An Aer Lingus pilot who claims he was sacked for blowing the whistle on alleged “toxic” fume events on commercial jets has described how he believes he came to suffer a brain injury while in command of a flight three years ago.

Former Airbus A320 captain Tom O’Riordan was giving evidence on Monday as his legal team began setting out its case in one of the longest-running whistleblower penalisation cases to proceed at the employment tribunal.

Aer Lingus strongly denies that any crew or passengers have been put at risk and says it dealt with O’Riordan and his concerns properly.

He said he and his first officer detected an “exhaust smell” while preparing an Airbus A320, registration EI-DEN, in advance of a return flight to Shannon Airport on June 4th, 2023.

An Aer Lingus engineer reported an oil leak at the auxiliary power unit, or APU, and disconnected the machine, which was to supply electric and pneumatic power while the main engines were off, he said.

O’Riordan said the smell “dissipated” after that and that he took it “on good faith” that the aircraft was ready to go.

The flight to Shannon was “uneventful”, but on the return leg, while descending back to Heathrow with a full load of passengers, the “exhaust” odour returned, he said.

At first, the flight crew were set to return to Dublin as passengers, but were told the following morning by the company flight operations department that EI-DEN was “serviceable” and they were to fly it back, said the complainant.

The aircraft’s technical log recorded a “decontamination procedure” on the jet’s air conditioning, he said.

“I would have accepted the aircraft in good faith that the engineers had performed their duties as required,” he said.

On descent into Dublin, “the fumes returned again”, he said, “a wet old smelly sports sock type of smell”.

He said he felt unwell during final approach and developed a “piercing headache” and nausea while taxiing.

“The left midsection of my face was numb and my eye was frozen … I felt clammy and faint, I still had the headache and nausea, and this metallic taste in my mouth,” he said.

“I actually thought I was going to die; it was really bad, really, really bad,” said O’Riordan.

He spent four nights in hospital after being taken off the flight deck by paramedics, he said.

O’Riordan told the WRC in 2024 he suffered “chronic fatigue syndrome and brain damage” due to “exposure to toxic fumes” on the flight. He is now pursuing a personal injury action in the High Court.

Aer Lingus’s legal team said O’Riordan had engaged in “a campaign of disruption” while out sick, including the alleged posting of “falsehoods and untruths” on social media, mounting a picket on its offices, and a hunger strike.

He was sacked from his €153,000 a year post after facing disciplinary action in relation to the activity, the tribunal has heard.