NTSB Safety Alert SA-069 - Pilots Prevent Carbon Monoxide Poisoning

SAFETY

ALERT 069 September 2017

HIGHWAY

MARINE

RAILROAD

PIPELINE

AVIATION

Pilots: Prevent Carbon Monoxide

Poisoning

The risk of carbon mono xide poisoning is

overlooked and underestimated!

The problem

Carbon monoxide (CO) is a colorless, odorless, tasteless gas by-product of internal

combustion engines and is found in exhaust gases. Sufficiently high levels of CO in your bloodstream will lead to oxygen starvation and the onset of symptoms (such as headaches, drowsiness, nausea, or shortness of breath).

M any internal combustion engine airplanes are heated by air that has been warmed

by circulating air around the exhaust system using a heater shroud. A defect or leak

in the exhaust pipes or muffler can introduce CO into the cockpit.

Pilots often overlook or dismiss the onset of symptoms and don’t connect them

with the possibility of exposure to CO. Continued exposure increases risks to pilots, including impaired judgment and decreased ability to control the airplane and, eventually, incapacitation and death.

2 / NTSB Safety Alert 069 / September 2017Related accidents

The National Transportation Safety Board (NTSB) has investigated several accidents (some fatal)

in which pilots were incapacitated following CO exposure, such as the following:

A Mooney M20C airplane crashed in a field following the pilot’s incapacitation; the pilot was seriously injured.

Shortly after departure, the pilot lost consciousness

and air traffic control was unable to contact the pilot. The airplane continued to fly for about 1.5 hours until the fuel in the selected tank was exhausted. The pi -

lot's CO level was at least 28% (and likely higher) at the time of the accident. CO levels between 10% and 20% can result in confusion, impaired judgment, and diffi -

culty concentrating. Postaccident examination of the airplane found a fracture in the exhaust/heater muffler (see left photograph in figure 1) and exhaust deposits inside the muffler shroud (right photograph in figure 1). This allowed the exhaust gas to enter the cabin, exposing the pilot to CO. ( CEN17LA101 )

Figure 1. Photographs of a cracked muffler and exhaust

deposits in the muffler shroud.

Witnesses observed an experimental amateur-built, Hefty Polar Cub airplane flying erratically at a low altitude before impacting terrain. A postcrash fire ensued, and the pilot was fatally injured. Toxicology testing revealed that

the pilot’s CO level was 48%; no soot was found in his airways, indicating the CO was not a result of the fire; thus, the NTSB determined that the pilot’s severe CO impairment likely caused the pilot’s loss of control. Examination of the airplane’s exhaust system revealed that the exhaust/heater muffler was fractured, allowing CO to enter the cockpit (see figure 2). ( ANC16FA065 )

Figure 2. Fractured exhaust muffler from a Hefty Polar Cub airplane (left) and a close-up photograph of the fracture in the

exhaust muffler (right).

NTSB Safety Alert 069 / September 2017 / 3 About 3 hours into a 3.5-hour postmaintenance flight, a Cessna 207 airplane impacted trees and a river. The

pilot was fatally injured. Toxicology tests identified a CO level of 21% in the pilot’s blood, which likely adversely affected his performance. The airplane's original cabin heat system had been modified with a “winter heat kit” that, according to maintenance records, had not been installed in accordance with Federal Aviation Administration (FAA) field approval procedures. The full heat system was not recovered, and it was not possible to determine the exact source of the CO. ( ANC15FA032 )

A Bellanca 14-19-3A descended from cruise flight at a rate of 2,900 ft per minute and collided with power lines

and trees. The pilot was fatally injured. The wreckage examination revealed cracks and holes in the muffler wall and exhaust gas penetration into the interior of the shroud. Toxicology tests identified a CO level of 37% in the pilot’s blood. Most of the CO detected in the pilot’s blood was likely from inhalation during the flight; the CO levels would have impaired his ability to safely fly the airplane. (CEN14FA024 )

What can you do?

I nstall a CO detector and replace the device and its batteries in accordance with manufacturers’

guidelines. Detectors mounted on the instrument panel with aural alerts and a flash notification

are more likely to draw your attention and alert you to a potential hazard.

Dur ing an annual or 100-hour inspection, make sure your mechanic thoroughly inspects

exhaust systems, air ducting, firewalls, and door/window seals. Always perform an advanced preflight inspection after maintenance.

Be informed and familiarize yourself with your airplane’s exhaust system. Review and comply

with any airworthiness directive, advisory circulars, and service bulletins regarding the exhaust system. Speak with your mechanic about regular inspections, the condition of the

muffler, and the replacement schedule of parts.

Dur ing preflight inspections, check the security and condition of the exhaust system. Look

for cracking at the ends of the muffler; if you see signs of soot or exhaust flames, don’t fly the

airplane until it is examined by a mechanic. If you cannot see the muffler, inspect the shroud

for any evidence of soot that might indicate cracking in the muffler.

Dur ing flight, if you believe you have been exposed to CO, don’t hesitate to act.

• Early symptoms are vague and may involve a headache or nausea. Other symptoms include

impaired judgment, disorientation, or dizziness. Most people don’t recognize the problem until it’s

too late.

• Pr olonged exposure can have increasingly dangerous effects on your ability to control the airplane.

Open windows, turn off the heat, land as soon as practical, and seek emergency medical attention.

4 / NTSB Safety Alert 069 / September 2017Interested in more information?

The following FAA resources are accessible via www.faa.gov:

“Carbon Monoxide (CO) Contamination in Aircraft – Detection and Prevention ” (Advisory Circular [AC] 20-32B)

contains information on the potential dangers of CO exposure from faulty engine exhaust systems or cabin

heaters, means of detecting CO, and procedures to follow when exposure is suspected.

“Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair” (AC 43-13-1B)

contains inspection methods and repair techniques in chapter 8 to prevent exhaust system failures that could

lead to CO exposure.

“Engine Exhaust and Carbon Mono xide Detectors” (Special Airworthine ss Information Bulle tin CE-10-19R1)

informs owners and operators of the impor tance of installing CO detectors.

FAA brochure Carbon Monoxide: A Deadly Menace contains medical informat ion concerning the sympt oms of CO

exposure and methods of avoiding exposure.

A companion

video to this safety alert can be accessed from the Aviation Safety Alerts link.

The reports for the accidents referenced in this safety alert are accessible by NTSB accident number from the

Aviation Accident Database link, and each accident’s public docket is accessible from the Accident Dockets link

for the Docket Management System.

The NTSB’s Aviation Information Resources web page, www.ntsb.gov/air ,

provides convenient access to NTSB aviation safety products. This Safety

Alert and others can be accessed from the Aviation Safety Alerts link at

www.ntsb.gov .

The NTSB is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—highway, marine, railroad, and pipeline. The NTSB determines the probable cause of the accidents and issues safety recommendations aimed at preventing future accidents. For more information, visit www.ntsb.gov.www.twitter.com/ntsb

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