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 VSI.
TCAS display shows when:
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:
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:
For no-bearing resolution or traffic advisories, the RA or TA label is displayed in the lower centre of the VSI display just below the airplane symbol and the advisory data tag information is displayed to the right of the label. The data tag contains the distance, altitude, and the vertical motion arrow.
When the resolution or Traffic Advisory is outside the displayed range on the VSI, one-half of the symbol will appear at the appropriate bearing at the edge of the display. The symbol will appear in its proper colour and have its data tag displayed, providing there is room.
Proximate traffic is another airplane that is neither a Resolution Advisory or a Traffic Advisory but is within:
When the proximate traffic is within the display range, the TCAS proximate traffic symbol is displayed. 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 this information about the other airplane:
Other traffic is another airplane that is within the display range 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 and within 2700 feet vertically.
When the other traffic is within the display range, then the TCAS other traffic symbol is displayed. 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 VSIs 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.
TCAS provides colour-coded visual advisory areas behind the vertical speed indicator's scale. These colour-coded indications provide guidance as to what vertical speed region to avoid (RED). If a change in vertical speed is necessary, the specific region of vertical speed to "fly-to" is indicated in GREEN.
Note: If there is more than one threat, two red arcs may flank the range of required vertical speeds.
The amber RA FAIL message is displayed when resolution advisories are not available. The amber TCAS FAIL message is displayed when the TCAS system is not operational.
The amber TD FAIL message is displayed when the VSI is unable to provide traffic displays.
When the white message TA ONLY is displayed, TCAS can not provide resolution advisories. All other traffic that would have been resolution advisories are predicted as traffic advisories.
The white TCAS OFF message is displayed when the TCAS mode is not selected.
The white message TCAS TEST is displayed when TCAS is in the test mode.
INCREASE DESCENT resolution advisories are inhibited below 1,450 feet Radio Altitude.
DESCEND resolution advisories are inhibited below 1000 feet 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.
The EICAS advisory message TCAS FAIL is displayed if TCAS cannot display TCAS Resolution Advisory guidance and symbols. TCAS voice alerts will not occur.
EICAS Messages