A Human Error Approach to Aviation Accident Analysis

The Human Factors Analysis and Classification System

Douglas A. Wiegmann, Scott A. Shappell

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351962353
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Aeronautic & Astronautic Engineering
• Index: Technology & Engineering

Human error is implicated in nearly all aviation accidents, yet most investigation and prevention programs are not designed around any theoretical framework of human error. Appropriate for all levels of expertise, the book provides the knowledge and tools required to conduct a human error analysis of accidents, regardless of operational setting (i.e. military, commercial, or general aviation). The book contains a complete description of the Human Factors Analysis and Classification System (HFACS), which incorporates James Reason's model of latent and active failures as a foundation. Widely disseminated among military and civilian organizations, HFACS encompasses all aspects of human error, including the conditions of operators and elements of supervisory and organizational failure. It attracts a very broad readership. Specifically, the book serves as the main textbook for a course in aviation accident investigation taught by one of the authors at the University of Illinois. This book will also be used in courses designed for military safety officers and flight surgeons in the U.S. Navy, Army and the Canadian Defense Force, who currently utilize the HFACS system during aviation accident investigations. Additionally, the book has been incorporated into the popular workshop on accident analysis and prevention provided by the authors at several professional conferences world-wide. The book is also targeted for students attending Embry-Riddle Aeronautical University which has satellite campuses throughout the world and offers a course in human factors accident investigation for many of its majors. In addition, the book will be incorporated into courses offered by Transportation Safety International and the Southern California Safety Institute. Finally, this book serves as an excellent reference guide for many safety professionals and investigators already in the field.

1
Errare Humanum Est – To Err is Human

On September 17^th … at 4:46 pm, the aeroplane was taken from the shed, moved to the upper end of the field and set on the starting track. Mr. Wright and Lieutenant Selfridge took their places in the machine, and it started at 5:14, circling the field to the left as usual. It had been in the air four minutes and 18 seconds, had circled the field 4½ times and had just crossed the aeroplane shed at the lower end of the field when I heard a report then saw a section of the propeller blade flutter to the ground. I judged the machine at the time was at a height of about 150 feet. It appeared to glide down for perhaps 75 feet, advancing in the meantime about 200 feet. At this point it seemed to me to stop, turn so as to head up the field towards the hospital, rock like a ship in rough water, then drop straight to the ground the remaining 75 feet…

The pieces of propeller blade [were] picked up at a point 200 feet west of where the airplane struck. It was 2½ feet long, was a part of the right propeller, and from the marks on it had apparently come in contact with the upper guywire running to the rear rudder. … [The propeller] struck [the guywire] hard enough to pull it out of its socket and at the same time to break the propeller. The rear rudder then fell to the side and the air striking this from beneath, as the machine started to glide down, gave an upward tendency to the rear of the machine, which increased until the equilibrium was entirely lost. Then the aeroplane pitched forward and fell straight down, the left wings striking before the right. It landed on the front end of the skids, and they, as well as the front rudder was crushed.

Lieutenant Selfridge … died at 8:10 that evening of a fracture of the skull over the eye, which was undoubtedly caused by his head striking one of the wooden supports or possibly one of the wires. … Mr. Wright was found to have two or three ribs broken, a cut over the eye, also on the lip, and the left thigh broken between the hip and the knee (1^st Lieutenant Frank P. Lalm, 1908).

Note, this pioneer of aviation safety was actually Frank P. Lahm, not Lalm as identified in this letter to the Chief of the Army Signal Corps.

What began as an unofficial orientation flight at Fort Meyer, Virginia in the summer of 1908, ended in tragedy, as have many flights since. Sadly, the annals of aviation history are littered with accidents and tragic losses such as this (Figure 1.1).

Since the late 1950s, however, the drive to reduce the accident rate has yielded unprecedented levels of safety. In fact, today it is likely safer to fly in a commercial airliner than to drive a car or walk across a busy New York City street. Still, it is interesting that while historians can recount in detail the strides that the aviation industry has made over the last half century, one fundamental question remains generally unanswered: “Why do aircraft crash?”

Figure 1.1 The first fatal aviation accident

Source: arlingtoncemetary.com

The answer may not be as straightforward as you think. For example, in the early years of aviation it could reasonably be said that the aircraft itself was responsible for the majority of aircraft accidents. That is, early aircraft were intrinsically unforgiving and, relative to their counterparts today, mechanically unsafe. However, the modern era of aviation has witnessed an ironic reversal of sorts. It now appears to some that the aircrew themselves are more deadly than the aircraft they fly (Mason, 1993; cited in Murray, 1997). Indeed, estimates in the literature indicate that somewhere between 70 and 80 percent of all aviation accidents can be attributed, at least in part, to human error (Shappell and Wiegmann, 1996).

So, maybe we can answer the larger question of why aircraft crash, if only we could define what really constitutes that 70 to 80 percent of human error referred to in the literature. But, even if we did know, could we ever really hope to do anything about it? After all, errare humanum est — to err is human (Plutarch, c.100 AD). So, isn’t it unreasonable to expect error-free human performance? Maybe … but, perhaps a lesson in how far aviation safety has come since its inauspicious beginnings nearly a century ago will provide us with some clues about where we need to go next.

Aviation Safety Trends

Figure 1.2 Overall (top) and fatal (bottom) commercial air carrier accidents worldwide 1961-99

Most aviation accident statistics cited in the literature today begin with data collected in the late 1950s and early 1960s. Representative of this type of data are the two graphs presented in Figure 1.2. In the top graph, the number of commercial aviation accidents that have occurred worldwide since 1961 are plotted annually against the number of departures. When the data are depicted in this manner, a sharp decline in the accident rate since the early 1960s becomes readily apparent. In fact, the number of commercial accidents has decreased to a point where today, fewer than two accidents occur worldwide for every one million departures (Boeing, 2000; Flight Safety Foundation [FSF], 1997). What’s more, this trend is generally the same (albeit not as dramatic), whether you consider the overall number of commercial aviation accidents, or just those associated with fatalities. In either case, it can reasonably be said that commercial aviation safety has steadily improved over the last 40 years. Indeed, aviation has become one of the safest forms of transportation, leading the National Transportation Safety Board to proclaim in 1990 that a passenger boarding a U.S. carrier then had over a 99.99 percent chance of surviving the flight (NTSB, 1994a).

Figure 1.3 Accident trends for U.S. general and military aviation

Improvements in aviation safety, however, are not unique to commercial aviation. General aviation accident rates have also plummeted over the last several decades (Figure 1.3, top). A similar trend can also be seen when accident data from the U.S. Navy/Marine Corps (middle) and U.S. Air Force (bottom) are plotted across years. Indeed, the accident rates among these diverse types of flying operations have dropped impressively since the late 1950s and early 1960s, indicating that all aspects of aviation have benefited from advances aimed at making the skies safer.

So, what can we attribute these improvements in aviation safety to over the last half-century? Given the rather dramatic changes evident in the accident record, it is doubtful that any single intervention was responsible for the decline in the accident rate. Rather, it is likely the result of a variety of factors, such as advancements in technology, equipment, operating procedures, and training practices (Nagel, 1988; Yacavone, 1993).

Figure 1.4 U.S. Naval aviation accident rate and intervention strategies across calendar years 1950 to 2000

Source: U.S. Naval Safety Center

To give you a better feel for how various interventions have improved aviation safety, let us consider several of these initiatives within the context of Naval aviation. In Figure 1.4, a number of technical innovations and standardization programs introduced into the U.S. Navy/Marine Corps over the last several decades have been superimposed on the annual accident rate. Arguably, these efforts were not solely responsible for the decline observed in the accident rate. After all, nowhere does this figure address improvements in aircraft design and the introduction of new aircraft in the fleet. Still, there is little question among Naval experts that these interventions played a significant role in the level of safety currently enjoyed by the U.S. Navy/Marine Corps.

Figure 1.5 Original straight carrier flight deck (top) and improved angled carrier flight deck (bottom)

Source: U.S. Navy

Consider, for example, the development of the angled carrier deck aboard Naval aircraft carriers in the early to mid-1950s. Many Naval history buffs may recall that early aircraft carrier flight decks were single straight runways, which created a number of safety problems - especially when one aircraft was trying to take off from the bow of the ship while another was unexpectedly aborting a landing on the stern (Figure 1.5, top). Not surprising, aircraft would occasionally collide! To remedy this safety hazard, the angled carrier deck was developed, which allowed aircraft to take off from the bow of the ship in a different direction from those landing on the stern, avoiding any potential conflict in their flight paths; a very wise intervention indeed (Figure 1.5, bottom).

Another major factor affecting safety in the U.S. Navy/Marine Corps was the establishment of the Naval Aviation Safety Center (now known as the Naval Safety Center) in the mid-1950s. On the surface, this might not seem to be particularly revolutionary given today’s standards. However, for the first time, a major command in the U.S. Navy was assigned the sole responsibility and authority for monitoring and regulating safety issues in the fleet. This single act elevated aviation safety to the highest levels of the U.S. Navy/Marine Corps, as the command reported directly to the Chief of Naval Operations.

Still, other safety programs have helped improve Naval aviation safety as well. For example, in the early 1960s, the replacement air group concept was created, requiring pilots to receive specialized training in advanced aircraft before flying them in the fleet. While it may sound intuitive to some that pilots should gain some tactical experience in their aircraft before flying them in combat or other operations, this was not always the case. As recently as WWII, pilots would receive basic flight training and then transition to the fleet, entering the operational arena with very little time in their combat aircraft.

More recently, the establishment of formal squadron safety programs, the development of aircrew coordination training, and the implementation of a periodic human factors review of fleet aviators have all contributed significantly to Naval aviation safety by identifying problems and hazards before they resulted in accidents. Undeniably, safety initiatives such as these have saved countless lives in the U.S. Navy/Marine Corps and have elevated Naval aviation safety to unprecedented levels.

Beyond saving lives, the military, like any other business, is often driven by the so-called “bean counters.’* Yet, even the bean counters have to be smiling when you consider the cost savings realized as a result of improvements in aviation safety. Consider that until recently the U.S. Navy/Marine Corps flew an average of 2 million flight hours per year (today it’s closer to 1.5 million flight hours per year). If the rate of major accidents today were still at levels observed in 1950, over 800 aircraft would have been lost in 2000 alone! Needless to say, the U.S. Navy/Marine Corps would be quickly out of the aviation business altogether, if that were the case. Thankfully, improvements in all forms of aviation safety, including Naval aviation, have remedied this trend.

Some Reasons for Concern

Even though the overall accident rate in civil and military aviation is indeed excellent, certain aspects of the data are “unsettling” (Nagel, 1988, p. 264). As can be seen from the graphs presented earlier, improvements in aviation safety have slowed substantially during the last few decades. This plateau has led some to conclude that further reductions in the accident rate are improbable, if not impossible. In other words, we have reached a point at which accidents may simply be the “cost of doing business.” However, if we accept this philosophy we must also be prepared to accept the consequences. For example, on the military side of aviation, the financial cost of aircraft accidents is growing astronomically. As illustrated in Figure 1.6, the amount of money and resources lost due to U.S. Naval aviation accidents is enormous, even though these accidents occur much less frequently than other types. Indeed, the loss incurred from aviation accidents cost the U.S. Navy/Marine Corps some 3.3 billion in the last five years alone - more than five times that seen with all other accidents combined. Obviously, if the mishap rate were allowed to continue at its current level, either taxes would have to go up to buy more airplanes (not a politically popular option), or the military would have to operate with fewer and fewer aircraft (not a strategically savvy move either).

Figure 1.6 Monetary costs of accidents in the U.S. Navy/Marine Corps from fiscal year 1996 to 2000

Source: Fraser (2002)

There may be reason for concern within commercial aviation as well. Consider, for example, that worldwide air traffic is expected to increase significantly over the next several years as the industry continues to grow (FSF, 1997). Now let’s assume for the moment that the current commercial accident rate is already “as good as it’s going to get.” Naturally, if you increase the number of flights while maintaining the same accident rate, the overall frequency of accidents will inevitably increase as well. To illustrate this point, the current commercial jet accident rate, expected traffic growth, and frequency of accidents have been plotted together in Figure 1.7. Sadly, if these estimates remain unchanged, there may be as many as 50 major airline accidents occurring worldwide per year during the first decade of the new millennium. This equates to nearly one accident a week!

Figure 1.7 Number of commercial jet accidents, accident rates, and traffic growth - past, present, and future

Source: Flight S...