AP commanding minimum speed on climb

[scandinavian13 5,192]

 

 

My mistake, didn't know it wasn't meant for me

 

No prob - it was very generic on my part, so I can see why you could see it as including you, too.

[davidz 26]

Were you levelling off at a SID altitude restriction? SPD | xx | VNAV PTH should only appear for an altitude restriction when in the climb phase. Otherwise it would be THR REF | xx | VNAV SPD.

 

What was the magenta (bugged) speed on the PFD? Along with the FMA, the magenta bugged values on the PFD tell you what the autoflight system is trying to do. In both SPD thrust mode and VNAV SPD pitch mode, the autoflight system will try to achieve the magenta speed.

[Gnacino 48]

I've had this same problem occur yesterday.  I've been flying the same route, same airports till I get in a routine.  Programing the FMC the same as well, same fuel load.  I just got my throttles fixed.  Going down the runway, LNAV & VNAV armed, keeping the nose on the FD.  At 1000', Put the AP on, and like the post starter said, it doesn't accelerate.  The airspeed drops to 180.  I tried putting on FLCH, airspeed doesn't get up but the VS is to high, around 3500.  I flip the VS instead.  Put the VS to 1000.  Still the airspeed does not pick up.  At this point, I ended the flight, exited FSX and restarted the same flight with the same parameters.  Rotated and got to FL380, no problem.  Like the first guy said, maybe I did something wrong.  Or like the PIC of the Asian 777, Sum Ting Wong;)

 

Gnacino

[downscc 1,327]

Ok so I managed to replicate it. Same setup, 30% fuel, 98% payload. LTBA runway 36L departure VADE1E SID. First waypoint had a 220/2200A, then /4000B, then /13000B. After that the next waypoint was at my cruise alt. Now the strange thing is, even on the ground, the FMC had 170 as the speed it was shooting for after the 220/2200A waypoint. Then at the first waypoint at my cruise altitude, the speed was m .82. So I took off, and sure enough, I reached the first waypoint at 220 kts per the restriction, then afterward it reduced back to 170. I had to manually enter 250 as the speed restriction to get the plane to speed up. The FMA was showing SPD/LNAV/VNAV PTH. And when I entered the manual 250 restriction, the AT didn't advance, it stayed at around 77% and used pitch to pickup speed. So why is this happening? Maybe it's specific to the SID? But I've had it happen at another airport as well, so I'm at a loss

 

It looks like a coincidence that it reduces to 170, which is the default approach speed... and like Gibbs I don't like coincidences. I think what is happening is the 220 kt constraint is being handled like all constraints which is AT OR BELOW and since 170 is below 220 there is no surprise. What you are expecting is 737 behavior and it isn't going to happen. The FMS is not able to configure the aircraft for safe flight at your weight at 220 kts so it is basically handling the task over to you. Continue after takeoff with MCP SPD and since that matches the FMA SPD/LNAV/VNAV PTH I think you'll be doing what the airplane "expects." As for the other issues in this thread (I don't like mutliple issue threads) I don't have a clue.

[uhntissbaby111 58]

Were you levelling off at a SID altitude restriction? SPD | xx | VNAV PTH should only appear for an altitude restriction when in the climb phase. Otherwise it would be THR REF | xx | VNAV SPD.

 

What was the magenta (bugged) speed on the PFD? Along with the FMA, the magenta bugged values on the PFD tell you what the autoflight system is trying to do. In both SPD thrust mode and VNAV SPD pitch mode, the autoflight system will try to achieve the magenta speed.

 

The bugged speed was 179 ( the LEGS page speed of 170 was below stalling speed in a clean config so it was bugged at the lowest safe speed). So the Autoflight system is doing everything correctly, just for some reason the speed it's shooting for in the LEGS page is defaulting to 170 when it should be Econ climb, or 250 below 10000

 

Adam

And also, yes I was leveling off, that's why it showed SPD. On initial climb out it was THR REF. And after the constraint it went back to THR REF

 

Adam

[Alaaar 34]

Guys - just for the record:

 

It's is HUGELY important that you tell us EXACTLY what the aircraft thought it should be doing when you're seeing potential issues like this.  The FMA (the thing that the top of the PFD) will tell us most of that story right off the bat.  Anything else would really help, like a screencap of the FMC climb page, but the FMA is really important.  You may think "oh hey, MCP!" but no...the FMA tells you a lot more.

 

It tells you - and therefore those trying to help - what the aircraft was trying to do at the time, and can really help us sort user versus computer error pretty quickly.

 

 

 

 

Yeah, those would be important.

 

 

 

 

haha...sorry, but I have to take a quick shot at that 

 

TOGA

 

TOGO

Hey Kyle excuse my English it's like my 5th language

[scandinavian13 5,192]

 

 

Hey Kyle excuse my English it's like my 5th language

 

haha - no worries at all.  I was just makin a quick joke.  :wink:

 

It's a common mistake.  I actually just figured that you just hit the wrong key on the keyboard.

[Alaaar 34]

1- After TO,  AP is off,  AT is active ...plane is accelerating 

 

 

 

2-After 10,000ft, AP is on, speed is reducing to 170 as per SID 

 

 

 

4-FMC shows no restrictions 

 

 

 

5-CLB page 

 

 

 

6-@ TOC plane accelerates to cruise speed 

 

​I hope that was useful ...it must be something wrong I am doing .....

[uhntissbaby111 58]

Alaaar

 

Do you happen to remember if you selected the SID from the DEP/ARR page before entering the route in the route page?

[Alaaar 34]

yes sir  I did

[scandinavian13 5,192]

 

 

​I hope that was useful ...it must be something wrong I am doing .....

 

Having flown that SID numerous times, I can definitely say it's not the nav data...hmm.

[uhntissbaby111 58]

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

[Alaaar 34]

I ll give a try Adam ....thanks 

 

FYI its KIAD-KJFK   route is PALEO AGARD SPEAK CANNY DONIL LEEAH ACY CYN COL CRI

 

SID is BUNZZ2 FROM RWY19L 

[downscc 1,327]

I'm lost, "-After 10,000ft, AP is on, speed is reducing to 170 as per SID " but if there was a SID restriction it would be on the LEGS page.. also, probably no where will you find such a low speed restriction above 10000. No name has above has a good question (names required in this forum, sorry). Also in #4 the symbols for leading edge slats appear.. why? I think this is a troll.

[Tabs 2,790]

Ok guys - will try all of this later today.