Possible Bug:
250/10000 speed restriction not honored (during cruise phase). 757 and 767

Flight Phase:
Level-off to cruise (below 10,000ft)

Manual Reference:
No manual needed

Issue:
When cruise altitude is below 10,000, at level off, the CS 757/767 ignores the SPD TRANS of 250/10000 and accelerates to cruise speed (well above 250KIAS).

Can any one with a little more real world experience chime into whether or not it's a bug? It's not written in my airline manual anywhere at all, I've read all the VNAV chapters today and no clue, it's rare you'll be in CRZ phase below 10000 (except lately lots super short of repo flights IRL!), but now I wonder. I know every other plane I've flown IRL has honored any climbing restrictions to cruise if the restriction is lower than the cruise speed.

The B744 has a similar thing where by if you don't put in the speed restriction under speed trans then it will speed away.

Alex T wrote on Apr 28^th, 2020 at 10:17pm:


It's been quite a while since I have cruised below 10k so I can't really recall what the FMC did in CRZ... I'm pretty sure I didn't even operate in VNAV that low.

However, the "fix" or way to cope would be to enter 250 in the ECON SPD.  That will honor the speed of 250 below 10.  In VNAV CRZ there is not speed/altitude constraint since you would be in level cruise flight.

I'll have a chance to play with the plane this weekend, so I'll check to see what it does with a cruise below 10.

You just lost me) Is there a bug or not? 

On all my flights where I've had to level off below 10,000' (after the descent), I have never had a problem with the 767 holding the speed around the 240-250 knots.

Alex T wrote on Apr 29^th, 2020 at 1:29am:

I didn't think it was, but I'll check on the next flight that that happens on.

Markoz wrote on Apr 29^th, 2020 at 1:28am:



I think the question was when you're in cruise mode below 10k does the plane command 250 to adhere to the requirement or will it want to do over that.  Like you, I've never seen the plane command above 250 below 10 in the descent mode (or climb for that matter).

I did a flight from ONT to LAX and I never even looked to see what VNAV ECON Cruise had in store for us.  Once off the ground we were held low with crossing traffic so I used V/S to avoid any TCAS issues so we never even entered VNAV cruise. 

I DO know on my previous plane the FMC wouldn't adhere to the 250 below 10 in cruise unless we intervened. 

As for this being a bug or not, standby and I'll have an answer soon!

Do you remember if your Cruise page gave you 250, or another number above that?

The aircraft should not accelerate above 250kts below 10000' in VNAV if you have that speed restriction entered on the Climb page. (SPD Trans/SPD Restr).   
The FMC Legs page should not show a speed higher than 250/10000'.
The speeds on the legs page are wrong below 10000'.
One waypoint has a speed restriction on the arrival of 210/5000. The next waypoint is showing 307 kts etc.

Secondly when going direct to a waypoint with a speed restriction on the FMC Legs page,  the Captain Sim 757/767 immediately decelerates/accelerate to that speed irrespective of the distance to that waypoint. Also not correct.

I also notice when selecting an STAR on the arrival page on the FMC the first waypoint seems to missing from the STAR.
Tried a few airports and several different STARS, first waypoint was always missing on my system. Newest Airac installed from Navigraph.

LNAV is also a bit inaccurate. Has a tendency to turn early and undershoot the turn on an SID etc. Resulting in left and right turn oscillations.

I see the 757 got the same speed issues etc. Been reported numerous times. Bit surprised this had not been addressed. 

Offset capability?
FMC ALTN page?
FMC COMM page?
RNP Entry?
EICARS, for weather/atis uplinks etc?

Would be nice if Captain sim also incorporated an IPAD/TABLET on the window bracket for performance calculations and charts etc.
Most serious developers seems to be adding this feature nowdays .

Chris

They clearly know what is not correct with this airplane. Lots of reports relating to the Vnav speed management etc.
I see the same issues on the 757 and that aircraft have been on the market for a while without any attempts to fix this basic Boeing FMS management.
I like realism and the simulation should get the basics correct as a minimum. 
It has potential, but it is far behind when it comes to correct speed management and accurate and precise flight path management.

Alex T wrote on Apr 29^th, 2020 at 4:05am:


Alright, I had a chance to load this up and try it out.  Granted both of these pictures were taken while on the ground, both times the FMC defaulted to a speed of 250 for the cruise.  I didn't get a chance to see what would actually happen in cruise flight, so unfortunately this was as good as I could get.

I loaded the same scenario in the FMC on the ground and I get a speed above 250 as well.  A quick edit of the ECON speed on VNAV CRZ fixes it to the way it should be.  The real FMC will perform this edit on it's own. 

I know that it goes back to my original post for a work around, but as far as I can tell this is indeed a bug.  Hope this info helps!

RW FMC 8000' cruise: https://imgur.com/a/1joQKRk
RW FMC 5000' cruise: https://imgur.com/a/MCAPD8Y
P3D FMC 5000' cruise no edit: https://imgur.com/a/bofbopL
P3D FMC 5000' cruise speed edit:https://imgur.com/a/hTHb4px

The speed restriction of 250/10000ft is only set during climb, it is on VNAV CLB page. When the plane reaches the desired cruice altitude, preselected on PERF or VNAV CRZ page, it changes his performance to the one entered on that page. It is part of the preflight to analyze and set the speed that you want to be set on cruise.

Michel wrote on May 1^st, 2020 at 8:25pm:


Or is this from real qorld experience? I know the 737 doesn't do that and the FMSs are somewhat similar.