Cross-checking Process
Cross-checking Process
Description
The human mind is fallible and error can occur for many reasons, for example, from a misheard message, from memory slip, or from incorrect appreciation of the situation.
Error is particularly likely in certain circumstances, especially when there is pressure to complete a task quickly (e.g. to expedite departure or during an emergency or abnormal situation), but may also occur in normal everyday situations.
Error in aviation can have severe consequences and the cross-checking process is used wherever possible to eliminate error.
Cross-checking and the Pilot
The cross-checking process is a vital element of a pilot's duties, particularly in a multi crew situation where the roles of the two pilots are defined as Pilot Flying (PF) and Pilot Not Flying (PNF). The PNF - alternatively referred to as the Pilot Monitoring - has responsibility for monitoring the actions and awareness of aircraft control of the PF.
Whilst the monitoring role of a PNF must not be limited to specific parts of flight crew duties, Company SOPs should include a minimum list of defined actions which are to be cross-checked, for example:
- One pilot calculates aircraft performance and makes mass and balance calculations; the other pilot closely monitors, cross-checks or duplicates the calculations.
- A Load and Trim Sheet prepared (exceptionally) by a member of a flight crew must be subject to meaningful cross checking before acceptance.
- ATC clearances will normally be monitored by both pilots and consequent action including readback taken by one pilot will be confirmed/monitored by the other.
- Equipment settings such as altimeter pressure settings, cleared altitude, frequency change and navigation routings, are set by one pilot and cross-checked by the other.
- Adherence to defined Stabilised Approach gates and to calculated Reference Speeds and AFM Limitations
Cross-checking and the Controller
Cross-checking is equally important for the ATCO, and comprises two elements:
Cross-checking the actions of pilots
Where possible, the controller should monitor the actions of the pilot, either by reference to the situation display or by visual observation, to ensure that instructions are followed correctly.
The extent to which a controller can cross-check the actions of pilots depends on his/her workload; however, every effort should be made to do so in situations where error is likely to occur. For example, when the pilots are dealing with an aircraft unserviceability, or when the pilot appears to be inexperienced, confused, or have limited language ability. A particular example of a situation where monitoring by radar or directly may be conducive to safety is the execution of issued VFR clearances in airspace such as Class 'D'; in this situation, loss of separation against IFR traffic can occur due to poor situational awareness of the IFR aircraft flight crew, who might wrongly assume that they benefit from ATC-controlled separation from VFR traffic as well as from other IFR traffic.
Controllers should pay particular attention to aircraft manoeuvring on the ground near runway hotspots and to potential conflicts which can arise in the air when intersecting runways are in use simultaneously and this involves intersecting approach, missed approach or take off flight paths.
System support can be used to help controllers with performing this task. Examples of this are various monitoring tools, e.g. for a potential or actual level bust, horizontal deviation, the downlink of Mode S selected level, etc. Nevertheless, controllers should be aware that such tools are not supposed to replace the existing ATC procedures.
Cross-checking the actions of colleagues
Cross-checking is a normal part of the duties of an ATC Assistant if these exist; otherwise, controllers rarely have the free capacity to monitor the duties of other controllers and such action could not be expected to form part of their duties. Nevertheless, the following areas are important:
- When there are two controllers assigned to a sector, the communication with aircraft is normally done by the executive controller. The planner controller however also monitors the radio exchanges (to the extent possible) so that they can detect lapses, incorrect readbacks, etc.
- Also not official and subject to personal workload, a tower and an approach controller (or a tower and a ground controller) may monitor the other controller's frequency e.g. to make sure an agreed coordination is appropriately communicated to the aircraft.
- Controllers taking over responsibility for a sector have much information to absorb and the potential for error or oversight is high. The controller going off duty should monitor the actions of their replacement for a few minutes after hand-over to ensure that neither has overlooked any significant aspect of the prevailing traffic situation and to be available to deal with any questions that might arise;
- Inexperienced controllers or controllers who are new to their positions may not become fully proficient for some time. Appropriate mentoring procedures should be in place until their unaided performance is assessed as satisfactory.
- When a controller is dealing with an abnormal situation, e.g. an aircraft emergency or very high density traffic, the enlistment of any off-duty controllers to assist can be an important safety net.
Accidents & Incidents
Events in the SKYbrary database which include Ineffective Monitoring as a contributory factor:
On 13 January 2023, in good night visibility, an augmented crew Boeing 777-200 failed to comply with its departure taxi clearance and with its Captain taxiing crossed a runway in front of a 737 taking off. ATC responded to an automated conflict warning by cancelling the takeoff clearance and a high speed rejected takeoff was initiated from approximately 105 knots with minimum separation as the 777 cleared the edge of the 737 takeoff runway approximately 300 metres. The Investigation concluded that the 777 operator’s risk controls and the airport’s methods for detecting and preventing dangerous runway conflicts were both inadequate.
On 16 September 2019, an ATR 72-200 diverted to Itaituba when landing at its intended destination Manaus was prevented by its unexpected closure due to an aircraft accident. During this diversion, intermittent indications of low fuel quantity were annunciated and one engine subsequently ran down on final approach and the other whilst backtracking after landing. It was found that due to a series of undetected faults in the aircraft’s fuel quantity sensing system, the flight deck indications of fuel tank contents were over reading and the low fuel indication system was also malfunctioning for the same reason.
On 12 March 2022, an ATR76-600 Captain made an unstabilised approach to Jabalpur before a first bounce more than half way 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 but 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 very experienced Captain had misaligned the aircraft whilst the extremely inexperienced First Officer was too busy to monitor the Captain’s actions.
On 25 October 2021, a Boeing 737-800 had just reached its cruise altitude after takeoff from Perth when a fuel imbalance message was displayed on the system panel. Despite specified indications for a fuel leak as the cause of this message not being met, it was determined that the left engine should be shut down. A ‘PAN’ was declared and a diversion to Kalgoorlie completed. Inspection there found the fuel imbalance was within normal limits and that crew diagnosis of a fuel leak had been flawed. Non-standard closure of the crossfeed valve was suspected as the origin of the imbalance.
Further Reading
- Checklists and Monitoring in the Cockpit: Why Crucial Defenses Sometimes Fail, July 2010
- A Practical Guide for Improving Flight Path Monitoring, November 2011
UK CAA
- Monitoring Matters: Guidance on the development of Pilot Monitoring Skills, CAA Paper 2013/02.
Flight Safety Foundation ALAR Briefing Notes:
