At the last SICASP/WG2 meeting held in September 1995 in Germany, the WG laid down its future work program for the panel. Of particular interest to this agenda item was their task “f” which read as follows; “ review proposals for other uses of ACAS to determine whether any further technical specifications are required and ensure that the collision avoidance functions is not affected. The target date was set for 1998” . It was also decided by the WG that the Airborne Separation Assurance Systems (ASAS) applications should be treated as part of this task “f”.

To start the discussion I would like to quote the author of a paper submitted at the above mentioned SICASP meeting regarding future applications:

“fuelled by the desire of some TCAS operators (mainly in the US) to gain maximum return on their TCAS investment, several proposals have been floated to utilise the current TCAS surveillance for In Trail Climb/Descent, Station Keeping on Final Approach etc.. Although initially embraced with some enthusiasm by the FAA, there is now realisation that the existing TCAS surveillance, designed to support the collision avoidance function, is of insufficient integrity to support most of the uses suggested. It is generally recognised within SICASP and in ACAS/TCAS forums that it is inevitable that an improved traffic display will be used for purposes other than collision avoidance. Not surprisingly, enhanced TCAS surveillance capability (TCAS IV technology ) and the associated cockpit display of traffic information is now seen to be a prerequisite for applications other than collision avoidance. It is appropriate to examine such proposed applications for technical integrity, operational requirements and potential benefit to operators. However it is essential that there not be degradation of the core collision avoidance function of ACAS/TCAS.

The concept of an ASAS was introduced to the WG by the French. ASAS would be independent of ACAS, but would potentially support other airborne surveillance applications. Although independent of ACAS its cockpit interface would be a CDTI which might well take the form of an improved TCAS display”.

Following is a brief description of five proposed applications utilising TCAS Surveillance and TCAS Display, drawn from the FAA Flight Standards Dept.

OCEANIC IN-TRAIL CLIMB/DESCENT/PASSING MANOEUVRE

a) Description :- To use the TCAS surveillance function and the TCAS traffic display to permit a trailing aircraft to climb or descend through another aircraft’s altitude or to pass the other aircraft laterally.

b) Proposed Operational Procedure :- The TCAS surveillance would be used to identify the lead aircraft and to verify the range between the two aircraft in the initial phases of implementation, a clearance would be requested from the responsible ATS provider to execute the manoeuvre. Once the manoeuvre was approved, the TCAS traffic display would be used to monitor the distance and closure with an intruder. The longer range proposal which requires a change in the air traffic management procedures, is to permit the manoeuvre to be initiated without an ATS clearance and the performing aircraft would simply report the manoeuvre was in progress or had been completed.

c) Target Airspace:- Initially oceanic airspace. Concept could be extended to other en-route airspace.

d) Minimum Performance standards in Existence:- No formal standards or requirements have been developed. While papers outlining the application indicate that the trail aircraft will require discrete, positive identification of the other aircraft, its intent i.e. , next waypoint location , altitude and predicted time, and either the lead aircraft’s speed or the closure rate between the two aircraft.

OCEANIC LEAD AIRCRAFT CLIMB/DESCENT

a) Description:- Use the TCAS surveillance function and the TCAS traffic display to permit a leading aircraft to climb or descend through another aircraft’s altitude.

b) Proposed Operational Procedure:- The TCAS surveillance would be used to identify the trail aircraft and to verify the range between the two aircraft. In the initial phases of implementation a clearance would be requested from the responsible ATS provider to execute the manoeuvre. Once the manoeuvre was approved the TCAS traffic display would be used to monitor the distance and the closure rate with an intruder. The longer range proposal, which requires a change in the air traffic management procedures., is to permit the manoeuvre to be initiated without an ATS clearance and the performing aircraft would simply report the manoeuvre was in progress or had been completed.

c) Target airspace :- Initially oceanic airspace. Concept could be extended to other en- route airspace.

d) Minimum Performance Standards in Existence :- No formal standards or requirements have been developed. White papers outlining the application indicate that the lead aircraft will require discrete, positive identification of the other aircraft, its intent i.e. next waypoint location, altitude , and predicted time; and either the trailing aircraft’s speed or the closure rate between the two aircraft.

IN TRAIL SPACING OR STATION KEEPING

a) Description:- Use the TCAS surveillance function and the TCAS traffic display to permit a trailing aircraft to maintain a defined distance from another aircraft.

b) Proposed Operational Procedure:- The ATS provider would issue a clearance to a trailing aircraft to maintain a set distance behind another aircraft. This clearance could also permit the trail aircraft to close to a defined distance before beginning the maintenance of the separation. The TCAS surveillance would provide the required tracking information on the intruder and the TCAS traffic display would be used to show the pilot the distance between his own aircraft and the lead aircraft.

c) Target Airspace:- Proposed for use in the en-route and terminal airspace with the intent of increasing capacity in the en-route airspace. The application would be used to reduce separation in non-radar environments. In the terminal area, the application would be used to meter traffic over the final approach fix at a given time and speed. It could also be used at airports with closely spaced parallel approaches to increase capacity by assigning the spacing to be maintained from the aircraft on the parallel runway.

d) Minimum Performance Standards in Existence:- No formal standards or requirements have been developed. White papers outlining the application indicate that the trail aircraft will require discrete, positive identification of the other aircraft; its intent, i.e., next waypoint location, altitude , and predicted time, and either the lead aircraft’s speed or the closure rate between the two aircraft.

SITUATIONAL AWARENESS FOR AIRCRAFT ON FINAL APPROACH

a) Description:- Use the TCAS surveillance function and the TCAS traffic display to provide increased situational awareness for aircraft holding in position on a runway and for final approach.

b) Proposed operational Procedure :- The TCAS traffic display and the TCAS logic would be used to provide collision avoidance protection for an aircraft on final approach. TCAS would track the aircraft either holding in position or entering the arrival runway. The TCAS traffic display in the aircraft on the ground would also provide that pilot with increased situational awareness by displaying potential threat aircraft on final approach.

c) Target Airspace:- Proposed for use in the immediate vicinity of the arrival and departure runways.

d) Minimum Performance Standards in Existence :- No formal standards or requirements have been developed . White papers outlining the application indicate the implementation of this application will require some form of co-operative surveillance such as ADS-B.

INCREASED SITUATIONAL AWARENESS

a) Description:- Use the TCAS surveillance function and the TCAS traffic display to provide increased situational awareness for aircraft.

b) Proposed Operational Procedure:- The TCAS traffic display would be used to provide the pilots with additional information on the intruder aircraft displayed by TCAS. Using cross-linked information between the two aircraft, the TCAS aircraft would be able to obtain intent information on the intruder aircraft. The intent information could include information on the active waypoint (position, crossing altitude, time over the waypoint , etc.) ; the selected altitude; and aircraft state data. The application could be expanded to utilise the additional information in the CAS logic.

c) Target Airspace:- Proposed for use in all airspace.

d) Minimum Performance Standards in Existence:- No formal standards or requirements have been developed. White papers outlining the application indicate that the implementation of this application will require some form of co-operative surveillance such as ADS-B.

Besides the above mentioned and described applications, below is included an extended list of possible applications of ACAS/ASAS.

i)  At Ramp :- Surveillance of immediate area around aircraft, in particular behind aircraft.

ii)  Push back:- As for at ramp.

iii)  Taxi out :-

i)  Surface movement surveillance, especially in low visibility;

ii)  Self separation whilst taxing;

iii)  Self guidance in low visibility;

iv)  Warning of proximity to traffic on common/intersecting runway or taxiway;

v)  Stop Bar/Hold Point display, especially in low visibility.

iv)  Take Off :-

i)  Runway Surveillance;

ii)  Runway incursion warning.

v)  Climb :-

i)  Self separation from other aircraft;

ii)  Flight path monitoring; noise abatement corridors.

vi)  Cruise :-

i)  Self separation – free flight concept;

ii)  Traffic monitor (surveillance) to 100nm;

iii)  In-trail climb/descent;

iv)  Lateral overtake.

vii)  Descent :- As for climb

viii)  Approach :-

i)  Self separation;

ii)  Runway surveillance;

iii)  Runway incursion warning.

ix)  Landing :- As for takeoff.

x)  Taxi in :- As for Taxi out

xi)  Ramp arrival :- Surveillance of ramp area.