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Plan Continuation Bias
(Plan) Continuation Bias is the unconscious cognitive bias to continue with the original plan in spite of changing conditions.
The following explanation of continuation bias is derived from a Transport Safety Board of Canada accident report.
To make decisions effectively, a pilot or controller needs an accurate understanding of the situation and an appreciation of the implications of the situation, then to formulate a plan and contingencies, and to implement the best course of action. Equally important is the ability to recognize changes in the situation and to reinitiate the decision-making process to ensure that changes are accounted for and plans modified accordingly. If the potential implications of the situation are not adequately considered during the decision-making process, there is an increased risk that the decision and its associated action will result in an adverse outcome that leads to an undesired aircraft state.
A number of different factors can adversely impact a pilot's decision-making process. For example, increased workload can adversely impact a pilot's ability to perceive and evaluate cues from the environment and may result in attentional narrowing. In many cases, this attentional narrowing can lead to Confirmation Bias, which causes people to seek out cues that support the desired course of action, to the possible exclusion of critical cues that may support an alternate, less desirable hypothesis. The danger this presents is that potentially serious outcomes may not be given the appropriate level of consideration when attempting to determine the best possible course of action.
One specific form of confirmation bias is (plan) continuation bias, or plan continuation error. Once a plan is made and committed to, it becomes increasingly difficult for stimuli or conditions in the environment to be recognized as necessitating a change to the plan. Often, as workload increases, the stimuli or conditions will appear obvious to people external to the situation; however, it can be very difficult for a pilot caught up in the plan to recognize the saliency of the cues and the need to alter the plan.
When continuation bias interferes with the pilot's ability to detect important cues, or if the pilot fails to recognize the implications of those cues, breakdowns in situational awareness (SA) occur. These breakdowns in SA can result in non-optimal decisions being made, which could compromise safety.
In a U.S. National Aeronautics and Space Administration (NASA) and Ames Research Center review of 37 accidents investigated by the National Transportation Safety Board, it was determined that almost 75% of the tactical decision errors involved in the 37 accidents were related to decisions to continue on the original plan of action despite the presence of cues suggesting an alternative course of action. Dekker (2006) suggests that continuation bias occurs when the cues used to formulate the initial plan are considered to be very strong. For example, if the plan seems like a great plan, based on the information available at the time, subsequent cues that indicate otherwise may not be viewed in an equal light, in terms of decision making.
Therefore, it is important to realize that continuation bias can occur, and it is important for pilots to remain cognizant of the risks of not carefully analyzing changes in the situation, and considering the implications of those changes, to determine whether or not a more appropriate revised course of action is appropriate. As workload increases, particularly in a single-pilot scenario, less and less mental capacity is available to process these changes, and to consider the potential impact that they may have on the original plan.
Accidents and Incidents
SKYbrary includes the following reports relating to events where continuation bias was considered to be a factor:
- A343, Auckland New Zealand, 2013 (On 18 May 2013 an Airbus A340 with the Captain acting as 'Pilot Flying' commenced its night take off from Auckland in good visibility on a fully lit runway without the crew recognising that it was lined up with the runway edge. After continuing ahead for approximately 1400 metres, the aircraft track was corrected and the take off completed. The incident was not reported to ATC and debris on the runway from broken edge lights was not discovered until a routine inspection almost three hours later. The Investigation concluded that following flights were put at risk by the failure to report.)
- IL76, St John's Newfoundland Canada, 2012 (On 13 August 2012, an Ilyushin IL76 freighter overran landing runway 11 at St John's at 40 knots. The Investigation established that although a stabilised approach had been flown, the aircraft had been allowed to float in the presence of a significant tail wind component and had not finally touched down until half way along the 2590 metre long runway. It was also found that reverse thrust had then not been fully utilised and that cross connection of the brake lines had meant that the anti skid pressure release system worked in reverse sense, thus reducing braking effectiveness.)
- B772, San Francisco CA USA, 2013 (On 6 July 2013, an Asiana Boeing 777-200 descended below the visual glidepath on short finals at San Francisco after the pilots failed to notice that their actions had reduced thrust to idle. Upon late recognition that the aircraft was too low and slow, they were unable to recover before the aircraft hit the sea wall and the tail detached. Control was lost and the fuselage eventually hit the ground. A few occupants were ejected at impact but most managed to evacuate subsequently and before fire took hold. The Probable Cause of the accident was determined to be the mismanagement of the aircraft by the pilots.)
- A332, vicinity Perth Australia, 2014 (On 9 June 2014, a 'burning odour' of undetermined origin became evident in the rear galley of an Airbus A330 as soon as the aircraft powered up for take off. Initially, it was dismissed as not uncommon and likely to soon dissipate, but it continued and affected cabin crew were unable to continue their normal duties and received oxygen to assist recovery. En route diversion was considered but flight completion chosen. It was found that the rear pressure bulkhead insulation had not been correctly refitted following maintenance and had collapsed into and came into contact with APU bleed air duct.)
- PC6, Evora Portugal, 2012 (On 29 July 2012, the rudder of a Pilatus PC6 detached in flight and fell onto the stabiliser/elevator preventing its normal movement. Pitch control was gained using the electric stabiliser trim and a successful touchdown was achieved on the second attempt. However, directional control could not be maintained and a lateral runway excursion followed. Investigation attributed the rudder failure to maintenance error which went undetected. Unapproved dispensation by the maintenance organisation involved, which allowed some dual inspections for correct completion of safety critical tasks to be carried out by the same person, was considered to be a significant contributory factor.)
- TSB. Air Transportation Safety Investigation Report A18P0031 Loss of Control and Collision with Terrain. 14 August 2019.
- 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.