Cabin Air Quality and Contamination
Cabin Air Quality and Contamination
Background
The issue of cabin air quality on commercial aircraft, as well as the possible contamination of that air with fumes and contaminants introduced via bleed air from the engine or auxiliary power unit as part of the pressurization and heating and cooling functions, remains controversial.
Most modern, pressurized commercial aircraft use heated air drawn or “bled” from the engines or auxiliary power unit (APU) for cabin and cockpit air conditioning. As described by the U.S. Federal Aviation Administration (FAA) Civil Aerospace Medical Institute (CAMI) in a 2015 report, “air supplied to a pressurized aircraft cockpit and cabin occurs via an environmental control system (ECS). Fresh air from outside the aircraft, known as replacement or make-up air, enters the ECS in most large transport category commercial airplanes via the aircraft engines. The compressed air is then ‘bled’ through ports and is cooled before being mixed in a manifold with recirculated air, ultimately becoming distributed throughout the cockpit and cabin.”
Fume events or contaminated air quality events (CAQE) may occur as a result of the interaction of incoming make-up air and heated oils or hydraulic fluids from leaking or failed seals in the engine compartment, or from leaks around the APU.
“Factors inside the engine compartment that influence the generation of contaminants include types and amounts of oil and hydraulic fluids, temperature and humidity. Factors inside the aircraft that influence contaminant concentrations include the size of the occupied space and the number of complete air changes per hour (i.e., the volume of make-up air versus the volume of exhausted cabin air),” according to the CAMI report.
FAA and other regulatory agencies have said that fume events are rare. The CAMI report described events arising from the APU or ECS as “extremely rare.” The Australian Civil Aviation Safety Authority‘s Expert Panel on Aircraft Air Quality (EPAAQ) said, in its 2011 report, that “on the available evidence, reported fume events were quite rare, whether expressed on the basis of the number of flights or the number of hours flown.” The EPAAQ report also said, however, that “the panel was unable to find consistent or systematic reporting systems which specifically targeted aircraft incidents being used by Australian or international airlines to enable statistical incidences to be verified.”
Overall Air Quality
Results of a European Union Aviation Safety Agency (EASA) study released in 2017 said that cabin/cockpit air quality is similar to or better than what is observed in normal indoor environments, such as offices, schools and dwellings. The EASA study comprised 69 contaminant measurement flights performed between July 2015 and June 2016. No occupational exposure limits or guidelines were violated during flights conducted to assess air quality, said the study.
“To state the obvious, there is no contaminant-free indoor environment,” the report said. “The aircraft cabin is no exception. However, due to the exceptional high air-exchange rates in aircraft, the cabin air has been proven to be less polluted compared to normal indoor environments. … Volatile contaminations in the cabin are thus depleted quickly. Since the bleed air itself is suspected to be the source of hazard contaminants such as OPC [organophosphorus compounds], a special attention was paid to the detection of TCP [tricresyl phosphate] as a marker for engine oil contamination and the present physical ventilation situation in aircraft.”
In its Medical Manual, the International Air Transport Association (IATA), says “…to summarise the current body of knowledge, aircraft cabin air quality during normal operation is perfectly acceptable and often better than other well accepted indoor environments.”
Fume Events
Although rare fume events, or CAQEs, do occur, and potentially could pose health issues to passengers and crew and safety of flight issues if crew were to become incapacitated.
In a 2018 paper on “Cabin Fumes,” the International Federation of Air Line Pilots’ Associations (IFALPA), said, “When a fume event occurs, cabin air contamination can cause short-term physical effects which may compromise flight safety. Sufficient scientific concern exists requiring more studies in order to determine any short- and long-term effects of fume exposures.”
IATA documentation says that while in most events, there is no impact on crew or passengers, “in some events, crew and/or passengers experience symptoms. … Health effects are usually short lived and resolve over hours to days. These can include Irritation of the eyes, nose, mouth or throat, shortness-of-breath, headache, nausea and abdominal discomfort and tiredness. Some crew who have been involved in CAQEs subsequently experience ongoing ill health and may link their symptoms to the exposure, however the research to date has not established any causative link.”
On its website, the U.K. Civil Aviation Authority says that long-term ill health due to any toxic effect from cabin air is understood to be unlikely, although such a link cannot be ruled out.
IFALPA maintains that it is “unclear” whether fume events cause long-term health effects. It is acknowledged that flight crew are exposed to minimal seal leakage even in normal operations. This may explain why only some of the crew experience symptoms whilst others remain asymptomatic after a fume event. Those whose “cumulative dose” exceeds a certain threshold may experience symptoms. There is concern, as yet unproven, that this may have cumulative long-term health effects. Genetic differences in metabolism may play a role in the cumulative effects. The Global Cabin Air Quality Executive (GCAQE) is an organization focused on addressing the issue of bleed air contamination. GCAQE, whose members include numerous pilot and flight attendant labor organisations, maintains that possible long-term health effects include numbness in fingers and limbs, memory impairment, headaches, dizziness, nausea, breathing difficulties, chest pain, skin rashes, and weakness and fatigue.
It should be emphasised that flight crew members should don oxygen masks immediately at the first sign of smoke or fumes in the flight deck.
Recommendations
Most parties involved in the ongoing debate support further scientific research into the matter and improved, standardised reporting of the occurrence and response to fume events. There also have been calls for the installation of air quality monitoring equipment on aircraft, compliance with appropriate maintenance procedures to avoid situations such as overfilling of engine and APU oil and to maintain seals, the use of less toxic oils and other fluids, and a move away from bleed air systems.
Labour organisations encourage their members to learn to recognise fume events, and to respond to and report the presence of fumes in the aircraft air supply. Precision in reporting is considered important to helping to identify the source of fumes. These organisations also provide guidance on post-event response and actions to be taken, including coordinated reporting and medical examinations.
In March 2022, legislation known as the Cabin Air Quality Act of 2022, was introduced in the Congress. One of the bill's sponsors said at the time that the legislation is intended to protect commercial airline passengers adn crew from toxic cabin air. The bill, if passed in its original state, would require that pilots, flight attendants and aircraft maintenance technicians receive training on identifying toxic smoke and fumes.It also would require FAA to record and monitor reports of smoke or fume events, authorize FAA to conduct investigations into such events and direct carriers to install and operate onboard detectors and other air quality monitoring equipment.
Accidents and Incidents
On 2 January 2024, an Airbus A350-900 collided with a Bombardier DHC8-300 almost immediately after a night touchdown in good visibility at Tokyo Haneda after the DHC8 had entered the runway for departure without clearance. Both aircraft caught fire. The DHC8 was destroyed and five of the six occupants died. The A350 then veered off the runway and stopped but all 379 occupants evacuated prior to complete destruction by fire. A TWR visual-only runway incursion warning was unnoticed for over a minute and stop bar lighting was out of service for upgrading and anyway only routinely used in low visibility.
On 9 February 2023, a Boeing 777-200ER was en route near Marseille when the cabin crew observed smoke coming from a rear galley oven, which was spreading into the rear passenger cabin. After an initial use of multiple Halon fire extinguishers, the smoke ceased after about 20 minutes, but the fumes remained. Although this meant no ongoing emergency existed, some cabin crew and passengers experienced breathing difficulties and it was decided to return to Amsterdam. The cabin crew response to the situation was subsequently assessed as contrary to applicable procedures and relevant cabin crew training seemingly inadequate.
On 6 June 2023, a Boeing 717-200 was on base leg about 10 nm from Hobart, Australia, when chlorine fumes became evident on the flight deck. As the aircraft became fully established on final approach, the captain recognised signs of cognitive impairment and handed control to the initially unaffected first officer. Just before touchdown, the first officer was similarly affected but was able to safely complete the landing and taxi in. The same aircraft had experienced a similar event two days earlier with no fault found. The Investigation determined that the operator’s procedures for responding to crew incapacitation in flight had been inadequate.
On 15 December 2019, an Airbus A330-200 turned back to Sydney shortly after departure when a major hydraulic system leak was annunciated. The return was uneventful until engine shutdown after clearing the runway following which APU use for air conditioning was followed by a gradual build up of hydraulic haze and fumes which eventually prompted an emergency evacuation. The Investigation found that fluid leaking from ruptured rudder servo hose had entered the APU air intake. The resulting evacuation was found to have been somewhat disorganised with this being attributed mainly to a combination of inadequate cabin crew procedures and training.
On 5 August 2019, an Airbus A321 crew declared a MAYDAY immediately after clearing the landing runway at Valencia when a hold smoke warning was annunciated. An emergency evacuation was completed without injuries. This warning followed “white smoke” from the air conditioning system entering both the passenger cabin and flight deck in the four minutes before landing which had prompted the pilots to don oxygen masks. The Investigation found the white smoke was the direct consequence of an oil leak from the right engine as a result of the misalignment and breakage of a bearing and its associated hydraulic seal.
Further Reading
BFU (Germany)
- Study of Reported Occurrences in Conjunction with Cabin Air Quality in Transport Aircraft BFU (Germany), 2014
CASA/ATSB (Australia)
- An analysis of fumes and some events in Australian aviation, Aviation Research Report AR-2013-213, 20 May 2014.
- Contamination of aircraft cabin air by bleed air — a review of the evidence, Expert Panel on Aircraft Air Quality,
EASA
- CAQ: Preliminary cabin air quality measurement campaign, Final Report EASA_REP_RESEA_2014_4, Fraunhofer Institute for Toxicology and Experimental Medicine, 2014.
FAA
- Aircraft Cabin Bleed Air Contaminants: A Review, Gregory A. Day, DOT/FAA/AM-15/20, November 2015.
- Cabin Air Quality
IATA
- Health & Safety for Passengers & Crew, IATA website, accessed 25 June 2019.
- Cabin Air Quality Event — FAQs, May 2018.
- “Guidance for airline health and safety staff on the medical response to Cabin Air Quality Events,” IATA.
UK CAA
- Cabin Air Quality, CAA website, accessed 25 June 2019.
Resources
Categories
