Can Cabin Air Become Toxic?

An Airbus A320 takeoff from Chicago O’Hare Airport to fly to Minneapolis. The aircraft will be flying for three days, and this is the first leg. All during the flight, the crew, including pilots and flight attendants smelled a “musty socks” odor.

During the previous flight from Chicago to Boston, a frequency change for the next sector was given by ATC. It was almost a routine procedure and these pilots used to enter the numbers directly into the radio head. But, this time they find it difficult to enter the numbers and had to write it down.

For some time, the copilot was feeling a tingling sensation and now he realizes that he is suffering from the effects of tunnel vision. He puts the oxygen mask and there was decrease in symptoms.

The condition of pilot, in the left seat, is worse still, he is barely conscious and slumped. The copilot shakes him and asks him to put the oxygen mask. Both the pilots were safe now and landed the plane safely.

The pilots did not had any memory as to how they landed the airplane, they also did not remember the conversation they had with the mechanic on the fume event. The next day, the condition of both the pilots was bad enough to halt the trip in the middle.

The copilot went to emergency room immediately and was treated for “inhalation injury”. The captain was diagnosed with internal bleeding due to abdominal cramping.

After two months, the first officer reported that it looks like captain is losing his cognitive skills. One day, the captained called the ambulance as he due to loss of feeling in the limbs and violent body tremors. After this incident, different types of irrational behavior was exhibited by the captain.

In one of the episode, he got in a useless argument with an unknown lady at a hotel, and law-enforcement had to be called to intervene.

Due to his behavior, police officers got the feeling that he is a drug addict, but only anti-anxiety medication were found in his bloodstream. On the way to the hospital, the captain breathed his last.

Did the captain died due to the fume incident that happened two months back? Medical diagnosis did not revealed any definitive conclusion.

Can the standard-design bleed air system of jet-engine which provides cabin pressurization and temperature control be the source of problem?

This scary story was told by the copilot, who is now a captain in Spirit Airlines, Eric Tellman. The tragic incident made his to work on the problem and make sure it doesn’t happen again.

How exactly he did it?

Captain Tellman was given the task to research and mitigate the dangers associated with fume inhalation during flight. He is educating airline crews and others about its dangers.

The cabin environmental control systems (ECS) have used bleed-air in jet airplanes since the time of Boeing 707. The first fume event was documented in the year 1939.

Cigarette smoking was banned completely in airplanes in the early 90’s. Before that, cigarette smoke used to mash other odors.

Now cabins are smoke free and in case fumes are detected, our noses will have “olfactory fatigue” in nearly three minutes. This means we are desensitized to toxic smell.

When bleed air is contaminated with other chemicals, oftentimes, it has an odorless gas, carbon monoxide, which cannot be detected by our nose. This gas has different effects on different bodies, in some cases, nothing at all.

No definitive guidelines have been provided by airlines and the FAA for reporting fume events. Apart from this, a fume event, in case it is without a smoke event, need to be reported only when there is a mechanical problem and the flight safety is compromised.

The fact that flight attendants and / or passengers experienced harmful effects due to odor is not necessarily a reportable situation.

Smells can also be misinterpreted by crews and Tellman is guilty of it. While flying the 727, Tellman was told that musty socks smell can be due to packs water separators.

The smell may disperse rapidly, but it may have been toxic fumes. Mechanics, flight attendants and pilots, all should be trained to recognize specific odors. They cannot rely on their personal opinions.

Before we move ahead on the topic of fume, you should understand that it is not an epidemic. Toxic fumes need legitimate concern and are not a risk on every airline flight.

From where all these toxic fumes can come from?

Contaminants that can seep into the ECS by way of engine bleed air can be in the form of deicing fluid, hydraulic fluids and lubricating oils. These fluids can break down into potentially toxic fumes due to extremely high temperatures.

How can these fluids enter the ECS?

It is during descent when the power is moved back to idle, that it can usually happen. The high pressure air that is trapped in the bearing seals of pack compressors can escape, which can force these fluids in the bleed system.

One more culprit is in the form of APU, which is shut down before departing. APU has residual oil which can seep out at the time of operation and this can ultimately move into the ECS.

In normal circumstances, toxic fluids do not enter the bleed air system. Leakage may happen due to component failures for engine bearings, oil-pressure-switches and seals. Over servicing of hydraulic fluid or oil can also make these chemicals leak out of vent tubes.

Initial symptoms arising from these fumes can be in the form of sweating, dizziness, fatigue, cognitive dysfunction, headache, chest tightness, tremors, anxiety vomiting, nausea, stomach cramps and low blood pressure. This symptoms can get worse in the next 24 hours.

What is the solution?

First, training should be given to pilots to recognize these fumes and what are the symptoms associated with it.

Most aviators are aware of high-altitude hypoxia, but they may not be aware of “hypemic” hypoxia, in which the ability of blood to carry oxygen is reduced due to chemical poisoning.

There is a need to create or revise the checklist for fume events. There should be better communication between mechanics, flight attendants and pilots to keep this danger away. Fume events need to be documented more proactively and more specifically.

Apart from these solutions, newly developed non-bleed covnersion system should be adopted, improved filtration systems should be used or a design that does not make use of engine bleed air can be better alternatives.

New airplanes such as the Boeing 787 are completely devoid of such risks as the ECS of this airplane does not use engine bleed air.

Happy Flying!

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