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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:
- B752, en-route, Northern Ghana, 2009 (On 28 January 2009 the crew of a Boeing 757-200 continued takeoff from Accra Ghana despite becoming aware of an airspeed discrepancy during the take off roll. An attempt to resolve the problem failed and the consequences led to confusion as to what was happening which prompted them to declare a MAYDAY and return - successfully - to Accra. The left hand pitot probe was found to be blocked by an insect. The Investigation concluded that a low speed rejected takeoff would have been more appropriate than the continued take off in the circumstances which had prevailed.)
- DH8D, Kathmandu Nepal, 2018 (On 12 March 2018, a Bombardier DHC8-400 departed the side of landing runway 20 at Kathmandu after erratic visual manoeuvring which followed a mis-flown non-precision approach to the opposite runway direction and was destroyed. The Investigation concluded that the accident was a consequence of disorientation and loss of situational awareness on the part of the Captain and attributed his poor performance to his unfitness to fly due to mental instability. A history of depression which had led to his release from service as a military pilot and a subsequent period of absence from any employment as a pilot was noted.)
- F50, vicinity Nairobi Kenya, 2014 (On 2 July 2014, a Fokker 50 fully loaded - and probably overloaded - with a cargo of qat crashed into a building and was destroyed soon after its night departure from Nairobi after failing to climb due to a left engine malfunction which was evident well before V1. The Investigation attributed the accident to the failure of the crew to reject the takeoff after obvious malfunction of the left engine soon after they had set takeoff power which triggered a repeated level 3 Master Warning that required an automatic initiation of a rejected takeoff.)
- A319, vicinity Tunis Tunisia, 2012 (On 24 March 2012, an Air France Airbus A319 Captain continued descent towards destination Tunis at high speed with the landing runway in sight well beyond the point where a stabilised approach was possible. With 5nm to go, airspeed was over 100 KIAS above the applicable VApp and the aircraft was descending at over 4000fpm with flaps zero. EGPWS activations for Sink Rate, PULL UP and Too Low Terrain apparently went unnoticed but at 400 feet agl, ATC granted a crew request for a 360° turn. The subsequent approach/landing was without further event. Investigation attributed the event to “sloppy CRM”.)
- A319, Rio de Janeiro Galeão Brazil, 2017 (On 19 July 2017, an Airbus A319 crew ignored the prescribed non-precision approach procedure for which they were cleared at Rio de Janeiro Galeão in favour of an unstabilised “dive and drive” technique in which descent was then continued for almost 200 feet below the applicable MDA and led to an EGPWS terrain proximity warning as a go around was finally commenced in IMC with a minimum recorded terrain clearance of 162 feet. The Investigation noted the comprehensive fight crew non-compliance with a series of applicable SOPs and an operational context which was conducive to this although not explicitly causal.)
- 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.