Table 1.

Summary of empirical research on maintenance processes in flying phobia.

Study	Country	Population	Sample size and characteristics	Design	Focus of study	Findings
SELECTIVE ATTENTION
van Almen and van Gerwen, 2013	Netherlands	General population, individuals who completed an open-access questionnaire on the website of a foundation which offers treatment for flying phobia	N = 9116 Mean age 34.37 years (SD = 11.80)	Correlational	Evaluating the relationship between fear of flying (as measured by FAM) and voluntary allocation of attention toward (monitoring) or away (blunting) from threatening information as measured by Miller Behavioral Style Scale (consists of descriptions of four hypothetical uncontrollable stressful situations).	Individuals who reported higher levels of monitoring of threat in response to hypothetical stressful scenarios reported higher levels of flying anxiety (as measured by FAM). (Note: the self-reported voluntary allocation of attention may arguably be classified as a cognitive strategy rather than reflecting selective attentional processes).
PERCEIVED THREAT/FEARED OUTCOME
Hawkins-Gilligan et al., 2011	USA	University students, recruited from university class-rooms	N = 109	Correlational	Evaluating whether flying-embedded fears (i.e., fears regarding other stimuli associated with flying such as agoraphobic or height-focussed fears), as measured by the Fear Survey Schedule, and individuals' flying-specific conditioning experiences (including direct, observational and verbal) predicted fear of flying symptomology as measured by FAS subscales and an adapted version of the Fear Survey Schedule.	All 5 fear of flying measures were predicted by at least one flying-embedded fear (relating to fears surrounding social outcomes, heights, agoraphobic fears and fears relating to water). Previous conditioning experiences only predicted one of the 5 fear of flying measures and this was labeled as “weakly” predicting this variable. The authors concluded that the results suggest that the fear of flying is based on several flight-embedded innate fears rather than fears conditioned through learning.
McNally and Louro, 1992	USA	Flying phobics, based on DSM-III-R criteria for specific phobia and individuals with panic disorder with agoraphobia (PDA; based on DSM-III-R criteria) who sought help for fear of flying	N = 34, 17 flying phobics, Mean age 36.12 (SD = 6.73) 17 PDA participants Mean age 26.82 years (SD = 8.58)	Structured interviews and descriptive statistics	Evaluating reasons for flight avoidance and feared outcomes in a group of individuals with simple phobia and those with PDA who sought help for fear of flying.	Individuals with specific phobia of flying reported fears around external threat (plane crashing) as primary concerns. PDA participants reported that their fears primarily related to internal threat (panic attacks and consequences).
Möller et al., 1998	South Africa	Flying phobics, based on scoring 5 or more out of 10 on the Questionnaire on Attitudes Toward Flying	N = 22, 15 flying phobics, Mean age 47.7 years, 7 non-fearful flyers, Mean age 44.8 years	Experimental	Evaluating whether the fear of flying is associated with the reporting of irrational evaluative beliefs when faced with hypothetical flying scenarios. Fearful and non-fearful fliers were presented with six threatening and six non-threatening flying scenarios as part of Articulated Thoughts in Simulated Situations procedure.	The flying phobic group reported more irrational thoughts and higher subjective anxiety ratings across experimental scenes compared to the non-fearful fliers. Irrational thoughts reflected an overestimation of the seriousness of threat (“awfulizing”) and underestimating perceived ability to cope (“low frustration tolerance”).
Van Gerwen et al., 1997	Netherlands	Flying phobics, based on self-referral to fear of flying program	N = 419, Mean age 40.9 years, (SD = 10.4)	Semi-structured interview and self-report questionnaires	Evaluating clinical characteristics of flying phobia including presence of panic attacks, situational avoidance, flight history, level of flight anxiety and primary concerns when flying.	Identified four subtypes of flying phobia: (1) Individuals with no panic attack symptoms primarily concerned with aircraft accidents and the need for situational control; (2) individuals who fear loss of control over themselves or social anxiety and pay significant attention to somatic sensations; (3) individuals whose fears center on water and/or claustrophobia and agoraphobia and report panic attacks associated with flying; and (4) individuals who primarily present with fears reflecting acrophobia (irrational fear of heights).
Wilhelm and Roth, 1997	USA	Flying phobics, based on DSM-III-R criteria, individuals with Panic Disorder and Agoraphobia (PDA), individuals with a history of Panic Disorder with Agoraphobia (PDH) and non-phobic control group, individuals who responded 0 or 1 out of 10 when rating their flying anxiety, recruited from the general population	N = 87, 37 flying phobics, Mean age 44.0 years (SD = 10.5), 18 PDA participants, Mean age 50.3 years (SD = 10.0) 11 PDH participants Mean age 44.5 years (SD = 11.6) 21 non-phobic controls, Mean age 44.1 years (SD = 13.7)	Correlational and use of structured interview	Evaluating clinical characteristics of flying phobia including onset of symptoms, flight history and experience of traumatic flying events and feared outcomes/concerns when flying.	Flying phobics, PDA and PDH participants reported equivalent concerns about external dangers (e.g., plane crash, pilot making mistake), though PDA and PDH participants reported greater concern regarding internal or social anxiety stimuli during flights.
COGNITIVE BIAS
Mühlberger et al., 2006	Germany	Flying phobics and Spider phobics (based on DSM-IV criteria)	N = 34, 17 spider phobics, Mean age 27.4 years, (SD = 9.3) 17 flying phobics, Mean age 44.2 years (SD = 9.6 years)	Experimental	Examined presence of expectancy and covariation bias by exposing participants to pictures of spiders, flight accidents and neutral cues followed by either a startling noise or no stimulus whilst measuring skin conductance responses, startle response and event-related brain potentials.	Flying phobics and spider phobics displayed a threat-disorder-specific expectancy bias and skin conductance responses but only spider phobics demonstrated a disorder-specific covariation bias.
Pauli et al., 1998	Germany	Flying phobics, based on high FFS scores and non-phobic control group based on low FFS scores	N = 28, 14 flying phobics, Mean age 32.8 years (SD = 7.7) 14 non-flying-phobics, Mean age 30.7 years (SD = 6.9)	Experimental	Examined covariation bias in flying phobia through pairing fear-relevant stimuli (slides of aeroplane crash sites) or fear-irrelevant stimuli (slides of aeroplanes in flight or mushrooms) and electric shocks.	Flying phobics demonstrated a covariation bias and reported higher covariation estimates for fear-relevant slides and shocks than fear-irrelevant slides and shocks, relative to non-flying phobics.
Vriends et al., 2012	Switzerland	Flying phobics, based on DSM-IV criteria, and non-phobic control group recruited from university	N = 72, 33 flying phobics, Mean age 36.4 years (SD = 9.3) 39 “healthy controls”, Mean age 36.1 years (SD = 11.1)	Experimental	Evaluating associative learning in flying phobia. Participants viewed a series of distracters interspersed with pairings of novel objects with frightening and pleasant stimuli.	Flying phobics demonstrated a stronger conditioning effect and subjective ratings of conditioned stimuli as frightening compared to healthy controls.
RESPONSE TO PHOBIC CUES/TRIGGERS
Bogaerde and De Raedt, 2013	Belgium	Flying phobics, based on Mini International Neuropsychiatric Interview and non-phobic control group recruited from non-phobic passengers on exposure flight	N = 103, 54 flying phobics, Mean age 40.22 years 49 non-phobic controls, Mean age 41.85 years	Experimental	Evaluating oxygen saturation (SpO2), anxiety and subjective somatic associations of flying phobics and controls on a plane at ground level and at cruising altitude.	Both groups demonstrated a decrease in SpO2 from ground level to cruising altitude. Flying phobics reported more somatic sensations and elevated anxiety at ground level. At cruising altitude flying phobics reported significantly greater somatic sensations but anxiety was no longer significantly greater than controls.
Bornas et al., 2004	Spain	Flying phobics, based on scoring more than 1.5 standard deviations above the mean on the FFQ in a sample of 230 undergraduate students. Non-phobic control group based on scoring the mean plus or minus one standard deviation on the FFQ.	N = 30, 15 flying phobics, 15 non-phobic controls, Mean age of total initial sample from which participants were selected (N = 230) 22 years (SD = 3.2)	Experimental	The study evaluated self-implication (self-rated engagement with stimulus) during simulated exposure to flight-related pictures, sounds or pictures and sounds combined. Measures of heart-rate variability (reflecting degree of autonomic flexibility and ability to respond to environmental demands), subjective anxiety and subjective rating of self-implication were recorded.	The study found the phobic group demonstrated significantly higher measures of anxiety than the non-phobic group. Flying-related sounds elicited greater anxiety than flying-related pictures. There were no significant group differences in subjective ratings of self-implication (whether reflecting attentional deployment or cognitive engagement with stimulus) and no correlation between self-implication and anxiety. Flying phobics who displayed low heart-rate variability displayed higher self-implication in relation to flight-related sounds than flying phobics with high heart-rate variability.
Bornas et al., 2006	Spain	Flying phobics, based on DSM-IV criteria	N = 61, Mean age 39.07 (SD = 11.24)	Experimental	Measured individual heart-rate response at baseline, during a paced breathing task and then on exposure to a video of a flight scenario.	Participant heart-rate increased from baseline to paced breathing exercise and decreased from paced breathing to exposure to flight video.
Busscher et al., 2010	Netherlands	Flying phobics, based on DSM-IV criteria and non-phobic control group recruited from the general population	N = 163, 127 flying phobics, Mean age 40.4 years (SD = 11.0) 26 non-phobics, Mean age 43.4 (SD = 13.5)	Experimental	Evaluating participant responses to a neutral video, phobic stimulus (video depicting a flight-scenario) and a recovery period across phobic and non-phobic groups. Measures of heart-rate, subjective anxiety, and cardiac autonomic response were taken.	Significantly higher subjective anxiety was reported by the phobic group on exposure to the flight-related stimulus but group differences were not found on physiological measures. Within the phobic group heart-rate and cardiac response were moderately strongly coupled with subjective anxiety.
BEHAVIORS/COPING RESPONSE
Girodo and Roehl, 1978	Canada	Flying phobics, identified from an undergraduate sample based on likert scale indicating flight apprehension	N = 56, Mean age 21 years	Experimental	Evaluating the impact of training participants in two cognitive coping strategies (coping self-talk and information regarding what would occur when flying) on self-reported anxiety before, during and following a flight in which an unexpected negative event occurred. Participants were split into four groups: coping self-talk, information, combined and control.	No differences were recorded between subjective anxiety between groups when flying, individuals who had been trained in coping self-talk reported less anxiety associated with an unexpected negative flying event.
Kraaij et al., 2003	Netherlands	Flying phobics, based on DSM-IV criteria, who sought treatment for fear of flying	N = 261, Mean age = 38.4 years (SD = 10.14)	Correlational	Evaluating the cognitive coping strategies that individuals with fear of flying report using to regulate their emotions during a flight experience based on responses to the CERQ. FAS and FAM were also administered.	Participants reported using strategies including focussing on planning, rumination, and putting in perspective. Greater use of self-blame, rumination, acceptance and/or catastrophizing were all associated with higher levels of subjective anxiety associated with flying.
Nousi et al., 2008	Netherlands	Flying phobics who sought treatment for fear of flying, grouped according to: (1) those who had never flown; (2) those who had flown and experienced no adverse incidents; and (3) those who had experienced adverse or traumatic flights.	N = 489 (from an initial sample of 2001) 174 in Group 1, Mean age 46.63 years (SD = 13.4) 200 in Group 2, Mean age 39 =.63 years (SD = 10.8) 115 in Group 3, Mean age = 28.32 (SD = 10.1)	Experimental	Evaluating the prevalence and characteristics of individuals (including flying anxiety as measured by FAS and FAM) with different flying histories and their predictive value of flying histories in treatment outcome. The evaluation of a group of fearful fliers who had never flown may be used to infer the impact of situational avoidance.	Participants who had never flown reported higher levels of fear of flying and general anxiety and demonstrated greater reduction in anxiety following treatment. The authors concluded that participants who had never flown before may have fear which reflect more generalized avoidance tendencies and may over-predict the magnitude and intensity of their anxiety.
Wilhelm and Roth, 1997	USA	Flying phobics, based on DSM-III-R criteria, individuals with Panic Disorder and Agoraphobia (PDA), individuals with a history of Panic Disorder with Agoraphobia (PDH) and non-phobic control group, individuals who responded 0 or 1 out of 10 when rating their flying anxiety, recruited from the general population	N = 87, 37 flying phobics, Mean age 44.0 years (SD = 10.5), 18 PDA participants, Mean age 50.3 years (SD = 10.0) 11 PDH participants Mean age 44.5 years (SD = 11.6) 21 non-phobic controls, Mean age 44.1 years (SD = 13.7)	Correlational and use of structured interview	Evaluating clinical characteristics of flying phobia including onset of symptoms, flight history and experience of traumatic flying events and feared outcomes/concerns when flying.	Individuals with flying phobia reported utilizing avoidance, alcohol and medication to attenuate anxiety symptoms associated with flying.
ANXIETY SENSITIVITY
Busscher et al., 2010	Netherlands	Flying phobics, based on DSM-IV criteria, who sought treatment for fear of flying and non-phobic control group recruited from the general population	N = 163, 127 flying phobics, Mean age 40.4 years (SD = 11.0) 26 non-phobics, Mean age 43.4 (SD = 13.5)	Experimental	Evaluating participant responses to a neutral video, phobic stimulus (video depicting a flight-scenario) and a recovery period across phobic and non-phobic groups. Measures of heart-rate, subjective anxiety, and cardiac autonomic response were taken.	Anxiety sensitivity did not moderate the relationship between subjective anxiety and physiological measures of anxiety in the flying phobic group (additional findings noted above).
Busscher et al., 2013	Netherlands	Flying phobics, based on DSM-IV criteria, who sought treatment for fear of flying	N = 50, Mean age 28.4 years (SD = 10.6)	Experimental	Evaluating the relationship between reported flight anxiety, physiological arousal (as measured by heart-rate, respiratory sinus arrhythmia and pre-ejection period) and anxiety sensitivity, during an exposure to a real flight scenario on an aeroplane.	Results indicated that anxiety sensitivity moderated the relationship between changes in physiological arousal and self-reported flight anxiety but not between self-reported somatic sensations and flight anxiety.
Busscher et al., 2015	Netherlands	Flying phobics who sought treatment for fear of flying	N = 79, Mean age 40.4 (SD = 11.0)	Experimental	Evaluating emotional processing theory in relation to flight phobia by investigating whether success of exposure therapy (i.e., future reduction in anxiety) is predicted by activation of subjective and physiological fear responses and their within-session and between-session habituation. Participants underwent measurements of self-reported and physiological anxiety (including heart-rate, respiratory sinus arrhythmia) during within-session habituation and between session-adaption to exposure to flying-related stimuli, simulated flight and a real flight.	Within-session habituation and between-session adaption was recorded on physiological and subjective measures during exposure but this did not predict treatment outcome. The authors concluded that results provided only weak support for emotional processing theory.
Bogaerde and De Raedt, 2008	Belgium	General population, recruited from university undergraduate population	N = 160, Mean age 31 years	Correlational	Evaluating the role of anxiety sensitivity in the fear of flying by administering the FAS, FAM and Anxiety Sensitivity Index.	A stronger relationship between in-flight anxiety and somatic sensations was found for individuals with high anxiety sensitivity relative to those with low anxiety sensitivity, suggesting that anxiety sensitivity moderates this relationship.
Bogaerde and De Raedt, 2011	Belgium	Flying phobics, based on DSM-IV criteria, and non-phobic control group recruited from non-phobic passengers on exposure flight	N = 103, 54 flying phobics, Mean age 40.2 years 49 non-phobic controls, Mean age 41.9	Correlational	Evaluating the role of anxiety sensitivity by measuring anxiety sensitivity, subjective anxiety on a visual analog scale, flying anxiety (on FAS) and subjective bodily sensations in participants immediately before taking a flight.	Anxiety sensitivity was found to moderate the relationship between somatic sensations and flying phobia symptoms, with somatic sensation predicting flight anxiety in high anxiety sensitivity individuals but not in low anxiety sensitivity individuals.
MEMORY
Bogaerde et al., 2012		Flying phobics, based on scoring 4 on a 1-to-4 likert scale of flying anxiety, and non-phobic control group both recruited from undergraduates	N = 25, 12 flying-phobics, mean age 18.7 years (SD = 0.9). 13 non-phobic controls, mean age 18.8 years (SD = 2.8)	Experimental	Investigating threat in fear of flying through measuring participant free recall of external vs. internal threat words and neutral words in a dichotic listening task.	Flying phobics displayed greater recall of internal threat words (i.e., consequences of anxiety sensations) than non-flying phobics. No group differences were found for external threat words or neutral stimuli.
WORRY
Aitken et al., 1981	UK	Flying phobic air-crew (RAF aircrew referred for treatment) and non-flying phobic air-crew controls	N = 40 20 flying phobics, 28.6 years (SD = 5.5) 20 Non-flying-phobics 30.4 years (SD = 5.1)	Experimental and Correlational	Aimed to compare the characteristics of flight phobic air-crew compared to non-flight phobic air-crew by administering self-report worry questionnaire, clinical interview, psychophysiology measures (heart-rate and galvanic skin response to repeated auditory tone) and a battery of personality inventories.	Results indicated no significant difference on measures of personality but the flying phobic group displayed greater fluctuations in skin conductance and habituated less to a repeated auditory tone. The flying phobic group reported greater worries concerning flying and also concerning their marital partners. More of the flying phobic group also reported a family history of a flying-related trauma.
Bergstrom and McCaul, 2004	USA	General population, recruited from university psychology undergraduates	N = 115, Mean age 21.3 years	Correlational	Assessing worry as a predictor of flying-related decision making 34 days after the September 11th terrorist attacks in the USA.	Subjective worry predicted estimates of one's own and others' willingness to fly.
Martinussen et al., 2011	Norway	General population, recruited from passengers in arrivals hall at airport	N = 270, Mean age 35.1 years (SD = 14.5)	Correlational	Assessing fear of flying (using FAS), positive emotions toward air travel and stress/worry related to check-in and security checks.	Flying-related anxiety was predicted by gender (female), recent flying experience, and stress/worry regarding check-in and security checks.

Wilhelm and Roth (1997) and Busscher et al. (2010) are described under two headings as they report outcomes in two areas of interest but are single publications. Mean age and standard deviation of sample are reported to two decimal places where available. Our search did not identify any investigation of mental imagery, intolerance of uncertainty or any other processes implicated in the maintenance of anxiety disorders. The organization under each area of maintenance does not connote mutual exclusivity in study focus/outcome, e.g., selective attention may be hypothesized to be demonstrated in the higher levels of recall of internal threat words in the study by Bogaerde et al. (2012). FAS, Flight Anxiety Situations Questionnaire (Van Gerwen et al., 1999); FAM, Flight Anxiety Modality Questionnaire (Van Gerwen et al., 1999); FFQ, Fear of Flying Questionnaire (Bornas et al., 1999); FFS, Fear of Flying Scale (Johnsen and Hugdahl, 1990); CERQ, Cognitive Emotion Regulation Questionnaire (Garnefski et al., 2002).