Continuation Bias
Continuation Bias
Definition
(Plan) Continuation Bias is the unconscious cognitive bias to continue with the original plan in spite of changing conditions.
Discussion
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:
On 13 January 2023, in good night visibility, an augmented crew Boeing 777-200 failed to comply with its departure taxi clearance and with its Captain taxiing crossed a runway in front of a 737 taking off. ATC responded to an automated conflict warning by cancelling the takeoff clearance and a high speed rejected takeoff was initiated from approximately 105 knots with minimum separation as the 777 cleared the edge of the 737 takeoff runway approximately 300 metres. The Investigation concluded that the 777 operator’s risk controls and the airport’s methods for detecting and preventing dangerous runway conflicts were both inadequate.
On 12 March 2022, an ATR76-600 Captain made an unstabilised approach to Jabalpur before a first bounce more than half way along the runway and a final touchdown 400 metres from the runway end. The First Officer took control but did not commence a go-around and the aircraft overran the runway before stopping. The Captain had just over four months command experience and had made six similar ‘high-severity long-flare’ approaches in the previous five days but these had gone undetected because although such exceedances were supposedly being tracked by company flight data monitoring, this event was not being tracked.
On 16 February 2023, a Boeing 737-700 took off from Las Vegas in excellent night visibility aligned with the right hand runway edge lights instead of the unlit centreline without pilot awareness during or after the takeoff. Minor nosewheel tyre damage found after flight did not trigger an operator investigation and the airport only discovered the runway edge lighting damage two days later and did not identify and advise the operator until over a week had passed. The very experienced Captain had misaligned the aircraft whilst the extremely inexperienced First Officer was too busy to monitor the Captain’s actions.
On 11 February 2022 an Airbus A320 making a visual approach to Guadeloupe at night was advised by ATC of a descent below the minimum safe altitude after continuing the approach after visual reference was temporarily lost. A repeat of this warning by ATC prompted crew recognition that the aircraft was not on the required approach track or profile and a go around was initiated from 460 feet agl. The decision to attempt a visual approach in unsuitable circumstances and a delay in recognising the need for a go-around were found to have been symptomatic of poor tactical decision making.
On 14 September 2022, a Boeing 787-9 inbound to Mumbai lost separation against a Boeing 787-8 also inbound to Mumbai on the same airway when it began a descent from FL410 to FL340 at night without clearance close to an air traffic control sector boundary. ATC soon observed the error but a delay in achieving contact with the 787-9 resulted in it descending to FL389 before being instructed to return to its cleared level. As it passed through FL390 descending and then again when climbing, it came within 3nm of the same-direction 787-8 which was level as cleared at FL390.
On 2 March 2023, an Airbus A380-800 landing at Singapore in heavy rain drifted to the right of the runway centreline after the autopilot was disengaged before touching down close to the runway edge. The aircraft continued to drift right and the right main landing gear briefly left the runway and damaged several edge lights before regaining it. The handling pilot did not use the correct technique to regain the runway centreline before or after touchdown and go-around calls from the monitoring pilot shortly before and immediately after touchdown were respectively not understood/heard despite compliance with such calls being mandatory.
On 31 January 2022, a Bombardier Challenger 604 pilot lost control during the final stages of a London Stansted night crosswind landing. A bounced nose-gear-first touchdown was followed by a brief runway excursion onto grass before a return to the runway and a climb away. A diversion to London Gatwick followed without further event but subsequent inspection revealed structural and other damage sufficient to result in the aircraft being declared an economic hull loss. The Stansted touchdown was found to have occurred after a premature flare at idle thrust continued towards the stall and a momentary stick pusher activation occurred.
On 24 October 2021, a Bombardier DHC8-400 inbound to Belagavi initially advised to expect a non-precision approach to runway 08 was subsequently cleared for an equivalent approach to runway 26. An approach to runway 08 was then flown without ATC intervention or pilot error recognition, but with no actual consequences. The error was attributed to pilot expectation bias and distraction and controller failure to order a go-around after eventually realising what was happening. The context that had facilitated the errors was considered to be procedure and performance inadequacy at both the aircraft operator and ATC.
On 8 June 2022, a Boeing 757-200 making a night visual approach to Tulsa inadvertently landed on runway 18R instead of 18L as briefed and cleared. ATC did not intervene. Neither pilot recognized the error until the captain realized there was less runway ahead than he had expected. He had planned to "roll long," expecting a the turnoff at the end of the much longer runway 18L. Although both pilots reported not being fatigued, it was concluded that lack of recognition of their error suggested otherwise, and probably facilitated plan continuation bias aided by inability to efficiently integrate available information.
On 3 February 2022, a Boeing 737-200F collided with a tree shortly after a daylight normal visibility takeoff from Puerto Carreño which resulted in engine stoppage although a subsequent restart was partially successful and a return to land was subsequently completed without further event. The collision was attributed to a combination of a slightly overweight takeoff and a slight delay in rotation which in the prevailing density altitude conditions prevented the rate of climb necessary to clear the obstacle. The context for the accident was assessed as a deficient operational safety culture at the company involved.
On 27 January 2020, an MD83 made an unstabilised tailwind non-precision approach to Mahshahr with a consistently excessive rate of descent and corresponding EGPWS Warnings followed by a very late nose-gear-first touchdown. It then overran the runway end, continued through the airport perimeter fence and crossed over a ditch before coming to a stop partly blocking a busy main road. The aircraft sustained substantial damage and was subsequently declared a hull loss but all occupants completed an emergency evacuation uninjured. The accident was attributed to the actions of the Captain which included not following multiple standard operating procedures.
On 24 October 2021, a Shorts SD360 intending to land at the international airport serving Ndola did so at the recently closed old international airport after visually navigating there in hazy conditions whilst unknowingly in contact with ATC at the very recently opened new airport which had taken the same name and radio frequencies as the old one. The Investigation found multiple aspects of the airport changeover and re-designation had been mismanaged, particularly but not only failure to publish new flight procedures for both airports and ensure that NOTAM communication of the changes internationally had been effective.
On 6 December 2018, a Boeing 737-700 overran the 1,770 metre-long landing runway at destination by 45 metres after entering the EMAS. Normal visibility prevailed but heavy rain was falling and a 10 knot tailwind component existed. The event was attributed to the pilots’ continuation bias in the face of deteriorating conditions and a late touchdown on the relatively short runway. A lack of guidance from the operator on the need for pilots to re-assess the validity of landing data routinely obtained at the top of descent was identified.
On 4 March 2019, an Embraer 145 attempting to land off an ILS approach at Presque Isle in procedure-minima weather conditions flew an unsuccessful first approach and a second in similar conditions which ended in a crash landing abeam the intended landing runway substantially damaging the aircraft. The accident was attributed to the crew decision to continue below the applicable minima without acquiring the required visual reference and noted that the ILS localiser had not been aligned with the runway extended centreline and that a recent crew report of this fault had not been promptly passed to the same Operator.
On 29 November 2017, a Boeing 737-900 on an ILS approach at Atlanta became unstable after the autothrottle and autopilot were both disconnected and was erroneously aligned with an occupied taxiway parallel to the intended landing runway. A go-around was not commenced until the aircraft was 50 feet above the ground after which it passed low over another aircraft on the taxiway. The Investigation found that the Captain had not called for a go around until well below the Decision Altitude and had then failed to promptly take control when the First Officer was slow to begin climbing the aircraft.
References
- TSB. Air Transportation Safety Investigation Report A18P0031 Loss of Control and Collision with Terrain. 14 August 2019.
Related Articles
Further Reading
- 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.
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