An official incident report has confirmed that a Lufthansa Airbus A321 flight from Frankfurt, Germany to Seville, Spain on 17 February last year flew for 10min without any pilot supervision because the copilot, alone on the flight deck at the time, suffered a “sudden and severe incapacitation” which was defined in the report as a “seizure”.

An experience of my own many years ago was strikingly similar to this, so we will return to that subject in a moment after examining the events on Lufthansa’s Frankfurt – Seville flight last year.

Once Flight LH77X was established in the cruise over northern Spain at flight level 350 (35,000ft), carrying six crew and 199 passengers, the captain discussed pertinent weather conditions on the route with the copilot, who was the pilot flying, and then left the flight deck for a toilet break at 10:31:00 (UTC). Exactly 36 seconds after the captain had left the flight deck, the copilot suffered an epilepsy-like seizure, according to the Spanish accident investigation authority CIAIAC.

There was no immediate indication to the absent captain that anything was wrong, because the autopilot and autothrust remained engaged, despite some inadvertent switch selections by the copilot, and the fact that his right foot was pressing the rudder pedal hard – but fortunately not hard enough to cause the autopilot to trip out.

Meanwhile the sector controller for Spain’s Pau ATC region attempted three times to establish radio contact with LH77X, but received no reply.

At 10:39:00 the captain was ready to return to the flight deck, and he attempted a standard entry procedure, but there was no response from the copilot who would have had to approve it. After three further attempts he decided to employ the flight deck emergency access code, but while he was doing that the copilot, “pale, sweating and moving strangely”, opened the door from the inside.

The captain took control of the aircraft at 10:42:00, and at his request the cabin crew helped the copilot into the forward galley area, administered first aid, and obtained the help of a doctor from among the passengers. Meanwhile the captain decided to divert the aircraft to Madrid, the nearest airport, rather than continuing to Seville. The A321 landed safely and the copilot was taken to hospital, but released after examination.

The CIAIAC report quotes the definition of a “seizure” under these circumstances as “an abnormal paroxysmal excessive discharge of cerebral cortical neurons”. The copilot had no medical record of any such event previously, and said he had not experienced anything like it before. The medical judgement as reported by the CIAIAC is that, even had the copilot been tested specifically for such a condition, it would not have been detectable unless he had suffered a seizure in the presence of a medical observer.

The report’s main recommendation for the future is that, any time one of the pilots has to leave the flight deck, a member of the cabin crew should join the remaining pilot in the cockpit until the absent pilot returns. This is actually a previously established procedure which had fallen into disuse simply because incapacitation is so rare. But if it had been applied in this case, the cabin crew would have been able to alert the captain immediately about the copilot’s condition, and help him re-enter the flight deck quickly.

Meanwhile here is an account of my personal experience of airborne seizure – and precursors to it – that is highly relevant to cases like this one.

During my time as a qualified flying instructor (QFI) in the RAF I had gradually developed a condition which caused me to suffer minor seizures which, at the time, I did not recognise. They just felt like momentary mental “absences” that I attributed – for example – to having had a few drinks too many in the Officers Mess the night before. At the time I was in my late 20s, and had been flying pressurized jets and turboprops for eight years,

But my wife noticed these “absences”, and reported them to an RAF doctor who then approached me about them. I dismissed the matter as unimportant, and he did not pursue the issue further.

I recall having an “absence” while on short final approach to land a Jet Provost, solo, at RAF Linton on Ouse. I can’t actually remember the touchdown itself, but can remember rolling out at the end of the runway and turning onto a taxiway back to the pan, by which time I felt fine. But the thought of this event – now that I know more about my condition at that time – chills me.

Some months later I suffered a fully-fledged seizure during my sleep, and my wife called the doctor, who attended immediately. When I awoke I felt as if I had been beaten up.

I was taken to an RAF hospital and tested via electro encephalograph (ECG), and underwent brain scans. The diagnosis – given the evidence of the seizure – was that I was “probably” prone to epilepsy, but the condition was defined as “idiopathic”, meaning there was no medically detectable sign of it.

Continuing to fly professionally after that was not an option, so I left the RAF and became an aviation journalist.

At the time I believed my symptoms might have been caused by an sudden and unexpected application of quite high negative G during a practice aerobatic sequence flown by one of my student pilots. But the medics could find no sign of brain damage.

Over the decades since that time, in my job as an aviation journalist, I learned about “Aerotoxic Syndrome”, the name given to a condition caused by damage to the brain and nervous system by neurotoxic chemicals from aero engine lubricants and hydraulic fluids. High doses, gained via a “fume event” in the cockpit or cabin, can cause instant cognitive problems, although these may fade with time. But in other individuals, regular exposure to low doses of neurotoxins over a long time can gradually build up in the body, degrading the nervous systems of pilots and cabin crew.

These organophosphate chemicals, containing known neurotoxins, are delivered to the cockpit and cabin by aircraft air conditioning and pressurization systems, where the air is sourced directly from jet or turboprop engine compressors. Engine oil seals constantly leak fluid at low levels, so when the highly compressed – and therefore hot – air is delivered to the air conditioning system, it contains pyrolized neurotoxic aerosols. This is the air that the crew breathe.

In some individuals, that constant low-level poisoning builds up in their system until it causes visible symptoms of neurological damage. In other individuals, their systems gradually purge the chemicals, making symptoms last only a short time. But so far there is no way of knowing in advance which kind of system individual aircrew have.

In my case, today I no longer have even slight seizures, neither do I have to take any medication which, for more than 25 years, I had to do constantly to keep the symptoms at bay. Neurologists say, nonetheless, that they cannot declare me free of epilepsy or related neurological conditions because they still do not know enough about the subject to be certain. I suspect what has happened is that, since I left the RAF, I fly only occasionally, so my system has had time to purge itself of the neurotoxins that regular flying delivered to me.

I wish the Lufthansa copilot of flight LH77X on 17 February 2024 well, and hope he gets all the support he needs to continue his career, if that is deemed possible.

Meanwhile for him, and all those who want to know more about Aerotoxic Syndrome, FlightGlobal has a useful account here.