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 17 October 2022, an Airbus A320neo was unable to even make an approach at either its intended destination of Riohacha or its designated alternate after those airports were both closed because of adverse convective weather which developed over a significant part of Northern Columbia. A MAYDAY was declared due to low fuel and only 282 kg remained after the eventual landing at Santa Marta. Decision making by both the aircraft Operator and the flight crew involved and a lack of reliable communication between them was deemed contributory to what came very close indeed to being a hull loss accident.

On 3 January 2024, a Boeing 737-800 taxiing for departure at Copenhagen was cleared to the assigned holding point, unaware that snow clearance vehicles had been tasked with slush clearance from the same taxiway route and the departure runway. On seeing that two such vehicles had pulled off the taxiway onto the adjacent hard surface and stopped, the aircraft captain, judging that sufficient wingtip clearance would exist, continued taxiing past. However, one of the vehicle drivers expressed concern about the perceived clearance. The investigation concluded that better tactical communication between airport management and air traffic control could have helped.

On 22 January 2022, an Airbus A320 departing the uncontrolled airport at Hayden, Colorado, announced its intended runway 10 takeoff despite calls from a Beech King Air 350 that it was inbound to reciprocal runway 28. When the A320 crew subsequently announced they were commencing takeoff from 10, the King Air Pilot responded by asking if the A320 was intending a quick turnout. Almost immediately after confirmation, the A320 captain rotated 24 knots before the correct speed with a resulting tail strike. Once airborne, an evasive right turn was commenced with the reciprocal-direction King Air just over 2 nm away.

On 17 October 2023 a Boeing 737-800 passing FL130 after departing Manchester received a cabin pressurisation warning, and the crew recognised that both engine air bleeds were off. After correcting this, climb was continued without donning oxygen masks until an air conditioning pack fault occurred, which prompted the operator to request a return which was uneventful. The bleeds-off condition had arisen after maintenance and had then not been recognised at release to service or during crew preflight checks. 

On 18 December 2022, an Airbus A330-200 in cruise at FL400 in visual meteorological conditions (VMC) was flown through the isolated top of a building convective cloud after its vertical development rate was underestimated. A short but severe turbulence upset and brief loss of control resulted. A few minutes earlier air traffic control (ATC) had advised that “moderate to extreme precipitation and turbulence could be expected for the next 40 miles." Cabin service was in progress, and the turbulence resulted in 24 unsecured cabin crew and passengers being injured, four seriously. Some cabin trim detached and some equipment was damaged.

On 13 January 2023, in good night visibility, a Boeing 777-200 with an augmented crew did not comply with its departure taxi clearance and crossed a runway in front of a 737 on the takeoff roll. ATC responded to an automated conflict warning by cancelling the takeoff clearance, and the 737 initiated a high-speed rejected takeoff from approximately 105 knots. Minimum separation as the 777 cleared the edge of the departure runway was approximately 300 metres. The investigation concluded that the 777 operator’s risk controls and the airport’s methods for detecting and preventing runway conflicts were both inadequate.

On 12 March 2022, an ATR76-600 captain made an unstabilised approach to Jabalpur, India, leading to a first bounce more than halfway 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. 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 experienced captain had misaligned the aircraft whilst the 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. This advisory came as the crew continued the approach after visual reference was temporarily lost. A repeat of this warning by ATC prompted crew recognition that the aircraft was low and off the required approach track. 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 with a Boeing 787-8 also inbound to Mumbai on the same airway. The 787-9 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 contacting 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 correct technique to regain the runway centreline, and go-around calls from the monitoring pilot shortly before and immediately after touchdown were 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. 

References

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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