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>TCAS OFF - message inhibit

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Member
Registered: May 2010
Posts: 99
Location: Brussels
Hi |-|ardy,

just ran across this in the 744 FCOM here. You might want to check if this needs attention in an upcoming PSX update...

Chapter 15
Alerts inhibited during take-off
EICAS advisory message TCAS OFF - inhibited on ground until 400ft RA.

Alerts inhibited during landing
EICAS advisory message TCAS OFF - inhibited from 400ft RA until go-around at 400ft RA.

This seems logic as it gets rid of the nuisance message on ground as it is the normal TCAS setting at that stage.

Regards,
Sylvain
Moderator
Registered: May 2009
Posts: 5140
Hi Sylvain,

thanks! I missed that one.

I'll put in on my todo list ...


Cheers,

|-|ardy
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
Inhibited for take-off, but it still appears after start etc.."during" is the operative word.

Peter
Member
Registered: May 2010
Posts: 99
Location: Brussels
Hi Peter,

Thanks for chiming in!

Strange choice of those 744 engineers - On 767 the TCAS OFF message is (quite logicaly IMO) always inhibited below 400ft radio altitude... which is what made me curious about the PSX behaviour in the first place.

How does the EICAS defines beginning of takeoff on the 744 in this case??

Cheers,
Sylvain
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
Do you know, now I think about it, I'm not sure...one gets so used to seeing it in PSX...
And I have seen recall pressed so many times for real....

I think you are right! :-)

Peter
« Last edit by Britjet on Sat, 08 Aug 2015 22:43:10 +0000. »
Moderator
Registered: May 2009
Posts: 5140
There are several basic alert inhibit functions (described in detail in the PSX manual on pages 529 to 531).

Maybe the TCAS OFF message inhibit is related to some of these conditions described?

For example, the condition "400 ft RA" is often used in pilot manuals, but maintenance manuals reveal that this condition (for example) is more complex than just "400 ft RA" alone: certain devices may fail, and then another condition is used instead etc. (PSX models all conditions.)


|-|ardy
Member
Registered: May 2010
Posts: 99
Location: Brussels
Where is John H Watson when you need him?? :mrgreen:
Member
Registered: May 2010
Posts: 843
Are we talking about the general takeoff inhibit for EICAS CAUTION messages (see below) or a special air/ground inhibit for TCAS? Sylvain's text doesn't really exclude this message appearing on the ground prior to takeoff. i.e. prior to 80kts CAS being achieved.

My old notes certainly show TCAS OFF appearing on the ground.

I have a photograph of this message on the ground, but this was during Standby Power only ops, but whether this was produced by a loss of power to part of the air/ground system or Rad Alt system, I don't know.

This message is overridden by the TCAS SYSTEM EICAS message.

Rgds
JHW
« Last edit by John H Watson on Sun, 09 Aug 2015 04:09:56 +0000. »
Member
Registered: May 2010
Posts: 843
P.S. Regarding TCAS OFF and TCAS SYSTEM messages, the British Airways Maintenance manual says that if the Left ATC Transponder is selected and you pull the Left ATC CB (with the TCAS in TA/RA) the TCAS OFF message will appear on the ND and EICAS. If you pull both ATC CB's, you will get a TCAS SYSTEM message. This is described in one of the maintenance tests.

In a way, this makes sense. TCAS OFF just means you have the wrong settings on your control panel (you can correct the error by changing ATC transponders). TCAS SYSTEM means that you can't correct the problem (unless you reset one of the CBs).
Member
Registered: May 2010
Posts: 99
Location: Brussels
Hmmmm Interesting...
That would mean it should indeed be displayed on the ground at the gate but disappear during takeoff roll only to re-appear above 400ft.
Where's the logic in that?! :lol:

My FCOM also stipulates:
>TCAS OFF - TCAS mode TA or TA/RA not selected.
but does this mean it only relates to the setting of the switch and excludes system failure?

We all know the FCOM wording is often rather vague so I would go with the AMM explanation.

Cheers,
Sylvain
Member
Registered: May 2010
Posts: 843
Quote
Are we talking about the general takeoff inhibit for EICAS CAUTION messages or a special air/ground inhibit for TCAS?


Disregard. I was thinking about the master lights/aural for CAUTIONs. The TCAS OFF is an Advisory message with no light/aural
« Last edit by John H Watson on Sun, 09 Aug 2015 04:19:01 +0000. »
Member
Registered: May 2010
Posts: 843
P.S. Caution/Advisory Message inhibit only applies to engine start :oops:
Member
Registered: Sep 2014
Posts: 165
Location: Near Paris
Sylle wrote
Where's the logic in that?! :lol:


Of course I'm not an airline pilot, but I think I can see a logic in it.
It kind of prevents you from forgetting to switch your TCAS on before takeoff, while avoiding nuisance message DURING the takeoff roll in case you forgot anyway.
During taxi you get the message, but thanks to that logic you want it cleared prior to takeoff.

Don't know if my interpretation makes sense to you ?

Cheers !

Charles

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