**4. Discussion**

The one-year RR of 3.68 of aircraft-assisted pilot suicides in the U.S. after 11 September 2001, is in line with the results of rescue worker's suicide mortality reported by Jordan et al. [22], and some earlier copyca<sup>t</sup> reports by Fink et al. [8]; see also Sisask and Värnik [7]. While fatal aviation accidents are rare, large or long-term register studies such as the study of Blettner et al. [27] and Politano and Walton [3] enable assessments to detect plausible effects of such events. General population suicide rates have been relatively stable during the time period of this study, but have increased in the U.S. during the last few years [28,29].

In studies from other countries, in England and Wales no increase of suicides was observed after 11 September 2001 [30] and there was no detectable change in the suicide rates in the Germany study [31]. An analysis of suicide rates from the Netherlands by de Lange and Neeleman [32] showed evidence of an increase in the suicide rates in the weeks after 11 September. Regarding trauma and stress related disorders, a Danish study by Hansen et al. [33] reported an increase in trauma and stress -related disorders after 11 September 2001, in line with several U.S. studies [34,35].

In one suicide flight involving a young pilot after 11 September 2001, the plane crashed intentionally into a high office building. According to the report there was a suicide note but it was not included in the accident investigation data. The helicopter pilots who intercepted this airplane attempted to signal the young pilot to land. According to the helicopter pilots, the student pilot saw their hand gestures and gestured back, but they could not determine the meaning of the gestures. Investigation of this incident led to a Federal Aviation Administration security notice release.

In the incidents investigated in this study, previous depression with suicide attempts was described in one case, ongoing treatment for depression in two cases, and a history of substance abuse and arson conviction in one case. Toxicology revealed that in six of these incidents there were medications or substance misuse not compatible with flying according to FAA. Some pilots with no information on previous psychological or psychiatric issues had recent stressful personal situations, such as legal or interpersonal difficulties.

The choice of crashing an aircraft to commit suicide among some pilots may in part be understood through the desire to combine passion for flying with death, reflecting an intimate bond between the pilot and his means of dying. Occasionally there may also be a hope that the incident would be construed as a medical fatality if the evidence were to be destroyed in the crash (for instance if the aircraft disappears).

One of the Class 1 pilots had a history of substance dependence. He was convicted of driving when intoxicated on several occasions and of arson, and had acute stressors. He left a suicide note. Another Class 1 pilot with no known immediate stressful events or health-related issues asked air traffic control to call for airport rescue and firefighting, and "also if you could tell my family and friends that I love them very much". Thus, he could be reached immediately before the lethal act. The third Class 1 pilot with military helicopter experience told the dispatcher he was going to meet someone. At no time did he display any signs of stress or unusual behavior. There were no records of previous incidents, and he had flight experience with various helicopters. This description gives an impression of a person who made a decision and enacted it; he was not in contact with any air traffic control facility at the time of the incident.

Previous suicide attempts and major depression are risk factors for completed suicide, but data on depression among aviators is limited [13,36]. In civil aviation, ongoing symptomatic major depression is not compatible with flying duties. After full remission and sufficient follow-up, International Civil Aviation Organization (ICAO) and aviation authorities currently accept psychological and some pharmacological treatments for aviators to prevent recurrence [14,15].

In aviation, full remission of depressive or stress-related symptoms, good compliance, and a reasonable follow-up time post-recovery are a prerequisite to the consideration of an aviator's return to flying duties [13–15,36–38]. Accepted antidepressants used to prevent symptoms are assessed

through specific programs that focus on comprehensively assessing fitness to fly, symptoms, treatment adherence, and especially aero-medically relevant side-effects (e.g., fatigue).

In relation to mental health and suicide, it should be noted that among pilots regular health examinations contribute to the recognition of risk factors of suicidal behavior. The actual risk factors for pilots may somewhat differ from the general population, in relation to the role of any defined psychiatric disorders [13,39,40].

The limitations of this study include the fact that our data are based on information in the accident investigations, and we do not have access to additional medical information for determining aviator suicides nor to any information on aviators' attempted suicides prior to the incidence. The data are reliant on NTSB reports, and these reports are incomplete in some cases and certain details remain unknown. The news information after 11 September and timing of news delivery was not analyzed, but there are several studies from the U.S. on psychological effects after 11 September 2001 [6,25,41]. We do not think that any flying pilot in the U.S. could have avoided the news, due to immediate alerts and airspace closures in the U.S. The role of media research and balancing Werther and Papageno effects in general population suicide prevention is more thoroughly assessed elsewhere [42–45]. However, we consider our pilot AAS estimates to be conservative since those fatal aviation incidents where autopsy indicated suicide, but NTSB accident investigations did not agree, were excluded.
