Unless the already low accident rate in aviation is reduced even further, the increased traffic volume will lead to an average of 25 accidents per year, with over 1,000 fatalities. Because 70% to 80% of all aviation accidents are considered to involve human error, one promising avenue appears to be investments in a better understanding of, and better support for, human performance and human-machine interaction. This includes improved system and feedback design as well as new forms of pilot training to reduce the potential for errors and their catastrophic consequences . Although the need for introducing these changes is widely recognized, progress is slow and faces a number of challenges. The economic pressure and competition in the worldwide aviation industry are intense, and manufacturers and carriers are careful not to invest in proposed solutions without guaranteed safety (and financial) paybacks. In addition, the time of national standards and regulations in the aviation domain has ended. Many proposed changes in design, training, or operations need to be accepted and applied worldwide. This need for international consensus slows down, and sometimes prevents, progress. Yet another obstacle is the fact that some in the aviation industry still consider increased automation to be the solution to, rather than a potential source of, human factors problems. To them, observed difficulties are the consequence of human error rather than symptoms of mismatches between human(s), machine(s), and the environment in which they collaborate . In the post-September 11, 2001 environment, such air accident investigations have assumed new importance and relevance, which directly relates to the problem considered in this study which is discussed further below.
1.1 Statement of the Problem
Airline operating conditions that may affect aircraft damage severity include flying conditions, phase of aircraft flight, pilot utilization, and type of airline service (Phillips & Talley) . Between 1989 and 1997, there was an increase in the rate of accidents caused by ground crew error. Most of these accidents did not result in serious injury or loss of life but rather were accidents in which a vehicle such as a catering or fuel truck collided with an aircraft and damaged it or in which an aircraft was pushed back from the gate into another aircraft that was taxiing past (Oster et al.) . In some cases, these types of aviation accidents may reflect an increase in inexperienced ground crew resulting from the industry's rapid growth in recent years following deregulation; however, in other cases, the most probable cause of such aviation accidents is increased ground congestion at many of the nation's airports . Although airline traffic grew substantially in the latter part of the 1990s, airport capacity has grown very little in the past two decades and the result has been more aircraft trying to operate at the same time in the same limited amount of space . Today, an average of one time every day there is a safety-related accident, incident, or threat reported in the U.S., with the majority of incidents going unreported. The press usually covers only major accidents that result in total and absolute fatalities (Some reasons why planes crash) .
1.2 Purpose of Study
The purpose of this study was to provide a comprehensive analysis of the relevant literature concerning air accidents and their investigation to identify current issues, problems and trends that bear further investigation.
1.3 Importance of Study
The aviation industry represents a strategic component of the nation's security infrastructure, as well as an essential part of the economy. Furthermore, despite the challenges faced by the aviation industry following the terrorist attacks of September 11, 2001 and the escalating costs of energy, the United States continues to rely on air travel for a wide variety of personal, business and military purposes. In this environment, identifying opportunities for improving current approaches to air accident investigations just makes good business sense, and represents a timely enterprise that can contribute to the growing body of knowledge.
1.4 Scope of Study
While air accidents and their investigations were reviewed from different countries, there was a specific focus on the United States.