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ATM Contribution to Go-around Safety
From SKYbrary Wiki
|Category:||Loss of Control|
|Content source:||Flight Safety Foundation|
- 1 Introduction
- 2 R/T Communication
- 3 Management and Control of Aircraft
- 4 Airspace Designation and Procedure Design
- 5 Awareness
- 6 Related Incidents
- 7 Go-Around Safety Forum (2013) Findings and Conclusions
- 8 Related Articles
- 9 Further Reading
- 10 References
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:
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.
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.
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.
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.
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).
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.
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:
- vectoring onto final approach at too short a range from touchdown
- vectoring aircraft such that the glideslope is intercepted from above instead of (as preferable) from below and in level flight
Managing Go-Arounds 
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 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:
- Complexity – Missed 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. . 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 .
- 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 .
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:
- Collect relevant data from stakeholders – reports, communication and radar recordings, flight data, contextual interviews
- Share-out your own data with the Industry and “Share-in” lessons learnt and best practices from Industry
- Analyse all information and data for relevance and to create options for improvement and risk mitigation
- Test options for validity and impact through exercises, simulations and safety assessments
- '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.
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:
- Unstabilised Approach: Inappropriate ATC Speed Instructions
- Unstabilised Approach: Delayed Descent Instructions
- Unstabilised Approach: Late Runway or Approach Type Change
- Unstabilised Approach: Vectoring Resulting in Intercepting the Glidepath from Above
- Unstabilised Approach: Lack of or Wrong Information About Distance to Touchdown
- Unstabilised Approach: Vectoring into Short Final Distances
- Unstabilised Approach: Vectoring to Runways with Significant Tailwind Component
- Rejected Landings
- Missed Approach
- Go-around Decision Making
- Go-around Execution
- Go-around Training
- Stabilised Approach
- Go-Around Safety Forum, Brussels 2013: Findings and Conclusions.
- Go-Around Safety Forum, Brussels 2013: Presentations.
- Go-Around Safety Forum, Brussels 2013: Videos of Presentations.
- Stabilised Approach Awareness Toolkit for ATC. SKYbrary Toolkit.
- Go-Around Procedures at Vienna Airport. Presentation by C. Kern & C. Bednar, AustroControl 2013.
- Automatic Late Go-Around and Missed Approach Detection. Presentation by J. Brüggen, ATC Netherlands 2013.
- ATM Contribution to Safe Go-Around. Presentation by T. Blajev, EUROCONTROL 2013.
- Voluntary ATM Incident Reporting (EVAIR) Analyses. Presentation by D. Stankovic, EUROCONTROL 2013.
- GoArounds: STEADES In-depth Analysis. Presentation by Giancarlo Buono, IATA 2013.
- Go-Around Accident and Incident Report Review. Presentation by Capt. Ed Pooley, The Air Safety Consultancy & FSF European Advisory Committee 2013.
- Study on Aeroplane State Awareness during Go-Around - an English translation of a Study by BEA based on the results of closed investigations conducted by the BEA or by other non-French investigation authorities. The Appendices are missing as they have not been translated into English.
- ^ ATM Contribution to Safe Go-Around Presentation by T. Blajev,EUROCONTROL 2013
- ^ a b Automatic Missed Approach and Late Go-Around Detection. Presentation by J. Brüggen, ATC Netherlands, 2013.
- ^ ATM Procedures Aspects for Safe Go-Around. Presentation by C. Kern & C. Bednar, AustroControl, 2013.
- ^ ATM Contribution to Safe Go-Around. Presentation by T. Blajev, EUROCONTROL 2013
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