Present IFATCA policy on the matter, adopted at the 1988 conference , states that:

The AOPG is at the moment only dealing with dependent Simultaneous Intersecting Runway Operations (SIRO), especially on the lay out aspects/criteria for this type of operation such as, definitions, the hold short procedure, reduced landing distance available (RLDA), markings and lighting, information to be published, METEO-criteria, runway condition criteria etc. Another kind of operation recognised by ICAO is SCIA, to describe Simultaneous Converging ILS Approaches. (The same as in 1.4 DCIA ?). Also the term DEPENDENT is used , so INDEPENDENT also exist, but the correct meaning and difference is not yet clear!

The ECAC / APATSI (European Civil Aviation Conference / Airport/Air Traffic System Interface) Project Board produced a manual on Mature ATC procedures, which introduces a concept of Simultaneous Operations on Intersecting/Converging Runways (SIMOPS), in order to increase airport capacity. In the document the Converging Runway Display Aid (CRDA) is introduced. CRDA can support the use of Dependent Converging Instrument Approaches (DCIAs) in IMC, which can result in a “dramatic” increase in capacity.

The intention of this paper is to avoid the introduction of different procedures for SIRO, SCIA , SIMOPS DCIA in different regions and to formulate a common IFATCA view on this subject. (ref. WP 119, agenda item B8.1.2.2.1 1994)

There is operational experience with controllers from Australia, Canada, Netherlands, Denmark, USA ( and maybe from more states) with these kind of operations and with their local or regional procedures. (ref. WP 119 1994). SIMOPS (used by APATSI and Australia), SCIA (used by ICAO Europe) and DCIA (used by the FAA) are more or less describing the same operation: simultaneous IFR operations to converging runways. SIRO ( used by ICAO) describes simultaneous operations on intersecting runways ( SIMOPS in Australia also includes this kind of operations).

In SC 1’s opinion, the above procedures are dependant , when special procedures have been evolved , and are being used to manage the crossing point of two intersecting / converging runways. Where the two runways involved are spaced to allow conflict free operations to continue without a special procedure, then these operations are considered to be independent. If it is necessary to differentiate between simultaneous operations on intersecting and on converging runways, clear definitions of intersecting and converging runways should be given.

Simultaneous operations on Intersecting/Converging Runways can consist of 3 types of situation:

a) departure and departure;

b) departure and landing;

c) landing and landing.

In situation a), (departure/departure) where the possible conflict lies at the crossing point of the two runways, normal separation criteria (including wake turbulence criteria) should be used by ATC. In situation b), ( departure and landing ) , there are 3 risks for a conflict ; 1). at the crossing point, 2). a conflicting missed approach and 3). in the case of a balked landing ATC can use time technique , wait until the landing is completed before the crossing point, then depart. He is applying visual separation with his controllers judgement. Low capacity. With SIRO, the landing pilot is instructed to hold short of the crossing runway, where departures are taking place. The Hold-Short Procedure. In situation c), (landing / landing) the same 3 risks for a conflict exist as in situation b), it is not the tower controller that can control the runway crossing point or missed approach crossing point, by staggering the approaches during the sequencing, by making sure that radar separation exists at the moment aircraft A is overshooting and crossing the runway of aircraft B, which is then the radar separation distance away from the crossing point, on final of the other runway. With these types of operations, there is hardly any capacity gain and the staggering technique, without any technical assistance to the controller, is difficult to apply very accurately.

With SIRO and the’ hold short procedure’ (see above) there is much more capacity gain. But these operations will always be dependent. This procedure should take into account possible overruns of the hold short lines (than crossing the other runway , where a departure or landing simultaneously takes place), possible overshoots , and balked landings. There should be a buffer established between the end of the published landing distance available and the intersecting runway. A risk will always exist; the possible conflict situation is concluded random. By giving traffic information, a part of the responsibility is moved to the cockpit. The controller is ‘monitoring’ visually the possible conflict situations and is hoping that nothing will go wrong. Especially in IMC , the controller needs adequate equipment and specific Diverging Missed Approach Procedures (DMAP) in order to control the runway crossing point or missed approach crossing point. On the runway special marking and lighting are needed, to accommodate these procedures. In both VMC and IMC collision risk analysis should be carried out before starting these operations.

In the USA a special operation has been developed by the MITRE Corporation together with the FAA , called Dependent Converging Instrument Approaches (DCIA), with the objective to protect simultaneous missed approaches on converging landing runways in IMC in order to increase landing capacity. A special software tool has been developed by Mitre to assist ATC in staggering converging approaches with more accuracy. This tool is called – Converging Runway Display Aid (CRDA), and uses the radar echoes of traffic on the primary runway to provide ghost-images on the secondary runway. These ghost-images are presented at the same distance from the intersection ( the so called reference point) of the two runways as the original radar-echo. With CRDA, ATC is able to stagger traffic on the two runways in such a way that, in case of simultaneous missed approaches the flightpaths are protected, not with the normal radar separation but with a minimum protection of 1 NM (or more) at the reference point.

After trials at St. Louis, FAA authorised DCIA using CRDA in 1992 and it is currently in use at St. Louis and more USA airports are scheduled to use the aid and the procedure.

Schiphol Airport in Amsterdam, The Netherlands is currently preparing DCIA procedures using CRDA for two runway combinations. A validation and testing programme together with the National Aerospace Laboratory ( NLR ) and Mitre took place in November 1994. Training and implementation should take place between November 1994 until April 1995. Operational experience with DCIA and CRDA should be available beginning in 1995 in Holland. Points to note are ; the very long straight in final approach which is needed to establish the stagger; the required greater accuracy of all controllers concerned; extensive speed control on final ( to reduce as well as increase speed) ; co-ordination between TWR and APP; the responsibility for the stagger distance; information to pilots and training of controllers.

In Australia, procedures were changed to require operators to become signature to ‘ Letters of Agreement ( LOA )’ before SIMOPS was available to the individual operator. This was brought about as a result of difficulties experienced by some operators not being fully conversant with SIMOPS procedures. It became clear that in the light of the Australian experience a thorough collision risk analysis , involving controllers and pilots , needs to take place, in order to devise procedures , to produce segregated or separated missed approaches, and to define roles and responsibilities of ATC and pilots. The Australian Bureau of Air Safety Investigation, reporting on incidents involving this procedure, recommend procedure changes to ensure ” pilots landing on intersecting runways can pass through the intersection without risk of collision, should their aircraft fail to stop before the intersection as required.”

Another question is, at what point do converging runways become opposing runways? FAA criteria state that the angle between the runways should be an occluded angle of between 15 and 100 degrees.

To Conclude

SIMOPS, SCIA, SIRO, DCIA with CRDA, or what ever acronym they are using for simultaneous operations on intersecting or converging runways, will be introduced only for the benefit of capacity.

ICAO EUR (AOPG) is studying on regional provisions (RCM) for simultaneous operations on intersecting or converging runways , with reduced runway declared distances (RLDA), especially the hold short procedure.

ECAC APATSI is dealing with simultaneous operations on intersecting / converging runways (SIMOPS) and Dependent Converging Instrument Approaches (DCIA) using Converging Runway Display Aid (CRDA).

Good co-ordination between ICAO and ECAC working groups is essential, and first of all they must agree about the exact meaning of the phrases , wordings and acronyms used describing all kinds of operations, to avoid different and maybe opposing interpretations. The provision of adequate and specific markings and lighting, the calculation of RLDA’s, the introduction of RTF phraseologies and the publication of these procedures should all be on a world-wide basis. Local or regional introduction of operations as detailed above should be restricted to local operators encompassed by LOA’s, until world-wide standards have been established.

In improving the capacity of aerodromes without a profound study of the safety aspects, these procedures are getting closer and closer to the acceptable safety limits. One has to invest in the appropriate ATC equipment, new procedures and additional staff, to maintain the high standard of safety when increasing the capacity of aerodromes. The effect of these procedures on TCAS equipment should also be investigated, to ensure that possible Resolution Advisories (RA’s) do not interfere with these simultaneous operations. This could be best achieved by requiring TCAS equipped aircraft to select Traffic Advisory (TA) mode prior to entering a designated area.

It’s SC 1’s opinion, that procedures which manage the crossing point of two intersecting/converging runways , are dependent, as in the event of any unexpected occurrence the associated risks of the aircraft involved can never be mutually exclusive. Collision risk analysis should be carried out before implementing these operations, involving pilots and controllers and should include simulation and real-time trials utilising data from the local airport and operators intending to operate with these procedures.

It is recommended that:

The introduction of Simultaneous IFR Operations on Intersecting/Converging Runways should only take place when :

1. The ATC facilities involved have the appropriate equipment, staffing levels, and training;

2. 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;

3. Until world-wide standards have been established, the introduction of local or regional operations should be restricted to local operators by Letters of agreement;

4. 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.