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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:
- A320 / A139 vicinity Zurich Switzerland, 2012 (On 29 May 2012, a British Airways Airbus A320 departing Zürich and in accordance with its SID in a climbing turn received and promptly and correctly actioned a TCAS RA 'CLIMB'. The conflict which caused this was with an AW 139 also departing Zürich IFR in accordance with a SID but, as this aircraft was only equipped with a TAS to TCAS 1 standard, the crew independently determined from their TA that they should descend and did so. The conflict, in Class 'C' airspace, was attributed to inappropriate clearance issue by the TWR controller and their inappropriate separation monitoring thereafter.)
- HUNT, manoeuvring, vicinity Shoreham UK, 2015 (On 22 August 2015 the pilot of a civil-operated Hawker Hunter carrying out a flying display sequence at Shoreham failed to complete a loop and partial roll manoeuvre and the aircraft crashed into road traffic unrelated to the airshow and exploded causing multiple third party fatalities and injuries. The Investigation found that the pilot had failed to enter the manoeuvre correctly and then failed to abandon it when it should have been evident that it could not be completed. It was concluded that the wider context for the accident was inadequate regulatory oversight of UK civil air display flying risk management.)
- EC25, vicinity ETAP Central offshore platform, North Sea UK (On 18 February 2009, the crew of Eurocopter EC225 LP Super Puma attempting to make an approach to a North Sea offshore platform in poor visibility at night lost meaningful visual reference and a sea impact followed. All occupants escaped from the helicopter and were subsequently rescued. The investigation concluded that the accident probably occurred because of the effects of oculogravic and somatogravic illusions combined with both pilots being focused on the platform and not monitoring the flight instruments.)
- B738/B738, vicinity Oslo Norway, 2012 (On 31 October 2012, a Norwegian Air Shuttle Boeing 737-800 on go around after delaying the breaking off of a fast and high unstable ILS approach at Oslo lost separation in IMC against another aircraft of the same type and Operator which had just taken off from the same runway as the landing was intended to be made on. The situation was aggravated by both aircraft responding to a de-confliction turn given to the aircraft on go around. Minimum separation was 0.2nm horizontally when 500 feet apart vertically, both climbing. Standard missed approach and departure tracks were the same.)
- A319, vicinity Tunis Tunisia, 2012 (On 24 March 2012, an Air France Airbus A319 Captain continued descent towards destination Tunis at high speed with the landing runway in sight well beyond the point where a stabilised approach was possible. With 5nm to go, airspeed was over 100 KIAS above the applicable VApp and the aircraft was descending at over 4000fpm with flaps zero. EGPWS activations for Sink Rate, PULL UP and Too Low Terrain apparently went unnoticed but at 400 feet agl, ATC granted a crew request for a 360° turn. The subsequent approach/landing was without further event. Investigation attributed the event to “sloppy CRM”.)
- 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.)
- AS3B, vicinity Sumburgh Airport Shetland Islands UK, 2013 (On 23 August 2013, the crew of a Eurocopter AS332 L2 Super Puma helicopter making a non-precision approach to runway 09 at Sumburgh with the AP engaged in 3-axes mode descended below MDA without visual reference and after exposing the helicopter to vortex ring conditions were unable to prevent a sudden onset high rate of descent followed by sea surface impact and rapid inversion of the floating helicopter. Four of the 18 occupants died and three were seriously injured. The Investigation found no evidence of contributory technical failure and attributed the accident to inappropriate flight path control by the crew.)
- PRM1, vicinity Annemasse France, 2013 (On 4 March 2013, a Beechcraft Premier 1A stalled and crashed soon after take off from Annemasse. The Investigation concluded that the stall and subsequent loss of control was attributable to frozen deposits on the wings which the professional pilot flying the privately-operated aircraft had either not been aware of or had considered insignificant. It was noted that the aircraft had been parked outside overnight and that conditions had favoured frost formation. The presence of a substantial quantity of cold-soaked fuel had favoured frost formation. The presence of a substantial quantity of cold-soaked fuel in the wing tanks overnight was also noted.)
- DHC6, Jomson Nepal, 2013 (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.)
- AT72, Helsinki Finland, 2012 (On 19 August 2012, the crew of a Flybe Finland ATR 72-200 approaching Helsinki failed to respond appropriately to a fault which limited rudder travel and were then unable to maintain directional control after touchdown with a veer off the runway then following. It was concluded that as well as prioritising a continued approach over properly dealing with the annunciated caution, crew technical knowledge in respect of the fault encountered had been poor and related training inadequate. Deficiencies found in relevant aircraft manufacturer operating documentation were considered to have been a significant factor and Safety Recommendations were made accordingly.)
- SH33 / MD83, Paris CDG France, 2000 (On the 25th of May, 2000 a UK-operated Shorts SD330 waiting for take-off at Paris CDG in normal visibility at night on a taxiway angled in the take-off direction due to its primary function as an exit for opposite direction landings was given a conditional line up clearance by a controller who had erroneously assumed without checking that it was at the runway threshold. After an aircraft which had just landed had passed, the SD330 began to line up unaware that an MD83 had just been cleared in French to take off from the full length and a collision occurred.)
- RJ85, en-route, north of Tampere Finland 2009 (On 17 December 2009, a Blue 1 Avro RJ85 experienced progressive fuel starvation during continued flight after the crew had failed to carry out the QRH drill for an abnormal fuel system indication caused by fuel icing. Although hindsight was able to confirm that complete fuel starvation had not been likely, a failure to recognise the risk to fuel system function arising from routine operations in very cold conditions was identified by the subsequent investigation.)
- … 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.