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 30 July 2023, an Airbus A320 departed Toulouse from an intersection other than the one from which it was cleared to use without the flight crew or the tower controller noticing the error. The available takeoff distance was 500 metres less than required, and rotation occurred with only approximately 500 metres of runway remaining. The crew error was attributed to a combination of “high workload and expeditious mindset, limited attentional capacity, sub-optimal performance and confirmation bias." That the tower did not notice the crew error was assessed as a contributory factor which allowed the incorrect takeoff to occur.
On 6 November 2022 adverse weather delayed an ATR42 beginning its visual-only approach to Bukoba. When an approach was commenced, adequate visual reference was not maintained due to continued adverse weather. No corrective action was taken in response to three successive automated excessive descent rate alerts or the first officer’s calls to reduce descent rate. Although response did follow a ‘PULL UP’ warning, it was too late to prevent a high-energy impact with the surface of Lake Victoria close to the shoreline, and both pilots and 17 of the passengers were killed.
On 23 February 2024, an Embraer E190 lost airspeed during initial climb after departing Honiara without either pilot initially noticing it. When one did notice, the response, a partial flap retraction, increased the loss of control risk. But the other pilot then realised what corrective action was required and took it. The origin of the problem was found to have been pilot error in preflight guidance panel setup, and delayed recognition of the consequences after takeoff. The underlying origin of the circumstances encountered was assessed as inappropriate preflight standard operating procedures and inconsistency in the content of two Embraer manuals.
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.
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:
