>TCAS OFF - message inhibit

[Sylle]

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

[Hardy Heinlin]

Hi Sylvain,

thanks! I missed that one.

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


Cheers,

|-|ardy

[Britjet]

Inhibited for take-off, but it still appears after start etc.."during" is the operative word.

Peter

[Sylle]

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

[Britjet]

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

[Hardy Heinlin]

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

[Sylle]

Where is John H Watson when you need him??  :mrgreen:

[John H Watson]

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 ( and >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

[John H Watson]

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).

[Sylle]

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

[John H Watson]

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

[John H Watson]

P.S. Caution/Advisory Message inhibit only applies to engine start  :oops:

[tango4]

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

[Hardy Heinlin]

... 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 ...

Is the same principle applied to the right-hand side?

I.e. if the right ATC Transponder is selected and you pull just the right ATC CB (with the TCAS in TA/RA), will the TCAS OFF message appear?


Cheers,

|-|ardy

[John H Watson]

Is the same principle applied to the right-hand side?

That's the way I see it.

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).

[IefCooreman]

I get the impression we are missing what the "inhibit" actually does? I'll try to check tomorrow, but from memory, here is what happens on the 747 + fly-by-wire + extra headroom - 2 obsolete engines widebody version (:-))

The inhibit does not inhibit the message from existing, the inhibit stops the EICAS alert from popping on the EICAS.

You are on the ground: the EICAS message will not pop-up when you play with the XPDR. Some smaller airports you taxi without XPDR, others you taxi with XPDR. You don't need to be warned, switching it is "normal". But the EICAS message itself still functions as a sort of "active status indicator" for the system. If you push the recall button, the message will show in the list if the TCAS is OFF. This way you can still check if the system is actually working or not in case this would be necessary (ie ground radar not receiving your XPDR while it is ON).

You are becoming airborne (takeoff situation): the message will pop-up on the EICAS if the pop-up had been inhibited prior to that when you climb through 400ft RA (and the TCAS OFF situation still exists). It is not normal to be flying a Boeing jet in commercial aviation without XPDR/TCAS system so you need to be warned now. Any other TCAS problem after that will pop-op on the EICAS immediatly.

Same applies for the approach phase/go-around phases below 400ft RA. No pop-up anymore, but it shows on recall.

[John H Watson]

The inhibit does not inhibit the message from existing, the inhibit stops the EICAS alert from popping on the EICAS.

I'll have to re-read the maintenance manual again. I don't recall the test procedures asking to push the " recall" button or simulating >400'. Having said that, it is an old manual. There may have been a software/hardware update.

Are you saying that the <TCAS OFF won't even appear for CB being pulled?

[IefCooreman]

We are not allowed to pull CB's :-).

But as you mentioned, TCAS's "health" is indicated by the EICAS TCAS message. TCAS activated is indicated by TCAS OFF, I presume with automatic switching between transponders if one would fail.

Not the TCAS OFF, but the TCAS FAIL on the ND together with TCAS EICAS message indicates the TCAS system has failed for whatever reason.

If you power up the inertial systems on the B777 ie, you get TCAS FAIL on both ND (if it appears on EICAS I have to check but it seems logical). Once all systems are running for the TCAS, the ND indication changes to TCAS OFF if it has been selected so on the XPDR panel, the EICAS TCAS indication disappears and is replaced by TCAS OFF. However, on the ground, this EICAS is inhibited so it will not pop-up. You need to push recall to see it.

The TCAS EICAS (NOT "TCAS OFF") falls under the "general" takeoff inhibit that inhibits all EICAS advisory messages from 80kts airspeed up to (400ft RA or 20 sec after liftoff, or... see manuals) to avoid high speed aborts for unnecessary reasons. It is not inhibited on the ground like the TCAS OFF EICAS. It will pop-up automatically during engine start, during taxi, and during the takeoff roll untill 80kts. This is logical because it has an effect on the continuation of the flight and you need to make the pilots aware of that (TCAS is legally required in many airspaces, etc...).

I think...

[IefCooreman]

I think...

I thought wrong apparently!

The definition of "on ground" by Boeing for the inhibits seems only to discuss the takeoff roll. I've tried to generate the TCAS OFF advisory message on several occasions during our flight today. The TCAS OFF message seems to be inhibited from the start of the takeoff roll to 400ft RA. The TCAS message is inhibited from 80kts airspeed to... (see fcom because the end is more complicated defined).

*It is displayed on the EICAS from the start, even when our gyro system is aligning and the ND shows TCAS FAIL.
*The inhibit works during the engine start. If you switched of the TCAS during engine start, the advisory EICAS pops up only after both engines have completed the start cycle.
*During taxi (prior takeoff and after landing) there is no inhibit. Switching the TCAS off, the advisory EICAS pops up.

I couldn't really try switching the TCAS off during the takeoff and landing roll as I've got some other things to look at :-).

Hope this helps a little.

[Britjet]

That sounds like another one for me to try when I get chance?

Peter