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Aircraft Flight Operations

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Adapted from the 3rd edition Encyclopaedia article “Aviation - flying personnel” authored by H. Gartmann.

This article deals with the occupational safety and health of the crew members of civil aviation aircraft; see also the articles “Airport and flight control operations”, “Aircraft maintenance operations” and “Helicopters” for additional information.

Technical Crew Members

The technical personnel, or flight crew members, are responsible for the operation of the aircraft. Depending on aircraft type, the technical crew includes the pilot-in-command (PIC), the co-pilot (or first officer), and the flight engineer or a second officer (a pilot).

The PIC (or captain) has the responsibility for the safety of the aircraft, the passengers and the other crew members. The captain is the legal representative of the air carrier and is vested by the air carrier and the national aviation authority with the authority to carry out all actions necessary to fulfil this mandate. The PIC directs all duties on the flight deck and is in command of the entire aircraft.

The co-pilot takes his or her orders directly from the PIC and acts as the captain’s deputy upon delegation or in the latter’s absence. The co-pilot is the primary assistant to the PIC in a flight crew; in newer generation, two-person flight deck operations and in older two-engine aircraft, he or she is the only assistant.

Many older generation aircraft carry a third technical crew member. This person may be a flight engineer or a third pilot (usually called the second officer). The flight engineer, when present, is responsible for the mechanical condition of the aircraft and its equipment. New generation aircraft have automated many of the functions of the flight engineer; in these two-person operations, the pilots perform such duties as a flight engineer might otherwise perform that have not been automated by design.

On certain long-distance flights, the crew may be supplemented by a pilot with the qualifications of the PIC, an additional first officer and, when required, an additional flight engineer.

National and international laws stipulate that aircraft technical personnel may operate aircraft only when in possession of a valid licence issued by the national authority. In order to maintain their licences, technical crew members are given ground school training once every year; they are also tested in a flight simulator (a device that simulates real flight and flight emergency conditions) twice a year and in actual operations at least once a year.

Another condition for the receipt and renewal of a valid licence is a medical examination every 6 months for airline transport and commercial pilots over 40 years old, or every 12 months for commercial pilots under 40 years old and for flight engineers. The minimum requirements for these examinations are specified by the ICAO and by national regulations. A certain number of physicians experienced in aviation medicine may be authorized to provide such examinations by the national authorities concerned. These may include air ministry physicians, airforce flight surgeons, airline medical officers or private practitioners designated by the national authority.

Cabin Crew Members

The cabin crew (or flight attendants) are primarily responsible for passenger safety. Flight attendants perform routine safety duties; in addition, they are responsible for monitoring the aircraft cabin for security and safety hazards. In the event of an emergency, the cabin crew members are responsible for the organization of emergency procedures and for the safe evacuation of the passengers. In flight, cabin crew may need to respond to emergencies such as smoke and fire in the cabin, turbulence, medical trauma, aircraft decompressions, and hijackings or other terrorist threats. In addition to their emergency responsibilities, flight attendants also provide passenger service.

The minimum cabin crew ranges from 1 to 14 flight attendants, depending on the type of aircraft, the aircraft’s passenger capacity and national regulations. Additional staffing requirements may be determined by labour agreements. The cabin crew may be supplemented by a purser or service manager. The cabin crew is usually under the supervision of a lead or “in-charge” flight attendant, who, in turn, is responsible and reports directly to the PIC.

National regulations do not usually stipulate that the cabin crew should hold licences in the same way as the technical crew; however, cabin crew are required by all national regulations to have received appropriate instruction and training in emergency procedures. Periodic medical examinations are not usually required by law, but some air carriers require medical examinations for the purposes of health maintenance.

Hazards and Their Prevention

All air crew members are exposed to a wide variety of stress factors, both physical and psychological, to the hazards of an aircraft accident or other flight incident and to the possible contraction of a number of diseases.

Physical stress

Lack of oxygen, one of the main concerns of aviation medicine in the early days of flying, had until recently become a minor consideration in modern air transport. In the case of a jet aircraft flying at 12,000 m altitude, the equivalent altitude in the pressurized cabin is only 2,300 m and, consequently, symptoms of oxygen deficiency or hypoxia will not normally be encountered in healthy persons. Oxygen deficiency tolerance varies from individual to individual, but for a healthy, non-trained subject the presumed altitude threshold at which the first symptoms of hypoxia occur is 3,000 m.

With the advent of new generation aircraft, however, concerns about cabin air quality have resurfaced. Aircraft cabin air consists of air drawn from compressors in the engine and often also contains recirculated air from within the cabin. The flow rate of outside air within an aircraft cabin can vary from as little as 0.2 m3 per minute per person to 1.42 m3 per minute per person, depending upon aircraft type and age, and depending on location within the cabin. New aircraft use recirculated cabin air to a much greater degree than do older models. This air quality issue is specific to the cabin environment. The flight deck compartment air flow rates are often as high as 4.25 m3 per minute per crew member. These higher air flow rates are provided on the flight deck to meet the cooling requirements of the avionic and electronic equipment.

Complaints of poor cabin air quality from cabin crew and passengers have increased in recent years, prompting some national authorities to investigate. Minimal ventilation rates for aircraft cabins are not defined in national regulations. Actual cabin airflow is seldom measured once an aircraft is put into service, since there is no requirement to do so. Minimal air flow and the use of recirculated air, combined with other issues of air quality, such as the presence of chemical contaminants, micro-organisms, other allergens, tobacco smoke and ozone, require further evaluation and study.

Maintaining a comfortable air temperature in the cabin does not represent a problem in modern aircraft; however, the humidity of this air cannot be raised to a comfortable level, due to the large temperature difference between the aircraft interior and exterior. Consequently, both crew and passengers are exposed to extremely dry air, especially on long-distance flights. Cabin humidity depends on the cabin ventilation rate, passenger load, temperature and pressure. The relative humidity found on aircraft today varies from about 25% to less than 2%. Some passengers and crew members experience discomfort, such as dryness of the eyes, nose and throat, on flights that exceed 3 or 4 hours. There is no conclusive evidence of extensive or serious adverse health effects of low relative humidity on flight personnel. However, precautions should be taken to avoid dehydration; adequate intake of liquids such as water and juices should be sufficient to prevent discomfort.

Motion sickness (dizziness, malaise and vomiting due to the abnormal movements and altitudes of the aircraft) was a problem for civil aviation crews and passengers for many decades; the problem still exists today in the case of small sports aircraft, military aircraft and aerial acrobatics. In modern jet transport aircraft, it is much less serious and occurs less frequently due to higher aircraft speeds and take-off weights, higher cruising altitudes (which take the aircraft above the turbulence zones) and the use of airborne radar (which enables squalls and storms to be located and circumnavigated). Additionally, the lack of motion sickness also may be attributed to the more spacious, open design of today’s aircraft cabin, which provides a greater feeling of security, stability and comfort.

Other physical and chemical hazards

Aircraft noise, while a significant problem for ground personnel, is less serious for the crew members of a modern jet aircraft than was the case with the piston-engined plane. The efficiency of noise control measures such as insulation in modern aircraft have helped to eliminate this hazard in most flight environments. Additionally, improvements in communications equipment have minimized background noise levels from these sources.

Ozone exposure is a known but poorly monitored hazard for air crew and passengers. Ozone is present in the upper atmosphere as a result of the photochemical conversion of oxygen by solar ultraviolet radiation at altitudes used by commercial jet aircraft. The mean ambient ozone concentration increases with increasing latitude and is most prevalent during spring. It can also vary with weather systems, with the result of high ozone plumes descending down to lower altitudes.

Symptoms of ozone exposure include cough, upper airway irritation, tickle in the throat, chest discomfort, substantial pain or soreness, difficulty or pain in taking a deep breath, shortness of breath, wheezing, headache, fatigue, nasal congestion and eye irritation. Most people can detect ozone at 0.02 ppm, and studies have shown that ozone exposure at 0.5 ppm or more causes significant decrements in pulmonary function. The effects of ozone contamination are felt more readily by persons engaged in moderate to heavy activity than those who are at rest or engaged in light activity. Thus flight attendants (who are physically active in flight) have experienced the effects of ozone earlier and more frequently than technical crew or passengers on the same flight when ozone contamination was present.

In one study conducted in the late 1970s by the aviation authority in the United States (Rogers 1980), several flights (mostly at 9,150 to 12,200 m) were monitored for ozone contamination. Eleven per cent of the flights monitored were found to exceed that authority’s permissible ozone concentration limits. Methods of minimizing ozone exposure include choice of routes and altitudes that avoid areas of high ozone concentration and the use of air treatment equipment (usually a catalytic converter). The catalytic converters, however, are subject to contamination and loss of efficiency. Regulations (when they exist) do not require their periodic removal for efficiency testing, nor do they require monitoring of ozone levels in actual flight operations. Crew members, especially cabin crew, have requested that better monitoring and control of ozone contamination be implemented.

Another serious concern for technical and cabin crew members is cosmic radiation, which includes radiation forms that are transmitted through space from the sun and other sources in the universe. Most cosmic radiation that travels through space is absorbed by the earth’s atmosphere; however, the higher the altitude, the less the protection. The earth’s magnetic field also provides some shielding, which is greatest near the equator and decreases at the higher latitudes. Air crew members are exposed to cosmic radiation levels inflight that are higher than those received on the ground.

The amount of radiation exposure depends on the type and the amount of flying; for example, a crew member who flies many hours at high altitudes and high latitudes (e.g., polar routes) will receive the greatest amount of radiation exposure. The civil aviation authority in the United States (the FAA) has estimated that the long-term average cosmic radiation dose for air crew members ranges from 0.025 to 0.93 millisieverts (mSv) per 100 block hours (Friedberg et al. 1992). Based on FAA estimates, a crew member flying 960 block hours per year (or an average of 80 hours/month) would receive an estimated annual radiation dose of between 0.24 and 8.928 mSv. These levels of exposure are lower than the recommended occupational limit of 20 millisieverts per year (5-year average) established by the International Commission on Radiological Protection (ICRP).

The ICRP, however, recommends that occupational exposure to ionizing radiation should not exceed 2 mSv during pregnancy. In addition, the US National Council on Radiation Protection and Measurements (NCRP) recommends that exposure not exceed 0.5 mSv in any month once a pregnancy is known. If a crew member worked an entire month on flights with the highest exposures, the monthly dose rate could exceed the recommended limit. Such a pattern of flying over 5 or 6 months could result in an exposure which also would exceed the recommended pregnancy limit of 2 mSv.

The health effects of low-level radiation exposure over a period of years include cancer, genetic defects and birth defects to a child exposed in the womb. The FAA estimates that the added risk of fatal cancer resulting from exposure to inflight radiation would range from 1 in 1,500 to 1 in 94, depending on the type of routes and number of hours flown; the level of added risk of a serious genetic defect resulting from one parent’s exposure to cosmic radiation ranges from 1 in 220,000 live births to 1 in 4,600 live births; and the risk of mental retardation and childhood cancer in a child exposed in utero to cosmic radiation would range between 1 in 20,000 to 1 in 680, depending upon the type and amount of flying the mother did while pregnant.

The FAA report concludes that “radiation exposure is not likely to be a factor that would limit flying for a non-pregnant crew member” because even the largest amount of radiation received annually by a crew member working as much as 1,000 block hours a year is less than half the ICRP recommended average annual limit. However, for a pregnant crew member, the situation is different. The FAA calculates that a pregnant crew member working 70 block hours per month would exceed the recommended 5-month limit on about one-third of the flights they studied (Friedberg et al. 1992).

It should be stressed that these exposure and risk estimates are not universally accepted. Estimates are dependent upon assumptions about the types and mix of radioactive particles encountered at altitude and the weight or quality factor used to determine dose estimates for some of these forms of radiation. Some scientists believe that the actual radiation hazard to air crew members may be greater than described above. Additional monitoring of the flight environment with reliable instrumentation is needed to more clearly determine the extent of inflight radiation exposure.

Until more is known about exposure levels, air crew members should keep their exposure to all types of radiation as low as possible. With respect to inflight radiation exposure, minimizing the amount of flight time and maximizing the distance from the source of radiation can have a direct effect on the dose received. Reducing monthly and yearly flight time and/or selecting flights which fly at lower altitudes and latitudes will reduce exposure. An air crew member who has the ability to control his or her flight assignments might choose to fly fewer hours per month, to bid for a mix of domestic and international flights or to request leaves periodically. A pregnant air crew member might choose to take a leave for the duration of the pregnancy. Since the first trimester is the most crucial time to guard against radiation exposure, an air crew member planning a pregnancy also may want to consider a leave especially if she is flying long-distance polar routes on a regular basis and has no control over her flight assignments.

Ergonomic problems

The main ergonomic problem for technical crew is the need to work for many hours in a sitting but unsettled position and in a very limited working area. In this position (restrained by lap and shoulder harness), it is necessary to carry out a variety of tasks such as movements of the arms, legs and head in different directions, consulting instruments at a distance of about 1 m above, below, to the front and to the side, scanning the far distance, reading a map or manual at close distance (30 cm), listening through earphones or talking through a microphone. Seating, instrumentation, lighting, cockpit microclimate and radio communications equipment comfort have been and still remain the object of continuous improvement. Today’s modern flight deck, often referred to as the “glass cockpit”, has created yet another challenge with its use of leading-edge technology and automation; maintaining vigilance and situational awareness under these conditions has created new concerns for both the designers of aircraft and the technical personnel who fly them.

Cabin crew have an entirely different set of ergonomic problems. One main problem is that of standing and moving around during flight. During climb and descent, and in turbulence, the cabin crew is required to walk on an inclined floor; in some aircraft the cabin incline may remain at approximately 3% during cruise as well. Also, many cabin floors are designed in a manner that creates a rebound effect while walking, putting an additional stress on the flight attendants who are constantly moving about during a flight. Another important ergonomic problem for flight attendants has been the use of mobile carts. These carts can weigh up to 100 to 140 kg and must be pushed and pulled up and down the length of the cabin. Additionally, the poor design and maintenance of the braking mechanisms on many of these carts have caused an increase in repetitive-strain injuries (RSIs) among flight attendants. Air carriers and cart manufacturers are now taking a more serious look at this equipment, and new designs have resulted in ergonomic improvements. Additional ergonomic problems result from the need to lift and carry heavy or bulky items in restricted spaces or while maintaining uncomfortable body posture.


The workload for air crew members depends on the task, the ergonomic layout, the hours of work/duty and many other factors. The additional factors affecting the technical crew include:

  • duration of rest time between present and last flight and the duration of sleep time during the rest period
  • the pre-flight briefing and problems encountered during the pre-flight briefing
  • delays preceding departure
  • timing of flights
  • meteorological conditions at the point of departure, en route and at the destination
  • number of flight segments
  • type of equipment being flown
  • quality and quantity of radio communications
  • visibility during descent, glare and protection from the sun
  • turbulence
  • technical problems with the aircraft
  • experience of other crew members
  • air traffic (especially at point of departure and destination)
  • presence of air carrier or national authority personnel for purposes of checking crew competency.


Certain of these factors may be equally important for the cabin crew. In addition, the latter are subject to the following specific factors:

  • pressure of time due to short duration of flight, high number of passengers and extensive service requirements
  • extra services demanded by passengers, the character of certain passengers and, occasionally, verbal or physical abuse by passengers
  • passengers requiring special care and attention (e.g., children, the disabled, the elderly, a medical emergency)
  • extent of preparatory work
  • lack of necessary service items (e.g., insufficient meals, beverages and so on) and equipment.


The measures taken by air carrier managements and government administrations to keep crew workload within reasonable limits include: improvement and extension of air-traffic control; reasonable limits on hours of duty and requirements for minimum rest provisions; execution of preparatory work by dispatchers, maintenance, catering and cleaning personnel; automation of cockpit equipment and tasks; the standardization of service procedures; adequate staffing; and the provision of efficient and easy-to-handle equipment.

Hours of work

One of the most important factors affecting both technical and cabin crew member occupational health and safety (and certainly the most widely discussed and controversial) is the issue of flight fatigue and recovery. This issue covers the broad spectrum of activity encompassing crew scheduling practices—length of duty periods, amount of flight time (daily, monthly and yearly), reserve or standby duty periods and availability of time for rest both while on flight assignment and at domicile. Circadian rhythms, especially sleep intervals and duration, with all their physiological and psychological implications, are especially significant for air crew members. Time shifts due either to night flights or to east/west or west/east travel across a number of time zones create the greatest problems. Newer generation aircraft, which have the capability of remaining aloft for up to 15 to 16 hours at a time, have exacerbated the conflict between airline schedules and human limitations.

National regulations to limit duty and flight periods and to provide minimum rest limitations exist on a nation by nation basis. In some instances, these regulations have not kept pace with technology or science, nor do they necessarily guarantee flight safety. Until recently there has been little attempt to standardize these regulations. Current attempts at harmonization have given rise to concerns among air crew members that those countries with more protective regulations may be required to accept lower and less adequate standards. In addition to national regulations, many air crew members have been able to negotiate more protective hours of service requirements in their labour agreements. While these negotiated agreements are important, most crew members feel that hours of service standards are essential to their health and safety (and to that of the flying public), and thus minimum standards should be adequately regulated by the national authorities.

Psychological stress

In recent years, aircraft crew have been confronted with a serious mental stress factor: the likelihood of hijacking, bombs and armed attacks on aircraft. Although security measures in civil aviation worldwide have been considerably increased and upgraded, the sophistication of terrorists has likewise increased. Air piracy, terrorism and other criminal acts remain a real threat to all air crew members. The commitment and cooperation of all national authorities as well as the force of worldwide public opinion are needed to prevent these acts. Additionally, air crew members must continue to receive special training and information on security measures and must be informed on a timely basis of suspected threats of air piracy and terrorism.

Air crew members understand the importance of starting flight duty in a sufficiently good mental and physical state to ensure that the fatigue and stresses occasioned by the flight itself will not affect safety. Fitness for flight duty may occasionally be impaired by psychological and physical stress, and it is the responsibility of the crew member to recognize whether or not he or she is fit for duty. Sometimes, however, these effects may not be readily apparent to the person under duress. For this reason, most airlines and air crew member associations and labour unions have professional standards committees to assist crew members in this area.


Fortunately, catastrophic aircraft accidents are rare events; nonetheless, they do represent a hazard for air crew members. An aircraft accident is practically never a hazard resulting from a single, well-defined cause; in almost every instance, a number of technical and human factors coincide in the causal process.

Defective equipment design or equipment failure, especially as a result of inadequate maintenance, are two mechanical causes of aircraft accidents. One important, although relatively rare, type of human failure is sudden death due, for example, to myocardial infarction; other failures include sudden loss of consciousness (e.g., epileptic fit, cardiac syncope and fainting due to food poisoning or other intoxication). Human failure may also result from the slow deterioration of certain functions such as hearing or vision, although no major aircraft accident has been attributed to such a cause. Preventing accidents from medical causes is one of the most important tasks of aviation medicine. Careful personnel selection, regular medical examinations, surveys of absence due to illness and accidents, continuous medical contact with working conditions and industrial hygiene surveys can considerably decrease the danger of sudden incapacitation or slow deterioration in technical crew. Medical personnel should also routinely monitor flight scheduling practices to prevent fatigue-related incidents and accidents. A well-operated, modern airline of significant size should have its own medical service for these purposes.

Advances in aircraft accident prevention are often made as a result of careful investigation of accidents and incidents. Systematic screening of all, even minor, accidents and incidents by an accident investigation board comprising technical, operational, structural, medical and other experts is essential to determine all causal factors in an accident or incident and to make recommendations for preventing future occurrences.

A number of strict regulations exist in aviation to prevent accidents caused by use of alcohol or other drugs. Crew members should not consume quantities of alcohol in excess of what is compatible with professional requirements, and no alcohol at all should be consumed during and for at least 8 hours prior to flight duty. Illegal drug use is strictly prohibited. Drug use for medicinal purposes is strictly controlled; such drugs are generally not allowed during or immediately preceding flight, although exceptions may be allowed by a recognized flight physician.

The transport of hazardous materials by air is yet another cause of aircraft accident and incidents. A recent survey covering a 2-year period (1992 to 1993) identified over 1,000 aircraft incidents involving hazardous materials on passenger and cargo air carriers in one nation alone. More recently, an accident in the United States which resulted in the deaths of 110 passengers and crew involved the carriage of hazardous cargo. Hazardous materials incidents in air transportation occur for a number of reasons. Shippers and passengers may be unaware of the dangers presented by the materials they bring aboard aircraft in their baggage or offer for transport. Occasionally, unscrupulous persons may choose to illegally ship forbidden hazardous materials. Additional restrictions on the carriage of hazardous materials by air and improved training for air crew members, passengers, shippers and loaders may help to prevent future incidents. Other accident prevention regulations deal with oxygen supply, crew meals and procedures in case of illness.


Specific occupational disease of crew members are not known or documented. However, certain diseases may be more prevalent among crew members than among persons in other occupations. Common colds and upper respiratory system infections are frequent; this may be due in part to the low humidity during flight, irregularities of schedules, exposure to att large number of people in a confined space and so on. A common cold, especially with upper respiratory congestion, that is not significant for an office worker may incapacitate a crew member if it prevents the clearing of pressure on the middle ear during ascent and, particularly, during descent. Additionally, illnesses that require some form of drug therapy may also preclude the crew member from engaging in work for a period of time. Frequent travel to tropical areas may also entail increased exposure to infectious diseases, the most important being malaria and infections of the digestive system.

The close confines of an aircraft for extended periods of time also carry an excess risk of airborne infectious diseases like tuberculosis, if a passenger or crew member has such a disease in its contagious stage.



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