**1. Background**

Copycat phenomenon (suicidal behavior provoked by media exposure) in pilot aircraft-assisted suicides (AASs) has been studied since the 1970s with inconclusive results [1,2], while longitudinal case series on pilot AASs have shown the difficulty of predicting rare events [3,4].We have previously analyzed pilot AASs after the Germanwings pilot murder-suicide incident [5], with no increase in pilot AASs was observed in the U.S. or Germany during a two-year period after the incident as compared to the previous five-year period.

The negative impact of exposure to atrocities on mental health is well documented, from trauma and-stress related disorders, to the level of copyca<sup>t</sup> suicides [6–9]. The exposure to traumatic events

through media alone is sufficient to cause psychological distress or even stress-related disorders [10]. Copycat behavior can be defined as suicidal behavior provoked by media exposure, also described as the "Werther effect" (from Goethe's novel Die Leiden des Jungen Werthers). In addition, the term "Papageno effect" has been proposed to describe protective media measures [7,11]. The name originally refers to a bird catcher character from Mozart's Magic Flute, who became suicidal but recovered after his friends intervened [7,11]. World Health Organization (WHO) has guidance on responsible media reporting after suicide, and recent National Institute for Health and Care Excellence (NICE) guidelines on suicide prevention have also focused on the impact of media [12,13].

Pilots are generally regarded as being psychologically resilient and healthier than the general population due to initial health assessment of specialized aeromedical examiners, which excludes individuals with severe risk factors for suicidal behavior, such as repeated suicide attempts or current major depression. Mandatory health assessments are regularly repeated, as requested in aviation authorities' guidance on aviation medical examiners (AME)s [14,15]. At an individual pilot level, mental health fitness assessments may have an impact on aviation safety [16]. However, the use of several aircrafts in the September 11 attacks focused attention internationally on the actions of aviators and also on the potential vulnerability of aviation safety with excessive and repeated media coverage. In relation to military pilots, the U.S. Air Force has published fairly constant suicide rates for that time period in an analysis of the U.S. Air Force suicide prevention program [17].

A study by Claassen et al. [18] has shown no increase in suicide rates in the general population in areas surrounding the three airline crash sites in New York, the Pentagon in Washington D.C, and Somerset County in Pennsylvania after 11 September 2001. Claassen et al. [18] concluded that geographical proximity is less important compared to other event characteristics and more research is needed regarding relevant social factors. This is in line with the study of Mezuk and coworkers [19], who reported no increase in New York suicide rates after the attack. Monthly homicide statistics in the New York City area did not reveal an increase in homicide or suicide rates after 11 September 2001 [20,21].

Although Pridemore and colleagues [21] showed that the rate of homicide or suicide deaths in New York was not increased following the attacks of 11 September 2001, Jordan et al. [22] showed that the standardized mortality ratio (SMR) for suicide was elevated (SMR = 1.82) among rescue recovery workers, while SMR for all-cause mortality was not elevated (SMR = 0.69). In another study of mortality among World Trade Center rescue workers, Stein et al. [23] reported a lowered all-cause and cause-specific mortality among rescue workers during a time period of 2002–2011 and did not find any association relating to the duration of rescue work and mortality. These long-term follow-up study results are not conclusive, inviting more analyses among different professional groups related to similar types of incidents. Starkman [24] has reported a one-year increase in suicide attempts after 11 September 2001 in Michigan, U.S, and the effect was greatest in the months following the attacks.

One aspect to explore is the research on suicidal ideation. In a survey of 871 adults who experienced loss during the September 11 attacks, individuals with complicated grief had significantly high rates of suicidal ideation even after adjusting to comorbid depression [25]. Additionally, suicidal ideation was increased in another primary care cohort after 11 September 2001 ( *N* = 444) in Manhattan [6].

The aim of this study is to evaluate possible changes in pilot aircraft-assisted suicides after the 11 September 2001, terrorist murder–suicides in the U.S.
