Toxic air: cabin air quality could have deadly results

 - September 23, 2008, 6:39 AM

The quality of cabin air remains a concern for aircraft manufacturers in their quest to ensure the safety of crewmembers and passengers. Even small oil leaks have laid the groundwork for a disturbing sequence of events that too often figure in routine flight report summaries covering airliner and corporate aircraft crews and passengers.

In one case, a Nov. 12, 1999, flight from Stockholm to Malmo, Sweden, the crew of a BAe 146 operated by Braathens Malmo Aviation reported feeling “strange” and experiencing a “moonwalk sensation.” During the third leg of the three-leg flight, the cabin manager went to the cockpit to find that both pilots were wearing their oxygen masks. According to the captain, he was so close to blacking out that he instructed the first officer to take command and land the airplane.

Another BAe 146 crew had a similar experience in 2000 at Birmingham in the UK. Both pilots had to be hospitalized and the CAA issued an AD requiring inspection of relevant oil seals.

In April 2005 the British Air Line Pilots Association organized an international aero industry conference on contaminated air protection at which 50 experts from five countries presented papers covering all aspects of cockpit and cabin contamination by smoke and fumes from bleed air contaminated by oil leaks.

Bleeding part of the high-pressure air from the compressor section of the jet engine has long been accepted as the standard to supply, among other services, cabin pressurization. With time in service, all aircraft develop engine oil leaks, but some record more fume incidents than others, and the BAe 146 and Boeing 757 top the tables.

However, it is not just the oil that causes difficulty, but also the chemicals added to improve its wear properties. With heating they can lead to disturbing effects–such as eye irritation, nausea, dizziness and disorientation–for those who breathe the fumes. One of these additives, the organophosphate tricresyl phosphate (TCP), which is added to improve lubrication properties, when heated can cause irritation, skin sensitivity and poisoning of the nervous system. Safety information for jet engine oils produced by BP and Exxon, incorporating TCP, warns against the exposure to these when they have been heated or are in a mist format. NYCO, an independent French oil company, has stopped using TCP in its aviation oils and has substituted an additive that it claims has no undesirable side effects.

The conference found that all who fly in jets face these hazards, which produce long-term medical difficulties in contradiction to FAR 25.831. This requires that the crew and passenger compartment air be free from harmful or hazardous concentration of gases or vapors.

Former Capt. John Hoyte, chairman of the Aerotoxic Association (, believes that exposure to these toxins led to his medical grounding. Over a period of 14 years, he experienced a gradual deterioration of health, including loss of memory, fatigue, speech deterioration and internal head pressure.

Unfortunately, pilots who suffer from the effects are often reluctant to report the condition because they believe that they would not have the support of their employers and might jeopardize their employment prospects. In addition, many passengers and crewmembers who are suffering from the effects of toxic air consult their personal physicians. Unfamiliar with the subject, these doctors might not recognize the symptoms for what they are and might prescribe inappropriate treatment. Because of this lack of data it is not possible to arrive at a specific number of people who are currently sufferers, but some feel it is probably many thousands. Britain’s Cranfield University is researching the subject and expects to publish its findings next year.

Eminent Psychologist Enlisted

The Global Cabin Air Quality Executive, an international association representing flight crews and other aviation workers who have had their health
affected by toxic air aboard aircraft, is querying the British Department of Transport’s appointment of an eminent psychologist, Dr. Helen Muir, to lead its investigation into the matter while refusing to accept evidence from the association and other involved organizations.

Despite negative reaction by experts in the aviation industry when alternatives to the use of bleed air for pressurization have been proposed, Boeing emphasizes “no engine bleed systems” for its 787 Dreamliner.