Runny nose, annoying cough and a sore throat that won't go away? Time was when your doctor would recommend a good holiday. But today, the question "When were you last on an aeroplane?" is more likely to pinpoint the source of an infection than suggest a cure.
The practice of recirculating cabin air to cut fuel costs is being increasingly blamed for spreading diseases among airline passengers and crew - diseases ranging from severe gastro-intestinal infections that have struck down 200 at a time to drug-resistant strains of TB that only respond to the most prolonged and unpleasant courses of treatment. We have all heard stories of gasping passengers fainting at the back of economy class, and few air travellers will not have suspected that the virus which ruined their holiday was picked up on the outward flight.
Yet despite a growing awareness among passengers, flight attendants and health professionals that inadequate ventilation can damage the health of anyone who spends more than a few hours in a plane, airlines and their regulators worldwide seem reluctant to grant air quality higher status on their safety agenda.
So great is the concern with lack of regulation and what many see as a culture of secretiveness within the industry that a British charity organisation now proposes to challenge airlines to adopt a common set of standards and to open themselves up to independent scrutiny.
The Oxford-based Aviation Health Institute (AHI) hopes to persuade companies to use top-quality air as a selling point, much as they now boast about leg-room, fine wines or metal cutlery. The aim is to harness the competitive forces that many believe have been responsible for driving down the quality of cabin air since the oil crisis of the late 1970s.
It is a paradox of air travel that the older the aircraft, the fresher the air. Planes such as the Concorde and the Boeing 737-200 rely for their ventilation entirely on fresh air drawn through the engines, ducted into the front of the cabin and expelled at the rear end. This air is extremely dry, which has its own health implications. But at least it enters the aircraft free from micro-organisms, and passengers can counteract the dryness by drinking water. What's more, in these older planes, the cabin air is completely replaced every three minutes.
Diverting air in this way, however, reduces the efficiency of the jet engines by up to 2 per cent, and for this reason, airlines reacted to the threat of dearer fuel 20 years ago by ordering aircraft with a ventilation system in which half of the air in the cabin is simply filtered, mixed with fresh air and recirculated. The result is a 50-50 blend of fresh and used air - the latter containing less oxygen and more carbon dioxide, in addition to any particles and organisms that may not have been trapped by the filters.
It is the commercial pressure on airlines to stretch this 50-50 ratio of fresh and recirculated air even further, and the limitations of official controls, that worries Farrol Kahn, director of the AHI. At present, only the concentration of carbon dioxide in cabin air is controlled by law, and Kahn believes the temptation to move from 50 per cent to 55 or even 60 per cent recirculated air is enormous.
"Everyone is doing it. If you look at your bottom line and you have to cut millions of pounds off operating expenses, you sit there and think, well maybe next year we can push it to 65 per cent stale air."
Kahn believes that airline pilots - whose air supply is of a much higher quality, partly for the benefit of the electronic equipment in the cockpit - can be under indirect pressure to decrease the level of air conditioning in the cabin during a flight. "They don't give the pilots written instructions saying, `You will ventilate the air every 12 minutes instead of every three,' and so on. They simply say, `Guys, we need to cut costs. You're the best judges of how to do that. Do it. And if, at the end of the year, we've saved 30 tonnes of fuel, fantastic!' "
In an aeroplane every piece of onboard equipment ultimately takes its power from the engines. On many aircraft, says Kahn, individual air conditioning units can be switched off, or run at lower settings. "If you switch off one or two units, particularly after the meal when people are sleeping, then you are saving in total maybe 2 per cent of fuel costs over a year." In the past 12 months, there have been four reported incidents of planes running short of fuel in British airspace.
Paradoxically, Kahn says, the introduction of non-smoking flights may make it easier for airlines to reduce airflow, because the presence of tobacco smoke indicated that the air was not being changed quickly. He would like to see airlines commit themselves publicly to providing maximum airflow through cabins at all times. He also believes companies should fit the most effective filters, operating at 99.97 per cent efficiency, and maintain them to the highest standards. The Centers for Disease Control and Prevention in Atlanta has documented a number of cases of transmission of TB on board airliners, and says long-haul flights in particular place passengers and crew in a uniquely hazardous environment.
Kahn has been in contact with many airline medical departments, visited engineering works and talked to engineers and maintenance staff. He says he has encountered widespread concern about the quality of filters and the frequency with which they are changed. Now the health implications of poor maintenance have been highlighted in a new report published by researchers at the University of Strathclyde. Peter Bain, a lecturer in Human Resource Management, and researcher Carol Boyd, a former flight attendant, examined the issue of air quality from the point of view of the staff who spend their working hours confined to crowded cabins.
Many crew members, they say, complain of symptoms normally associated with so-called "sick building syndrome" - "recurring or constant lethargy and headaches and a range of influenza/coldtype eye, nose and throat complaints."
According to Bain: "Quicker turnaround times mean that the engineers and maintenance staff will focus on the mechanical efficiency of the plane in terms of whether it can fly and how long it will fly. Cleaning out and repairing filters is a low priority."
The Strathclyde report dismisses the industry's frequent assurances that recirculated cabin air is filtered to the same degree as hospital air. Bain and Boyd point out that hospital air is itself suspect. A survey carried out by the Society of Radiographers, they say, concluded that its members were being made ill by contaminated air-conditioning and ventilation systems in British hospitals.
These concerns are shared by US airline staff. In a speech to labour organisations in Washington last year, Patricia Friend, international president of the Association of Flight Attendants, said increased air links with countries where highly infectious and potentially fatal diseases were widespread posed new dangers for crew and passengers.
The decision to change from 100 per cent fresh air to a mixture of fresh and recirculated air was undertaken, said Friend, without evaluating the health and safety effects, "in the absence of a clear definition of `good air quality', and at a time of increased dependence on air travel as a vehicle of necessity rather than choice".
Taken together with the hazards of reduced and fluctuating air pressure in an airliner cabin - a factor which was recently cited by UK medical researchers as a possible cause of cot death - bad air was a major concern for flight attendants. The association is also known to be concerned about the possible contamination of cabin air by toxins present in organophosphate-based hydraulic fluid and others which may be produced when turbine lubricants are broken down by the high temperatures inside a jet engine. One source claimed that a small dose of such substances, leaking into the air conditioning through faulty seals, would cause flu-like symptoms.
A spokesman for the CAA confirmed that the only control on the quality of cabin air concerned the concentration of carbon dioxide, but added that this in itself tended to limit the proportion of recycled-to-fresh air in the cabin. Although the authority only has jurisdiction over UK-registered aircraft, he said, the limit of 0.5 per cent corresponded to that set by both the EU and US.
"Obviously we don't have someone flying on every flight, but we check this by way of spot checks, by continuous monitoring of the airline and by looking at their records. You can download all the cockpit information from an aircraft very easily these days and see what's going on, although obviously with 3.5 million flights a year through the UK, we can't look at every one."
Most airline passengers, he felt sure, would be at greater risk of cross-infection at work. "I used to work in a shopping centre," he said, "and all you got to breathe all day was the air going around that shopping centre."
