Horizontal FD bar lowers at early climb phase! Options

[Christos]

Hi all,
I have a problem with the horizontal bar of the flight director at climbing.
In many occasions, after take off the horizontal bar actually lowers and following it means to loose height at this phase bringing me lower of the actual VNAV path.
Then I have to handfly it (disconnect A/T) until a higher altitude and only then the horizontal bar guides correctly the VNAV path.
My procedure:
EPR take off set
Accelerate, A/T on, V1, rotate and follow flight director,
At 200 ft press NAV,
Then (not always) horizontal FD bar lowers gradually...

Trying the exactly same procedure with the PMDG MD-11 creates no problem (Sorry for the comparison, I have nothing else to compare it with).

Help appreciated,
Christos

[Jared]

Hi all,
I have a problem with the horizontal bar of the flight director at climbing.
In many occasions, after take off the horizontal bar actually lowers and following it means to loose height at this phase bringing me lower of the actual VNAV path.
Then I have to handfly it (disconnect A/T) until a higher altitude and only then the horizontal bar guides correctly the VNAV path.
My procedure:
EPR take off set
Accelerate, A/T on, V1, rotate and follow flight director,
At 200 ft press NAV,
Then (not always) horizontal FD bar lowers gradually...

Trying the exactly same procedure with the PMDG MD-11 creates no problem (Sorry for the comparison, I have nothing else to compare it with).

Help appreciated,
Christos

First of why are you trying to chase the flight directors? its not recommended cause it could cause a tail strike, aim for 7 to 8 degrees pitch then pitch into the flight director or V bars not to exceed 20 ANU and most operators would not allow a roll mode till 400 AGL second what is the FMA indicating when you get the pitch down command? it shouldn't change until you select a pitch mode, if you remembered to press the TOGA switches during pre flight.

Btw most climb profiles that I know of has you pitch down to 10 ANU at acceleration height

[Olivier Moens]

A reason for the bar to go lower is that your current speed is lower than the MCP selected one. As speed is maintained by the picth attitude for a fixed thrust setting, the FD will tend to lower the nose to reach the selected speed.

[Jared]

A reason for the bar to go lower is that your current speed is lower than the MCP selected one. As speed is maintained by the picth attitude for a fixed thrust setting, the FD will tend to lower the nose to reach the selected speed.

If he is over pitching then yep that could be too, I'm still interested in what his FMA looks like when gets the command by the V bars.

This post has been edited by Jared: 15/10/2010, 18:55

[NeilC]

I have to say that I have occasionally noticed the opposite.

With the FMA showing TAK OFF, the FD tells you to raise the nose, which would decrease your speed past V2+10. I ignore this, and fly the correct speed (using the ASI).

It only happens sometimes, but then again, in the real world things ain't perfect either!

I think that the Original Poster is maybe referring to the VNAV mode, so he has selected VNAV?

I normally fly the ICAO 1 procedure (V2+10 to 800ft, then Climb thrust, maintain V2+10 until 3000ft, then accelerate), so I only arm the VNAV mode at 3000ft. I have never tried at low level.

Neil

[Jared]

When I select VNAV the V bars will command about 10 ANU which is what the NADP 1 and 2 profile calls for and what I'm already doing for profile 2 if I'm on profile 1 I don't pitch down clean up and select VNAV till 3,000 AGL to stay with the profile, so is VNAV supposed to command lower pitch? Yes, because it wants the plane to accelerate, so in that case I don't understand the OPs problem, kind of like the user who wondered why the plane lost performance on T/O and I pointed out that he had the anti ice systems operating when he didn't need them.

This post has been edited by Jared: 16/10/2010, 1:59

[Christos]

Thanks for your replies. Based on thme it seems that I could overcome the problem. This is how.

Swithing on A/P stricktly at 200 ft solves the problem (and also switching on NAV) at 400 ft.
I did not know that thrust is controlled by AP and not AT alone.
I had in some cases only AT on (not the AP yet) and tried to handfly her well above 1000 ft. (A usual way in which I fly the PMDG MD-11 until acceleration speed).
But with the maddog things are different. It seems that the aircraft was thus overspeeding and although I followed the FD bars the horizontal bar lowered at some point during the initial climb phase at about 800 - 1200 ft. I got no indications in the FMA.
But as said, swithing on AP at 200 ft solves the problem. Then it goes smoothly up to 1500 ft where I engage the VNAV and the aircraft is lowering to around 10 degrees pitch up.

Reply on if this makes sense? I mean do pilots in real life always swith on AP at 200 ft?

Christos

[Jared]

Thanks for your replies. Based on thme it seems that I could overcome the problem. This is how.

Swithing on A/P stricktly at 200 ft solves the problem (and also switching on NAV) at 400 ft.
I did not know that thrust is controlled by AP and not AT alone.
I had in some cases only AT on (not the AP yet) and tried to handfly her well above 1000 ft. (A usual way in which I fly the PMDG MD-11 until acceleration speed).
But with the maddog things are different. It seems that the aircraft was thus overspeeding and although I followed the FD bars the horizontal bar lowered at some point during the initial climb phase at about 800 - 1200 ft. I got no indications in the FMA.
But as said, swithing on AP at 200 ft solves the problem. Then it goes smoothly up to 1500 ft where I engage the VNAV and the aircraft is lowering to around 10 degrees pitch up.

Reply on if this makes sense? I mean do pilots in real life always swith on AP at 200 ft?

Christos

Most operators, most being the key word here, allow a min of 400 feet AGL before the AP can be turned on it is also min altitude for a roll mode to be selected, I don't have time now, but when I can I'll add to this post the two profiles I use.


ADDITION:

NADP 2 (Normal T/O):

1. Execute normal T/O roll

2. At a min of 400 AGL select HDG SEL or NAV (as required)

3. 1000 AGL - Lower pitch to 10 ANU, select climb power, and retract flaps on schedule ( flaps 1 - 13 V2 + 5 and 15 -24 V2 + 15), select VNAV

4. At SR bug - retract slats

5. At clean speed - set bank angle (if desired) complete after T/O checklist

NADP 1 (Speical T/O):

1. Execute normal T/O roll

2. At a min of 400 AGL select HDG SEL or NAV (as required)

3. 1500 AGL - Select climb power

4. 3000 AGL - Lower pitch to 10 ANU retract flaps on schedule ( flaps 1 - 13 V2 + 5 and 15 -24 V2 + 15), select VNAV

5. At SR bug - retract slats

6. At clean speed - set bank angle (if desired) complete after T/O checklist



Note: This operator does not use flaps 14.

This post has been edited by Jared: 18/10/2010, 1:01