A Summary of Unmanned Aircraft Accident/Incident Data: Human Factors Implications - Part 2
Navy Data
Information regarding UA accidents for the Navy was collected from the Naval Safety Center. A summary of UA mishaps occurring between 1986 and 2002 was received from the Naval UA Pioneer training command in Pensacola, Florida, via the Naval Safety Center (Kordeen Kor, personal communication). The summary lists 239 mishaps, including the mishap level, date, location, and a brief description. The brief description, while not providing much detail, allowed the general classification of the mishap, including whether the mishap was or was not related to human factors.
Air Force Data
Air Force accident/mishap information was collected from the Air Force Judge Advocate General’s Corps Web site, http://usaf.aib.law.af.mil/. The Web site gives the executive summaries of Air Force Class A mishaps, organized by year. Lower-level mishaps were not available. A total of 15 Class A UA mishaps were retrieved from the Web site, covering the dates from December 6, 1999, to December 11, 2003. In addition to these executive summaries, a complete accident investigation board report of the December 6, 1999, accident was received electronically from Major Curtis McNeil of the Judge Advocate General’s Corps office. Also, a summary of Air Force accidents and human factors issues related to UA was received electronically from Major Anthony P. Tvaryanas (Tvaryanas, 2004).
Data Reliability Issues
Unfortunately, the data regarding UA accidents are not usually as detailed as that surrounding manned aircraft. One reason for this lack of detail is that most UA used in the military are much less expensive than manned aircraft and so do not warrant the same level of analysis. In addition, the military does not release much of the detailed information regarding specific UA accidents to the general public.
There are also problems regarding the classification of UA in the military. The Army, for example, only recently has begun to classify UA as aircraft. Before, they were classified only as vehicles. Therefore, accidents involving Army UA were treated in the same fashion as ground vehicles. A similar situation existed until recently for the Navy. In effect, there are really no highly detailed accident investigations performed for UA accidents, with the exception of the Air Force. The Air Force, however, will not release detailed reports to the general public and puts restrictions on the writing of reports based on such detailed data. Consequently, much of the reported accident data collected for this report consists of summaries of several accidents or simple one-sentence statements regarding individual accidents.
Classification Procedure
Classification of the accident data was a two-step process. In the first step, accidents were classified into broad categories based on whether it was clear the accident was related to human factors or was a failure of an aircraft component. For some aircraft systems, other categories were included based on information specific to that aircraft. The category “Aircraft” included problems associated with the failure of a mechanical or electrical component of the airframe. An “Unknown” category was used if there were accidents with insufficient information for categorization. A category of “Maintenance” was also included if there was evidence that an action by maintenance personnel contributed to the accident. An example would be a failure by a maintenance technician to check the oil level prior to a flight, leading to an engine failure during the flight. This category was separated from human factors because it did not involve a member of the flight crew and because UA maintenance is an important topic by itself that should be addressed separately. Note that accidents could be classified into more than one category. For example, an accident could be classified as both “Aircraft” and “Human Factors” if a mechanical failure was also accompanied by an inappropriate or inadequate display indication to the crew.
In the second step, those accidents classified as related to human factors were classified according to specific human factors issues that are commonly addressed in current research. These issues included alerts/alarms, display design deficiencies, procedural errors, and skill-based errors. Other human factors issues were included for a particular aircraft if evidence was available from the reports indicating it was an important factor in the accident. Classification was based on the stated causal factors in the reports, the expressed opinion of safety center personnel, and the personal judgment of the author.