A320 cockpit - traffic visible through windshield, TCAS RA active

By Paul Toensing  |  Custom GPT Solutions  |  May 2026  |  ~8 min read

The Three-Voice Problem

There is a particular kind of confidence that builds up in a pilot's first few thousand hours. You learn to trust your eyes. You learn that the airplane usually does what you expect. And you learn that when the system says one thing and your training tells you another, your training is usually the safer bet.

TCAS RA compliance is the exception. It is the one situation in which your eyes are the worst instrument in the cockpit, and the published procedure is the only path that preserves the safety solution.

Every TCAS RA scenario has the same structure. Three voices arrive within three seconds: your visual assessment of the traffic, the TCAS commanded maneuver, and an ATC instruction that may or may not align with either. The procedure is unambiguous on the order: follow the RA in the correct sense, advise ATC using the standard phraseology, then resolve the visual picture if there is one to resolve. The discrete procedural details - response times, the preventive-versus-corrective distinction, the AP/FD TCAS specifics - are covered in the A320 TCAS RA procedure Q&A. This piece is about the architecture behind the procedure, and the parts of the manual that most pilots have never had to articulate under examiner pressure.

The AP/FD TCAS Distinction That Changes the Rule

The most-quoted shorthand for the A320 TCAS RA response is: AP off, both FDs off, fly the green sector. That shorthand is accurate for a specific aircraft configuration - and not quite right for another.

On A320s without the AP/FD TCAS function installed, the shorthand holds. Disconnect the AP, disconnect both FDs to ensure A/THR is in speed mode and to remove the FD command bars that would otherwise compete with the VSI green sector, and fly the RA manually.

On A320s with AP/FD TCAS installed - a function included in the Honeywell TPA-100B Change 7.1 standard - the AP status does not change when the RA triggers. The FDs automatically engage if not already engaged, and the AP/FD TCAS guidance provides the vertical commands directly. The pilot monitors that the V/S stays out of the red area and intervenes manually only if the automated guidance is not satisfying the RA.

This is the kind of distinction that surfaces in oral exams and rarely in line operations. An examiner who asks about the TCAS RA response will frequently follow up with "and how would that change if the aircraft had AP/FD TCAS installed" - specifically to see if the candidate knows the configuration matters.

Why TCAS Goes Quiet Below 1,000 Feet

Below 1,000 ft AGL, the A320 automatically reverts to TA ONLY if TA/RA was previously selected. All RAs are inhibited and converted into TAs. The system has decided that at this altitude, the terrain is a higher-priority threat than the conflicting traffic.

The published inhibition altitudes are more granular than the top-line 1,000 ft rule. RA aural messages are inhibited below 1,100 ft AGL in climb or 900 ft in descent. DESCEND RAs are inhibited below 1,200 ft in climb or 1,000 ft in descent. INCREASE DESCENT RAs are inhibited below 1,650 ft in climb or 1,450 ft in descent. The system also reverts to TA ONLY whenever a windshear, stall, or GPWS alert is active - those systems take priority.

The operational implication: in the terminal area, the system is silent on RAs by design. The crew is expected to integrate visual scanning, ATC instructions, and the awareness that TCAS is operating at reduced capacity. The assumption "if TCAS were going to alert me, it already would have" is structurally incorrect below the inhibition threshold.

CLIMB RA During a Go-Around: Both Procedures Apply

If a CLIMB RA triggers during an approach in CONF 3 or FULL, the procedure is unambiguous: perform a go-around and follow SRS orders, while monitoring that the V/S stays out of the red area on the VSI.

The AP and FD can be kept engaged during the go-around. The SRS manages the climb profile. The VSI green band confirms separation from the intruder. Both procedures apply simultaneously and they do not conflict - the SRS will produce a climb attitude that satisfies the RA in almost all geometries. The pilot's job is to recognize that the published procedure is layered, not exclusive, and to intervene only if the automated profile is taking the aircraft toward the red area.

This is one of the most useful pieces of the FCOM that almost never appears in informal pilot conversations. The incorrect instinct is to choose between the go-around and the RA. The correct answer is that they run together.

NAV TCAS FAULT Is Not NAV TCAS STBY

A common oral exam trap: the candidate is shown an ECAM screen with NAV TCAS FAULT and proceeds to describe the procedure for a TCAS in standby mode. They are two different alerts with different causes and different procedures.

NAV TCAS FAULT triggers when there is an internal failure of the TCAS computer. ECAM STATUS shows INOP SYS TCAS. The procedure involves advising ATC and reverting to procedural separation - the system cannot be recovered by mode selection.

NAV TCAS STBY triggers when the system is in standby, usually because the crew selected it there. The first step is to verify the mode selection, not to assume the computer has failed.

Both messages produce the same consequence - no RA protection - but they have different causes. An examiner who asks about NAV TCAS FAULT will frequently follow up with "and how would you know it wasn't STBY" to confirm the candidate understands the distinction.

The Reporting Obligation Most Pilots Underestimate

OM-A GEN 8.3.7 is unambiguous: an RA shall be reported as an incident by means of an ASR. Any RA. Not "any RA that produced a significant deviation," not "any RA where you weren't sure if the maneuver was big enough to matter." The reporting trigger is the RA itself, regardless of the magnitude of the resulting flight path change.

An RA that produced a 200-foot deviation is a data point. An RA that produced no deviation at all - because the original flight path was already inside the green area - is still a data point. The safety management system depends on volume to identify trends. It improves with reporting. It does not improve with judgment calls about whether a specific RA was "worth" reporting.

The Reversal RA

If the geometry changes and the original RA no longer resolves the conflict, TCAS may command a Reversal RA - for example, an initial CLIMB commanded to reverse into a descent. The technique is identical to an increased-rate corrective RA: smoothly and firmly follow the new green area within 2.5 seconds.

The green band on the VSI is a dynamic envelope, not a fixed number. Pilots who chase a numeric V/S can drive the aircraft back into the red as the band shifts. The instrument to watch is the VSI green sector. The instrument to ignore is your preconception of what the correct V/S should be.