavily contaminated’. The APU (S/N 3216), which had only been installed on the aircraft since 28 March 2024, was replaced on 4 May 2024. The subsequent workshop report noted that the external condition was ‘oil stained and dirty’. that there was an ‘ingestion of oil’, i.e. that oil leaking externally had been ingested into the APU.
Aircraft Registration Data
Registration mark
EI-DEJ
Country of Registration
Ireland
Date of Registration
DfhAnhqigdkjnjnm Subscribe to unlock
Manufacturer
AIRBUS INDUSTRIE
Aircraft Model / Type
A320-214
ICAO Aircraft Type
A320
Year of Manufacture
LeAn Subscribe to unlock
Serial Number
Npqg Subscribe to unlock
Maximum Take off Mass (MTOM) [kg]
HglAq Subscribe to unlock
Engine Count
A Subscribe to unlock
Engine
BfbphAdjgp pji Subscribe to unlock
Main Owner
QqAminbmgn pnhkbA fiecklcmn Subscribe to unlock
Incident Facts

Date of incident
Apr 24, 2024

Classification
Incident

Airline
Aer Lingus

Departure
Madrid, Spain

Destination
Dublin, Ireland

Aircraft Registration
EI-DEJ

Aircraft Type
Airbus A320

ICAO Type Designator
A320

This article is published under license from Avherald.com. © of text by Avherald.com.
Article source

You can read 2 more free articles without a subscription.

Subscribe now and continue reading without any limits!

Subscribe now
Are you a subscriber? Login
Subscribe

Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.

Compare our plans

Send tip

Support AeroInside by sending a small tip amount.

Send tip

Related articles

Newest articles

Subscribe today

Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.

Pick your plan and subscribe

Partner

ELITE Logo

ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.

SafetyScan Pro

SafetyScan Pro provides streamlined access to thousands of aviation accident reports. Tailored for your safety management efforts. Book your demo today

AeroInside Blog
Popular aircraft
Airbus A320
Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American Airlines
United
Delta
Air Canada
Lufthansa
British Airways