AP commanding minimum speed on climb

[uhntissbaby111 58]

My apologies for not signing my post, my name is Adam

 

 

Adam

[scandinavian13 5,192]

 

 

Also in #4 the symbols for leading edge slats appear.. why? I think this is a troll.

 

whoa there...

 

That's just the pitch limit reference bar, displayed in two cases:

1. Flaps not up (as you mentioned)
2. Flaps up, but low airspeed

[downscc 1,327]

Thanks Kyle, I was close but at the time you posted I was deep in the FCOM trying to verify what those symbols represented. I take back the troll comment, just frustrated because I don't understand the problem and I am an engineer.

[Alaaar 34]

Could you do me a favor, do the exact same flight you do. EXCEPT, enter your route first without the SID, then enter your PERF information and execute. Then go to the DEP/ARR page and select your SID and RWY. If your problem is like mine, this should solve the issue

 

Adam

I think the key is entering the PERF page info before the SID is selected

Adam  sorry same thing happened to me the speed kept on minimum 

[scandinavian13 5,192]

 

 

I take back the troll comment, just frustrated because I don't understand the problem and I am an engineer.

 

haha - you and me both.  Some days I need to remind myself that it's not my problem to solve.  Observe and report...

[downscc 1,327]

So, if i select the SID and RWY before entering the route and filling out the PERF page, the FMC commands to slow of a speed. If i enter the route, then fill out the PERF page, THEN select my RWY and SID, the speeds are normal.

I tested the SID/RWT before PERF primarily because that is my typical flow (load at gate ground air/power, while peeps are loading I am entering route then given time to get the load sheet from gate I then enter FUEL/PAYLOAD and PERF) I did not duplicate the problem, here are my steps: Load default engines running at end of runway, INIT & ORIG/DEST then SID & RNW, enter route and arrival/approach, ACTIVATE & EXECUTE. Then PERF INIT CI=100, then remove fuel as required to land at destination with appropriate load/weight, THRUST LIM & T/O pages. I am flying KIAH-KATL LCH2 BTR Q24 PAYTN WARRR1. Take off with TOGA/VNAV & HDG SEL, fly using FD to 10,000 then engage LNAV and she accelerates to expected climb speed. Something else is going on here, assuming location and navdata have nothing to do with it.... also assuming it has something to do with AFDS-FMS interaction, probably looking at FMS. Or maybe something at the time that A/P modes take over from less automated modes.

[uhntissbaby111 58]

So after work today i tried doing the flight from LTBA-LSZH to try and replicate the problem. And this time everything worked out fine, so again im at a loss. I think i might just try a reinstall of FSX this weekend and see if maybe thatll fix it

 

Adam

[scandinavian13 5,192]

 

 

I think i might just try a reinstall of FSX this weekend and see if maybe thatll fix it

 

I wouldn't, honestly.  That's a lot of work and opens yourself up for a bunch of other issues.

 

Reinstalling is seldom the answer.  I hate that people throw it around so needlessly here.

[Oli 1]

Hi,

 

I have the same problem here - took off from EDDP, LNAV VNAV armed - I tuned on the autopilot at around 1200 ft.

Everyrhing was fine, when suddenly after one minute or so, the FMC commanded a very low speed, like 178.

Above 10000 feet, it commanded 198 feet.

I hit FLCH and it worked fine.

I hit VNAV again and the commanded speed decreased again to 198 (at around 14000 feet)

The indicated modes form the MCP are THR / LNAV / VNAV SPD

I have no clue why this would happen - I entered my route before choosing the SID.

 

Once in Cruise mode, I reverted to VNAV and it worked fine - the commanded speed was correct.

 

One more thing - I used the CLB2 derated climb thrust and then reverted to one (which did not change anything). I started my flight loading the cold and dark panel state.

 

Thanks,

 

Olivier

[creppel 3]

I tried again with entering SID thereafter PERF:

 

Standing on the ground a mindful pilot would see there is something wrong.

Where comes the SEL SPD 159 from?

Maybe from the first waypoint?

VNAV CLB page: ACT 159 ??

No need to say what happends after departure.

Still manual...

Hmm SEL SPD 170

A/P on

[uhntissbaby111 58]

Creppel,

 

That's exactly the same behavior I am seeing. The legs page is showing 170 for speed. And actually, I believe the speed select on the ground of 159 is correct, as your first target airspeed is v2+15, and in your case 159 is just that. Now we just have to figure out what is causing the FMC to target 170 for the speed

 

Adam

[Alaaar 34]

I started to think it has something to do with flight plan ( I mean how the T7 reacts to flight plan & SID) ......I tried the NGX with similar conditions it behaved normally 

[Oli 1]

Hi,

 

I noticed something strange - here is my test flight route (EDDP --> EDDP)

EDDP LELMA BRU LUKOP GAMKO EDDP

 

There is a speed restriction at GAMKO (170 knots).

When I take off, the FMC keeps commanding 170 knots which is way too low. If I delete the speed restriction at GAMKO, then the commanded speed rises to 240 knots which is more correct, even though GAMKO is some 170 miles away.

 

If I take off without GAMKO, it works well, when I insert GAMKO after takeoff, it hads a 170 knts restriction to this waypoint (in big numbers, not a calculated restriction) and the commanded speed falls back to 170. It is like it does not want to accelerate and slow down for GAMKO but slow down straight away.

 

Would you have any idea why that is? It seems like a strange behavior.

 

Happy flying,

 

Olivier

[3-2-1-Now 126]

Yesterday I was on descent and speed entered was 300 yet it kept falling below 250IAS until I clicked FLCH then back to VNAV.

 

Altitude at the time, and speed restrictions in the flight plan?

 

Best regards,

Robin.

[Alaaar 34]

Creppel,

 

That's exactly the same behavior I am seeing. The legs page is showing 170 for speed. And actually, I believe the speed select on the ground of 159 is correct, as your first target airspeed is v2+15, and in your case 159 is just that. Now we just have to figure out what is causing the FMC to target 170 for the speed

 

Adam

Adam how do you start your flight ...Cold & Dark or other state ??   thanks