American Airlines B767 V/S mode behaviour

[teropa]

Hi,

A pretty specific question, but here goes:

Do the American Airlines B767s need a lower or higher MCP ALT (than what the a/c is flying at that moment) to enable the usage of V/S mode, or does the
V/S window open no matter what is selected on MCP ALT if V/S mode is chosen ?

Just so no one wonders, this is related to a certain flightsim development.

cheers
Tero

[Shaka Zulu]

Opens up both ways....

[None]

It'll fly away from MCP altitude

One of the cautions associated with using vertical speed on the 757/767 is that the jet will disregard the MCP altitude setting in certain scenarios (climb or descend away from MCP altitude). Vertical speed is very useful on almost every flight. However, it is prudent to carefully watch its progress.

[teropa]

Thanks guys,

The reason I asked is because there was an assumption, that AAL 767s had this feature differently than in other 57/67s, ie. that the V/S window will open ONLY if a lower or higher MCP ALT is dialed in.

Tero

[teropa]

Oh btw,

Does anyone here have a differing opinion on this ? Has someone seen AAL 767s where V/S window will NOT open unless you dial in a lower/higher MCP ALT ?

Tero

[Localiser Green]

Check out 757.org.uk for useful info on the 757/767, quote:

VS is a pitch lock and requires caution when used. Although the autothrottle will attempt to control airspeed within the power available, when very high rates of climb or descent are selected this is obviously not possible. Secondly, unlike VNAV and FL CH, when in VS mode it is possible to fly away from the altitude selected in the ALT select window, depriving the crew of ALT CAP protection and in some cirumstances, of the white ALT ALERT lights.

[teropa]

Loc green,

Yes, I'm aware of the standard operation of the V/S mode. I have Boeing 757/767 AOMs (many versions even), and none of them say that V/S could have the option, that it will not operate unless using MCP ALT lower/higher than present.

I heard from the sim programmer that AAL 767s have it setup that way, that they indeed need a different altitude setting for V/S to operate, and I find this hard to believe .

Tero

[Shaka Zulu]

U need to dial a diff MCP altitude before V/S unlocks and is annunciated on the FMA...
Seems the same across Boeing fleet

[teropa]

Shaka Zulu,

Are you saying that if I don't change the MCP ALT from the level I'm flying at the moment, pressing V/S will have no effect ? That the mode will not engage and the window will not open ?

Tero

[Captain Stable]

That is what he is saying - quite correctly.

[teropa]

Captain Stable,

Understood. Just the confusion. Earlier he posted "opens up both ways", when I asked if it needed a higher/lower ALT or not...

Tero

[NSEU]

"Seems the same across Boeing fleet"

Can anyone confirm that this is true of the B747-400?

I don't know what to make of the following statement/s in our 747-400 engineering training manuals:

"The vertical speed window on the MCP unblanks and synchonizes to the present V/S.

It will synchronize to 000 if the previous mode was:
#ALT (Altitude Hold)
#Takeoff or go-around and the vertical speed is negative"


Thanks in advance.
Rgds.
NSEU

[Captain Stable]

I can't confirm it is true of the 744. However, the following that you quote:-

The vertical speed window on the MCP unblanks and synchonizes to the present V/S.

It will synchronize to 000 if the previous mode was:
#ALT (Altitude Hold)
#Takeoff or go-around and the vertical speed is negative"

seems clear to me - the V/S window opens at your current vertical speed (and can then be adjusted). If you had been in Alt Hold mode, it will open at zero. If you were in take-off or go-around modes but descending, it will also open at zero - commanding to remain level.

Don't know if that helps or not.

[Shaka Zulu]

Sorry my post was easy to misread!
And indeed it seems to be the same across the Boeing fleet but indeed I can't confirm either if the 744 has got this function. I don't think so since they are you using a similar sort MCP.
And Why would V/S be available if you are in ALT HOLD or VNAV PATH modes?

As Captain Stable says maybe V/S will be annunciated on the FMA but it seems not logic to me that you can actually wind a different V/S in than 0 in ALT HOLD mode.
Definitely not on 73 75 76

[two speed prop 3]

Shaka Zulu,

I'm afraid I disagree with you. If you are in ALT Hold at 20000' with 20000' set in the MCP window and you press VS you will enter VS mode. The window will show 000 which you can then adjust up and down. The same is true with VNAV Path, give it a go.

[None]

It will fly away

As TSP 3 says, it will fly away, unless there is some very unusual modifaction to the AA 757/767 AFS that we are not aware of.....that being the reason for teropa's first post which started this thread. Additionally, if the jet is in a descent and you push V/S, it will enter V/S and maintain the V/S present at the time it was selected. Same for a climb.

[teropa]

Thanks guys,

I was beginning to think everything I had learned from 57/67 afds was wrong . I think it would be really weird if AAL had this kind of modification in their birds, but IF they do, then I guess it has been added for the sake of additional safety.

Anyone flying AAL here who could make an end to the speculation ?

Tero

[Shaka Zulu]

Ehm it doesn't work....

[teropa]

Shaka Zulu,

You are sure, that the AAL (specifically, NOT generally) 767 needs a lower/higher MCP alt for the V/S mode to engage? By engage I mean that it will show V/S on the FMA and that the V/S window will open (with either a value or 0000, depending on the sit.) and SPD mode engage with current speed.

Because the usual 757/767 config for that mode is that it will fly away from MCP alt, and will engage in ANY altitude, regardless of MCP alt settings.

Tero

[teropa]

Hi again,

So is there a definite answer for this WRT AAL 767s ?

I would appreciate one . There seem to be conflicting opinions, but...

Anymore input on this, anyone ?

thanks!

Tero