Autopilot AP/FD TCAS mode

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▪︎This content is Not an official document and does not represent the views of Airbus or any other aviation authority.

▪︎The information provided may be incorrect or misinterpreted and should not be relied upon for decision-making.

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The TCAS warning is one of the memory items in Airbus procedures. However, do you recall the correct procedures aside from following the green area on the vertical speed indicator?

Of course, in previous aircraft without an autopilot TCAS mode, it might have been easier to remember and apply.

But with an autopilot TCAS system, there are additional things to remember.

TCAS advisories

CAS divides aircraft into the following four zones, and among these zones,

there are Traffic Advisory (TA) and Resolution Advisory (RA).

PFD indication of TCAS arming

there is also 3rd line at the FMA in lateral mode and veritcal mode, like there is 3rd line in autothrust mode column.

The FMA displays TCAS on Line 3 of the "AP/FD Vertical Modes" column. Therefore, if another AP/FD vertical mode is armed, the FMA displays both modes.

AP/FD TCAS MODE

When a TA is triggered (TCAS ARMED)

Unlike the aircraft without AP/FD modes, When the AP/FD TCAS mode engages, any engaged (armed) AP/FD lateral mode remains engaged (armed).

When a RA is triggered - (TCAS ENGAGE)

According to the Flight Crew Operating Manual (FCOM), when the aircraft experiences a TCAS Resolution Advisory (RA), it will typically continue to follow its previous lateral mode, such as the departure Standard Instrument Departure (SID). However, in aircraft without an autopilot TCAS mode, it will revert to the heading (HDG) mode, as the first memory item for TCAS RA is to disengage the autopilot and flight director (FD)

When Clear of Conflict

When the "CLEAR OF CONFLICT" aural alert sounds, the AP/FD TCAS mode automatically disengages.

The AP/FD provides guidance toward the previous FCU selected altitude.

Even though the AP/FD TCAS mode disengages, the autopilot is supposed to remain engaged,

so the memory item(with TCAS AP/FD aircrafts) is to monitor and follow the autopilot/flight director (AP/FD)

Operating Techniques in FCTM

In aircraft without the AP/FD TCAS mode,

when a Traffic Advisory (TA) is generated, the Pilot Flying (PF) announces, 'TCAS, I have control.'

If a Resolution Advisory (RA) is generated, the PF disconnects the autopilot, promptly and precisely follows the VSI green sector within 5 seconds, and requests the disconnection of both Flight Directors (FDs).

it is manual manuever.

but the aircrafts with AP/FD TCAS MODE

if a TA is generated, The PF announces "TCAS blue" ,

The flight crew must always follow the TCAS RA orders in the correct direction.

if the the AP is off, follows the FD orders. but if in autopilot . PF should monitor vertical speed with autopilot.

Memory item of TCAS WARNING with TCAS AP/FD aircraft

it would be very alarming situation when to monitor vertical speed with autopilot when the aircraft is maneuvering RA with autopilot.

he FCTM also specifies that if a Traffic Advisory (TA) is triggered, the flight crew should immediately check for the arming of the AP/FD TCAS mode.

If the AP/FD TCAS mode does not arm, it indicates a failure or the absence of this mode on the aircraft. In such cases, the Pilot Flying (PF) should announce 'TCAS, I have control,' and the flight crew must be prepared to manually follow the Resolution Advisory (RA) orders

When we hear 'TRAFFIC, TRAFFIC' for a Traffic Advisory on an aircraft with autopilot, we should immediately check for the arming of the TCAS mode. Subsequently, we should respond with 'TCAS blue' or 'TCAS, I have control, immediately' which determines the pilot's next action in case of a Resolution Advisory (RA).

Even during a TCAS autopilot RA maneuver, it's essential to monitor the vertical speed (VS). If, for any reason, the aircraft's vertical speed does not reach the green area on the vertical speed scale during an RA, the Pilot Flying (PF) should disconnect the autopilot and override the Flight Director (FD) orders. as the memory item caution says.

Performance limit

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.

CLIMB RA during approach in CONF 3 or FULL

During the go-around, the flight crew check that the vertical speed remains out of the red area
of the vertical speed scale, and take over if necessary.

For example, the flight crew should take over if the vertical speed gets back to the red area of the vertical speed scale when the aircraft intercepts the FCU selected altitude.