Just How Dangerous Are Helicopters, Anyway?

by Joe De Maio


Helicopters have a bad reputation. Many people unfamiliar with them think that helicopters are a collection of rotating parts, ready to fly apart and cause disaster at any time. Or they have seen a tail rotor shot off by a missile in an action movie and picture themselves spiraling to the ground, victims of inherent instability. People have had to make judgements about the riskiness of helicopter flight without good information, not because data about helicopter safety doesn’t exist, but because it had never been organized to give a clear picture of the risks of helicopter flight. At NASA Ames Research Center we undertook to develop such an organization of the data from over one thousand helicopter accidents investigated by the NTSB. [See information below on the study report.]

We began by asking what is the risk of a helicopter accident, and how does that risk compare to risk associated with other modes of travel. When we compared helicopters to airliners, we found that airliners have an accident rate (per departure) about one tenth that of helicopters, no surprise there. We were somewhat surprised that about 10% of accidents involve fatalities for both airliners and helicopters. This means that fatal accidents are about ten times more likely for helicopters, because accidents generally are about ten times more likely, but the accidents themselves are neither more nor less fatal.

Of course, airliners and helicopters are apples and oranges, differing in size, speed, flight environment and pilot population. General aviation aircraft as a group are much more similar to helicopters, minus the rotating parts. And their accident rate is more similar too. In fact the accident rate (per hour) for helicopters and general aviation is nearly identical, about eight accidents per 100,000 hours. Again about one tenth of accidents involve fatalities.

So maybe smaller vehicles are just more dangerous. Then what about cars? They are small. And we all know that the most dangerous part of any flight is the drive to the airport. The automobile safety data is measured in miles, not hours, so we used an average speed of 33.3 MPH to convert it to hours. Then we got a surprise. Not only were cars safer than helicopters, by a factor of twenty, they were safer than airliners, by a factor of two! Of course airliners travel about ten times faster than cars, so their accident rate per mile is about five times lower. In any case small size does not lead to high risk.

When we looked into helicopter accidents in detail, we found that some missions have their own special risks. For example aerial applicators (both fixed and rotary wing) are at greater risk for wire strikes. But mission risks do not account for the higher general accident rate.

We looked at accidents as function of helicopter cost. More expensive helicopters show a much lower accident rate than do less expensive helicopters. In fact the rate for very expensive helicopters is nearly the same as that for airliners. At the other end of the cost spectrum, inexpensive helicopters have the highest accident rate and account for most helicopter accidents. Low-end helicopter accidents are less severe then those that happen to more expensive helicopters. The pilots of more expensive helicopters avoid situations that lead to less severe accidents, or they respond to these situations to avoid an accident.

Pilot training, experience and judgement may be the most important factors in safe flight. Personal and instructional flying account for the bulk of accidents, and these are done mostly in low cost helicopters. Personal pilots have different types of accidents from professional pilots. The predominant first event of personal accidents is loss of control. For all types of flying for hire, loss of engine power is the most common first event. Personal pilots and students make up the least experienced part of the pilot population, and personal pilots are the most inclined to neglect safety rules and recommendations.

What it comes down to is that for helicopters, as for other vehicles, the part most likely to cause an accident is the nut behind the controls. So fly as if your life depends on it, because it does!

Source: http://safecopter.arc.nasa.gov/Pages/XXX/Stray%20Pieces/Joe.html (March 25, 2004)


An Analysis of US Civil Rotorcraft Accidents by Cost and Injury (1990 - 1996)

Authors: Iseler, Laura; De Maio, Joe; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION, MOFFETT FIELD, CA, AMES RESEARCH CENTER

Abstract: A study of rotorcraft accidents was conducted to identify safety issues and research areas that might lead to a reduction in rotorcraft accidents and fatalities. The primary source of data was summaries of National Transportation Safety Board (NTSB) accident reports. From 1990 to 1996, the NTSB documented 1396 civil rotorcraft accidents in the United States in which 491 people were killed. The rotorcraft data were compared to airline and general aviation data to determine the relative safety of rotorcrafi compared to other segments of the aviation industry. In depth analysis of the rotorcrafi data addressed demographics, mission, and operational factors. Rotorcraft were found to have an accident rate about ten times that of commercial airliners and about the same as that of general aviation. The likelihood that an accident would be fatal was about equal for all three classes of operation. The most dramatic division in rotorcrafi accidents is between flights flown by private pilots versus professional pilots. Private pilots, flying low cost aircraft in benign environinents, have accidents that are due, in large part, to their own errors. Professional pilots, in contrast, are more likely to have accidents that are a result of exacting missions or use of specialized equipment. For both groups judgement error is more likely to lead to a fatal accident than are other types of causes. Several approaches to improving the rotorcraft accident rate are recommended. These mostly address improvement in the training of new pilots and improving the safety awareness of private pilots.

Limitations: APPROVED FOR PUBLIC RELEASE

Description: Technical memo.

Pages: 34

Report Date: MAY 2002

Report number: A442804