46TH ANNUAL CONFERENCE, Istanbul, Turkey, 16-20 April 2007
WP No. 85
Aerodrome – Converging Runway Operations
Presented by TOC
There are various types of simultaneous operations on converging/intersection runways in operation at airports all over the world. All are related to achieving maximum use of runways. It is expected that, as pressure on airport capacity grows, more and more of those procedures will be introduced. At this stage, it appears that little coherent work is being done by ICAO to harmonise converging runway operations, and it is therefore paramount for IFATCA to have concise Policy on such procedures.
1.1 Two related topics are Simultaneous Intersecting Runway Operations (SIRO) and Land and Hold Short Operations (LAHSO). Other terms, such as Simultaneous Operations on Intersecting/Converging Runways (SIMOPS) and Simultaneous Operations on Intersecting Runways (SOIR) have also been used. All are related to achieving maximum use of runways, whilst maintaining safety.
1.2 It is expected that, in order to enhance airport capacity, SIRO and LAHSO will be expanded and extended. It is therefore appropriate for IFATCA to review its policy on SIRO and study LAHSO. Due to the scope of the subject, TOC has decided to cover the issue in two separate working papers. This paper is only about airborne operations to and from intersecting and/or converging runways. LAHSO, ie. intersecting runway and taxiway operations on the ground are being dealt with in a separate paper (B.5.4).
2.1.1. There is no official definition in ICAO documents for crossing/intersecting or converging runway operations. There are various references in ICAO doc. 4444 (PANS-ATM) to parallel and near-parallel runways, and some references to crossing runways, but nothing on converging but not intersecting runways. There is also an ICAO manual on Simultaneous Operations on parallel or near-parallel Instrument Runways (SOIR Manual Doc 9643). Note again that this is not for intersecting runways or converging runways. IFATCA therefore proposes the new term Converging Runway Operations (CROPS) as it covers all operations on multiple runways that are not parallel. LAHSO and SIRO would then be examples of subsets of CROPS.
2.1.2. CROPS are in use at various locations around the world. For example they have been used in Australia for nearly twenty years. If Air Traffic Service Providers (ATSPs) intend to introduce CROPS, IFATCA insists that all Safety Management Systems (SMS) are implemented and the following information be used in the procedures as no related ICAO Standards and Recommended Practices (SARPs) exist. If procedures cannot be safely determined then CROPS should not be introduced or remain in operation.
2.1.3 When looking at airborne separation of aircraft operating to or from converging runways, it of no significance whether the runways actually intersect or not. Depending on the types of operation, the flight paths of those aircraft might cross anyway either during the approach, the departure or the missed approach segments of the flights (of course there might also be configurations where no crossing of flight paths occurs at all). A clearance for final also allows the aircraft to conduct the Published Missed Approach (PMA); this PMA may conflict with other missed approach paths, departures or arrivals. Therefore little assurance of separation is provided if two aircraft are cleared for final on converging approaches simultaneously.
2.1.4 As go-arounds occur infrequently, controllers have little experience of those events. It is particularly difficult to train new aerodrome controllers due to the varying aircraft performance characteristics and possible relative positions. Access to an ATC simulator capable of demonstrating the variety of aircraft positions possible in a go- around situation would enhance controller awareness of the problems and make a positive contribution to the safety of the system.
2.2 IFATCA Policy
2.2.1 There is IFATCA policy for Simultaneous IFR Operations on Intersecting/Converging Runways. There are two main concerns that have prompted TOC to review the policy:
- The apparent willingness of airport operators and ATSPs, pressured to increase airport capacity, to label operations to and from non-intersecting but nevertheless converging runways “independent” – simply based on the fact that there is no need to apply separation at a runway intersection. As detailed under 2.4.2, LAHSO are also used to try and get rid of the intersection separation requirement, and thus label CROPS in combination with LAHSO as “independent”
- Even where ATSPs do acknowledge the need for intersection separation, the SIDs and missed approaches from and to the different runways are designed in such a way that, even if separation at the intersection is achieved, controller intervention is still required if an aircraft conducts a missed approach or aborts the landing. Procedures that achieve (demonstrated by a safety case) at least avoidance (even though no “standard” ATC separation exists) could be a way to increase aerodrome capacity without relying on controller intervention and reducing levels of safety.
2.2.2 The issue of dependent avoidance has also been discussed, and highlighted a need for policy. It is important that there be avoidance or separation (not just traffic information) and responsibilities must be defined.
2.3 Dependent, Independent and Segregated Operations
2.3.1 When discussing parallel runway operations, ICAO uses three terms – dependent, independent and segregated. The terms however are not defined in relation to converging runway operations, and so the following definitions are proposed for inclusion in the IFATCA manual.
2.3.2 A dependent runway operation is when a clearance or instruction to a landing or departing aircraft is conditional (dependent) on an action of another aircraft or vehicle.
2.3.3 An independent runway operation is when a clearance or instruction to a landing or departing aircraft is not constrained by consideration of the position or cleared route of any other aircraft or vehicle.
Note 1: Independence requires that if a rejected landing, missed approach, etc is executed by one or more aircraft then there is still no constraint on the aircraft receiving the clearance or instruction.
Note 2: Independence does not have to take into account emergencies and non- compliance with clearances – which will be managed as required.
2.3.4 An avoidance procedure is to prevent aircraft collision but does not necessarily use an Air Traffic Control (ATC) separation standard.
Note: The procedure must demonstrate the required safety established by safety analysis and then be formally approved for use.
2.3.5 An example of a segregated parallel runway operation on staggered runways is that runway centre-lines are spaced at least 730m apart and that the missed approach path of a landing aircraft diverges by at least 30 degrees from the departure track of the aircraft taking off. Something similar must be implemented in relation to converging runway missed approaches.
2.3.6 A Rejected Landing Procedure (RLP) is a documented and published heading procedure used when one or more aircraft involved in the procedure are unable to land whereby the trajectory of the aircraft is guided clear of possible conflicting traffic and their wake turbulence. This procedure would normally be flown visually, however terrain clearance may be provided by the FMS as new approach technologies (ie RNP) become more commonplace. Unless alternate instructions are given by ATC, pilots are expected to execute the procedure as published and remain clear of clouds. ATC should keep the RLP track clear of other aircraft.
2.3.7 A clear distinction must be made between an RLP and the PMA of an instrument approach. In any CROPS agreement, once a participating aircraft reports “visual”, it should be agreed that the PMA procedure is cancelled and the RLP is effective as the aircraft’s clearance.
2.3.8 This provides for a level of separation when the loss of ability to communicate with aircraft occurs and controllers have no possible means of providing a landing clearance or alternative instructions. Examples are: failure of aircraft to transfer to tower frequency; radio failure in the aircraft; radio failure in the Tower; or an open microphone blocking the frequency.
2.4 CROPS and controller responsibility
2.4.1 What are the obvious advantages of independent versus dependant operations? To the controller, independent procedures mean that no intervention on his or her part is required. The responsibility for separation lies with the designer of the procedure. No controller intervention means greater safety and less workload per aircraft, possibly resulting in a higher number of aircraft that may be controlled at any given time. To the airport operator and/or the ATSP, it means a higher airport capacity.
2.4.2 Dependent procedures on the other hand require controller intervention. The responsibility for separation lies with the controller, resulting in a higher workload and a reduction in capacity.
2.4.3 Avoidance Procedures will most likely include a visual separation segment at some stage. The visual separation will either be applied by the aerodrome controller, or be delegate to one of the pilots involved in the procedure.
2.5 Introduction of CROPS
2.5.1 The appropriate risk analysis should be carried out between ATSPs and Airlines utilising CROPs and this analysis shall involve pilots and controllers, which should include simulation and real-time trials utilising data from the local airport and operators intending to operate with these procedures. The local Runway Safety Team shall also be involved. This ensures safety and correct promulgation of procedures as well as ascertaining whether any aircraft performance limitations will restrict the use of the procedures. The safety assessment should also include all other operations at the aerodrome that may effect – or be affected by – CROPS; e.g. VFR lanes over the airport..
2.5.2 CROPS procedures shall detail acceptable meteorological conditions, especially relating to crosswind and downwind conditions, cloud base, visibility, and windshear, as well as runway conditions. If the procedure requires the participating aircraft to remain in VMC, the minimum ceiling required for CROPS should be at or above the minimum radar vectoring altitude, thereby not putting the aerodrome controller in a position where he or she is forced to vector aircraft into cloud below the MRVA in order to avoid collision.
2.5.3 Aircraft experiencing operational difficulties should be excluded from CROPS procedures.
2.5.4 The responsibilities for separation must be clearly defined between the aerodrome and approach control unit. One such example could be that aircraft are handed back to approach only after radar separation has been re-established between all aircraft concerned.
3.1 From a controller’s point of view, independent operations on converging runways mean that all procedures to and from those runways (obviously including missed approaches and rejected landings) should be designed in a way that provides at least avoidance without intervention by the aerodrome controller. There will be runway configurations where this is easily achievable, but some will not. The latter therefore have to be dependent operations.
3.2 Operations on intersecting runways also fall under the term CROPS, but they are normally not considered independent since a separation standard must be applied at the intersection.
3.3 Dependent runway operations require controller intervention. It is therefore important to ensure that controllers are not faced with procedures that are on the face independent but still require controller intervention at some stage. ATSPs and airport operators might be tempted to increase aerodrome capacity by labelling dependent runway operations independent, putting responsibility on the controller without a means to cope.
3.4 Procedures that achieve (demonstrated by a safety case) at least avoidance (even though no “standard” ATC separation exists) could be a way to increase aerodrome capacity without relying on controller intervention.
3.5 IFATCA should work with ICAO in the production of SARPs detailing the use of CROPS.
3.6 Further investigation on separation responsibility during visual manoeuvring while conducting CROPS, is required.
It is recommended that;
4.1 The following definition of Converging Runway Operations:
Converging Runway Operations (CROPS) is the use of converging, but not necessarily intersecting, runways for take-off and/or landing.
is included in the IFATCA Manual on page 3221.
4.2 The following definition of Dependent runway operation:
A dependent runway operation is when a clearance or instruction to a landing or departing aircraft is conditional on an action of another aircraft or vehicle.
is included in the IFATCA Manual on page 3221.
4.3 The following definition of independent runway operation:
An independent runway operation is when a clearance or instruction to a landing or departing aircraft is not conditional on an action of another aircraft or vehicle.
is included in the IFATCA Manual on page 3221.
4.4 The following definition of Avoidance Procedure:
An Avoidance Procedure is a designed procedure to prevent aircraft collision but does not necessarily use an air traffic control (ATC) separation standard.
Note: The Avoidance Procedure must demonstrate the required safety established by safety analysis and then be formally approved for use.
is included in the IFATCA Manual on page 3221.
4.5. IFATCA Policy on page 3221 of the IFATCA Manual:
“The introduction of Simultaneous IFR Operations of Intersecting /Converging Runways should only take place where:
a) The ATC facilities involved have the appropriate equipment, staffing levels, and training;
b) The appropriate risk analysis should be carried out involving pilots and controllers, which should include simulation and real-time trials utilising data from the local airport and operators intending to operate with these procedures;
c) Until world-wide standards have been established, the introduction of local or regional operations should be restricted to local operators by Letters of Agreement;
d) That specific procedures are introduced that will ensure that the approach sequence to each runway can be managed in such a way that each aircraft will be able to continue its approach , landing and possible missed approach safely.
Where aircraft are operating in the vicinity of the aerodrome, with less than the required IFR separation, the aircraft involved and any potential conflict point, must be visible to the aerodrome controller.”
4.6. IFATCA Policy is:
“Simultaneous Operations of Intersecting/Converging Runways should only take place under the following conditions:
- The ATC facilities involved have the appropriate equipment, staffing levels, and training;
- The appropriate risk analysis has been carried out involving pilots and controllers, which shall include simulation and real-time trials utilising data from the local airport and operators intending to operate with these procedures;
- Independent runway operations or Avoidance Procedures have been established;
- The procedures detail acceptable meteorological conditions, especially relating to wind conditions, cloud base, visibility and windshear, as well as runway conditions. If the procedure requires the participating aircraft to remain in VMC, the minimum ceiling required for CROPS shall be above the minimum radar vectoring altitude;
- Aircraft experiencing operational difficulties are excluded from CROPS procedures; and
- The responsibilities for separation are clearly defined between the aerodrome- and approach control unit”
and is included in the IFATCA Manual on page 3221.
Last Update: September 29, 2020