A320 TCAS RA Compliance: The FCOM Procedure Pilots Misread

What is the difference between a preventive and a corrective TCAS RA on the A320?

A preventive RA (e.g., MONITOR V/S) does not require a flight path change — maintain V/S out of the red area on the VSI[cite: 212].

A corrective RA (e.g., CLIMB, DESCEND) requires action: smoothly and firmly adjust or maintain V/S to reach the green area, applying approximately 0.25 g within 5 seconds[cite: 213]. For an increased-rate corrective RA (e.g., CLIMB NOW, INCREASE CLIMB), the technique tightens to 0.35 g within 2.5 seconds[cite: 214]. The categories and g-targets come directly from FCTM AS-TCAS[cite: 215].

When does an A320 automatically switch to TA ONLY mode?

Automatic TA ONLY selection occurs in two conditions if TA/RA was previously selected[cite: 217]. First, below 1,000 ft AGL, the system automatically reverts to TA ONLY and all RAs are inhibited and converted into TAs[cite: 218]. Second, when windshear, stall, or GPWS alerts trigger, the system reverts to TA ONLY for the duration of those higher-priority warnings[cite: 219].

What do you do if ATC orders you to descend during a CLIMB RA on the A320?

Follow the RA in the correct sense, even if it conflicts with the vertical element of an ATC instruction[cite: 224]. Advise ATC with the standard phraseology: "UNABLE, TCAS RA." [cite: 225] When clear of conflict, return promptly to the ATC clearance or instruction[cite: 225].

The ATC controller does not have real-time visibility into the coordinated TCAS solution and cannot manage it; the TCAS resolution is already negotiated between aircraft via the Mode S link[cite: 226, 227]. Compliance is not a courtesy — it is the only path that preserves the coordinated separation logic[cite: 228].

Does the A320 autopilot stay engaged during a TCAS RA?

It depends on the aircraft configuration[cite: 229]. For A320s without the AP/FD TCAS function, both FDs must be disconnected when the AP is disconnected, to ensure A/THR speed mode is active and to avoid confusion between FD orders and TCAS VSI guidance[cite: 230].

For A320s with AP/FD TCAS installed, when an RA triggers the AP/FD TCAS function provides vertical guidance directly: AP status does not change, and the FDs automatically engage if not already engaged[cite: 231]. Verify the specific aircraft equipment standard before applying a blanket "AP off, FDs off" rule[cite: 232].

What is a TCAS Reversal RA on the A320?

If the geometry changes and the original RA no longer resolves the conflict, TCAS may command a Reversal RA — for example, an initial CLIMB remaining commanded to reverse into a descent, or vice versa[cite: 234]. The technique is identical to an increased-rate corrective RA: smoothly and firmly follow the new green area within 2.5 seconds[cite: 235]. The green band on the VSI is a dynamic envelope, not a fixed number[cite: 236]. Pilots who chase a numeric V/S can drive the aircraft back into the red as the band shifts[cite: 237].

How does an A320 TCAS generate an RA against unequipped traffic?

TCAS can generate an RA only when the intruder provides altitude information — Mode C or Mode S transponder[cite: 239]. For intruders that do not report altitude, the relative altitude does not appear on the ND and TCAS never triggers an RA[cite: 240]. Against a Mode S-equipped intruder, the Mode S data link supports coordination: the two TCAS systems negotiate complementary maneuvers (one aircraft climbs, the other descends, or one holds level)[cite: 241]. The crew must always follow the RA in the correct sense, because the intruder may also be maneuvering in response to a coordinated RA[cite: 242].

What does NAV TCAS FAULT mean on an A320 ECAM?

NAV TCAS FAULT triggers when there is an internal failure of the TCAS computer[cite: 244]. ECAM STATUS shows INOP SYS TCAS[cite: 244]. This is distinct from NAV TCAS STBY, which triggers when the crew has set the TCAS to standby or the system has reverted to standby mode[cite: 245]. The two messages have different causes and procedures — do not conflate them[cite: 246]. With NAV TCAS FAULT, the crew should advise ATC and revert to procedural separation; with NAV TCAS STBY, verify the mode selection before assuming a failure[cite: 247, 248].

Can an A320 dispatch with TCAS inoperative?

Yes, under specific MEL conditions[cite: 249]. MEL item 34-40-05 (Traffic Collision Avoidance System) carries Repair Interval A, with 1 installed and 0 required for dispatch, placard required, may be inoperative for 10 consecutive calendar days[cite: 250]. If TCAS is inoperative, local-authority restrictions for takeoff and landing may apply; the crew and Engineering should inform IOCC to obtain relevant clearances before departure[cite: 251, 252]. For HKG specifically, call the ATC Watch Manager for approval or exemption[cite: 253]. Verify the operator-specific (O) and maintenance (M) procedures attached to the MEL item[cite: 254].

What is the A320 procedure for a CLIMB RA during a go-around?

For any CLIMB RA during an approach in CONF 3 or FULL: perform a go-around and follow SRS orders[cite: 256]. The AP and FD can be kept engaged during the go-around[cite: 257]. Monitor that V/S remains out of the red area and take over if necessary[cite: 258]. The RA does not override the standard go-around procedure — both apply together, with the SRS managing the climb profile and the VSI green band confirming separation[cite: 259].

Does the A320 PM look out for the intruder during a TCAS RA?

No. During an RA, the PM does not try to see the intruder[cite: 261]. That is explicit FCTM guidance, not a suggestion[cite: 262]. The PM monitors the PF's compliance with the green band, manages the radios using the standard phraseology, and confirms ECAM/FMA status[cite: 262]. Two pilots looking out the window for traffic that TCAS has already found is not crew coordination — it is abandoning the flight deck to satisfy curiosity[cite: 263]. The RA must be reported as an incident by ASR after the flight, per OM-A GEN 8.3.7[cite: 264].