Quora Question: What Is the Number One Cause of Airline Crashes?

Emergency teams remove pieces of wreckage at the site of the crashed TransAsia Airways plane Flight GE235 in New Taipei City February 5, 2015. Pichi Chuang/Reuters

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Answer from Tom Farrier, International Society of Air Safety Investigators (ISASI); more than 25 years' accident investigation experience.

You know you've asked a great question when it makes an expert start to answer, then stop, scratch his/her head, and go, "Hmm."

Short, sweet answer to your question: loss of control in flight, followed by controlled flight into terrain (CFIT). However, both types of accidents have markedly decreased over the last 20 years, by half in the former's case and by a third for the latter.

The nature of aircraft accidents in general has changed in ways both dramatic and subtle over the last 20 years or so. The really interesting aspect of this is that it's clear where emphasis on certain types of accidents has really borne fruit.

In the wake of the TWA 800 tragedy, two bodies were chartered—one by President Clinton, the other by Congress—to look at the state of aviation safety. Their reports may be found at FEBRUARY 12, 1997 and pepele, respectively. Apart from showing some truly visionary thinking (for example, "safety management systems" were conceptualized by the former years before ICAO and the FAA actually implemented them in the aviation environment), they suggested some "stretch goals" for accident reduction.

In response, the FAA, major airframe and engine manufacturers and major air carriers banded together in a government-industry effort known as the Commercial Aviation Safety Team. CAST agreed to use a popular annual compilation of aircraft accident data published by the Boeing Company as their basis for bench-marking progress.

When CAST looked at fatal accidents arrayed by the types of accidents in which they're experienced in a Pareto chart, it looked like this:

The Flight Safety Foundation already had been aggressively promoting their "Approach and Landing Accident Reduction" (ALAR) initiative for some time when CAST started its work. However, CAST wanted to make sure properly targeted efforts were made toward all of the issues underlying fatal accidents. So, they subjected each of the "tall bars" in the Pareto chart to separate "joint safety analysis team" (JSAT) studies, which were then translated into proposed courses of action by follow-on "joint safety implementation teams."

Most of the first round of CAST analyses were completed in the 2003-2004 timeframe. Compare the following Pareto chart with the one above:

Due to some taxonomy changes that took place in the intervening years, these don't allow a perfect apples-to-apples comparison, but they reflect enough of the same information organized in basically the same way to allow several observations:

1. Although TWA 800 was the precipitating accident that started all of this work (and despite years of wrangling over a hugely expensive change to fuel tank airworthiness requirements that only a relative handful of advocates considered necessary), TWA 800 has been the only accident attributable to a fuel tank explosion. There hasn't been a fatal accident involving such an event since.

2. Landing accidents have remained stubbornly resistant to reduction, despite major emphasis on stabilized approaches and better navigational aid support for most aircraft and airports. Unsurprising, given that aircraft are still moving pretty fast and aren't very maneuverable as they approach touchdown, but frustrating from a prevention perspective nonetheless.

3. The near-universal use of terrain awareness/avoidance warning systems (TAWS) on commercial airliners has significantly decreased CFIT accidents.

4. A major push by the FAA to combat "runway incursions" (aircraft, vehicles and people on runways when they shouldn't be) after the turn of the century was extremely successful.

5. CAST recommended "safety enhancements" for loss of control prevention and protection in three areas: aircraft design, policies and procedures, and aircrew training. (Page on cast-safety.org) Although the number of such accidents (and corresponding loss of life) has decreased substantially since the turn of the century, clearly there's more to be done in all of these areas.

6. In-flight fires and takeoff accidents have all but been eliminated; weather-related accidents seem to have tailed off, but 2014 may bump that category back onto the chart depending on the outcome of a couple of ongoing accident investigations.

Bottom line: regulators and the aviation industry looked at the numbers, attacked the problems that loomed largest, and have made a real difference over the past two decades. Nobody's resting on their laurels, but the numbers document the progress that's been made to date.

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