A320 Altitude Alert cancel pb inhibits TCAS RA warnings

[cristianxb1983]

Hello everyone this is my first post in this wonderful forum! I was doing my A320 recurrent sim session and discovered that while responding to a TCAS RA while diving to stay on the green side of the VSI and pressing the Master Caution pb to cancel the altitude alert due to the TCAS RA the TCAS warnings were silenced.... Is that a SIM problem or a system failure? We couldnt figure out what was it?

Thanks in Advance
Cristian

[rudderrudderrat]

Hi cristianxb1983,

FCOM 1.31.30 says "MASTER CAUT lights: The aural warnings cease when one pilot presses the MASTER WARN light (except for some red warnings, such as the overspeed and stall warnings)"

You must have had very fast reflexes, because I've not witnessed a crew respond to a TCAS RA so fast that, the Altitude Alert has been triggered before the end of the RA warning.

The simulator can't reproduce the vertical acceleration you will feel in real life. In the sim, it's easy to satisfy the TCAS required ROC/ROD unrealistically rapidly. In real life, you would probably be more gentle with the pitch change, and the TCAS warning (once or twice) will be over before the Alt Alert warning.

[cristianxb1983]

Tonight I will have my second chance to test that.. I tought GPWS and TCAS warnings where over everything else and couldnt be silenced once they were activated... Thanks for the prompt response!

[FlightPathOBN]

this is also FMS dependent...

Honeywell acts different than Smiths than Thales...

while it is difficult in this discussion to state and understand the nuances...

I will note this...for Smiths/ Honeywell the prox warning ROC at the FAF is set at 200', while the Thales is set at 400'. Aircraft equipped with the Thales will have more prox warnings on final than the others...
(interesting to note that the FAA ROC tapers from 200' at the threshold to 500' at the FAF, the 500 is to match the intermed segment ROC)

[MD-80]

I have also experienced a situation described by christianxb1983 in the simulator during TCAS RA. The problem is not inhibiting the whole RA command by pressing the MASTER CAUTION pb - Actually the green & red bands on the VSI don't inhibit but the aural warnings do if you press the MASTER CAUTION during TCAS aural messages.

The situation where I have observed the TCAS aural warning cancellation was during the CLEAR OF CONFLICT-aural message. We were established on the correct ROD on a TCAS RA and the altitude alert started to sound. We pressed the MASTER CAUTION pb to silence the altitude alert but at the same time the TCAS generated CLEAR OF CONFLICT-message started to sound. We heard only the beginning of that message CL... and the rest was silenced because the MASTER CAUTION pb action.

I agree with rudderrudderrat that reacting to TCAS RA so fast that altitude alert starts to sound BEFORE the TCAS RA aural command has ceased to sound sounds impossible.

This experience is only from the simulator. Can't say how it works in the aircraft. I've heard opinions where others say that it is only a sim "feature" & others say it will work in the same way also in the aircraft.

[minuteman]

There is a very simple solution to this "problem."

Don't cancel anything during a TCAS RA until you hear "Clear of Conflict"!

Live with the noise, follow the RA, as has already been stated by going to cancel the Altitude Alert you can easily cancel the "Clear of Conflict" message or an instruction to increase/modify/reverse either the climb or descent. For the sake of 25 seconds, a bit of noise is a small price to pay to avoid a collision!

What does your training department say? (I assume they knew about this feature of the system)

[MCDU2]

Our airline has an SOP that we do not inhibit any aural warnings during a TCAS RA for the reasons given above.

Consider what could potentially happen in a busy TMA if you inhibit the aural warnings and "miss" another intruder.

[Green Guard]

TCAS RA while diving to stay on the green side

Diving ?! :ouch:

[Graybeard]

I'm don't know about every newer plane, but at least the 737 and MD-80 models flying when TCAS was retrofitted in the early 1990s, TCAS audio was not wired through the Master Caution. It was direct to the speaker. TCAS RA alerts are higher priority than everything but Stall Warning. I don't see how the plane could be certified if the RA can be silenced by the Master Caution.

The Sim makers should know better.

GB

[gblen]

Company SOP is not to touch anything during TCAS RA. As mentioned previously, it can and will cancel instructions. Live with it until youre clear. Nice little gotcha if you get 2 TCAS RAs in youre sim session. One RA that leads into a second RA. If you press the Master caution to silence the altitude warning during the first RA youre in a spot of bother for the next one.