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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.
Unconscious bias in thinking leads to a pilot or controller following the originally-intended course of action. This bias appears to be stronger as the culmination of a task nears, for example during the flying of an approach to land or the maintenance of the planned separation between aircraft sequenced for approach to a particular runway.
Continuation Bias may have the effect of obscuring subtle cues which indicate that original conditions and assumptions have changed. It may also act in combination with other cognitive biases.
Accidents and Incidents
SKYbrary includes the following reports relating to events where continuation bias was considered to be a factor:
- DC91 / B722, Detroit MI USA, 1990 (On 3 December 1990 a Douglas DC9-10 flight crew taxiing for departure at Detroit in thick fog got lost and ended up stopped to one side of an active runway where, shortly after reporting their position, their aircraft was hit by a departing Boeing 727-200 and destroyed by the impact and subsequent fire. The Investigation concluded that the DC9 crew had failed to communicate positional uncertainty quickly enough but that their difficulties had been compounded by deficiencies in both the standard of air traffic service and airport surface markings, signage and lighting undetected by safety regulator oversight.)
- A109, vicinity London Heliport London UK, 2013 (On 16 January 2013, an Augusta 109E helicopter positioning by day on an implied (due to adverse weather conditions) SVFR clearance collided with a crane attached to a tall building under construction. It and associated debris fell to street level and the pilot and a pedestrian were killed and several others on the ground injured. It was concluded that the pilot had not seen the crane or seen it too late to avoid whilst flying by visual reference in conditions which had become increasingly challenging. The Investigation recommended improvements in the regulatory context in which the accident had occurred.)
- MA60, vicinity Kaimana West Papua Indonesia, 2011 (On 7 May 2011, the crew of a Xian MA60 lost control of their aircraft during an attempted go around at Kaimana after failing to obtain sufficient visual reference to complete the approach despite a significant violation of the minima for the required visual-only approach. The aircraft was destroyed by the high speed impact and all occupants were killed. The Investigation found that the crew had comprehensively failed to conduct the go around procedure as prescribed and it was suspected that the new-to-type Captain may have reverted to procedures for his previous jet aircraft type after ineffective type conversion training.)
- B190, Blue River BC Canada, 2012 (On 17 March 2012, the Captain of a Beech 1900C operating a revenue passenger flight lost control of the aircraft during landing on the 18metre wide runway at destination after an unstabilised day visual approach and the aircraft veered off it into deep snow. The Investigation found that the Operator had not specified any stable approach criteria and was not required to do so. It was also noted that VFR minima had been violated and, noting a fatal accident at the same aerodrome five months previously, concluded that the Operators risk assessment and risk management processes were systemically deficient.)
- C501, vicinity Trier-Fohren Germany, 2014 (On 12 January 2014, the crew of a Cessna 501 on a private business flight with a two-pilot crew attempted to make an unofficial GPS-based VNAV approach in IMC to the fog-bound VFR-only uncontrolled aerodrome at Trier-Fohren. However, after apparently mis-programming the 'descend-to' altitude and deviating from the extended centre, the aircraft emerged from the fog very close to the ground and after pulling up collided with obstructions, caught fire and crashed killing all occupants. The Investigation noted an apparent absence of pre-flight weather awareness beyond the intended destination and that there was a suitable fog-free diversion.)
- B733, Yogyakarta Indonesia, 2011 (On 20 December 2011, the experienced Captain of a Sriwijaya Air Boeing 737-300 flew an unstabilised non-precision approach to a touchdown at Yogyakarta at excessive speed whilst accompanied by a very inexperienced First Officer. The aircraft overran the end of the 2200 metre-long wet runway by 75 metres . During the approach, the Captain 'noticed' several GPWS PULL UP Warnings but no action was taken. The Investigation attributed the accident entirely to the actions of the flight crew and found that there had been no alert calls from the First Officer in respect of the way the approach was flown.)
- B735, vicinity Kazan Russia, 2013 (On 17 November 2013, the crew of a Boeing 737-500 failed to establish on the ILS at Kazan after not following the promulgated intermediate approach track due to late awareness of LNAV map shift. A go around was eventually initiated from the unstabilised approach but the crew appeared not to recognise that the autopilot used to fly the approach would automatically disconnect. Non-control followed by inappropriate control led to a high speed descent into terrain less than a minute after go around commencement. The Investigation found that the pilots had not received appropriate training for all-engine go arounds or upset recovery.)
- B738/A321, Prague Czech Republic, 2010 (On 18 June 2010 a Sun Express Boeing 737-800 taxiing for a full length daylight departure from runway 06 at Prague was in collision with an Airbus 321 which was waiting on a link taxiway leading to an intermediate take off position on the same runway. The aircraft sustained damage to their right winglet and left horizontal stabiliser respectively and both needed subsequent repair before being released to service.)
- PC6, Evora Portugal, 2012 (On 29 July 2012, the rudder of a Pilatus PC6 detached in flight and fell onto the stabiliser/elevator preventing its normal movement. Pitch control was gained using the electric stabiliser trim and a successful touchdown was achieved on the second attempt. However, directional control could not be maintained and a lateral runway excursion followed. Investigation attributed the rudder failure to maintenance error which went undetected. Unapproved dispensation by the maintenance organisation involved, which allowed some dual inspections for correct completion of safety critical tasks to be carried out by the same person, was considered to be a significant contributory factor.)
- A318/B738, Nantes France, 2010 (On 25 May 2010 an Air France Airbus A318 making an automatic landing off an ILS Cat 2 approach at Nantes experienced interference with the ILS LOC signal caused by a Boeing 737-800 which was departing from the same runway but early disconnection of the AP removed any risk of un-correctable directional control problems during the landing roll. Both aircraft were operating in accordance with their ATC clearances. Investigation attributed the conflict to the decision of TWR not to instruct the A318 to go around and because of diminished situational awareness.)
- A320, vicinity Lyons Saint-Exupéry France, 2012 (On 11 April 2012, a Hermes Airlines A320 commanded by a Training Captain who was also in charge of Air Operations for the airline was supervising a trainee Captain on a night passenger flight. The aircraft failed to establish on the Lyons ILS and, in IMC, descended sufficiently to activate both MSAW and EGPWS 'PULL UP' warnings which eventually prompted recovery. The Investigation concluded that application of both normal and emergency procedures had been inadequate and had led to highly degraded situational awareness for both pilots. The context for this was assessed as poor operational management at the airline.)
- SH36, vicinity Oshawa ON Canada, 2004 (On 16 December 2004, an Air Cargo Carriers Shorts SD3-60 attempted to land at Oshawa at night on a runway covered with 12.5mm of wet snow which did not offer the required landing distance. After unexpectedly poor deceleration despite selection of reverse propeller pitch, full power was applied and actions for a go around were taken. Although the aircraft then became airborne in ground effect, it subsequently failed to achieve sufficient airspeed to sustain a climb and an aerodynamic stall was followed by impact with terrain and trees beyond the end of the runway. The aircraft was substantially damaged and both pilots sustained serious injuries but there was no post-crash fire)
- … further results
- 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.