Evidence continues to grow in support of a former Norfolk pilot's claims about the health risks of contaminated air in passenger planes.

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For the past 11 years, John Hoyte has been at the centre of an international campaign aimed at highlighting so-called 'aerotoxic syndrome'.

The condition is said to be caused by toxic fumes entering passenger cabins and cockpits from aircraft engines.

It is feared to be behind the deaths of several pilots and crew members, but has long been denied by airline companies.

Mr Hoyte, from Bracondale in Norwich, worked as a commercial airline pilot for 30 years before taking early retirement due to ill health.

The 62-year-old believes his problems were caused by breathing in toxic fumes over the course of his career.

Now, there is growing evidence to support his claims about the health risks associated with fume events in aircraft.

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In a report recently published in the journal of the World Health Organization (WHO), scientist highlighted a link between contaminated cabin air and various health issues.

Meanwhile, the Civil Aviation Authority stated there was 'strong evidence' that some people experience acute symptoms following 'fume events' – when fumes leak into the cabin.

Earlier this year the NHS set up a care pathway for aircrew and passengers involved in fume events.

This includes a referral to a specialist clinic at St Thomas' Hospital in London.

Some pilots believe the issue is being 'covered up' by the airline industry and is similar to the asbestos scandal.

During a flight, crew and passengers breathe in a mixture of recycled cabin air and 'bleed air', which is drawn in from jet engines.

%image(14744947, type="article-full", alt="Peter Lawton, from Great Massingham, was a commercial airline pilot with Eastern Airways from 1999 to 2012. Photo: Peter Lawton.")

While that air is cooled, it is not filtered.

Some pilots claim that faults with engine seals can lead to cabin air being contaminated with heated engine oil fumes, which contain hazardous chemicals.

Symptoms are said to include memory loss, severe headaches, loss of balance and muscle weakness.

They say it would be easily remedied by airline companies installing air filters.

In October, EasyJet announced it was to trial a new air filtration system on its planes, which many saw as acknowledgement that the issue existed.

But a spokesman told this newspaper the move had no link to studies on aerotoxic syndrome.

%image(14744948, type="article-full", alt="EasyJet is installing air filters in its cabins to reduce smells. The airline said that decision was not linked to "aerotoxic syndrome". Photo: Gareth Fuller/PA Wire")

Mr Hoyte, Aerotoxic Association chairman, said: 'It is vital that both passengers and aircrew are made aware of the health implications of breathing toxic fumes whilst flying and that those in the medical profession know how to treat the symptoms.

'We are now calling for all airlines to follow the example of EasyJet and filter the 'bleed air' and poison detectors in all jet airliners.'

Other former pilots have also spoken about their concerns.

Peter Lawton, from Great Massingham, was a commercial airline pilot with Eastern Airways from 1999 to 2012. Before that he was a navigator in the Royal Air Force.

The 69-year-old believes contaminated bleed air is an issue, with many pilots referring to it as the 'dirty socks smell'.

'We would always joke that it was the co-pilot,' he said. 'But it is actually the smell of engine oil.

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'When I was in the military there was always the same smell [in the aircraft], but the difference was that in the military you had your own oxygen mask.'

A UK study into aerotoxic syndrome, published in the WHO journal this year, said air contaminated by engine oil can 'reasonably be linked to acute and chronic symptoms'.

It said there was an 'obvious need for a clearly defined internationally recognised medical protocol.'

An NHS article about the study concluded that the findings indicated that pilots - on rare occasions - have not been able to perform as usual due to poor air quality in the cabin.

It added: 'Also poor air quality has been linked to health problems in the long term.'

However, it noted there were some limitations of study which needed to be considered.

It said: 'The authors claim they have demonstrated a cause-and-effect relationship based on certain criteria.

'But with the exception of the acute air toxicity incident investigation reports in the second study, these types of study cannot prove causality.'

EasyJet installs air filters

In October, EasyJet announced it was looking to reduce incidents of 'unusual smells' in the cabin by installing new air filters.

The company is also developing detection systems to identify sources of smells and said it was working closely with experts to provide medical advice to individuals concerned with their health following a smell event.

A spokesman said a smell event was not the same as a fume event, as the former 'captures any event that causes an unusual smell in the aircraft'.

EasyJet said such events, on rare occasions, can lead to 'short-term' symptoms experienced by people on board.

But it claimed that on the 'balance of scientific opinion' there are no long-term health effects.

The company, which is working with the Pall Corporation on the filtration system, said:

'We feel that we're at the forefront of the industry in dealing with this issue.'

What airline companies had to say

British Airways said it would not operate aircraft if it believed there was a health or safety risk to customers and crew.

The company said research into cabin air quality had not shown that exposure to potential chemicals in the cabin caused long-term ill health.

It was asked whether it would be installing an air filtration system on its planes, but it did not answer.

Meanwhile, KLM, which flies from Norwich Airport, said cabin air quality is an industry-wide responsibility, which it takes 'extremely seriously'.

The company said it adhered to policy outlined by various aviation authorities, and that a recent study by the European Aviation Safety Agency found cabin air quality was the same, or better, than an average office.

A KLM spokesman said: 'Should studies show that the filters genuinely provide added value, KLM will install them on aircraft to which this applies.'