FAA Brochure - Carbon Monoxide

Percent (CO)

in BloodTypical Symptoms

<10 None

10-20 Slight headache

21-30Headache, slight increase

in respirations, drowsiness

31-40Headache, impaired

judgment, shortness

of breath, increasing

drowsiness, blurring of

vision

41-50Pounding headache,

confusion, marked

shortness of breath,

marked

drowsiness, increasing

blurred vision

>51Unconsciousness, eventual

death if victim is not

removed from CO sourceTable 1 : Carbon Monoxide (CO) Blood Levels and

Possible Symptoms

Carbon

Monoxide:

A Deadly Menace

OK-24-1154 9/18/2024symptoms are typical for an individual with normal

hemoglobin at sea level. You can expect these

symptoms to worsen at altitude and/or appear

sooner than they would otherwise. Wide personal

variations may also occur, depending on the

circumstances and whether or not the individual

smokes.

Protection From Carbon Monoxide

Exposure

First and foremost is pilot education and

awareness. Pilots must understand the danger

posed by carbon monoxide poisoning and should

be alert to the symptoms.

Any unusual cabin smell or sensation of illness

should call for immediate troubleshooting.

• Turn the cabin heat fully off.

• Increase the rate of cabin fresh air ventilation

to the maximum.• Open windows if the flight profile and aircraft’s

operating manual permit such an action.

• If available (provided it does not represent

a safety or fire hazard), consider using

supplemental oxygen.

• Land as promptly as possible.

• Do not hesitate to let Air Traffic Control know

of your concerns, and ask for vectors to the

nearest airport.

• Once on the ground, seek medical attention.

• Before continuing the flight, have the aircraft

inspected by a certified mechanic.

Safeguards

• The best protection against carbon monoxide

poisoning is to avoid exposure.

• Aircraft operators and pilots must ensure that

heating/ventilation systems and exhaust

manifolds in their aircraft are all in good

working order, as specified by the manufacturer

and the Federal Aviation Administration.

• Certified mechanics must conduct all required

inspections.

• Special attention should be paid to older aircraft

because of corrosion or simple wear and tear.

• A certified mechanic should verify firewall and

aircraft structural integrity and seal any defects.

• Finally, several devices are available to monitor

for carbon monoxide. The least expensive are

handheld or stick-on colorimetric devices that

change color in the presence of carbon

monoxide. While effective, they are not perfect

or nor. Powered detectors for aviation use

are available as either portable or panel

mounted units and provide greater reliability.

Don’t become a statistic.

Learn to prevent and avoid this deadly threat

to your flying safety.

Provided by

Aerospace Medical Education Division, AAM-400

To obtain copies of this brochure online:

https://www.faa.gov/pilots/safety/

pilotsafetybrochures/

or contact:

Federal Aviation Administration

Civil Aerospace Medical Institute

AAM-400

P.O. Box 25082

Oklahoma City, OK 73125

(405) 954-4831

An ‘Unconscious’ Landing

Plane Lands Itself in Hayfield as Pilot Slumbers

Physician Robert Frayser had lifted off in his Comanche

400 from the North Bend, Kansas, airport at 7 a.m.,

en route for a meeting in Topeka. He was flying alone,

cruising at 5,500 feet on autopilot, with the sun coming

up on a clear, beautiful day. Per established routine, he

switched the fuel selector to the auxiliary tank and set

up the navigation system for nearby Topeka.

About 90 minutes later, Dr. Frayser found himself in

a hay field. The engine was silent. He was confused,

disoriented, and groggy as he struggled to rouse himself

from a deep sleep. His head was throbbing.

Thinking he was still in the air, he went through his

landing checklist. As he became more oriented to his

surroundings, a new reality dawned: The airplane’s right

wing was nearly torn off from an impact with a tree, but

the plane was otherwise intact. Aside from a fractured

wrist, minor cuts, and bruises, he seemed to be relatively

uninjured. But he had no idea where he was. He had no

memory of landing.Dr. Frayser stated that there were no early warnings or

symptoms to alert him. “I just went to sleep.” The plane,

trimmed for cruise flight and on autopilot, flew a perfectly

straight course over Kansas and into Missouri until it

ran out of fuel, and then the autopilot gently brought the

Comanche in for landing.

Since the engine had stopped, no one heard the aircraft

glide to a landing on the open field. “I was alone,

disoriented, injured, and had a severe headache and

ringing in my ears,” he said. The aftermath of a near-fatal

accident caused by carbon monoxide poisoning.

Extracting himself from the aircraft, he struggled a

quarter of a mile through snow-covered fields for help,

finally stumbling onto a farmhouse. Dr. Frayser was taken

by ambulance to a hospital, where the emergency room

physician put him on 100 percent oxygen to overcome

near-fatal blood levels of carboxyhemoglobin.

Carbon monoxide poisoning from a cracked muffler had

allowed the deadly, odorless gas to seep into the cabin

through the heater and caused him to fall asleep. The

crack, which had apparently opened after the last annual

inspection, was concealed by the heat shield and could

not be detected during the pre-flight inspection. “The

crack could have been there for a long time, just waiting

for someone to turn on the heater,” he said. Frayser did

not have a carbon monoxide detector on board to alert

him of its presence.

Another 30 minutes in the air might have been fatal.

Carbon monoxide poisoning would have claimed

another victim.Overlooked Safety Issue

Carbon monoxide poisoning is a safety issue that

pilots tend to ignore, even though it is the most

common industrial poisoning accident in the United

States. When carbon monoxide poisoning occurs,

it can have significant and fatal consequences for

aircraft occupants.

Carbon monoxide is a by-product of the incomplete

combustion of carbon-containing materials. Aviation

fuel contains carbon and is a ready source of

carbon monoxide when burned. Expect carbon

monoxide whenever an internal combustion engine

is operating, and even though piston engines

produce the highest concentrations of carbon

monoxide, exhaust from turbine engines could also

cause carbon monoxide poisoning. In addition,

expect carbon monoxide whenever a fire occurs, as

commonly happens in a post-crash environment.

Carbon monoxide is truly a hidden menace because

by itself, it is both a colorless and odorless gas.

An individual would not be aware of its presence

until symptoms developed, or during treatment it

was determined exposure had occurred. The least

desirable situation would be incapacitation. In this

case, the victim is powerless to do anything about

the exposure. Fortunately, because it is a by-product

of combustion, carbon monoxide is frequently

associated with other gases that do have an odor

and color.

By avoiding an environment with known combustion

fumes, you will also avoid carbon monoxide. The true

problem comes when exposure is so gradual that

you don’t perceive it. You can become incapacitated

before you can vacate the environment. In an

airplane, the result most likely will be a fatal

accident.

Why Carbon Monoxide Poisoning

Should Concern Pilots

What is not known is the full extent of carbon

monoxide poisoning in aviation. Analysis of

toxicology samples from fatal U.S. aircraft accidents between 1967 and 1993 showed that at least 360

victims had been exposed to sufficient carbon

monoxide before or after the crash to impair their

abilities. Non-fatal carbon monoxide poisoning in

aviation is likely a more common occurrence than

currently believed. No one is sure how many times

pilots or passengers became ill, not realizing they

had been exposed to carbon monoxide. Because

no significant incident or incapacitation occurred,

the matter was not reported and, hence, not

investigated. Symptoms that could be attributed to

airsickness, altitude hypoxia, fatigue, or a variety

of other conditions actually could have been

carbon monoxide poisoning.

Toxicity Mechanism

Carbon monoxide has a very high affinity for

hemoglobin, the molecule in blood responsible

for transporting oxygen through the body.

Carbon monoxide has affinity of 240 times that

of oxygen. Carbon monoxide tightly attaches

to the hemoglobin, creating the compound

carboxyhemoglobin, which prevents oxygen from

binding, thereby blocking its transport. The result

is hypoxia but through a mechanism different from

that produced by altitude. However, with respect to

symptoms, the end-effects can be very similar.

There should be little or no carbon monoxide in the

blood of individuals who have not been exposed

to smoke or other by-products of combustion.

People living in polluted urban environments

may have between 3-10% carboxyhemoglobin

concentrations because of the carbon monoxide

contained in the smoke and fumes they inhale,

while a cigar smoker could have up to 15%.

People in certain occupations such as foundry

workers, welders, mechanics, firefighters, and

tollbooth or tunnel attendants that expose them to

products of combustion may also have elevated

carbon monoxide baseline levels.

Symptoms

The most common symptoms of carbon

monoxide exposure are shown in Table 1. These