Do Things Happen in Threes?

Do Things Happen in Threes?

By Dr. Todd Curtis

In the first seven months of 2005, there were relatively few events that threatened the lives of airline passengers. AirSafe.com identified only three fatal events in the first seven months of the year, a rate that if it continued would have made 2005 the year with the fewest serious events since AirSafe.com began tracking such events in 1996. However, August of 2005 was a completely different story. Starting with the August 2nd crash of an Air France A340 in Toronto, AirSafe.com identified five events, with all but the Toronto event involving fatalities.

A string of events such as these often leads to questions about safety from the AirSafe.com audience. Many of the common questions, such as where is the safest place to sit, are answered at the site's "Top 10 Airline Safety Questions" page at http://www.airsafe.com/ten_faq.htm. One other question that came up during August was "Do accidents always happen in threes?" It is easy to dismiss these types of questions out of hand because accidents, especially fatal ones, are extremely rare and the events that lead to these accidents often have little in common. For example, the five noteworthy events in August involved five different airlines, four different aircraft types and occurred in five different countries on three continents.

While it is easy to ignore the question of "do accidents happen in threes?" because it seems to imply that one event somehow causes two more events to occur, it is quite legitimate to ask a related question about how frequently groups of events occur over a relatively short period of time. Using the information within the AirSafe.com site, the following question was addressed: "How frequent are sequences of three or more significant aviation safety and security events where the time between events is ten days or less?"

For the purposes of answering this question, a significant event is one that is a fatal event as defined by AirSafe.com (see http://www.airsafe.com/events/method.htm for a detailed definition of a fatal event), or an event that is not a fatal event but is considered to be significant to civil aviation safety and security. For the purposes of answering this question, multiple fatal events due to the same cause (for example, the four fatal events associated with 9/11) were treated as one event. Significant events that are not fatal events are aviation related events that attract abundant media attention and public scrutiny. The August 2005 crash of the Air France A340 in Toronto is one example of a significant event that is not a fatal event.

AirSafe.com has tracked fatal events and significant events since 1996. A review of the AirSafe.com records revealed some interesting observations:

Every year except 1996 included at least one sequence of three significant events that were separated by ten days or less.

There were ten sequences of three or more significant events that were separated by ten days or less. Two were sequences of five events, two sequences had four events, and the other six consisted of three events each.

Most of the fatal and significant events tracked from 1996 to the present were not part of any sequence of three or more events.

Well-known events that were a part of one of these sequences include the Swissair MD-11 crash in 1998, the Concorde crash in 2000, and last month's crash of the Air France A340 in Toronto.

Well-known events that were not a part of one of these sequences include the ValuJet and TWA Flight 800 crashes in 1996, the Alaska Airlines crash in 2000, and the four crashes associated with 9/11.

For the past nine years, there has been at least one grouping of three or more fatal or significant events that occurred over a relatively short period. At the same time, no information has come about in the investigations of any of those events that indicates that there was any sort of cause and effect relationship among the events within those sequences.

After a review of the facts, one may reject the hypothesis that "things always happen in threes," but one must accept the reality that sometimes things happen in threes or fours or fives. Let us all hope that there are no sixes and sevens lurking about.

Dr. Todd Curtis is president of the AirSafe.com Foundation and creator of the web site AirSafe.com. Todd Curtis conducted research in several areas of aviation risk assessment and accident prevention. Author of the book Understanding Aviation Safety Data as well as a number of articles on Web site planning and airline safety. Licensed private pilot.