Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 1 ACAS II operations in the European RVSM environment ACAS II mandate in Europe (1/2)  Two steps: (1st January 2000: all civil fixed-wing turbine-engine aircraft having a maximum take-off mass exceeding 15,000 kg, or a maximum approved passenger seating configuration of more than 30 will be required to be equipped with ACAS II (1st January 2005: all civil fixed-wing turbine-engine aircraft having a maximum take-off mass exceeding 5,700 kg, or a maximum approved passenger seating configuration of more than 19 will be required to be equipped with ACAS II  ACAS II can trigger two types of advisories: (Traffic Advisories (TAs): To prepare the crew for a possible RA and to help in the visual search (Resolution Advisories (RAs): Avoidance manoeuvres in the vertical plane recommended to the pilot

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 2 ACAS II operations in the European RVSM environment ACAS II mandate in Europe (2/2)  TCAS II version 6.04a: (Is not fully compliant with the ICAO ACAS II SARPs (Is not operationally compatible with RVSM  TCAS II version 7.0: (Was developed to improve the general TCAS II performances (Addresses the issue of TCAS II version 6.04a operational incompatibility with RVSM  Practical implementation issues (supply, installation, certification)  temporary exemptions until 30 September 2001

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 3 ACAS II operations in the European RVSM environment RVSM implementation (2/2)

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 4 ACAS II operations in the European RVSM environment TCAS II description

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 5 ACAS II operations in the European RVSM environment Principles (1/2)  System designed to prevent mid-air collisions and near mid-air collisions  Autonomous and independent of any aircraft navigation equipment and ground systems  TCAS II is based on two main concepts: (time-to-go to the Closest Point of Approach (CPA); modified according to (altitude bands (sensitivity level)  In a one-second cycle, TCAS II: (Monitors other aircraft by interrogating their transponder (Selects an advisory when a range test and an altitude test are satisfied (Presents the information to the pilot

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 6 ACAS II operations in the European RVSM environment  RAs are co-ordinated between TCAS II equipped aircraft  Pilots should follow their RAs as accurately as possible  A manoeuvre in the opposite sense to the RA is hazardous Principles (2/2)

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 7 ACAS II operations in the European RVSM environment  TCAS II computes the time-to-go to the CPA (Based on the closure rate and the distance between aircraft  If this time is lower than the set threshold, the range test is satisfied Advisory triggering: range test (1/2) < 48 s (TA) < 35 s (RA) Intruder TCAS

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 8 ACAS II operations in the European RVSM environment Advisory triggering: range test (2/2)  Specific case of very low closure rates between aircraft:  If the distance between aircraft is lower than the set protection distance, the range test is satisfied 1.3 NM (TA) 1.1 NM (RA) Intruder TCAS (very low closure rate)

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 9 ACAS II operations in the European RVSM environment Advisory triggering: altitude test (1/2)  TCAS II computes the time to reach co-altitude (Based on the relative altitude between aircraft and the relative vertical speed  If this time is lower than the set threshold, the altitude test is satisfied < 48 s (TA) < 35 s (RA) < 25 s (RA for level aircraft) Intruder TCAS

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 10 ACAS II operations in the European RVSM environment  Specific case of level aircraft:  If the relative altitude between aircraft is lower than the set threshold, the altitude test is satisfied Advisory triggering: altitude test (2/2) 850 ft (TA) 700 ft (RA) 850 ft (TA) 700 ft (RA) TCAS  Advisory triggering  No advisory

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 11 ACAS II operations in the European RVSM environment Improvements of TCAS II version 7.0  Modification of altitude band boundaries: FL200-FL300  FL200-FL420  Additional improvements: (Decrease of the reduced time threshold for level aircraft (30 s  25 s) (Introduction of a Miss-Distance Filtering to filter RAs in the horizontal plane (Fewer RAs that go against the aircraft vertical trajectory (Triggering of weakening RAs to reduce deviations in very slow divergence

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 12 ACAS II operations in the European RVSM environment Standard RVSM vertical separation (1/2)  Both aircraft are level and separated by 1000 ft  TCAS II version 7.0: (Altitude thresholds: 850 ft for TAs and 700 ft for RAs (The altitude test is not satisfied  No advisory

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 13 ACAS II operations in the European RVSM environment Standard RVSM vertical separation (2/2)  TCAS II version 6.04a: (Altitude thresholds: 1200 ft for TAs and 800 ft for RAs (The altitude test for TAs is satisfied  Triggering of TAs  Concluding remarks: (TCAS II version 7.0 is compatible with 1000 ft vertical separation (Pilots of TCAS II version 6.04a equipped aircraft will experience a large number of TAs (If a TA is triggered, Pilots shall comply with the airline operational instructions Standard pilots’ behaviour is expected (No controllers’ action since TAs should not be notified by pilots

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 14 ACAS II operations in the European RVSM environment Vertical offset (1/3)  Two level aircraft at adjacent flight levels have a vertical offset  Considerations about altitude: (RVSM approved aircraft can have a 65 ft maximum vertical offset (Aircraft report their altitude by either 25 ft or 100 ft quanta (TCAS II can overestimate vertical offsets (e.g. 75 ft or 100 ft instead of 65 ft)

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 15 ACAS II operations in the European RVSM environment Vertical offset (3/3)  TCAS II version 6.04a: (Altitude thresholds: 1200 ft for TAs and 800 ft for RAs (Triggering of TAs between level aircraft separated by 1000 ft with or without vertical offsets  Concluding remarks: (TAs triggered by TCAS II version 7.0 because of vertical offsets are rare events: Two offsets  51 ft and 100 ft altitude report quantization (a small proportion of the fleet) (If a TA is triggered, Pilots shall comply with the airline operational instructions Standard pilots’ behaviour is expected (No controllers’ action since TAs should not be notified by pilots

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 16 ACAS II operations in the European RVSM environment Oscillation (1/2)  Two level aircraft at adjacent flight levels oscillate in the altitude keeping  RVSM approved aircraft can oscillate with a 65 ft maximum amplitude  This configuration is very similar to the vertical offset: (All calculations for vertical offsets are valid for oscillations

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 17 ACAS II operations in the European RVSM environment Turbulence (1/3)  Due to turbulence, an aircraft deviates towards another aircraft level at an adjacent flight level  TCAS II detects a high vertical closure rate configuration

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 18 ACAS II operations in the European RVSM environment 1000 ft level-off encounter (1/4)  One aircraft is levelling off at 1000 ft from another aircraft  TCAS II has no knowledge of the intent of own and intruder aircraft (Assumes that the current flight profiles will be maintained

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 19 ACAS II operations in the European RVSM environment 1000 ft level-off encounter (2/4)  Altitude test based on the time to reach co-altitude  Example: (TCAS II of the descending aircraft triggers a TA and an RA (TCAS II of the level aircraft triggers only a TA

Eurocontrol ACAS Programme ACTOR/wp3/SLID/D 03/08/01 - v1.0 Slide 20 ACAS II operations in the European RVSM environment Low closure rate encounter (1/3)  Two level aircraft at adjacent flight levels follow the same route. The trailing aircraft has a slow overtake  Slow overtake: (By itself does not trigger any advisory, but (Induces longer duration advisories when triggered by the previous configurations