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Continuation Bias

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Plan Continuation Bias

Article Information
Category: Human Behaviour Human Behaviour
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary

Definition

(Plan) Continuation Bias is the unconscious cognitive bias to continue with the original plan in spite of changing conditions.

Discussion

Unconscious bias in thinking leads to a pilot or controller following the originally-intended course of action. This bias appears to be stronger as the culmination of a task nears, for example during the flying of an approach to land or the maintenance of the planned separation between aircraft sequenced for approach to a particular runway.

Continuation Bias may have the effect of obscuring subtle cues which indicate that original conditions and assumptions have changed. It may also act in combination with other cognitive biases.

Accidents and Incidents

SKYbrary includes the following reports relating to events where continuation bias was considered to be a factor:

  • BN2A, vicinity Bonaire Netherlands Antilles, 2009 (On 22 October 2009, a BN2 Islander suspected to have been overloaded experienced an engine failure shortly after departure from Curaçao. Rather than return, the Pilot chose to continue the flight to the intended destination but had to carry out a ditching when it proved impossible to maintain height. All passengers survived but the Pilot died. The cause of the engine failure could not be established but the Investigation found a context for the accident which had constituted systemic failure by the Operator to deliver operational safety which had been ignored by an inadequate regulatory oversight regime.)
  • AT76, vicinity Moranbah Queensland Australia, 2013 (On 15 May 2013, an ATR 72-600 on a visual approach to Moranbah descended sufficiently low in order to avoid entering cloud that a number of TAWS Warnings were activated. All were a consequence of the descent to below 500 feet agl at a high rate of descent which appeared not to have been appreciated by the flight crew. The Investigation found that the option of an available and suitable instrument approach procedure more appropriate for the prevailing low cloud base was ignored.)
  • B738, Mangalore India, 2012 (On 14 August 2012, a Boeing 737-800 crew continued a previously stable ILS Cat 1 approach below the prescribed MDA without having acquired the prescribed visual reference. The aircraft was then damaged by a high rate of descent at the initial touchdown in the undershoot in fog. The occurrence was not reported by either the crew or the attending licensed engineer who discovered consequent damage to the aircraft. Dense fog had prevented ATC visual awareness. The Investigation attributed the undershoot to violation of minima and to both pilots looking out for visual reference leaving the flight instruments unmonitored.)
  • A321, vicinity Islamabad Pakistan, 2010 (On 28 July 2010, the crew of an Airbus A321 lost contact with the runway at Islamabad during a visual circling approach and continued in IMC outside the protected area and flying into terrain after repeatedly ignoring EGPWS Terrain Alerts and PULL UP Warnings. The Investigation concluded that the Captain had pre-planned a non-standard circuit which had been continued into IMC and had then failed to maintain situational awareness, control the aircraft through correct FMU inputs or respond to multiple EGPWS Warnings. The inexperienced First Officer appeared unwilling to take control in the absence of corrective action by the Captain.)
  • H25B, vicinity Akron OH USA, 2015 (On 10 November 2015, the crew of an HS 125 lost control of their aircraft during an unstabilised non-precision approach to Akron when descent was continued below Minimum Descent Altitude without the prescribed visual reference. The airspeed decayed significantly below minimum safe so that a low level aerodynamic stall resulted from which recovery was not achieved. All nine occupants died when it hit an apartment block but nobody on the ground was injured. The Investigation faulted crew flight management and its context - a dysfunctional Operator and inadequate FAA oversight of both its pilot training programme and flight operations.)

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Related Articles

Further Reading

  • The “Barn Door” Effect by C. West, Ph.D., NOAA - a paper about pilots’ propensity to continue approaches to land when closer to convective weather than they would wish to get while en route.