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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:
- PRM1, vicinity Samedan Switzerland, 2010 (On 19 December 2010, a Raytheon 390 inbound to Samedan from Zagreb made a daylight approach to runway 21 at destination in marginal VMC which involved a steep and unstable descent from which a landing was not possible. The subsequent go around was followed by entry to a visual right hand circuit which was contrary to local procedures due to terrain constraints. Overbanking in the turn towards final approach was followed by a stall and loss of control which led to ground impact which, with the post crash fire, destroyed the aeroplane and fatally injured both occupants.)
- B738, vicinity Denpasar Bali Indonesia, 2013 (On 13 April 2013, a Lion Air Boeing 737-800 flew a day non precision approach to runway 09 at Bali (Denpasar) and continued when the required visual reference was lost below MDA. Despite continued absence of visual reference, the approach was continued until the EGPWS annunciation 'TWENTY', when the aircraft commander called a go around. Almost immediately, the aircraft hit the sea surface to the right of the undershoot area and broke up. All 108 occupants were rescued with only four sustaining serious injury. The Investigation attributed the accident entirely to the actions and inactions of the two pilots.)
- A320/E190/B712, vicinity Helsinki Finland, 2013 (On 6 February 2013, ATC mismanagement of an Airbus A320 instructed to go around resulted in loss of separation in IMC against the Embraer 190 ahead which was obliged to initiate a go around when no landing clearance had been issued due to a Boeing 737-800 still on the runway after landing. Further ATC mismanagement then resulted in a second IMC loss of separation between the Embraer 190 and a Boeing 717 which had just take off from the parallel runway. Controller response to the STCA Alerts generated was found to be inadequate and ANSP procedures in need of improvement.)
- A310, Vienna Austria, 2000 (On 12 July 2000, a Hapag Lloyd Airbus A310 was unable to retract the landing gear normally after take off from Chania for Hannover. The flight was continued towards the intended destination but the selection of an en route diversion due to higher fuel burn was misjudged and useable fuel was completely exhausted just prior to an intended landing at Vienna. The aeroplane sustained significant damage as it touched down unpowered inside the aerodrome perimeter but there were no injuries to the occupants and only minor injuries to a small number of them during the subsequent emergency evacuation.)
- B738, Kingston Jamaica, 2009 (On 22 December 2009, the flight crew of an American Airlines’ Boeing 737-800 made a long landing at Kingston at night in heavy rain and with a significant tailwind component and their aircraft overran the end of the runway at speed and was destroyed beyond repair. There was no post-crash fire and no fatalities, but serious injuries were sustained by 14 of the 154 occupants. The accident was attributed almost entirely to various actions and inactions of the crew. Damage to the aircraft after the overrun was exacerbated by the absence of a RESA.)
- 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.