**1. Introduction**

Man has been fascinated by the flight of birds since the time immemorial. The science of flight from dream to reality was realized by Wright brothers in the year 1903. It was the first instance in the history of aviation that a powered, sustained, and controlled flight of airplane under the control of the pilot was achieved. One can see the tremendous progress made by man in the field of aviation in a short span of about 120 years; from small two-seat ab-initio trainer aircraft such as Cessna 152, to the large wide-body aircraft such as the Airbus A380 and the Boeing 777x, capable of carrying hundreds of passengers at transonic speeds, and Concorde, the first supersonic passenger-carrying commercial airplane.

Aircraft design and production encompass diverse areas such as aerodynamics, flight mechanics and controls, material science, power plant, landing gear and hydraulics, electrical and avionics, stress analysis, vibration, manufacturing techniques, special processes, nondestructive testing, metrology, quality control, assembly, integration, static testing, flight testing, certification aspects, and so on. A set of drawings that provide unambiguous and complete information to manufacture the aircraft is the starting point. It is through these drawings that the ideas of the designer are conveyed to the manufacturer. Manufacturing drawings are further translated into a set of "process sheets" by specialists in methods engineering, and these provide a step-by-step procedure in a lucid manner to the shop floor technicians to execute the work. Likewise, airplane flight manual and quick reference handbooks are made available to the flight test crew. Aircraft maintenance manuals contain clear information about periodic procedures to be adhered to, while carrying out aircraft maintenance activities.

To err is human. It is quite possible that human errors, in some form or the other, can creep into design, manufacturing, flight operation, and maintenance phases in the aviation sector. The error may go unnoticed due to various reasons and can result in catastrophic accidents endangering precious lives of passengers and crew. Nearly 75 percent of civil and military aviation accidents around the globe have been attributed to human errors at various levels. It is, therefore, pertinent to go through the aircraft accident databases available in open literature and bring out the vital factors leading to the disaster.

Aircraft designs have evolved over a period of time, as a result of the lessons learnt from the past accidents and incidents. This is also true when we consider corresponding improvements to airport infrastructure and maintenance facilities. It was during the early 1970s that the discipline of human factors began to draw the attention of international aviation community. Pioneering work has since then been done in the field of human factors to understand why aircraft accidents happen. Human factor models have also undergone continual improvements and adaptations to suit the evergrowing needs of air traffic.

Aviation accident database available in open literature has been used in the current work. Human factor analysis models currently in use have been studied. A new model for human factors analysis is proposed, keeping in view the likely improvements in aircraft designs and potential growth in air traffic in the years to come.

This book chapter is organized as follows. To begin with, summary of civil aviation accidents that have occurred during the last eight decades is presented. This is followed by a few representative case studies to bring out the root cause of the accident. The concept of human factors is introduced, along with brief description of various models in use, to understand the root causes leading to aviation accidents. An example of the application of human factors analysis and classification system (HFACS) framework is narrated. A new "seven-segment" concept is proposed to systematically analyze human factors. Way forward to even safer skies is presented.

#### **2. Civil aviation accidents during the last eight decades**

According to Federal Aviation Administration (FAA), an aircraft accident is defined as an occurrence associated with the operation of an aircraft, which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage [1]. Incident refers to

an occurrence other than an accident, associated with the operation of an aircraft, which affects or could affect the safety of operation; occurrence is an abnormal event, other than an incident or accident. Until an event (for example, low-speed abort) can be identified as an incident, it is regarded as an occurrence. An aviation accident is defined by the Convention on International Civil Aviation Annex 13 as an occurrence associated with the operation of an aircraft, which takes place from the time any person boards the aircraft with the intention of flight until all such persons have disembarked, and in which a) a person is fatally or seriously injured, b) the aircraft sustains significant damage or structural failure, or c) the aircraft is missing or is completely inaccessible [2].

The first fatal accident involving a powered aircraft was the crash of a Wright aircraft at Fort Myer, Virginia, in the United States on September 17, 1908, injuring its co-inventor and pilot, Orville Wright, and killing the passenger, Signal Corps Lieutenant Thomas Selfridge [3]. Orville later determined that the crash was caused by a stress crack in the propeller. The Wrights soon redesigned the Flyer to eliminate the flaws that led to this accident.

**Table 1** summarizes the number of fatal civil airliner accidents from 1945 through February 2022 [4]. At 864, United States is the country with the highest number of fatal civil airliner accidents, followed by Russia, Canada, Brazil, and Colombia. At 43, Argentina has the least fatalities.

**Figure 1** shows the distribution pattern of the number of civil aircraft accidents from the year 1918 through 2022 [5]. **Figure 2** shows the distribution pattern of the number of fatalities for the same period. A total of 28,442 aircraft accidents have resulted in 1,58,798 fatalities. Maximum peak is observed during 1940s, and there is a gradual decrease in the number of accidents from the year 1978. Considering the period between 2001 and 2022, a total of 3769 aircraft accidents have resulted in 20,172 fatalities. Fitting a linear trend line for the data between 2001 and 2022 would indicate a theoretical possibility of aircraft accidents tending to near-zero by mid 2040s.

Apart from potential fatalities, aircraft accidents may result in partial damages to the airframe, or even complete loss of hull, making the aircraft non-airworthy. A recent example is the fatal accident of a domestic passenger aircraft Boeing 737-89P on March 21st, 2022 in China with 123 passengers and nine crew members onboard [5]. The aircraft, whose file photo is shown in **Figure 3**, was scheduled to fly from Kunming to Guangzhou, but plunged midflight and crashed in Wuzhou, in the Guangxi region. All the 132 persons onboard the aircraft were killed in the accident, and the aircraft fully destroyed by the impact. Accident investigation is on. Black boxes of this aircraft are found in a severely damaged condition, making data retrieval a challenge by itself. According to media reports, a preliminary assessment by the US officials has ruled out any mechanical or technical faults with the aircraft, and the aircraft is suspected to have been intentionally put into a nose-dive [6].

On May 29, 2022, a Twin Otter aircraft operated by Tara Air was on a scheduled domestic flight from Pokhara Airport to Jomsom Airport, Nepal. The aircraft lost contact with air traffic controllers about 12 minutes after take-off and crashed in mountainous Mustang district of Nepal, killing all the 19 passengers and three crew members. Black box of the aircraft has been retrieved and accident investigation is ongoing.

In addition to fatalities, as many as 81 aircraft are reported to have gone missing and remain untraced till date [7]. According to a report released by Boeing [8], in the early days of flight, approximately 80 percent of accidents were caused by the machine and 20 percent were caused by human error. The trend has since then

#### *Aeronautics - New Advances*


#### **Table 1.**

*Countries/regions with the highest number of fatal civil airliner accidents since 1945.*

reversed, and now approximately 80 percent of the airplane accidents are caused due to human error (pilots, air traffic controllers, mechanics, etc.) and the remaining due to equipment failures. According to an analysis of 75 fatal airplane accidents carried out [9], over 70 percent of the accidents involved pilot factors mostly related to poor judgment and decision-making.
