Startle Reflex

Startle Reflex


Surprise is “an emotion typically resulting from the violation of an expectation or the detection of novelty in the environment” (American Psychological Society, 2022) and represents the difference between expectations and reality. That can mean something happening that is not expected or something not happening that was expected.

Surprise can be mitigated through training, procedures, crew resource management (CRM) and experience. See the separate article on Surprise.

The startle reflex, meanwhile, is “an unlearned, rapid, reflex-like response to sudden, unexpected, and intense stimuli (e.g. loud noises, flashing lights)” (APA, 2022)

‘Surprise’ and ‘Startle’ are associated with fundamentally different neurological and physiological activity.

Surprise is common, the startle reflex is rare.

The Startle Reflex

The startle reflex response is an involuntary neurological and physiological response to a sudden-onset unexpected event where normal conscious decision making is bypassed, invariably resulting in action recognisable as "irrational" in relation to the circumstances.

The startle reflex response usually follows an entirely unexpected "sudden change" event at a time of low workload and usually seems to affect the Pilot Flying (PF). Startle reflex is extremely rare; there are no documented cases of both pilots appearing to have been similarly affected at the same time.

Consequences, vulnerability and risk

The most serious consequences will be related to flight path control (Loss of Control). Startle Reflex risk appears to be higher if the flight situation is 'quiet' rather than 'busy'. The risk of inappropriate and irrational reflex-driven action in this respect is primarily where no visual reference exists, for example in cloud or on a dark clear night with no moon or cultural ground lighting.

Response by the unaffected pilot

Effective response requires recognition of a startle reflex response in the other pilot when simultaneously surprised. The unaffected pilot will have limited time to intervene and, if necessary, take control before an upset recovery becomes necessary. This may be difficult if a significant authority gradient exists. Even if the pilots have had upset recovery training, successful recovery from unfamiliar situations created after startle reflex occurs is not guaranteed.


  • Awareness of startle reflex should be covered in recurrent ground training including the need to monitor all three attitude indicators if an unaffected pilot observes unexplained control inputs.
  • CRM training should include the importance of rapid and effective response to any evidence of a startle reflex in the other pilot.
  • Pilots should be exposed to sufficient manual flying practice to maintain confidence in their skills when these are called for suddenly and unexpectedly.

Accidents in Which Startle Effect Was Considered a Factor

  • A332, en-route, Atlantic Ocean, 2009 (In 2009, startle reflex led to the 'pilot flying' in an Airbus A330 in the cruise in mid Atlantic level at FL350 failing to simply maintain the established stable pitch attitude when the autopilot, auto thrust and all three airspeed indications briefly failed at the same time due to transient pitot tube probe icing. Instead, he responded by making large and rapid nose-up input. An ineffective response from the other pilot did not involve a prompt takeover of control and the aircraft quickly entered a stall from which recovery was delayed until it was too late.)
  • CRJ2, en-route, northern Sweden, 2016 (On 8 January 2016, a Bombardier CRJ200 crew were suddenly presented with a failure of one of the two main PFDs and a consequent uncommanded Autopilot disconnection during the cruise in dark night VMC conditions. No attempt was made to identify the failure as a single system fault and to maintain control using the second serviceable main PFD - which had the same indications as the Standby Horizon. Control of the aircraft was lost beyond possible recovery with terrain impact occurring 80 seconds after the initial appearance of erroneous PFD indications which were attributed to malfunction of the corresponding IRU.)


Related Articles

Further Reading

Air Pilots




Civil Aviation Safety Authority Australia

Griffith University Aerospace Strategic Study Centre




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