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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:
- A320, vicinity Lyons Saint-Exupéry France, 2012 (On 11 April 2012, a Hermes Airlines A320 commanded by a Training Captain who was also in charge of Air Operations for the airline was supervising a trainee Captain on a night passenger flight. The aircraft failed to establish on the Lyons ILS and, in IMC, descended sufficiently to activate both MSAW and EGPWS 'PULL UP' warnings which eventually prompted recovery. The Investigation concluded that application of both normal and emergency procedures had been inadequate and had led to highly degraded situational awareness for both pilots. The context for this was assessed as poor operational management at the airline.)
- B735, Jos Nigeria, 2010 (On 24 August 2010, a Boeing 737-500 made an uncontrolled touchdown on a wet runway at Jos in daylight after the approach was continued despite not being stabilised. A lateral runway excursion onto the grass occurred before the aircraft regained the runway centreline and stopped two-thirds of the way along the 3000 metre-long runway. Substantial damage was caused to the aircraft but none of the occupants were injured. The aircraft commander was the Operator's 737 Fleet Captain and the Investigation concluded that the length of time he had been on duty had led to fatigue which had impaired his performance.)
- B752, vicinity Cali Colombia, 1995 (On 20 December 1995, an American Airlines Boeing 757-200 inbound to Cali, Colombia made a rushed descent towards final approach at destination and the crew lost positional awareness whilst manoeuvring in night VMC. After the crew failed to stow the fully deployed speed brakes when responding to a GPWS ‘PULL UP’ Warning, the aircraft impacted terrain and was destroyed with only four seriously injured survivors from the 163 occupants surviving the impact. The accident was attributed entirely to poor flight management on the part of the operating flight crew, although issues related to the FMS were found to have contributed to this.)
- DH8A, en-route SSE of Madang, Papua New Guinea, 2011 (On 13 October 2011, the Captain of a Bombardier DHC8-100 manually flying a low power, steep descent in an attempt to get below cloud to be able to see the destination aerodrome inadvertently allowed the speed to increase sufficiently to trigger an overspeed warning. In response, the power levers were rapidly retarded and both propellers entered the ground range and oversped. As a result, one engine was damaged beyond use and the other could not be unfeathered. A forced landing was made following which the aircraft caught fire. All three crew members but only one of the 29 passengers survived.)
- AT76, Lisbon Portugal, 2016 (On 22 October 2016, an ATR 72-600 Captain failed to complete a normal night landing in relatively benign weather conditions and after the aircraft had floated beyond the touchdown zone, it bounced three times before finally settling on the runway in a substantially damaged condition. The Investigation noted that touchdown followed an unstabilised approach and that there had been little intervention by the First Officer. However, it tentatively attributed the Captain’s poor performance to a combination of fatigue at the end of a repetitive six-sector day and failure of the operator to provide adequate bounced landing recognition and recovery training.)
- 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.