The AirSafe.com News: Do plane crashes happen in threes? - yes, and sometimes in fours and fives

Note:This an updated version of an article first published in February 2009

Since AirSafe.com was launched in 1996, the site has tracked fatal events and other significant events involving airline passengers. When these events occur, especially if two occur a just a few days apart, I sometimes get the "Do bad things like plane crashes always happen in threes?" question asked by visitors to the site, by members of the media, and by others.

I used to just dismiss the question out of hand because events like plane crashes, especially those involving passenger airliners, are very rare, and the circumstances are usually very different for each crash, often involving different airlines, different aircraft types, and even different countries.

Although it's easy to reject the original question, it is quite legitimate to ask a related question about how frequently groups of rare events occur over a relatively short period of time.

One day, just for fun, I turned the "things happening in threes" question into something that could be analyzed systematically using the information within AirSafe.com. I changed the general question into the following specific question: "How frequent are sequences of three or more fatal or significant aviation safety and security events where the time between events is ten days or less?"

For example, a sequence of three events could happen on the same day, or it could be over a period as long as 20 days, with a 10-day gap between the first and second event, and another 10-day gap between the second and third event.

The most recent sequence of three events took place over the course of seven days beginning with the crash of Malaysia Airlines flight MH17 on July 17th, followed by the crash of an TransAsia ATR airliner in Taiwan on July 23th, and ending with the crash of an Air Algerie MD83 in Mali on July 24th.

For the purposes of answering this question, I limited the data to those events that are regularly tracked by AirSafe.com. These would be plane crashes or other airline events that kill at least one passenger, or other events that AirSafe.com considers to be significant with respect to aviation safety or aviation security.

Multiple events due to the same cause (for example, the four crashes associated with 9/11) were treated as one event. Significant events that don't kill anyone sometimes attract more media attention than the average plane crash. The January 2008 ditching of a US Airways A320 in the Hudson River in New York was one example. It was very dramatic, it got a huge amount of media exposure, and no one was killed.

A review of the AirSafe.com records from 1996, the year AirSafe.com was launched, to July 2014 revealed some interesting facts:

With the exception of 2007, 2009, and 2013, every year since 1996 included at least one sequence of three fatal or significant events that were separated by no more than ten days. There was a sequence of five significant, but nonfatal, events in January 2008 (one of which involved Senator Barack Obama), and a sequence of eight events in 2010, seven of which involved fatalities.
There were 25 sequences of three or more events that were separated no more than ten days. One was a sequence of eight events, three were sequences of five events, five sequences had four events, and the other sixteen 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 fatal events that were a part of one of these sequences include the Swissair MD-11 crash in 1998, the Concorde crash in 2000, the August 2006 crash of a Comair jet, in Lexington, KY, the August 2008 crash of a Spanair MD83 in Madrid, and the July 2014 crash of Malaysia Airlines flight MH17.
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, the four crashes associated with 9/11, and the March 2014 loss of Malaysia Airlines flight MH370.
For 16 of the past 19 calendar years (1996 to 2014), there has been at least one grouping of three or more fatal or significant events that occurred over a relatively short period.
No information has come about in the investigations of any of those events that indicates that there was any sort of connection among the crashes that were part of a sequence of three or more events, or that suggested that earlier events in a sequence made a later event more likely.

After reviewing the facts, I no longer say that plane crashes don't happen in threes. Since 1996, they have happened in sequences of three, four, five, and eight.

- Todd Curtis

Fatal and serious events by year
1996, 1997, 1998, 1999, 2000
2001, 2002,2003, 2004, 2005
2006, 2007, 2008, 2009, 2010
2011, 2012, 2013, 2014

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