Aspects of the airline industry that affect the number of accidents and incidents, as well as the continuing effort to reduce this number as much as possible.

The aviation industry has a remarkable safety record. The total number of fatalities on board commercial jets in the years from 1959 to 1999 is less than one-half the annual U.S. automobile fatality rate. However, because so many people can be affected by one incident, aviation accidents make headline news. Although the airlines’ safety record is impressive, continuous efforts by the aviation industry, the federal government, and the airlines are aimed at reducing the accident rate to zero.

Statistics from the Boeing Company show that the ten-year commercial jet airplane accident rate from 1990 to 1999 was less than one accident per one million departures of scheduled air carriers. Even this statistic does not tell the whole story, however, because fatal injuries were not present in all of those aircraft accidents. Although accidents are very rare occurrences, reducing the accident rate remains important. If the number of departures doubled from ten million to twenty million annually and the rate of accidents remained the same, there would be an increase in the number of aircraft accidents.

Many organizations, both public and private, are actively involved in research to prevent safety problems before accidents occur. The National Aeronautics and Space Administration (NASA) is very involved in funding basic research into new technologies and cockpit displays to prevent accidents both on the ground and in flight. The NASA Aviation Safety Program is a partnership with the Federal Aviation Administration (FAA), the Department of Defense (DOD), aircraft manufacturers, airlines, and universities. Their collective efforts have contributed significantly to the reduction of the number of aircraft accidents.

Research reveals that more than 70 percent of all airline accidents can be attributed to human error, including that of pilots, air traffic control personnel, airport employees, and others. Government and industry officials have been implicated in some accidents because of delays in implementing certain safety warning devices. However, flight crews are ascribed with the majority of the errors that result in accidents. Aviation researchers are actively involved in determining how best to relieve this problem.

The discipline of human factors in aircraft operations has become focused not only on the causes of accidents but also on the best ways to incorporate lessons learned from them into the aviation system. Rarely does a single event result in an aircraft accident. Research has shown that most accidents can be blamed on a series of uncorrected errors, intervention at any point in which would likely have disrupted the pattern and prevented the accident. Although aircraft operations attempt to make corrections based on lessons learned, the implementation of such procedures remains a complex issue involving many personalities, agencies, airlines, manufacturers, and governments.

Accidents are rarely caused by a deliberate disregard of procedures. They are more generally caused by a series of uncorrected mistakes or by the development of a situation in which people become overwhelmed or find their capabilities are inadequate for the situation. Human performance in an accident or serious incident should be measured in terms of what could normally be anticipated and under what circumstances could a reasonable degree of correct performance have been expected from the persons involved.

Many aspects of human performance must be considered when evaluating crew behavior. Work experience, working conditions, skill, fatigue, low blood sugar, reduced oxygen, and use of medicines, drugs or alcohol can all affect a person’s capabilities. Environmental conditions, such as noise, vibrations, motion, and visual cues may also affect a person’s ability to perform. The least measurable aspect of one’s capability is one’s psychological state. At any given time, one’s emotion, awareness, memory, attention, complacency, boredom, judgment, perceptions, and attitude are all significant contributors to an individual’s psychological capability. The level and quality of interaction with others associated with the flight will affect the tenor of the entire experience.

Research into an aircraft accident reveals the specifics of the event and most often assigns the blame to the flight crew. Nevertheless, the question of why qualified, demonstratively competent, highly trained, medically fit, well-paid professionals failed to perform the job correctly, resulting in an accident, continues to demand an answer. In 1983, the National Transportation Safety Board (NTSB) established its Human Performance Division to place an emphasis on answering that question.

Investigations into crew behavior and organizational cultures reveal that the personalities of the individuals involved have a direct bearing on the flight crew’s general attitude. In the early days of commercial flight, the captain was considered the indisputable boss, and the other crewmembers were required to follow the captain’s orders. Although this hierarchical approach was the norm and expected, especially because most of the airline pilots at the time had been retired from the military, post-accident analysis revealed that if a subordinate crewmember had been more assertive, the accident chain might have been disrupted.

A new concept of crew interaction was adopted by United Air Lines in the 1980’s and became known as crew resource management (CRM). CRM challenged the paradigm of the captain-as-boss and introduced the concept of teamwork for decision making. It was a revolutionary idea at the time, and airlines holding the traditional view of cockpit authority were reticent to embrace this concept.

In 1989, United Air Lines Flight 232, whose pilot was able to land a hopelessly crippled DC-10 and saved the lives of half the passengers, forever changed the perception of CRM training from an interesting concept to an indispensable part of crew training. The crew’s remarkable teamwork was identified by the captain as the result of the CRM training that he and his fellow pilots received.

The CRM concept is now the accepted norm and required by federal regulations. Airline management uses CRM training as an opportunity to intervene in a broad class of poorly defined problems. Line-oriented flight training (LOFT) is a curriculum of real-time simulator exercises that introduce situations to flight crews that enable them to practice their CRM skills and receive comments on their performance from the instructor. This broad-scale approach to social communication-based behaviors and attitudes is in marked contrast to the previous norm of a top-down captain-copilot relationship. CRM teaches the value of using all members’ experience to solve a problem, even though the captain maintains the legal authority to make final decisions.

The success of CRM training has extended beyond cockpit crews. Airlines have discovered that cabin crews can also play a significant role in enhancing flight safety. Flight attendants, when included in preflight briefings by the captain, feel that their role in the safety of the flight is recognized. This inclusion contributes to the healthy tone of the flight and increases the likelihood that cabin crews would intervene in instances where communication between the cabin and cockpit was necessary.

Training is the single best method of ensuring airline safety. Airlines spend millions of dollars each year to evaluate pilot performance and to teach corrective actions and procedures based on current research.

Training instructs pilots how to perform their tasks. Procedures are designed to dictate the manner in which tasks are implemented by the flight crew, ground crew, and others with direct input to the flight. Training programs, standardization of procedures, quality control, and printed materials such as manuals and checklists are used by all airlines for the safe operation of flight. The prevention and elimination of human error through successful training programs is a vital safety step.

The purpose of checklists has been to alleviate the burden of pilots from trying to remember all the steps necessary to configure the aircraft for various flight regimes. The use of standardized checklists began about the time of the U.S. Airmail Service and evolved to a complex written list of actions to be performed, a system which has not changed in concept from those early days despite the modern computerized checklists.

The checklist is a critical tool for ensuring safe and consistent flight operations. Consistent, accurate use of the checklist is a safeguard to ensure that the aircraft is properly configured, operations are completed sequentially and efficiently, and the aircraft is prepared for flight.

The FAA’s Federal Aviation Regulations (FARs) require the checklist to include a starting engines check, a takeoff check, a cruise configuration check, an approach check, an after-landing check, and a shutdown check. The FARs also require a checklist for the emergency operations of fuel, hydraulic, electrical, and mechanical systems and instruments and controls, as well as engine inoperative procedures and any other emergency procedures necessary for a safe flight.

Significant research has been conducted in the area of checklist design and usage. The determination of which items should be included, their sequence, redundancy, action and verification, and by whom the checking should be done, is complex. Checklist presentation—on paper, electronically, or mechanically—will vary among airlines and aircraft types.

Since the 1950’s, continuing improvements in aircraft and engine design have significantly reduced the number of accidents based on these factors. High-bypass engine reliability, aircraft design, warning devices, and automation have all had a significant effect on reducing the airline accident rate.

Several major improvements in aircraft systems and technology contribute to the safety record of the industry. These include ground proximity warning devices, traffic alert and collision avoidance systems (TCAS), and new cockpit computers and displays that provide updated weather and flight status information directly to the cockpit.

The introduction of the ground proximity warning system (GPWS) has significantly reduced the number of accidents involving controlled flight into terrain since its introduction in the 1970’s. Controlled flight into terrain occurs when an airworthy aircraft, under the control of the flight crew, is flown unintentionally into terrain, obstacles, or water, usually with no prior awareness by the crew. Because controlled flight into terrain accidents represent the leading cause of aircraft hull losses annually, this safety device is particularly relevant. The GPWS system uses radar altimeter and aircraft configuration information to alert the flight crew of impending terrain. An advanced design, enhanced GPWS (E-GPWS) takes advantage of satellite Global Positioning System (GPS) technology and cockpit computer technology in third-generation aircraft to combine traditional GPWS with terrain mapping and GPS location information. E-GPWS is expected to reduce or eliminate the number of controlled flight into terrain accidents attributable to the flight crew’s loss of situational awareness.

In the decades following World War II, the steady increase in the number of flights by airlines and general aviation aircraft increased the likelihood of midair collisions, especially in the congested airspace over cities. In 1978, a Pacific Southwest Airlines Boeing 727 collided with a single-engine Cessna 172 over a populated area of San Diego, California, resulting in many deaths. In 1986, an Aeromexico DC-9 collided with a single-engine Cherokee over Cerritos, California. The aftermath of this accident and the memory of the 1978 midair accident motivated the FAA and the airlines to develop a technology to augment vision and assist pilots in detecting and avoiding other aircraft. This research led to the development and implementation of traffic alert and collision avoidance systems (TCAS). This system displays other transponder-equipped aircraft within a specified radius. TCAS II, implemented a few years later, gives pilots resolution advisories (RA) either to descend or to climb in order to avoid a collision. Since 1993, TCAS II has been required on all passenger aircraft with more than thirty seats. Commuter aircraft with from ten to thirty seats are required to be equipped with TCAS I.

Pilots widely and readily accept TCAS, finding it an indispensable cockpit tool. TCAS enhances pilots’ situational awareness and assists the visual location of aircraft advisories issued by air traffic control.

Because weather is such an integral part of aviation, improvements in severe weather information, prediction, and depiction have a significant relevance to improving the safety and comfort of flight. Thunderstorms, although easy to detect, have associated hazards, such as lightning, turbulence, heavy precipitation, icing, wind shear, and microbursts, that are more difficult to see and predict. These hazards are most dangerous when the aircraft is low to the ground, as in takeoff and landing. On-board weather detection systems enable pilots to see the thunderstorm and avoid its associated hazards.

Aircraft encounters with turbulence result in upsets and injuries every year. Turbulence accounted for 103 injuries on board commercial aircraft in the period from 1990 to 1999. Although turbulence is not uncommon in flight, the severity of turbulence ranges from uncomfortable to fatal. Types of turbulence include convective turbulence, mountain range turbulence, and clear-air turbulence.

Convective turbulence occurs in localized, vertical air movements. The most hazardous types are usually associated with thunderstorms. Mountain range turbulence, as the name implies, occurs when wind blows across rugged hills or mountains, creating updraft on the windward side and strong downdrafts on the lee side. Lenticular clouds that form on the lee side of a mountain range and cumulus-looking rotor clouds that form parallel to the ridge line of a mountain are indicators of strong winds and occasionally severe downdrafts and associated turbulence.

Clear-air turbulence is rough, bumpy air that sometimes buffets an airplane in a cloudless sky. It is usually found above altitudes of 15,000 feet and is often located near the jet stream winds. It is associated with a drastic change in wind direction, speed, air temperature, and horizontal or vertical wind shear. Research into the detection and avoidance of clear-air turbulence is important to reduce the injuries and fatalities on board aircraft.

Microburst and wind shear are atmospheric phenomena that have been implicated in several major airline accidents. Investigations into these crashes and computer simulations of the events have led to specific training procedures for pilots to escape from these extremely hazardous winds.

Low-level wind shear alerting system (LLWSAS) is a system of anemometers implemented in select airports to give air traffic tower controllers information on wind direction and speed at different locations on the airport. If the wind direction and velocity exceed a predetermined parameter, an alarm will sound in the tower. Timely dissemination of the wind directions and velocities to the pilots help them prepare for or avoid encounter with a wind shear.

Crowded skies inevitably lead to crowded airports. Increased congestion at major airports has consequences on the ground as well as in the airspace above. Although it is a rare occurrence, the ground collision of aircraft accounts for the worst aviation disaster in history: that which occurred between two fully loaded Boeing 747 jumbojets in Tenerife, Canary Islands, in 1977. From 1995 to 2000 there was a 60 percent increase in near-collisions on the ground, according to the NTSB.

The FAA places a high priority on the reduction of the number of runway incursions. New methods for pilots to determine their exact location on the airport in low-visibility or night situations are being researched. Improved airport markings, assessing new technologies, strategic plans for foreign air carrier pilot awareness, training, and review of pilot/controller communications phraseology are among the issues being explored to mitigate this safety problem.

• Boeing Commercial Airplane Group. 1999 Statistical Summary Airplane Safety. Seattle, Wash.: Boeing, 2001. A detailed description of accidents and incidents in table and chart form from 1959-1999.
• Hawkins, Frank H. Human Factors in Flight. 2d ed. Brookfield, Vt.: Ashgate Publishing, 1987. An in-depth textbook on pilot performance and behavior, based on academic sources of knowledge and practical operation of aircraft.
• Krause, Shari S. Aircraft Safety, Accident Investigation, Analysis, and Applications. New York: McGraw-Hill, 1996. A reference book with analysis of accidents caused by human factors, weather, midair collisions, and mechanical failure and their applications to the field.
• O’Hare, David, and Stanley Roscoe. Flightdeck Performance: The Human Factor. Ames: Iowa State University Press, 1990. A well-researched, technical book on accidents and their causes.
• Wells, Alexander T. Air Transportation: A Management Perspective. 4th ed. Belmont, Calif.: Wadsworth, 1999. A textbook covering all major topic areas in the air transportation field.

Accident investigation

Air carriers

Air traffic control

Airline industry, U.S.

Avionics

Cockpit

Communication

Federal Aviation Administration

Flight attendants

Instrumentation

Landing procedures

National Aeronautics and Space Administration

National Transportation Safety Board

Pilots and copilots

Runway collisions

Runways

Takeoff procedures

Taxiing procedures

Training and education

Weather conditions

Wind shear