Jumpseat: Can Cabin Air be Toxic?

The dangers of bleed air systems.

An Airbus A320 crew departs Chicago O’Hare Airport for Minneapolis. It is the first flight of a three-leg day, using the same airplane. Throughout the day, the pilots and flight attendants experience a “musty socks” odor. On the last flight, from Chicago to Boston, ATC gives a frequency change for the next sector. Despite having the capability to enter the frequencies directly into the radio head, as is typical procedure, both pilots can’t seem to remember the numbers and have to write them down.

In addition to a tingling sensation, the copilot eventually realizes that he is beginning to suffer the effects of tunnel vision. He dons the oxygen mask and his symptoms abate. In the left seat, the captain is slumped and barely conscious. Shaking him, the copilot manages to direct him toward the other oxygen mask. Both pilots recover sufficiently to accomplish an uneventful landing.

Neither pilot retains a memory of the landing, nor do they recall a discussion with the mechanic regarding the fume event. The following day, both pilots feel ill enough to call in sick in the middle of their trip. The copilot goes immediately to the emergency room and is treated and ­released for an “inhalation injury.”

The captain visits a doctor the following day and is ­diagnosed with internal bleeding as a result of abdominal cramping. Two months pass. The union’s professional standards committee fields calls from first officers who say that the captain appears to be losing his cognitive skills.

On one particular day, the captain calls an ambulance because of violent body tremors and loss of feeling in his limbs. After the ambulance incident, the captain begins to exhibit various forms of irrational behavior. During one episode, he engages in a senseless argument with an unknown woman at a hotel, which escalates into law-­enforcement intervention. Because of his behavior, police assume he is a drug addict. The only drug found in the captain’s bloodstream is an anti-anxiety medication. He dies in the police cruiser on the way to the hospital.

Was the fume event experienced two months earlier the cause of the captain’s death? A definitive medical conclusion was never reached. Could the source have been the standard-design jet-engine bleed air system used for temperature control and cabin pressurization?

This horror story was presented in a speech by the copilot, now a Spirit Airlines captain, Eric Tellmann, who has made it his mission to never allow such circumstances to happen again. How, exactly?

To the credit of Spirit Airlines’ management, Capt. Tellmann was tasked with the assignment of researching and mitigating the risk of inflight fume-inhalation events. Not only is he educating his airline’s crews, but others as well.

So why has this danger come to the forefront ­recently? After all, cabin environmental control systems (ECS) have utilized jet-engine bleed air since before the days of the Boeing 707. As a matter of fact, documentation of a fume event was recorded in 1939.

Before cigarettes were ­completely banned on airplanes in the early ’90s, smoking had the tendency to mask other odors. And now, without smoke-filled cabins, even if fumes are detected, after approximately three minutes our noses suffer “olfactory fatigue,” meaning we may become desensitized to a toxic smell.

The inadvertent breakdown of other chemicals in bleed air oftentimes includes carbon monoxide, an odorless gas undetectable through our nostrils. And physiologically, different body types are affected ­differently — or not at all.

The FAA and airline op specs do not provide definitive guidelines for reporting fume events. In ­addition, any fume event that is not ­accompanied by a smoke event is only ­required to be reported if a ­mechanical ­issue is involved or safety of flight is compromised. The fact that passengers and/or flight attendants experienced adverse effects from an odor is not necessarily a reportable circumstance.

Crews can also misinterpret smells. I’m guilty of misinterpretation. For countless hours of flying the 727, I was told that the musty socks odor was caused by the packs’ water separators. Although the smell seemed to dissipate quickly, it might have been toxic fumes. Pilots, flight attendants and mechanics all need training in recognizing specific odors. Personal opinions don’t cut it.

Before delving further into the fume topic, please understand that the situation is not an epidemic. ­Toxic fume events are not a risk on every airline flight, but they are cause for legitimate concern. What are the sources of these toxic fumes?

Toxic fume events are not a risk on every airline flight, but they are cause for legitimate concern. What are the sources of these toxic fumes?

Contaminants enter the ECS through the engine bleed system in the form of lubricating oils, ­hydraulic fluids and deicing fluid. The ­extremely high temperatures break down the fluids into chemicals that — depending on the exposure duration — could potentially lead to adverse effects from toxic inhalation. How do these chemicals enter the ECS?

The most common occurrence is during descent, when the power is ­retarded to idle. The high-pressure air that was trapped in the bearing seals of pack compressors can escape, forcing fluids into the bleed system. Another culprit is the APU, even ­after it is shut down before departure. Residual oil can leak from the APU during its operation at the gate and then find its way into the ECS.

Normally, toxic fluids should not enter the bleed air system. Component failures for oil-pressure ­switches, engine bearings and seals can allow leakage. Overservicing of oil or hydraulic fluid can also push the chemicals out of vent tubes.

The list of respiratory symptoms can range from moderate to ­severe: fatigue, dizziness, sweating, headache, cognitive dysfunction, ­weakness, anxiety, tremors, chest tightness, abnormal salivation, stomach cramps, nausea, vomiting, slow pulse and low blood pressure. It’s also possible that these symptoms won’t manifest until 24 hours later.

What needs to be done? First, ­pilots need training to recognize the fumes and associated inhalation ­impairment symptoms. Most of us are familiar with high-­altitude hypoxia but not with “­hypemic” ­hypoxia, which is the ­reduced ability of the blood to carry oxygen because of chemical ­poisoning.

Checklists need to be revised or created for fume events; a simple procedure to eliminate the offending portion of the ECS system has proved successful. Better communication between pilots, flight attendants and mechanics is essential to mitigate the danger. And documentation of fume events has to be more proactive and more specific.

Beyond these solutions, the use of improved filtration, the adaptation of a newly developed nonbleed conversion system, or a design that does not utilize engine bleed air are the most viable alternatives. Of course, flying the 787 eliminates the risk almost completely — the airplane doesn’t employ engine bleed air for the ECS.

Can cabin air be toxic? Possibly, but the risk can be mitigated or ­completely eliminated. For now, ­education is the best tool. And if you smell something, say something.