Pilots and air traffic controllers (ATCOs) perform lengthy and complex procedures in the course of their duties. An interruption breaks the thread of these procedures and can have undesirable consequences. Distractions can make it difficult for the pilot or ATCO to concentrate on the task in hand.
Types of Interruption
Interruption on the flight deck may result from causes within the aircraft, e.g. the occupant(s) of (the) flight deck supernumary crew seat (s), the activation of an caution or warning, the activation of a cabin crew call alert, unexpected information from ATC or the operating Company.
Interruption may also occur in the control room, e.g. due to a telephone call, a message from a colleague or detection of a potential airspace infringement or level bust.
Types of Distraction
Examples of circumstances where distraction may occur on the flight deck include non-relevant conversation, equipment malfunction and adverse weather.
For the ATCO, distraction may result from extraneous noise, e.g. loud conversation between colleagues, or from an uncomfortable or inconvenient position.
On the flight deck, the interruption of a procedure may result in missing a vital checklist action or failing to follow correctly a prescribed procedure.
In the control room, interruption may cause an ATCO to fail to take an intended action.
Distraction on the flight deck or in the control room may make it difficult for the pilot or ATCO to concentrate on his/her task, possibly resulting in error or omission.
Well designed and diligently applied Standard Operating Procedures (SOPs) should minimise the prevalence of, or significant effect from, interruptions and distractions. For example, the sterile flight deck procedure implemented by many airlines below FL100 reduces distractions and interruptions during a period which can be expected to result in relatively high-workload situations during most flights. However, these same arrangements are often not applied to critical elements of the pre flight process. As an example, departure performance calculations made by the crew prior to engine start are done at a time when the risk of interruption or distraction within, or external to, the crew is routinely high.
- A flight deck checklist is interrupted by an interphone call from the cabin crew; the checklist is subsequently resumed but an important action is omitted.
- A discussion of non-relevant matters is carried out on the flight deck and none of the crew members present notice that they have entered an active runway without clearance.
- Cross checking of take off performance calculations being made in the flight deck prior to engine start is interrupted by the arrival of the dispatcher.
- An ATCO misses an important message due to a radio playing in the control room.
- Review and if necessary improve SOPs
- Insist that SOPs are followed
- Review and if necessary improve the design of the ATCO’s position
- Review and if necessary improve crew resource management (CRM) and TRM training provisions
Accidents & Incidents
Events on the SKYbrary Accident and Incident Database where the Official Investigation included reference to Distraction as an element in causation:
On 24 October 2021, a Bombardier DHC8-400 inbound to Belagavi initially advised to expect a non-precision procedural approach to runway 08 was subsequently instructed and acknowledged clearance for an equivalent procedural 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 which had facilitated the errors was considered to be procedure and performance inadequacy at both the aircraft operator and ATC.
On 25 November 2021, a Fokker F50 departing Helsinki experienced an engine malfunction which resulted in un-commanded propeller feathering following which the associated engine continued to run until shutdown during which time it began to overspeed. Recovery to a landing was subsequently achieved but the failure experienced was untrained and this led to both direct and indirect consequences which resulted in a sub optimal crew response to the emergency. The Investigation also highlighted opportunities to improve aspects of the air traffic control emergency response during such emergencies and identified language proficiency certification issues.
On 20 July 2020, a Boeing 787-10 making an ILS approach to runway 09L at Paris CDG unexpectedly received landing clearance for runway 09R after transferring to TWR. The crew readback added explicit reference to the implied need to sidestep but elicited no further controller response and visual realignment to 09R followed. The controller then cleared a departing A320 to enter 09R but when its crew saw the 787 on very short final after crossing the holding point, they stopped, informed TWR and directly instructed the 787 to go-around. Investigation confirmed the controller’s error and noted their failure to monitor approaching traffic.
On 20 October 2021, the flight crew of a Bombardier CRJ1000 making a LNAV/VNAV approach at Nantes using Baro-VNAV minima read back an incorrect QNH which was not noticed by the controller. The crew then flew the approach approximately 530 feet below the procedure vertical profile which led to the MSAW system being activated and advised to the flight. The crew response was delayed until the controller had twice repeated the correct QNH after which the error was recognised and the vertical profile corrected. The investigation noted that neither the operator’s procedures nor aircraft instruments allowed straightforward crew detection of their error.
On 28 September 2022, a Boeing 787-9 and an Airbus A330-200 were successively cleared for takeoff from Sydney having been instructed to follow the same SID and climb to the same level - FL280. The A330 climbed faster than the controller anticipated and turned towards the next waypoint inside the preceding aircraft, resulting in a loss of separation. The Investigation found that the SID concerned did not provide separation assurance to aircraft with different performance characteristics because aircraft had to satisfy two separate conditions prior to turning which meant the turning point was not a fixed position.
On 23 January 2020, a Bombardier CRJ700 making a HUD-supported manual Cat 3a ILS approach to Lyon Saint-Exupéry in freezing fog conditions deviated from the required flight path localiser and reached a minimum of 265 feet agl before a go around was initiated without initially being flown in accordance with standard procedures. The Captain involved was relatively new to type and had not previously flown such an approach in actual low visibility conditions. The Investigation was not able to determine exactly what contributed to the approach and initial go around being misflown but identified a number of possible contributors.
On 1 November 2021, a deHavilland DHC6-300 crew en-route to Fort Simpson realised that they had insufficient fuel on board to reach their intended destination and therefore decided to attempt a diversion to the nearest available airport at Fort Providence. As fuel available dwindled, one engine was shut down but after an inadvertent fuel tank selection, the initially intended diversion was no longer possible and a forced landing in a bog was successfully accomplished. The Training Captain involved had developed a habit of performing checklists silently and from memory after gaining all his professional pilot experience at the same operator.
On 1 December 2021, a lightly loaded Boeing 737-800 became airborne near the end of the runway at Kuusamo with only engine run-up thrust set with only the abnormally low climb rate alerting the crew to their error. Serial failure by both pilots to follow relevant normal takeoff procedures followed after the type-experienced First Officer had been surprised when the aircraft began to move because his inexperience in brake use resulted in insufficient brake pressure being applied during the engine run-up. The Captain’s failure to notice the error was associated with allowing himself to be distracted by a non-urgent radio call.
On 6 January 2018, a Boeing 737-900 and an Airbus A320 both inbound to Surabaya with similar estimated arrival times were cleared to hold at the same waypoint at FL100 and FL110 respectively but separation was lost when the A320 continued below FL110. Proximity was limited to 1.9nm laterally and 600 feet vertically following correct responses to coordinated TCAS RAs. The Investigation found that all clearances / readbacks had been correct but that the A320 crew had set FL100 instead of their FL110 clearance and attributed this to diminished performance due to the passive distraction of one of the pilots.
On 16 June 2021, a Boeing 737-400 was taxiing for departure at night after push back from stand when the ground crew who completed the push back arrived back at their base in the tug and realised that the tow bar they had used was not attached to it. The aircraft was prevented from taking off and it was then found that it had taxied over the unseen towbar and sustained damage to both nose gear tyres such that replacement was necessary. The Investigation concluded neither ground crew had checked that the area immediately ahead of the aircraft was clear.
On 3 January 2019, prescribed vertical separation was lost between a Bombardier DHC8-400 and a Piaggio P180 on converging cruise tracks at FL 220 and only restored after a resulting TCAS RA was followed. The Investigation found both aircraft were being flown in accordance with their clearances and that the controller involved had not been aware of corresponding traffic and conflict alerting system activations. A specific traffic display fault which arose from failure to follow a routine software upgrade procedure correctly and the shift supervisor failing to recognise the need to act as controller when workload increased were assessed contributory.
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 2 September 2016, an ATR72-600 cleared to join the ILS for runway 28 at Dublin continued 800 feet below cleared altitude triggering an ATC safe altitude alert which then led to a go around from around 1000 feet when still over 5nm from the landing runway threshold. The Investigation attributed the event broadly to the Captain’s inadequate familiarity with this EFIS-equipped variant of the type after considerable experience on other older analogue-instrumented variants, noting that although the operator had provided simulator differences training, the -600 was not classified by the certification authority as a type variant.
On 15 November 2018, a Bombardier DHC8-300 made a main gear only touchdown at Stephenville with only minor damage after diverting there when the nose landing gear only partially extended when routinely selected on approach at the originally intended destination. The Investigation found that the cause was incorrect nose gear assembly which had allowed hydraulic fluid to leak and eventually led to it jamming. There was some concern at the way the flight was conducted following the problem which involved continuous smartphone communications with the operator and an overspeed which it was considered constituted an avoidable risk to safety.
On 27 April 2020, an ATR 72-200 freighter crew attempted a night takeoff in good visibility aligned with the edge of runway 06 and did not begin rejecting it until within 20 knots of the applicable V1 despite hearing persistent regular noises which they did not recognise as edge light impacts and so completed the rejection on the same alignment. The Investigation noted both pilots’ familiarity with the airport and their regular work together and attributed their error to their low attention level and a minor distraction during the turnround after backtracking.
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