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ATM Contribution to Go-around Safety

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Article Information
Category: Loss of Control Loss of Control
Content source: Flight Safety Foundation Flight Safety Foundation
Content control: EUROCONTROL EUROCONTROL

Introduction

The way in which Air Traffic Control (ATC) handle aircraft during approach and go around can affect safety in two ways, directly and indirectly. This applies to both go around decision making and the execution of go-arounds. Self evidently ATC has a direct responsibility for traffic separation and for such additional intervention as may be necessary to ensure that no wake vortex hazard arises. But an appreciation of how ATC action or inaction can help or hinder pilots who may need to declare (or be instructed to fly) a go around.

The effects of ATC can be separated into four different functions / activities:

  • R/T Communication – updating relevant information, the timing and content of instructions and the language used.
  • Management and Control of aircraft – separation and spacing, supporting stabilised approaches, radar vectoring, speed control and vertical clearance strategy.
  • Airspace Designation and Procedure Design – the degree of complexity and potential traps.
  • Awareness – information analysis, sharing, and learning from others.

Both the Related Articles and Further Reading sections below provide links to supporting material and it is recommended that controllers also visit the following two SKYbrary pages from where a wide-range of presentation, discussion and training material connected with this subject is accessible:

R/T Communication

Information Updates

Many go-arounds become necessary because of changes in the prevailing atmospheric conditions or runway status, for example:

  • wind direction may veer or back relative to the intended landing runway and materially alter the likely head, tail or crosswind components.
  • mean wind speed and/or the extent of any gustiness may vary
  • significant local variation in wind velocity may create wind shear and strong winds coupled with uneven terrain or significant obstructions can create significant mechanical turbulence at low level.
  • significant variation in surface temperature can affect be relevant to runway performance
  • runway braking action may be affected by frozen or liquid precipitation or other transitory contaminant.
  • visibility along the runway and visibility of it at the point where visual reference of it is required may vary
  • vehicles, animals, personnel or other aircraft may enter the runway or the ILS protected zone

These changes can directly affect aircraft performance both in the air and on the runway. Pilots must not only control the trajectory of their aeroplane but be ready to make an immediate go-around decision if at any time the commander judges that either aircraft controllability or aircraft energy state are not conducive to a continued safe approach. In respect of the intended landing, runway landing performance may be affected by many factors about which only indicative rather than strictly relevant data can be provided and a judgement about whether to continue often depends on a decision which is assisted by communication of the best information available.

Successful and safe landings are closely linked to the pilots ensuring that a stabilised approach is flown. This means that the prescribed procedures must be followed so that the aircraft is configured for landing in good time, is controlled at the right speed and describes the correct vertical profile as it flies along the extended runway centreline or, if required by an instrument approach procedure for which clearance has been given, along a slightly offset but convergent track.

The detail of the criteria established for a particular aircraft type to qualify as stabilised vary and are set by aircraft operators after taking into account relevant guidance from aircraft manufacturers and other agencies. However, all set at least one “gate” at which point a go around becomes mandatory if thresholds for the promulgated criteria are not met - or if they cease to be met after this gate has been successfully passed. - will require a go around to be made.

The key point here is to note that during the approach and landing phases of flight, pilot workload will be high and they may be too busy to request information updates and they may not readily “register” the importance of those that are communicated without any sense of urgency or significance. It is essential that important changes in previously-communicated information are passed in the right way.

Timing

Controllers will benefit from a generic understanding the typical sequence of aircraft control and management actions which are necessary when executing a go-around. During the initiation of a go around, workload will peak and it is important to restrict communication to the absolutely essential until the initial climb is established and reconfiguration achieved. Pilots understand the need to advise ATC of their current action and intentions as soon as possible after beginning a go-around but this may not be practicable until at least 1000 feet of climb has been made whilst following the previously conformed missed approach procedure.

Language

If more than one language is being used by ATC for R/T communication then it is likely that the situational awareness of pilots unfamiliar with that second language will be materially reduced which can have a significant effect on the overall conduct of a go-around.

Management and Control of Aircraft

The “art” of squeezing the maximum arrival and departure capacities from an aerodrome requires mastery of 4-dimensions in adjoining blocks of airspace and by several different people, each coordinating with each other. A single event within one part of this “total system” (a delayed departure, or a go-around) can be the cause of much re-planning and tactical changes which impact many air traffic controllers and pilots elsewhere.

We can say that:

  • statistically, air traffic controllers will occasionally make, or omit, decisions, which will cause an aircraft to be instructed to go-around or to decide to do so
  • go-arounds can immediately have a large impact on local operations as well as a wider impact on the ATC System.

It is therefore in the interest of controllers to recognise what can be done to:

  • reduce the likelihood of go-arounds, and
  • lessen the impact of them when they do occur.

Each sub-section below addresses different ATM methods for coordinating traffic and attaining capacity.

Speed

The most common inappropriate speed instruction from ATC is a requirement to fly at a higher speed than appropriate especially if this follows a late descent relative to the vertical profile for final approach. Optimum performance and handling speeds for different phases of flight will vary according to aircraft type and sometimes within aircraft type because of environmental conditions or variation in aircraft weight.

If pilots are instructed to maintain speeds which are excessive, then they may either decline to accept them with all the difficulties which that may cause ATC or, having accepted them, then get into a situation where the probability of becoming unstablised as a result of the secondary consequences of excess speed rapidly increases. It is worth bearing in mind that in mixed traffic situations where turboprops and jets are present, the former are able to respond to changes in speed control much more easily than the latter.

Controllers can reduce the chances of precipitating a go-around due to inadequate spacing by awareness of the potential performance of different aircraft. If it looks as though an approaching aircraft may have to be sent around because of unexpected runway occupancy or inadequate approach spacing then it is helpful if advice to the aircraft involved that this may occur is given as early as possible.

Delayed Descent

Delaying descent will have a similar effect as an instruction to maintain an excessive speed. A continuous descent approach (CDA) with speed control which progressively reduces is the ideal. Prior to an aircraft becoming established on final approach, controllers can assist pilots by advising track miles remaining to touchdown. This will allow pilots to manage aircraft performance and configuration in the best way.

Late Runway and/or Approach Change

A change in the cleared approach and/or the landing runway from that advised on the ATIS, which the pilots are likely to have heard during descent or been directly advised of may affect safety and will certainly increase the likelihood of go-around.

Prior to making a particular approach to a particular landing runway pilots must consider many factors and satisfy themselves that prescribed landing performance requirements can be met. They need to:

  • familiarise themselves with the approach track and vertical profile
  • check the required landing distance for the aircraft estimated landing weight in the prevailing conditions
  • familiarise themselves with the missed approach procedure
  • be both familiar with stabilised approach criteria and go-around procedures
  • program the FMS as required
  • confirm allocation of tasks and any variations to standard calls]
  • identify and review any specific problems such as expected runway braking action

The ideal time for all this is just before the top of descent and it should be complete no later than the commencement of the STAR or equivalent position. Any later and the chances of a poorly managed / flown approach increase and declaration of a go-around becomes more likely. Controllers may also wish to take into account, if known, the relative familiarity of a crew with their aerodrome and its approach procedures and runways.

So to summarise, controllers can reduce the probability of ‘forcing’ a go-around by:

  • ensuring that the expected approach and landing runway is advised early on and not then changed unless unexpected wind velocity changes occur
  • detecting the need for unavoidable runway /approach changes as soon as possible and immediately communicating them directly or by passing a message to the frequency being worked.
  • offering pilots additional time in the form of increased track miles or a holding pattern to prepare for unexpected changes
  • never offering (or acceding to requests for) alternative approaches or runways at a late stage because they are more ‘convenient’ for the pilots (e.g. a runway with less taxi in time or an approach with less distance to touchdown).

Tailwinds

Aircraft descent is controlled on the basis of vertical speed measured in feet per minute (fpm) but instrument approach vertical profiles are specified on the basis of their slope in feet per nm). At such shallow angles, the connection between the two is of course groundspeed in nm per minute. A tailwind component aloft or on final approach will require either more [[Distance to Touchdown | track miles or a increased rate of descent. Pilots are used to adjusting for this durimg most of the descent and approach but if a significant tail wind component exists near the ground - or there is a risk of one due to fluctuation in surface wind velocity, then the likelihood of a go around either because the approach has become unstabilised or because the AFM maximum tailwind component for landing has been exceeded is increased.

To reduce the chances of either of these scenarios, controllers can:

  • avoid designating landing runways with a significant tailwind component - over 5 knots
  • appreciate that a significant headwind component at runway elevation can follow a significant tailwind component earlier in the approach
  • become familiar with significant differences in track miles which the various aircraft types need to lose a given amount of altitude
  • utilise groundspeed information as an indirect guide to the strength of tailwind components on the approach.

Radar Vectoring

Vectoring aircraft to create a sequence for approach can increase the chances of an unstabilised approach and thus the chances of a go-around. These situations include:

Managing Go-Arounds [1]

A pilot decision to go-around will be made and actioned in accordance with the standard missed approach procedure unless an alternative instruction has been issued. Communicating late changes should be avoided

Imposing a low (less than 2000ft aal) stop height/altitude in the event that a go around is flown increases pilot workload by complicating the aircraft management task. This increases the probability of a level bust. missed approach procedures involving stepped climbs are also an unwelcome complication.

Controllers may feel that they can assist pilots by contacting them early during a go-around with instructions or choices in respect of a second approach. But such intervention would be premature since it could interfere with essential aircraft management tasks tasks and may also encourage pilots to accept an inappropriately rapid transition to another approach.

Detection of touchdown or go-around may not be guaranteed for ATC[2] and coordination between APP and TWR controllers or between TWR controllers responsible for different runways may delay relevant awareness of go-arounds. However, pilots know they should advise ATC as soon s possible after commencing a go around other than in response to an ATC instruction and controllers should not be may be tempted to call an aircraft in order to confirm this.

To contribute to safer go-arounds, ATC controllers should:

  • seek to avoid changes to the previously cleared missed approach procedure unless that change is an unequivocal simplification - for example a continued climb or less complex tracking.
  • accept that it may be as much as a couple of minutes before an aircraft which has unexpectedly commenced a go around advises this and its further intentions.
  • once an aircraft has completed at least a climb of 2000 feet and has indicated that a further approach is desired, ask how many track miles are required and do not “impose” a quick solution of your own on the assumption that it will be welcome.
  • be aware of the extent to which they are able to confirm both a landing roll to taxi speed and the commencement of a go-round. especially one initiated from or near to the runway.

Airspace Designation and Procedure Design

At a strategic level, ANSPs and their aerodrome operators and Safety Regulators should monitor arrival and departure procedures in the context of airspace designation so that changes that might enhance safety can be identified.

At a day-to-day level, existing risks created by prevailing airspace designation and procedure design should be considered:

  • ComplexityMissed Approach procedures that have multiple steps, especially in the initial stages of a go-around create opportunities for pilot error as do conditional turns or climbs e.g. after passing 500ft agl but not later than 3 DME'. Such conditions require working memory capacity at a time where this cannot be guaranteed so that either such clearances will be breached or compliance will lead the pilots losing situational awareness of aircraft control.
  • Confusion – Ideally, throughout the world it would be very safe to have only one Missed Approach procedure - the same for all runways. Of course this is not possible but if commonality between the Missed Approach procedures at a particular airport can be achieved, this can reduce the chances of error. This has been achieved at Vienna. [3]. It is particularly unfortunate if the design of Missed Approach procedures is predicated on local Noise Abatement requirements or poor design of adjacent airspace.
  • Compression – Some Missed Approach procedures can be ‘compressed’ or constrained within unduly small volumes of airspace. When initial stop altitudes are low (e.g. below 3000ft) and turns are required early at low level, these represent a distraction from the primary pilots task of flying and managing the aircraft as well as increasing the chances of a level bust.
  • Conflict – Missed Approaches may lead to conflict with other traffic in the vicinity of an aerodrome. Conflict may occur not only in respect of simple proximity with other aircraft but may also involve their wake vortices. At the local level, it is essential that ATC have effective means to assure the rapid detection and relevant awareness of any aircraft on go-around [2].
  • Circling Circling approaches are demanding to fly, and transitioning to a go-around from a circling approach can be inherently challenging and in a non radar environment difficult for ATC to provide assistance. The essential requirement is that any go around should, I the absence of a specifically contrary ATC clearance such as to enter the visual circuit, involve manoeuvring the aircraft by means of a climbing turn within the protected area to establish on the missed approach procedure for the instrument approach initially made whilst not exceeding the prescribed visual manoeuvre speed for circling -see [4].

Awareness

Raising and maintaining awareness of ATM contribution to go-around safety (i.e. of both the potential to hinder and the potential to help) is essential if positive action to support go around safety is to be taken. Raising awareness is often most effective at a local level through safety teams which include representatives from all stakeholders. A simple 5-step model can be used to build an effective local go-around safety programme:

  1. Collect relevant data from stakeholders – reports, communication and radar recordings, flight data, contextual interviews
  2. Share-out your own data with the Industry and “Share-in” lessons learnt and best practices from Industry
  3. Analyse all information and data for relevance and to create options for improvement and risk mitigation
  4. Test options for validity and impact through exercises, simulations and safety assessments
  5. 'Train all relevant personnel to prioritise reducing the circumstances where go arounds become more likely and to be able to react effectively to the risk of loss of separation when un-anticipated go arounds occur.

Related Incidents

A318/B739, vicinity Amsterdam Netherlands, 2007 (LOS HF): On 6 December 2007 an Airbus A318 being operated by Air France on a scheduled passenger flight from Lyon to Amsterdam carried out missed approach from runway 18C at destination and lost separation in night VMC against a Boeing 737-900 being operated by KLM on a scheduled passenger flight from Amsterdam to London Heathrow which had just departed from runway 24. The conflict was resolved by correct responses to the respective coordinated TCAS RAs after which the A318 passed close behind the 737. There were no abrupt manoeuvres and none of the 104 and 195 occupants respectively on board were injured.

Go-Around Safety Forum (2013) Findings and Conclusions

The Findings and Conclusions from the June 2013 Go-Around Safety Forum held in Brussels are comprehensive. The documented Conclusions are not equivalent to Recommendations but those related to ATM should nevertheless provide a valuable starting point for go-around safety improvement. They are summarised below:


Conclusions related to Air Traffic Management

  • GEN1 - EUROCONTROL Agency should review the ATCO Training Common Core Content to consider the applicability of adding specific objectives and supporting comments related to ATCO responsibilities regarding go-around/missed approach.
  • GEN2 - Aircraft Operators and ATC should improve the mutual understanding of each others' go-around practices/procedures.
  • ATM1 - Procedures which allow communication with aircraft operating on the same frequency at international airports carried out in languages other than English should be reviewed by means of a safety case to establish if they can contribute to loss of pilot situational awareness of potentially conflicting traffic during go-arounds.
  • ATM2 - A high priority should be accorded to the provision of RNP approach and missed approach procedures where current procedures involve circle-to-land and active radar surveillance of a transition to a go-around is not available. Consideration should be given to withdrawing circle-to- land procedures at aerodromes where neither option is available.
  • ATM3 - ANSPs should review and if necessary enhance the provision of go- around risk awareness training for controllers.
  • ATM4 - Ensure that the importance of a stabilised approach and compliance with final approach procedures is included in training and briefing for air traffic control staff (European Action Plan for the Prevention of Runway Excursions Recommendation 3.3.1). Implementation Advice - Training should include:
    • Appropriate speed control instructions
    • Timely descent instructions.
    • The importance of avoiding late change of runway or type of approach
    • Assigning a landing RWY with no significant tailwind component
    • Avoidance of vectoring too tightly onto final approach and intercepting glide path from above
    • Providing crew correct information about distance to touchdown
  • ATM5 - The agency responsible for procedure design should ensure that straightforward go-around procedures are available and published for each runway These go-around procedures should be designed in consultation with pilots who will be expected to use them. 
 Implementation Advice:
    • The MAP procedure for each runway should be the same or similar
    • Avoid low first stop altitude and early turn in the missed approach procedure (e.g. below 2000ft)
    • Avoid conditional go-around/MAP procedures, e.g. “after xxx but not later than yyy…”
    • Avoid lack of procedural de-confliction of the missed approach path from other traffic and wake turbulence exposure, especially for late go-arounds
    • Perform risk assessment if both RNP and conventional missed approach procedures are published
  • ATM6 - Flight crew should receive updated weather and RWY conditions information on final approach. Contingency arrangements/procedures should exist for use in windshear conditions. 
 Implementation Advice:
    • More relevant & quicker update of weather related information – visibility, wind, RWY status change e.g. quantity of water on the RWY
    • Improved information to be provided to crews on tailwinds, windshear and significant wind variation, including reports from preceding aircraft
    • RWY information should include FODs, animals on RWY, technical problems on the ground, laser interference, etc
  • ATM7 - Guidance should be developed for controllers regarding content and timings of go-around instructions. Implementation Advice:
    • Consider whether the go-around instruction should be in a separate transmission to the explanation for the instruction
    • ATCO should specify any non-standard MAP when issuing the approach clearance
    • ATCO should avoid last minute changes/instructions
    • Once a go-around is initiated, unnecessary RTF should be avoided
    • Pilot should inform ATC as soon as possible if deviations from the published go-around-procedure become required
  • ATM 8 - ANSPs should establish a formal interface between pilots and controllers where issues can be explored and a joint understanding can be reached. 
 Implementation Advice:
    • Pilots can be invited to attend controllers’ training sessions and vice versa
    • Facilitated open days for pilots at ATC Units and familiarization flights for ATCOs
    • Joint CRM training

Related Articles

Further Reading

References

  1. ^ ATM Contribution to Safe Go-Around Presentation by T. Blajev,EUROCONTROL 2013
  2. ^ a b Automatic Missed Approach and Late Go-Around Detection. Presentation by J. Brüggen, ATC Netherlands, 2013.
  3. ^ ATM Procedures Aspects for Safe Go-Around. Presentation by C. Kern & C. Bednar, AustroControl, 2013.
  4. ^ ATM Contribution to Safe Go-Around. Presentation by T. Blajev, EUROCONTROL 2013


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