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 multicrew situation where the roles of the two pilots are defined as Pilot Flying (PF) and Pilot Monitoring (PM). The PM has responsibility for monitoring the actions and awareness of the PF.
Whilst the monitoring role of a PM 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 29 April 2023, the flight crew of an Airbus A321 did not complete the intended touchdown at Abu Dhabi from the flare to land. Initiation of a go-around resulted in a tail strike due to improper high pitch control input whilst the airspeed was still low and the configuration not correct. The mishandling arose from confusion by both pilots as to the aircraft air/ground status after touchdown and involved significant dual sidestick input with no transfer of control. Once established in the climb, the remainder of the subsequent circuit to land was completed without further event.
On 4 December 2023, a Boeing 737-8200 crew misjudged positioning onto the ILS approach for arrival at London Stansted. Having decided to go around, they then continued to climb above the 3,000-foot missed approach altitude, which they had failed to set until alerted by the controller. The descent following a 1,000 feet level bust then continued back through the missed approach altitude at almost 9,000 fpm with an EGPWS ‘PULL UP’ warning just as recovery from 1,740 feet agl was initiated. After levelling at 3,000 feet, radar vectoring onto the ILS was provided with the approach then completed normally.
On 12 May 2022, an Airbus A319 about to become airborne at Chongqing veered off the side of the runway at high speed following an inadvertent and unintended rudder input by the non-flying pilot when distracted by unexpected movement of a loose object. Continuation over rough ground across an open ditch resulted in detachment of both engines and both main landing gear assemblies and a resulting fire, which impeded the emergency evacuation. The severe fire and impact damage to the aircraft rendered it a hull loss but the evacuation was completed with only a few minor injuries.
On 29 October 2021, a Bombardier CRJ900 lined up and began a night takeoff in fog at San Diego aligned with the left runway edge lights instead of the runway centreline. This damaged some of the edge lights and the aircraft wing and landing gear. The pilots stated they had been unaware of their error until aircraft damage was found after landing, despite returning closer to the runway centreline after about a third of their takeoff roll. Subsequent minor modifications to related operator runway lineup procedure were noted. The investigation also examined causes of a fuel imbalance during the incident flight.
On 4 March 2024, a Boeing 737-800 departing Bristol took longer than expected to become airborne and passed over the end of the runway at approximately 10 feet. It was then initially unable to climb at a speed much above V2 until it was recognised that the thrust set was significantly below that intended. Despite the flight being used for new captain line training, a check at 80 knots that correct thrust was set did not occur. The fact that the autothrottle had not been successfully re-engaged after it dropped out when takeoff thrust was being set went unrecognised.
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:
