CONTENTS
Amendment: Inclusion of ADJUST VERTICAL SPEED ADJUST.
http://www.eurocontrol.int/acas/
TCAS II is an on-board system designed to improve air safety by acting as a "last resort" method of preventing mid-air collisions by alerting the crew to manoeuvre the aircraft in the vertical plane when a risk of collision is detected. The QRH Non-Normal manoeuvres section contains details on pilot actions required for Traffic Avoidance.
FAA TCAS II is designed to provide collision avoidance protection in the case of any two aircraft that are closing horizontally at any rate up to 1200 knots and vertically up to 10,000 feet per minute.
TCAS uses the Mode S transponder to interrogate the operating transponders in other airplanes, tracks the other airplanes by analysing the transponder replies, and predicts the flight paths and positions. TCAS provides advisory, flight path guidance, and traffic displays of the other airplanes to the flight crew. Neither advisory, guidance, nor traffic display is provided for other airplanes that do not have operating transponders. TCAS II operation is independent of ground-based air traffic control.
To provide advisories, TCAS identifies a three-dimensional airspace around the airplane where a high likelihood of traffic conflict exists. The dimensions of this airspace are contingent upon the closure rate with conflicting traffic.
TCAS provides advisories and traffic displays:
Honeywell It is possible to see an aircraft flying the same course and direction as your own aircraft and be in close proximity to your aircraft, yet TCAS II may not consider it a threat. TCAS II calculates the closure rate of the intruder, and derives the time to the closest point of approach (CPA). If there is no closure rate, no advisory will be issued, unless the intruder is very close (within approximately 0.25 mile).
TCAS messages and TCAS traffic symbols can be displayed on the HSI in the MAP, VOR, and ILS modes. TCAS messages and TCAS traffic symbols cannot be displayed on the HSI in the PLAN mode. TRAFFIC, TA ONLY, and TCAS TEST are displayed in all EFIS modes.
As installed TCAS messages and TCAS traffic symbols can be displayed on the HSI in the MAP, CTR MAP, VOR, and APP modes. TCAS messages and TCAS traffic symbols cannot be displayed on the HSI in the CTR VOR, CTR APP, or PLAN modes. TRAFFIC, TA ONLY, and TCAS TEST are displayed in all EFIS modes.
TCAS display automatically shows when:
As installed
EuroControl Each symbol is displayed on the screen according to its relative position to own aircraft. The display accuracy depends upon the selected scale. When the 10 nm scale is in use the positional accuracy is ± 1 nm and approximately ±10° in bearing. Targets are artificially smoothed to prevent jitter.
TCAS II triggers an advisory when a range test and altitude test are both satisfied. These tests are performed on each altitude-reporting target every second.
The principle of the range test is to compute the time-to-go to the Closest Point of Approach (CPA) by dividing the distance between the aircraft by the closure rate. The range test is satisfied if this time is lower than a threshold value, typically 20 to 35 seconds for RAs and 35 to 48 seconds for TAs.
To address the specific case of very low closure rates, a protection distance has been introduced to avoid an intruder coming very close in range without triggering any advisories. For this type of encounter, the range test is satisfied if the distance between aircraft is lower than this protection distance of 1.1 nm for RAs and 1.3 nm for TAs.
The principle of the altitude test is to compute the time to reach co-altitude by dividing the relative altitude between aircraft by the relative vertical speed. The altitude test is satisfied if this time is lower than a threshold value, typically 20 to 35 seconds for RAs and 35 to 48 seconds for TAs. If the own aircraft is level, the time threshold value for RAs is reduced to 25 seconds to detect a possible level-off manoeuvre of the intruder and thus to avoid the triggering of the RA.
To address the specific case of level aircraft or aircraft with a very low relative vertical speed, the altitude test is satisfied if the relative altitude between aircraft is lower than a fixed vertical distance threshold of 850 ft for TAs and 700 ft for RAs.
A resolution advisory is a prediction that another airplane will enter the TCAS conflict airspace within approximately 20 to 30 seconds. If altitude data from the other airplane is not available, no resolution advisory can be provided.
When the TCAS issues a resolution advisory:
When the TCAS cyan message TFC is displayed on the HSI, and the resolution advisory is within the display range of the HSI, the TCAS RA traffic symbol and its accompanying data tag is displayed on the HSI. The TCAS RA traffic symbol is a filled red square.
TCAS II computes the most appropriate vertical manoeuvre in order to achieve a target vertical miss distance, which is equal to 600 ft.
A traffic advisory is a prediction that another airplane will enter the conflict airspace in 35 to 48 seconds. Traffic advisories are provided to assist the flight crew in establishing visual contact with the other airplane.
When TCAS predicts a Traffic Advisory:
When the TCAS cyan message TFC is displayed on the HSI and the traffic advisory is within the display range of the HSI, the TCAS TA traffic symbol and its accompanying data tag are displayed on the HSI. The TA traffic symbol is a filled amber circle.
For no-bearing resolution or traffic advisories, the RA or TA label is displayed below the red or amber TRAFFIC message, and the data tag information is displayed to the right of the label. The data tag contains the distance, altitude, and vertical motion arrow.
When the Resolution Advisory or traffic advisory is further from the airplane than the HSI range currently displayed, the TCAS red or amber message OFFSCALE is displayed on the HSI.
Proximate traffic is another airplane that is neither a Resolution Advisory or a Traffic Advisory but is within:
When the TCAS cyan message TFC is displayed on the HSI and the proximate traffic is within the HSI display range, the TCAS proximate traffic symbol is displayed on the HSI. The TCAS proximate traffic symbol is a filled white diamond. If the other airplane is providing altitude data, then a data tag is also displayed that contains the following information about the other airplane:
Other traffic is another airplane that is within the HSI display limits but is neither a Resolution Advisory, a Traffic Advisory nor Proximate Traffic. If the other airplane is not providing altitude information, other traffic becomes Proximate Traffic automatically when within six miles.
When the TCAS cyan message TFC is displayed on the HSI and the other traffic is within the HSI display range, then the TCAS other traffic symbol is displayed on the HSI. The TCAS other traffic symbol is a hollow white diamond. If the other airplane is providing altitude data, then a data tag like that described in the Proximate Traffic display is displayed.
The TCAS voice alert TRAFFIC, TRAFFIC sounds once when TCAS first predicts a new Traffic Advisory.
When TCAS first predicts a new Resolution Advisory, one of the following TCAS voice alerts sounds once:
The ‘crossing’ alerts tell the flight crew that the airplane will fly through the altitude of the other airplane when following the TCAS vertical guidance on the ADI.
If TCAS requires an increase or decrease in the vertical rate of climb, then one of the following TCAS voice alerts sounds once:
If TCAS requires a change in vertical direction from either an existing climb to a descent, or an existing descent to a climb, then one of the following TCAS voice alerts sounds once:
When separation from the other airplane is increasing and TCAS predicts there will be no Resolution Advisory, the TCAS voice alert CLEAR OF CONFLICT sounds once. However, the alert will not sound if the Resolution Advisory can no longer be calculated because TCAS cannot predict the track of the other airplane.
The following are the available TCAS voice alerts:
Present pitch attitude is within TCAS ADI vertical guidance pitch command. Keep pitch attitude out of red pitch command.
TCAS II Version 7 has replaced both REDUCE CLIMB, REDUCE CLIMB and REDUCE DESCENT, REDUCE DESCENT with ADJUST VERTICAL SPEED ADJUST.
When TCAS predicts a Resolution Advisory, TCAS vertical guidance is displayed on the ADIs for a manoeuvre to ensure vertical separation. The pitch manoeuvre is based on traffic airplane altitude information.
If the traffic airplane also has TCAS and a mode S transponder, TCAS vertical guidance is coordinated with the traffic airplane TCAS.
The HSI TCAS red message TRAFFIC is displayed when TCAS predicts a Resolution Advisory.
The cyan message TFC is displayed when TCAS traffic symbols and messages are or can be displayed. The message is not displayed if the TCAS message TCAS FAIL, TCAS OFF or TCAS TEST is displayed.
The amber message TRAFFIC is displayed when TCAS predicts a Traffic Advisory.
The red message OFFSCALE is displayed when TCAS predicts a Resolution Advisory that is at a distance greater than the HSI selected range.
The amber message OFFSCALE is displayed when TCAS predicts a Traffic Advisory (but not a Resolution Advisory) that is at a distance greater than the HSI selected range.
When the cyan message TA ONLY is displayed, TCAS cannot provide resolution advisories. All other traffic that would have been resolution advisories are predicted as traffic advisories.
The cyan message TCAS TEST is displayed when TCAS is in the test mode. The message is displayed on all HSI modes and ranges.
INCREASE DESCENT resolution advisories are inhibited below 1,450 feet Radio Altitude.
DESCEND resolution advisories are inhibited below 1000 ft Radio Altitude when descending, and below 1,200 feet Radio Altitude when climbing.
All Resolution Advisory are inhibited below 1,100 feet Radio Altitude when climbing and below 900 feet Radio Altitude when descending.
TCAS voice alerts are inhibited below 1,100 feet Radio Altitude when climbing and below 900 feet Radio Altitude when descending.
All TCAS alerts are inhibited by GPWS and windshear warnings.
The TCAS operating mode is controlled from the transponder panel. TCAS is normally operated in the TA/RA mode.
However, sometimes it is necessary to operate in the TA ONLY mode to prevent nuisance Resolution Advisory.
The TA ONLY mode is used during engine out operations to prevent Resolution Advisory when adequate thrust is not available to follow the Resolution Advisory commands. Also, the TA ONLY mode can be used when intentionally operating near other traffic that may cause resolution advisories, such as during parallel approaches and VFR operations.
(SB changes displays TCAS advisory message.) The EICAS advisory message TCAS is displayed if TCAS cannot display TCAS Resolution Advisory guidance on either ADI, and cannot display TCAS traffic symbols on either HSI. TCAS voice alerts will not occur.
(SB changes displays TCAS OFF advisory message.) The EICAS advisory message TCAS OFF is displayed if TCAS is not operating in the TA or TA/RA mode. No TCAS RA guidance is displayed on the ADIs, no TCAS traffic symbols are displayed on the HSIs, and no TCAS voice alerts sound.
The EICAS advisory message TCAS FAIL is displayed if TCAS cannot display TCAS Resolution Advisory guidance on either ADI, and cannot display TCAS traffic symbols on either HSI. TCAS voice alerts will not occur.
EICAS Messages