(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:
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 entirely to the actions of the Captain which included disregarding 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.
On 24 February 2016 a DHC6 (9N-AHH) on a VFR flight to Jomsom which had continued towards destination after encountering adverse weather impacted remote rocky terrain at an altitude of almost 11,000 feet approximately 15 minutes after takeoff after intentionally and repeatedly entering cloud in order to reach the destination. The aircraft was destroyed and all on board were killed. The Investigation attributed this to the crew’s repeated decision to fly in cloud and their deviation from the intended route after losing situational awareness. Spatial disorientation followed and they then failed to respond to repeated EGPWS cautions and warnings.
On 10 June 2018, a Boeing 737-800 departing Amsterdam with line training in progress and a safety pilot assisting only became airborne just before the runway end. The Investigation found that the wrong reduced thrust takeoff performance data had been used without any of the pilots noticing and without full thrust being selected as the end of the runway approached. The operator was found to have had several similar events, not all of which had been reported. The implied absence at the operator of a meaningful safety culture and its ineffective flight operations safety oversight process were also noted.
On 12 September 2020, during a largely autopilot-controlled ILS glideslope capture from above and despite being unstabilised after the crew had intentionally ignored required approach management procedures, a flight was continued without hesitation to a landing. The Investigation found that the operator’s oversight of operating standards relating to unstabilised approaches was systemically flawed and also insufficiently supportive of their ‘Evidence Based Training’ method used for pilot training. It was also noted that the Captain involved had stated to the Investigation that “he considered this flight as a non event”.
On 18 July 2018, an Airbus A330-300 failed to reject its night takeoff from Brisbane despite the absence of any airspeed indication for either pilot. A PAN call was made as a climb to FL110 continued. Once there, preparations for a somewhat challenging return were made and subsequently achieved. The Investigation noted multiple missed opportunities, including non-compliance with several procedural requirements, to detect that all pitot mast covers had remained in place and was extremely concerned that the takeoff had been continued rather than rejected. Flawed aircraft operator ground handling procedures and ineffective oversight of contractors were also deemed contributory.
On 18 September 2018, an Airbus A320 crewed by a Training Captain and a trainee Second Officer departing Sharjah was cleared for an intersection takeoff on runway 30 but turned onto the 12 direction and commenced takeoff with less than 1000 metres of runway ahead. On eventually recognising the error the Training Captain took control, set maximum thrust and the aircraft became airborne beyond the end of the runway and completed its international flight. The Investigation attributed the event to the pilots’ absence of situational awareness and noted that after issuing takeoff clearance, the controller did not monitor the aircraft.
On 11 September 2019, a Boeing 737-800 landed at night on Runway 13 at Malaga only 520 metres behind a departing Boeing 737-800 which was about to become airborne from the same runway. The Investigation noted the relatively low level of aircraft movements at the time, that both aircraft had complied with their respective clearances and that the landing aircraft crew had judged it safer to land than to commence a late go around. The conflict was attributed to non-compliance with the regulatory separation minima and deficient planning and decision making by the controller.
On 16 May 2013, a DHC6-300 on a domestic passenger flight made a tailwind touchdown at excessive speed in the opposite direction of the of 740 metre-long runway to the notified direction in use and, after departing the runway to one side during deceleration, re-entered the runway and attempted to take off. This failed and the aircraft breached the perimeter fence and fell into a river. The Investigation identified inappropriate actions of the aircraft commander in respect of both the initial landing and his response to the subsequent runway excursion and also cited the absence of effective CRM.
On 7 August 2020, a Boeing 737-800 making its second attempt to land at Calicut off a night ILS approach with a significant tailwind component became unstabilised and touched down approximately half way down the 2,700 metre-long wet table top runway and departed the end of it at 85 knots before continuing through the RESA and a fence and then dropping sharply onto a road. This caused the fuselage to separate into three pieces with 97 of the 190 occupants including both pilots being fatally or seriously injured and 34 others sustaining minor injuries. Significant fuel spillage occurred but there was no fire.
On 3 May 2019, a Boeing 737-800 significantly overran the wet landing runway at Jacksonville Naval Air Station at night when braking action was less than expected and ended up in shallow tidal water. The Investigation found that although the approach involved had been unstabilised and made with a significant tailwind and with only a single thrust reverser available, these factors had not been the cause of the overrun which was entirely attributable to attempting to complete a landing after touching down on a wet runway during heavy rain in conditions which then led to viscous aquaplaning.
On 7 November 2018, a Boeing 747-400F overran wet landing runway 14 at Halifax at night and was sufficiently damaged as a result of exceeding the available RESA to render it a hull loss. The Investigation attributed the overrun to a combination of factors including use of un-factored landing distance, momentary mishandling of the thrust levers just after touchdown, a pilot-caused lateral deviation diverting attention from deceleration, inadequate braking and late recognition of an approach tailwind component. Poor NOTAM presentation of runway availability also led the crew to believe that the longer and more suitable runway 25 was not available.
- 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.