AP commanding minimum speed on climb

[uhntissbaby111 58]

I did the exact same flight with the NGX to see if it somehow pertains to the SID, but the NGX flew it just fine. So for some reason the 777 is commanding the low speed

 

 

Adam

[Peter Clark 21]

I saw this same thing this morning, figured operator error (not uncommon for me).. On climbout, LAX, PRCH departure, it went into THR REF/LNAV/VNAV SPD and the active mode in the CDU VNAV page was REDUCED SPEED CLIMB (or something to that effect). No thrust reduction at accel height, no speed-up at 10K. Ended up doing the climb in speed intervene, didn't get to play around and figure out why it wasn't in just ECON CLB.

[uhntissbaby111 58]

Looking at my VNAV page while on the runway ready for departure from LTBA, the vnav page is ACT 174KT CLB. And I don't see anything about a reduced climb. Still can't figure out why the FMC is calling for such a slow speed

 

 

Adam

Also, the progress page shows 174 as the speed selected. I didn't input that myself, it was there automatically

 

Adam

[uhntissbaby111 58]

Was reading in the FCOM just now and read that if the progess page shoes SEL SPD, it means that it was entered manually in the CDU, which i never did. So for some reason, the speed is getting input by itself. I did a test, i ran through all departures from LTBA, and they all call for the low speed. I then went to EDDM, and no problems. Could anyone else see if they experience the same from LTBA?

 

Adam

[Tabs 2,790]

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

 

 

Adam

 

Adam,

 

Can you please post the exact details of this flight (exact route etc)? I just tried it going LTBA-EDDF using that SID and I did not see this issue at all.

[barramundilure 152]

Deleted

[uhntissbaby111 58]

Of course Ryan,

 

Ok, so i spent the past hour trying different setups to see exactly what causes this and at what point. And i have narrowed it down. The flight is LTBA-LSZH. Take off from 36R (the PMDG navdata has it as 35R) VADE1 VADEN L610 UTEKA BABIT UT23 GRZ NEGRA (and i found that the STAR doesnt effect the slow climb speed). 30% fuel, 98% payload. The steps that cause the issue are as follows: Start up FSX, select the 722LR, LTBA, start on RWY 36R. I have the plane load in the defauly config, engines running. First thing, go to the FMC and set the fuel and payload. Then i go to the ident page, then init, then to route. Now here is the important part, i enter LTBA for departure, and LSZH for arrival. THEN, i go straight to the DEP/ARR page. Pick RWY 35R, and the VADE1 dep, activate and execute. Then i go back to the RTE, (and VADE1 to VADEN is already entered from selecting them from the DEP/ARR page), and i build the rest of the route from there, l610 UTEKA ect ect. When i check the LEGS page, as expected all speed/altitude spaces have dashes, except for the constraints. I then go to the PERF page and enter my ZFW, 5000 for reserves, FL350 and 50 for the CI. Now, after i execute that the LEGS page is populated with speed/altitude information. And thats where the problem is, after the first waypoint which has a constraint of 220/2200A, the commanded speed for waypoints BA041 and RIMBO is 170 kts.

 

Now, after trial and error, i found that this problem only happens if i go to the DEP/ARR page and pick my RWY and SID BEFORE i enter the route and execute. If, when i get to the RTE page for the first time, i enter LTBA and LSZH, then go to page 2, and enter VADEN L610 UTEKA ect ect, execute, got to the PERF page and enter the same info and execute,THEN i go to the DEP/ARR page, and select VADE1 and 35R and execute. when i go to the LEGS page, the speed commanded for BA041 and RIMBO is no longer 170, its 250 and 320 respectively just like it should!!

 

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 hope this makes sense and you are able to replicate it and its not just my computer. Because already did a full FSX reinstall and the problem occurs both before and after the install. If you have any further questions, or need clarification, please ask!!

 

Adam

And i realized that the PROG page behavior i noticed earlier is actually correct. After you select your V Speeds the PROG page shows a SPD SEL of V2+15, so thats not part of the problem

 

Adam

[spesimen 135]

i had this happen a few times, but it didn't seem related to the fmc order (i always do the route first)

 

in my case it was because i didn't de-rate my thrust and had a light takeoff weight. i shot up so fast that i was at 250 knots before i knew it while still hand flying and basically had to clean up my flaps just a few seconds after takeoff.

 

somehow this skipped the part where it resets the vnav speed bug from v2 to flaps 5 speed (i think, i was at 250 and cleaned up before i hit accel height??), and also the subsequent reset to full speed after 10000 didn't take either..

 

climbing with flch seemed to work and once i hit cruise everything worked like normal.

 

i do not have a comprehensive understanding of those modes yet so i figured it was user error. i find that if i de-rate a bit and carefully fly the FD (and watch closely for the speed bug to jump up) the issue never happens, it seemed like something about shooting past the accel height too quickly...

 

cheers

-andy crosby

[creppel 3]

Ok, I am not alone with that. ^_^

Yesterday I started out of KMIA and I had this behaviour with the 170 kts (rising with higher altitude).

That was the first time. FLCH is needed in that case.

Next time I try to make some sreenshots.

[IAF747 8]

Are both FDs on?

[Alaaar 34]

I had this situation yesterday:

• @ RWY.......LNAV & VNAV were engaged, advanced throttle to 55% then I pressed the TOGO hidden button
• Take off ..., advanced throttle lever to max (joystick) when reached acceleration height ...plane accelerated normally afterwards.
• I retracted flaps & gear on scheduled I reached about 240knts...... still AP off
• Passing 10,000ft I pressed AP while FD was centered 
• My attention went to CL, other panels & lights for few minutes
• Looking back to PFD,I noticed at the PFD that pitch angle is too high about 25 (there was no warning)
• Speed was at minimum for unknown reason as there are no SID restriction it should be about 309knts as per CLIB page 
• I increased speed manually 
• At cruise altitude level I engaged LNAV again and it maintained cruising speed as per FMC

Note: I intentionally kept AP disengaged tell 10,000ft 

 

Just for the record........ I will try to add some screen pics today if I can 

[scandinavian13 5,192]

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.

 

 

 

Just for the record........ I will try to add some screen pics today if I can 

 

Yeah, those would be important.

 

 

 

TOGO

 

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

 

TOGA

 

TOGO

[uhntissbaby111 58]

Kyle,

 

The FMA was showing SPD LNAV VNAV PTH. The AP was following the FMC correctly, it's the FMC that is telling the AP the wrong information. In my case, it's commanding a extremely low airspeed. Also, the climb page is fine, has the correct Econ climb speed, has the transition altitude, shows the next speed restriction, it's the LEGS page that has the issue

 

Adam

[scandinavian13 5,192]

 

 

The FMA was showing SPD LNAV VNAV PTH. The AP was following the FMC correctly, it's the FMC that is telling the AP the wrong information. In my case, it's commanding a extremely low airspeed. Also, the climb page is fine, has the correct Econ climb speed, has the transition altitude, shows the next speed restriction, it's the LEGS page that has the issue

 

Adam,

 

Despite this thread being started by you, for an issue you see, I was responding to the others who weren't including detail in their posts like you have been.  It's important that, if they are seeing the same issue, it can be narrowed down to the same cause, or dismissed as human error in their cases.

[uhntissbaby111 58]

Kyle,

 

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

 

Adam