Survey of Severe Spatial Disorientation Episodes in Japan Air Force Fighter Pilots Showing Increased Severity in Night Flight

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Takada, Hisada, Kuwada, Sakai and Akamatsu conducted research into cases detailing increased severity in spatial disorientation during night operations, as found amongst Japanese Air Force pilots.

Illustration 1 shows that the mean severity score of pilots who had their worst spatial disorientation episode at night was significantly higher than those who experienced theirs during the day.

Illustration 1: Frequency of severity scores according to time of day, their mean, SD and significance
Severity Scores Statistics
Time Of Day 1 2 3 4 5 Mean Mode SD Data Significance
Day 69 44 26 6 5 1.89 1.00 1.04 Less Significant
Night 49 58 39 14 7 2.23 2.00 1.09 More Significant (P<0.01)

Illustration 2 shows us that of the total amount of pilots who had their worst episode during the day, only 24% reported the episode to be above moderate in terms of severity whereas for pilots who had theirs during the night, 36% of them rated the episode as being above moderate in terms of severity.

Illustration 2: Percentage of pilots who experienced moderate to severe SD
Time Of Day Percentage
Day 24%
Night 36%

Illustration 3 shows that there was a factor of significance *(P<0.05) regarding the difference between daytime and nighttime visual illusions and their effect on severe spatial disorientation scenarios experienced by pilots.

Illustration 3: Illusion types that produced the
most severe SD scenarios
Time Of Day Illusion Types Significance
Day Vestibular Less Significance
Night Vestibular Less Significance
Day Visual More Significance*
Night Visual More Significance*
Day Other Less Significance
Night Other Less Significance

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Research approach

Exploratory research into the increase in spatial disorientation episodes at night


Questionnaires were received anonymously from 411 pilots representing 7 different Air Wings and Tactical Training Groups. The average age of the consenting pilot was 32.3 years and had a mean total flying time of 1,922 hours. The participants in the study who did not answer at least 50% of the survey questions were ruled out. The number of remaining to be used in the study totalled 332.


Takada et al (2009) utilised a Likert-type scale to identify the severity score of each pilot's worst spatial disorientation episodes, ranking them from 1 (Minor) to 5 (Severe). They combined these results with a set of independent variables:

  • Time Of Day
    • Day
    • Night
  • Illusion Type encountered
    • Vestibular
    • Visual
    • Other
  • Weather scenario experienced
    • VMC
    • IMC
    • VI (Visual/Instrument transition)

Data interpretation regarding weather scenarios has been omitted from this review due to the subjective nature of weather evaluation especially during night time operations. The common misunderstanding pilots have regarding IMC being equivalent to VMC at night was reason enough to disregard the results.

The mode was included to reinforce the finding of the study that while severe spatial disorientation is experienced at all times of the day and when pilots experience debilitating illusions, the majority of episodes recalled were only minor to moderate in nature.

Data analysis

This review tabulated standard deviation information as well as mode, and significance data.

[[tab Reference]]

1. Takada Yuko, Hisada Tetsuya, Kuwada Nauro, Sakai Masai & Akamatsu Tomomitsu (2009). Survey of Severe Spatial Disorientation Episodes in Japan Air Self-Defense Force Fighter Pilots Showing Increased Severity in Night Flight. Military Medicine, Volume 174, June 2009.

Contributors to this page

Authors / Editors

Benjamin Stark


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