Reducing Risk of Carbon Monoxide Poisoning in General Aviation Aircraft - Civil Aviation Safety Alerts (CASA) No. 2019-07


Owners, operators and maintainers of general aviation aeroplanes and rotorcraft equipped with heaters

File Classification No.: Z 5000-35
RDIMS No.: 15701665
Document No.: CASA 2019-07
Issue No.: 01
Effective Date: 2019-12-12


The purpose of this Civil Aviation Safety Alert (CASA) is to raise awareness of hazards that may result in exposure to carbon monoxide (CO), and to recommend preventive actions to reduce the risk that pilots and passengers in General Aviation (GA) aircraft will be adversely affected by exposure to this toxic gas.


Transport Canada (TC) issued Airworthiness Directive (AD) CF-90-03R2 almost thirty years ago, to mitigate risks from exhaust gases entering the aircraft heating system. That AD requires repetitive inspection of exhaust-type heat exchangers. These types of heat exchangers are used on many small aircraft to provide heated air for the comfort of occupants and for other environmental control purposes such as preventing condensation on windshields and other transparencies.

Although combustion-type heaters differ from exhaust-type heaters, they also have some risks. These types of heaters operate independently of the engine. Combustion-type heaters burn aircraft fuel to generate heat and include a heat exchanger to extract the heat of combustion. Like exhaust-type heaters, combustion-type heaters are designed to keep products of combustion separate from the heated air that will be supplied to the cabin of the aircraft.

One risk shared by both exhaust- and combustion-type heaters is CO poisoning: degradation of the component parts can allow this toxic gas, which is a by-product of combustion, to infiltrate the cabin of the aircraft. Exposure to CO is associated with headache, dizziness, fatigue, and at elevated doses, death. CO poisoning associated with degraded heating systems has been identified as the cause of many instances of GA pilot incapacitation.

AD CF-90-03R2 requires disassembly of exhaust-type heaters followed by detailed visual inspection (DVI) and repair or replacement of damaged parts. The AD also requires that pressure testing or other accepted methods be used to investigate any areas where degradation is suspected as a result of visual inspection. The AD requires these actions be performed at intervals not to exceed one year or 150 hours air time, whichever occurs first.

The DVI required by AD CF-90-03R2 will only be capable of detecting relatively large defects. A pressure/leak test is inherently capable of revealing defects that are too small to be found during DVIs. For that reason, some maintenance personnel have developed the practice of performing a pressure/leak test every time they accomplish the inspection required by AD CF-90-03R2.

Heating systems are not the only potential source of CO in GA aircraft: Research conducted on behalf of the Federal Aviation Administration (FAA) of the United States identified muffler and exhaust systems as the primary sources of CO when this poisonous gas was the cause of an accident. The report that the FAA published on this topic, DOT/ FAA/ AR-09/49 Detection and Prevention of Carbon Monoxide Exposure in General Aviation Aircraft is available on the internet at and contains information that is complementary to the information in this CASA. Leakage from the muffler and exhaust systems can enter the aircraft cabin either through the heating/ventilation system or through a leak in the firewall between the engine compartment and cabin.

The FAA published Special Airworthiness Information Bulletin (SAIB) CE-10-19 R1 to raise awareness of the report noted above. The SAIB also recommended actions that are intended to reduce risks associated with CO. The FAA also published Advisory Circular (AC Carbon Monoxide Contamination In Aircraft – Detection and Prevention. This AC also contains information that may be useful for operators and maintainers of GA aircraft. The FAA developed a one-hour online course, ALC-498 Aircraft Exhaust Systems, intended for Aircraft Maintenance Technicians. The course is available at

CO has no color or odor. The onset of CO poisoning can be insidious: victims are often unaware that their environment is contaminated by this poisonous gas and that their mental and physical functions are being degraded. For these reasons, a CO warning device is a very sensible investment for owners and operators of GA aircraft. A suitable CO detector will provide reliable, early warning of elevated levels of this poisonous gas, allowing the pilot to take appropriate actions. A CO detector can also enhance the effectiveness of aircraft maintenance actions. An inspection of the aircraft cabin with a detector can confirm that maintenance or repair of the exhaust or heating systems has corrected and/or not introduced damage that could be associated with the CO leaks. The type of functional check enabled by a CO detector is not otherwise possible.

TC has concluded that preventive actions in addition to those required by AD CF-90-03R2 may be beneficial for owners and operators of GA aircraft in Canada. These additional preventive actions are described in the following section of this CASA.

Recommended action:

When accomplishing the inspections required by AD CF-90-03R2, accomplish a pressure/leak test in addition to the visual inspection, instead of performing the leak check only if the visual inspection indicates a possible problem.

Conduct engine run-up tests with cabin heat on and check for CO in the cabin with a hand-held CO detector during 100 hour and annual inspections.

Continue to inspect the complete engine exhaust system during 100 hour/annual inspections and at inspection intervals recommended by the aircraft and engine manufacturers in accordance with their applicable maintenance instructions.

Use a CO detector while operating your aircraft. A CO warning device is a very sensible investment for owners and operators of GA aircraft. A suitable CO detector that is located appropriately and equipped with a properly set alarm will provide reliable, early warning of elevated levels of this poisonous gas allowing the pilot to take appropriate actions.

Contact office:

For more information concerning this issue, contact a Transport Canada Centre; or contact Ross McGowan, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639, facsimile 613-996-9178 or e-mail at

Original signed by

Rémy Knoerr
Chief, Continuing Airworthiness
National Aircraft Certification

The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.