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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 Tel Aviv Israel, 2012 (On 3 April 2012, the crew of an Air France Airbus A320 came close to loosing control of their aircraft after accepting, inadequately preparing for and comprehensively mismanaging it during an RNAV VISUAL approach at Tel Aviv and during the subsequent attempt at a missed approach. The Investigation identified significant issues with crew understanding of automation - especially in respect of both the use of FMS modes and operations with the AP off but the A/T on - and highlighted the inadequate provision by the aircraft operator of both procedures and pilot training for this type of approach.)
- 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.)
- A343, vicinity Paris CDG France, 2012 (On 13 March 2012, an A340-300 crew cleared for a Cat 3 ILS approach at Paris CDG with LVP in force failed to descend at a rate which would allow the aircraft to capture the ILS GS and at 2nm from the runway, when still 2500 feet above runway height, the ILS GS mode engaged on a false upper lobe of about 10° and as a result of the consequent rapid pitch up and speed reduction, aircraft control was almost lost. After a period of further confusion, a go around was initiated and the subsequent approach was uneventful.)
- B734, Timbuktu Mali, 2017 (On 5 May 2017, a Boeing 737-400 made a visual approach to Timbuktu and slightly overran the end of the 2,170 metre-long runway into soft ground causing one of the engines to ingest significant quantities of damaging debris. The Investigation found that the landing had been made with a significantly greater than permitted tailwind component but that nevertheless had the maximum braking briefed been used, the unfactored landing distance required would have been well within that available. The preceding approach was found to have been comprehensively unstable throughout with no call for or intent to make a go around.)
- B722, Lagos Nigeria, 2006 (On 7 September 2006, a DHL Boeing 727-200 overran the runway at Lagos by 400 metres after the First Officer was permitted to attempt a landing in challenging weather conditions on a wet runway off an unstable ILS approach. Following a long and fast touchdown at maximum landing weight, a go around was then called after prior selection of thrust reversers but was not actioned and a 400 metre overrun onto soft wet ground followed. The accident was attributed to poor tactical decision making by the aircraft commander.)
- 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.