question about the flight directors

[ZC553043]

hi every one !
i am a young chinese pilot, just change from B737-500 onto B737-800, a significant change on these two type is the flight instrument, especially the flight directors, the 500 i used to be on is using a old command bar, the 800 is using a new cross bar for the flight directors, at the very begin, i didn't got used to it . i often forget aboout the roll angle, cause the new one has not bank angle limitation on it. on the other hand the new one seems to be more sensitive. you guys here are so smart and kind pilots ,can you give me some suggestion about this? or canyou guys show me some articles or books about the two type of the flight directors?
thank you so much!!!

[alexban]

If I understood right you flew the 500 with V bar and now the 800 has xbar. There is no difference in how those two fd work,regarding bank limits,pitch ,etc.
It's just a matter of getting use to one of them. Pilots consider one or the other to be more accurate,depending on how they got accustomed to them.We have BAC1-11 pilots that love the Vbar (that was on the bac) and think this is the best FD. We have other pilots,first trained on the 737 with Xbar that consider this one to be the best.
Maybe the Vbar will give you a more intuitive picture of the situation,I guess,maybe it's easier to follow.
I think ,personal opinion,that the crossbar it's more accurate,but you'll have to monitor it closely,try to keep the bars in the box.If you'll let it slip ,it's maybe harder to bring the bars together as would've been with the Vbar. For a begginer,of course.
Once you get used to it you'll find it easy to use.
And don't try to blindely follow the FD.You should check the other indications ,speed,Vs...
Maybe one day the FD will fail,or ,more common,will give you some wrong command,you'll have to be aware of that.
All FD's give bank limitation,it's not something that depends of the type of FD installed. It depends of bank angle selector,of the fmc parameters,etc..
brgds alex

[ZC553043]

thank you so much for your reply!,i've learn alot from it.
and any gentlemen can tell me somthing about the 2 types of the FD design on the human factors? i mean why the design the 2 types of FD, which one is triditional which one is mordern? and from the human factors, what are their advantage and shot advantage? thank you so much.!

[411A]

The original cross bar design was developed by Sperry, and indeed the first flight director was the Sperry Zero Reader...fitted to many models of the DC-6 and several Lockheed Constellation aircraft...a long time ago.
Collins later on developed the 'V' (or command) bar design, and this type was used on many early civil jet transport types.

At first glance, the Collins 'V' bar design seems more useful, but I personally have developed over the years a preference for the Sperry cross bar design, as I personally find it much more accurate for CATII/III approaches.

Just a matter of opinion, of course, and I'm sure you will get others as well.

Hope this helps!:)

[mcdhu]

I'm with you on this one, 411A. The HS748 - military version - had the zero reader, but it was little used. Collins ''V'' bars are probably easier to use because the left/right and up/down are integrated into one demand, but the crossed wires, if followed, result in more accurate flying.

But, like a lot of things, pilots like what they know!!

Cheers,
mcdhu

[ZC553043]

thank you so much , gentlemen! any more informations?