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

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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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Related information
26 July 2014 - Todd Curtis discusses his findings on the Rudy Maxa Show (6:44)
Related article from Patrick Smith of AskThePilot.com
Losing three airliners in one week is not that rare

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AirSafe.com's Airline Safety Review for 2008

The year 2008 had the fewest fatal airline crashes in any year since AirSafe.com began it's annual review of airline safety events in 1996. This 13th annual review discusses seven fatal airline events, and fifteen other significant events from 2008.

As AirSafe.com looks back at the fatal and significant aviation safety events of last year, the most noticeable fact about this 13th annual review is that 2008 had fewer fatal airline events than any of the previous 12 years reviewed by AirSafe.com. The most was 19 fatal events in 1997, and the previous low was eight fatal events in 2003, 2006, and 2007.

AirSafe.com counts as a fatal event any airline flight where one or more passengers are killed, including those events involving hijacking, sabotage, and military action. This review counts only those events that occur on aircraft that can carry at least 10 passengers, and that are commonly used in regular airline service in North America, Western Europe, Australia, and Japan. Significant events are those events that were noteworthy for other reasons. Several of these 15 significant events were non-fatal events involving large jet airliners, but others included crashes involving celebrities, military aircraft, and smaller airline aircraft.

One of the more interesting observations from the 2008 review is that it represents the second consecutive year with no fatal airline events involving the US or Canada. That includes any US or Canadian airliner operating anywhere in the world, or any other airliner operating to or from the US or Canada. The last such event was the crash of a US airliner in Kentucky in August 2006. Since the introduction of jet airliner service to North America in 1958, there had been no previous two year period with zero airliner passenger fatalities.

To put this in a global context, Canada and the US account for about 60% of all airline traffic involving larger aircraft. In other words, 40% of these kinds of airline flights were responsible for 100% of the fatal passenger events. In 2008, the seven fatal events included one airliner from Europe, two each from Africa and Latin America, and two from countries of the former Soviet Union.

The fifteen other events in AirSafe.com's review were included either because of the amount of media attention they attracted, or because of the safety and security issues associated with the event. Among these 15 significant events were seven non-fatal jet airliner events. The most recent was a December 20 takeoff accident involving a Continental Airlines 737 in Denver. Although the plane experienced significant structural damage and a post-crash fire, all passengers and crew members successfully evacuated the aircraft.

The other significant airliner events included the first ever crash of a 777, two in-flight events involving Qantas, another two involving Air Canada, and a takeoff accident involving Iran Air.

The other eight significant events included an F/A-18 crash in San Diego, four fatal crashes involving small airliners, and three crashes involving celebrities. Rev. Sun Myung Moon, the head of the Unification Church, survived a helicopter crash in South Korea; Travis Barker, former drummer for the music group Blink-182, was one of two survivors of a crash of a chartered jet in South Carolina, and President-Elect Barack Obama was on board a plane that had a collision with a parked aircraft on the ground in Chicago.

For more information on all of these 2008 events, including links to incident reports, investigation updates, plane crash videos, and podcasts, please visit 2008.AirSafe.org. There you will also find links to additional information such as what you can bring on board, lists of banned items, instructions on how to successfully complain about your air travel experience, and fear of flying advice.

Listen to the Annual Review for 2008

Senator Barack Obama Involved in Aircraft Mishap on 12 January 2008

United States Senator and presidential candidate Barack Obama was a passenger in a Gulfstream 2 aircraft that collided with another aircraft on the ground at Midway Airport in Chicago. Senator Obama, members of his campaign staff, and Secret Service agents had just flown in from Nevada, where he had been campaigning. The left wingtip of the Gulfstream hit the right wingtip of a parked and unoccupied Cessna 208 aircraft.The impact was so minor that no one on the plane noticed any damage until later.

While the incident caused no injuries and only minor aircraft damage, it does bring up a potential public policy issue. Specifically, the issue of what should be considered an acceptable air transportation risk for presidential candidates. A comparison can be made with the policy on Secret Service protection for presidential candidates. Prior to the assassination of the presidential candidate Senator Robert F. Kennedy in 1968, there were no clear standards or legal requirements for physical security of presidential candidates. Security decisions were largely left up to local law enforcement and to the candidates' campaign staffs. After the assassination, the US Congress authorized protection of major presidential and vice presidential candidates and nominees.

The nature of the US presidential electoral process demands that candidates have to travel a great deal during the months leading up to the election. The candidates typically use a variety of air travel options, from scheduled commercial airliners to privately chartered aircraft. While there are risks with any type of air travel, the risks are higher for some kinds of flights. Senator Obama's aircraft was operating as a nonscheduled air carrier flight under Part 135 of the Federal Aviation Regulations, which are less strict than the Part 121 regulations for larger air carrier aircraft, and more strict than the Part 91 regulations for general aviation. Historically, the accident risk has been highest for Part 91 flight operations, significantly lower for Part 135 operations, and lower still for Part 121 operations. For example, in 2006 the NTSB estimated that the accident rate for general aviation flights was about four times greater than the Part 135 accident rate, and about 50 times greater than the rate for Part 121 air carrier flights.

The potential policy issue is whether exposure to air travel risks faced by presidential candidates should be limited by requiring that flights taken by candidates meet some minimum standard. A realistic limitation could take many forms, such as use of only approved aircraft operators or airlines, or perhaps requiring that candidates use government or military air transportation. The reasons for even considering such a a policy are the potentially negative political and social impacts of having a candidate seriously injured or killed during a campaign, especially from managable risks such as those associated with air travel.

Fortunately, Senator Obama was not injured in his aircraft mishap. However, given the risks that he and the other candidates will continue to face, it seems reasonable to consider some kind of risk reduction policy now, and by doing so perhaps preventing a catastrophic disruption to the political process.

Related Resources
Selected Fatal Events Involving US Political Figures
NTSB Accident Rate Estimates for 2006