TRAFFIC COLLISION AVOIDANCE SYSTEM (TCAS) OR AIRBORNE COLLISION AVOIDANCE SYSTEM (ACAS)
Is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control.
ACAS/ TCAS is based on secondary surveillance radar (SSR) transpornder signals, but operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft.
A320 TCAS PROCEDURE & MEMORY ITEMS
The TCAS recovery manoeuvre consists of memory items which ensure the correct application of the actions and associated callouts.
- Do not maneuver based on TA alone.
- If Trafic Advisory (TA) “TRAFFIC” is generated : PF announces “TCAS I HAVE CONTROL”
- If a Resolution Advisory (RA) is generated: “CLIMB” and“DESCEND” or “MAINTAIN VERTICAL SPEED MAINTAIN” or“LEVEL OFF, LEVEL OFF” or “MONITOR VERTICAL SPEED” type messages
The applicable memory items are performed, even if in conflict with ATC instructions
- AP (if engaged)………………………………………………….OFF
- BOTH FDs………………………………………………………… OFF
PM selects FD’s OFF after request of PF.
Respond promptly and smoothly to a RA by adjusting or maintaining the pitch, as required, to reach the green area and/or avoid the red area of the vertical speed scale.
Avoid excessive maneuvers while aiming to keep the vertical speed just outside the red area of the VSI , and within the green area. If necessary, use the full speed range between Vαmax and VMAX.
Respect stall, GPWS, or windshear warning.
- GO AROUND procedure must be performed when an RA “CLIMB” or “INCREASE CLIMB” is triggered on final approach
Resolution Advisories (RA) are inhibited below 900 ft.
- When “CLEAR OF CONFLICT” is announced:
Resume normal navigation in accordance with ATC clearance. AP/FD can be reengaged as desired.
The PF disconnects the AP , and smoothly and firmly follows the Vertical Speed Indicator (VSI ) green sector within 5 s, and requests that both FDs be disconnected in order to avoid possible confusion of FD but mostly to have the ATHR in speed mode.
- The PM disconnects both FDs, but will not try to see intruders.
- PF will should avoid excessive maneuvers, and keep the vertical speed outside the red area of the VSI and within the green area.
- If necessary the PF must use the full speed range between Vapha max and Vmax.
- STALL, GPWS and windshear need to be respected
- ATC is notified with the correct phraseology “ ……… XXX TCAS RA”
- Below 900ft Radio Altimiter, all RA’s are inhibited
- When the auto callout “CLEAR OF CONFLICT is announced, the appropriate actions must be taken:
- PF-> Requests both FD’s -> ON
- Auto Pilot (AP) as required
- ALT set and pull OPN CLB/DES modes
- HDG/NAV as required
- PM announces “Clear of conflict” to ATC.
The flight crew should comply with the vertical speed limitations during the last 2 000 ft of a climb or descent. In particular, the flight crew should limit vertical speeds to 1 500 ft/min during the last 2 000 ft of a climb or descent, especially when they are aware of traffic that is converging in altitude and intending to level off 1 000 ft above or below the flight crew’s assigned altitude.
Some aircraft are equipped with – AP/FD TCAS MODE ENGAGEMENT capability.
If an RA is triggered, the AP/FD TCAS mode automatically, and immediately engages.
The PF announces the AP/FD TCAS mode engagement, like any other FMA changes.
If the FDs are disengaged, they automatically engage. The FD pitch bar does not flash, and the triple-click aural alert does not sound, in order to avoid to disturb the PF during the evasive maneuver.
If the A/THR is disconnected, it automatically becomes armed or active.
If APs and FDs are OFF when the RA is triggered, HDG automatically engages.
TCAS PROCEDURE WITH AP/FD TCAS
If an RA is triggered:
‐ If the AP is engaged, the PF should keep it ON
The AP guides the aircraft in accordance with the RA orders.
‐ If the AP is not engaged:
• The PF smoothly and firmly flies the FD pitch bar
The FD orders guide the aircraft in accordance with the RA orders
• The PF can ask the PM to engage the AP.
‐ The PM monitors the evasive maneuver. He does not try to see the reported traffic.
The flight crew checks that the guidance of AP/FD TCAS mode leads the vertical speed out of the red area of the vertical speed scale, and in the green area if any.
If for any reason during an RA, the aircraft vertical speed does not reach the green area of the vertical speed scale, the PF should disconnect the AP, and override the FD orders, in order to lead the aircraft vertical speed out of the red area of the vertical speed scale.
If necessary, the PF must use the full speed range between Vαmax and Vmax.
‐ If any “CLIMB” aural alert sounds during the final approach, the flight crew should first apply the AP/FD TCAS procedure. When clear of conflict, depending on the situation, they can consider a go-around.
‐ The PM notifies the ATC
‐ When clear of conflict:
• The AP/FD TCAS mode automatically reverts to V/S, in order to capture the FCU selected altitude. In some cases, the AP/FD TCAS mode may revert to an altitude acquire mode or an altitude hold mode.
• The PM notifies the ATC
• The PF engages an appropriate vertical mode, or adjusts the vertical speed target, in accordance with ATC clearance.
The AP/FD TCAS mode is speed protected, i.e. it ensures that the aircraft speed remains between VLS- 5 kt and Vmax. Therefore, in the case the RA is triggered when the aircraft is close to its performance limits, the RA vertical speed target may not be reached with the AP/FD TCAS mode.
TCAS PROCEDURE WITHOUT AP/FD TCAS
If a RA is generated and the TCAS flight guidance mode is not available:
‐ The PF disconnects the AP, and smoothly and firmly follows the Vertical Speed Indicator (VSI ) green sector within 5 s, and requests that both FDs be disconnected.
Note: Both FD s must be disconnected once APs are disconnected:
• To ensure autothrust speed mode
• To avoid possible confusion between FD bar orders and, TCAS aural and VSI orders
‐ The PM disconnects both FDs, but will not try to see intruders.
‐ The PF will avoid excessive maneuvers, and keep the Vertical Speed outside the red area of the VSI and within the green area. If necessary, the PF must use the full speed range between Valpha max and Vmax.
‐ The PM must notify ATC.
‐ The flight crew should never maneuver in the opposite direction of the RA, because TCAS maneuvers are coordinated.
‐ In final approach, i.e. “CLIMB”, “CLIMB NOW”, “INCREASE CLIMB”, the flight crew will initiate a go-around.
‐ When clear of conflict, the flight crew must resume normal navigation, in accordance with ATC clearance, and using the AP, as required.