(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 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’ total absence of situational awareness noting 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.
On 14 October 2019, a Sikorsky S92A manoeuvring below low cloud in poor daylight visibility in an unsuccessful attempt to locate the intended private landing site flew north towards rising ground approximately ¾ mile east of it, coming within a recorded 28 feet above terrain near to occupied houses before making an emergency climb and over-torqing the engines followed by an unstable but successful second approach. The Investigation found relevant operator procedures absent or ineffective, an intention by the management pilot in command to reach the landing site despite conditions and uncertainty about the applicable regulatory context for the flight.
On 20 January 2020, a Bombardier DHC8-300 crew opted for a visual approach into Schefferville and after the First Officer significantly misjudged the approach, it was continued to a landing despite being well outside the operator’s stabilised approach criteria with the high rate of descent and excessive nose-up attitude resulting in structural damage to the aircraft. The Investigation noted the context for the event was inadequate operator procedures, pilot training and monitoring of procedural compliance in the presence of systemically ineffective regulatory oversight and observed that it appeared that unstabilised approaches at the operator may be occurring with unacceptable regularity.
On 22 December 2018, a Boeing 747-400 crew began to climb from FL310 without clearance and prescribed separation was lost against both an opposite direction Boeing 777-300 at FL 320 and another same direction Boeing 777-300 cleared to fly at FL330. The Investigation found that the 747 crew had requested FL 390 and then misunderstood the controller’s response of “level available 350” as a clearance to climb and gave a non-standard response and began to climb when the controller responded instructing the flight to standby for higher. Controller attempts to resolve the resultant ‘current conflict warnings’ were only partially successful.
On 13 September 2016, a Boeing 737-300 made an unstabilised approach to Wamena and shortly after an EGPWS ‘PULL UP’ warning due to the high rate of descent, a very hard landing resulted in collapse of the main landing gear, loss of directional control and a lateral runway excursion. The Investigation found that the approach had been carried out with both the cloudbase and visibility below the operator-specified minima and noted that the Captain had ignored a delayed go around suggestion from the First Officer because he was confident he could land safely as the two aircraft ahead had done.
On 29 January 2015, a Boeing 737-800 crew attempting to fly an NDB approach to Bergerac, with prior awareness that it would be necessary because of pre-notified ILS and DME unavailability, descended below 800 feet agl in IMC until an almost 1000 feet per minute descent when still over 8 nm from the runway threshold triggered an EGPWS ‘TERRAIN PULL UP’ warning and the simultaneous initiation of a go-around. The Investigation found that the PF First Officer was unfamiliar with NDB approaches but had not advised the Captain which resulted in confusion and loss of situational awareness by both pilots.
On 22 August 2019, the left engine of a Boeing 737-800 failed for unknown reasons soon after reaching planned cruise level of FL360 twenty minutes after departing Samos, Greece and two attempted relights during and after descent to FL240 were unsuccessful. Instead of diverting to the nearest suitable airport as required by applicable procedures, the management pilot in command did not declare single engine operation and completed the planned flight to Prague, declaring a PAN to ATC only on entering Czech airspace. The Investigation noted that engine failure was due to fuel starvation after failure of the engine fuel pump.
On 10 April 2018, a Boeing 737-800 crew making a night takeoff from Brasilia did not see a small aircraft which had just landed on the same runway until it appeared in the landing lights with rotation imminent. After immediately setting maximum thrust and rotating abruptly, the 737 just cleared the other aircraft, an Embraer 110 whose occupants were aware of a large aircraft passing very low overhead whilst their aircraft was still on the runway. The Investigation attributed the conflict primarily to controller use of non-standard phraseology and the absence of unobstructed runway visibility from the TWR.
On 26 January 2020, a Sikorsky S76B on a night VFR passenger flight was observed to emerge from low cloud shortly after ATC had lost contact with it following a report that it was climbing to 4000 feet. It had then almost immediately crashed into terrain, destroying the aircraft and killing all its occupants. The Investigation found that the helicopter had been serviceable and that the pilot had lost control after intentionally continuing into IMC and then attempting to climb which resulted in spatial disorientation. The aircraft operator’s inadequate risk management was found to have contributed to the accident outcome.
- 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.