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Startle Effect

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Category: Human Behaviour Human Behaviour
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The startle response, which in professional circles is also referred to as amygdala (or limbic) hijack, is the physical and mental response to a sudden intense and unexpected stimulus. This physiological reaction, which is most commonly known as the "fight or flight" reflex, will occur in response to what may be perceived as a harmful event: an attack, a threat to survival, or more simply, to fear itself. The fight or flight response enables us to react with appropriate action: to run away, to fight, or sometimes, to freeze to be a less visible target. In some circumstances, it can also lead to actions inappropriate for the situation.

In aviation, startle effect can be defined as an uncontrollable, automatic reflex that is elicited by exposure to a sudden, intense event that violates a pilot’s expectations.[1]


The startle effect includes both the physical and mental responses to a sudden unexpected stimulus. While the physical responses are automatic and virtually instantaneous, the mental responses - the conscious processing and evaluation of the sensory information - can be much slower. In fact, the ability to process the sensory information - to evaluate the situation and take appropriate action - can be seriously impaired or even overwhelmed by the intense physiological responses. These changes in physiological activity include:

  • Cardiovascular System: Heart rate increases, blood pressure rises and coronary arteries dilate to increase the blood supply to brain, limbs and muscles
  • Respiratory System: Depth and rate of breathing increases providing more oxygen to the body
  • Endocrine System: Liver releases additional sugar for energy. Adrenal glands release adrenalin
  • Muscular System: Muscles tense in readiness for immediate action
  • Excretory System: Sweat production increases
  • Nervous System: Brain activity changes, reactions become less reasoned and more instinctive


In addition to the previously listed temporary physiological changes which follow a high intensity stimulus, studies have determined that, following a startling stimulus such as a loud noise, basic motor response performance can be disrupted for as much as 3 seconds and performance of more complex motor tasks may impacted for up to 10 seconds.

The time that it takes to recover in a cognitive sense, after a startle event, must also be considered. Startle has been found to impair information processing performance on mundane tasks, such as the continuous solving of basic arithmetic problems, for 30 to 60 seconds after the event occurrence. The duration of the performance degradation increases as the task becomes more complex. Thus, the startle effect disrupts cognitive processing and can negatively influence an individual’s decision making and problem solving abilities.


As concluded by Martin, Murray and Bates in their paper The Effects of Startle on Pilots During Critical Events, the reliability of modern aircraft is, in part, to blame for inappropriate actions taken after a startle event:

"… one of the common themes as aircraft become more reliable is that pilots are surprised or startled by some event and as a result have either taken no action or alternatively taken the wrong action, which has created an undesired aircraft state, or in some cases, an accident. This surprise or startle is largely due to the enduring reliability of the aircraft and the aviation system, which has unwittingly created a conditioned expectation of normalcy among today’s pilots…The problem then is the level of expectation of novel or critical events is so low that the level of surprise or startle which pilots encounter during such events is higher than they would perhaps have had some decades ago when things went routinely wrong."[2]

On the flight deck, pilots may be exposed to a variety of stimuli that have the potential to elicit the startle reflex and response. Bird strike, aircraft upset, simultaneous failure of multiple engines and visual stimuli, such as sudden illumination by lasers, have all resulted in incidents where pilots have been startled or even disoriented. In aviation, the immediate impact of the startle reflex may induce a brief period of disorientation as well as short term psychomotor impairment which may well lead to task interruptions and/or a brief period of confusion. Should this happen, a period of time will be required for reorientation and task resumption. While performance after a startle event can be affected to the detriment of safety of flight, the greater concern stems from what the crew did, or did not do, during the conditioned startle response itself. It is here that decision making can be most significantly impaired, especially higher-order functions necessary for making judgments about complex flight tasks.

Strategies for Improving Startle Performance

Researchers have identified a number of strategies that can reduce the negative effects of startle and help improve pilot performance during and immediately following a startle event. These include:

  • Know your aircraft: Develop a sound technical knowledge of your aircraft type and maintain it with regular revision
  • Maintain handling skills: Be competent and comfortable flying the aircraft "without the automation"
  • Train appropriately: Simulator exercises should be conducted in a constructive manner with a focus on evidence based (most likely) events. However, there should also be constructive use of unexpected critical events
  • Be cognisant of your surroundings: Develop and maintain effective situational awareness skill-sets. The Pilot Monitoring (PM) should actively monitor the Pilot Flying (PF) and both should actively monitor the aircraft automation
  • Avoid complacency: Have a healthy expectation and suspicion for things going wrong
  • Anticipate threats: Utilise effective threat and error management (TEM) strategies
  • Have a plan: Mentally rehearse or foster crew discussion of a "plan of action" for both common non-normal events, and for the rare, "out of the ordinary" events such as ditching, upset or uncontrollable fire. Adopt a "what would I do if.." mindset

Accidents in Which Startle Effect Was Considered a Factor

  • A332, en-route, Atlantic Ocean, 2009 (On 1 June 2009, an Airbus A330-200 being operated by Air France on a scheduled passenger flight from Rio de Janeiro to Paris CDG as AF447 exited controlled flight and crashed into the sea with the loss of the aircraft and all 228 occupants. It was found that the loss of control followed an inappropriate response by the flight crew to a transient loss of airspeed indications in the cruise which resulted from the vulnerability of the pitot heads to ice crystal icing)
  • DH8D, vicinity Buffalo NY USA, 2009 (On 12 February 2009, a Bombardier DHC-8-400 also known as a 'Q400' which was being operated by Colgan Air on a scheduled public transport flight in the USA from Newark to Buffalo-Niagara under a Continental Airlines flight number as part of a codeshare agreement in place between the two operators was on an ILS approach to the destination runway in night VMC when control was lost and the aircraft crashed and burned in a residential area approximately 5 nm from the runway killing all occupants and one additional person on the ground)
  • A320, en-route Karimata Strait Indonesia, 2014(On 28 December 2014, an A320 crew took unapproved action in response to a repeating system caution shortly after levelling at FL320. The unexpected consequences degraded the flight control system and obliged manual control. Gross mishandling followed which led to a stall, descent at a high rate and sea surface impact with a 20º pitch attitude and a 50º angle of attack four minutes later. The Investigation noted the accident origin as a repetitive minor system fault but demonstrated that the subsequent loss of control followed a combination of explicitly inappropriate pilot action and the absence of appropriate pilot action.)

Related Articles

Further Reading


Civil Aviation Safety Authority Australia

Griffith University Aerospace Strategic Study Centre



  1. ^ FAA Advisory Circular 120-111 dated 4/14/15 - Upset Prevention and Recovery Training
  2. ^ Martin, W., Murray, P. and Bates, P. (2012). The Effects of Startle on Pilots During Critical Events: A Case Study Analysis. www98.griffith.edu.au