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Possible 250kts below 10k bug (Any chime-ins?) (Read 7249 times)

Alex T Senior Member Offline Posts: 415 Location: Boston, MA Joined: Jun 21^st, 2015 Gender:	Possible 250kts below 10k bug (Any chime-ins?) Apr 28^th, 2020 at 8:54pm	Print Post
	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.


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MrGarak Full Member Offline Posts: 26 Joined: Feb 4^th, 2018	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #1 - Apr 28^th, 2020 at 9:00pm	Print Post
	I've had this problem since day one with the 757 not surprised to see it's in the 767.


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Aussiesix8 New Member Offline Posts: 1 Joined: Apr 28^th, 2020	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #2 - Apr 28^th, 2020 at 9:44pm	Print Post
	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.


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Alex T Senior Member Offline Posts: 415 Location: Boston, MA Joined: Jun 21^st, 2015 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #3 - Apr 28^th, 2020 at 10:17pm	Print Post
	Aussiesix8 wrote on Apr 28^th, 2020 at 9:44pm: 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. Not quite the issue here, let me explain more. On all Boeing FMCs: 737,747,757,767,777 nothing needs to be entered into SPD TRANS, unless it needs to be different than 250/10000 on climb or 240/10000 on descent for a specific company/atc/performance reason. The question I'm asking is this: There's obviously no way to enter a speed restriction on the VNAV CRZ page, there is no box for SPD TRANS or SPD REST or anything. So, if the airplane changes to the CRZ phase, will it honor either the restriction from the climb, or the Descent, or none at all? If the real plane won't honor one (sounds crazy but I could see this being the case), then Captain sim got it right. That's what we're trying to figure out here.


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logan3db Full Member Offline Posts: 32 Joined: Jun 21^st, 2018	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #4 - Apr 29^th, 2020 at 12:08am	Print Post
	Alex T wrote on Apr 28^th, 2020 at 10:17pm: Aussiesix8 wrote on Apr 28^th, 2020 at 9:44pm: 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. Not quite the issue here, let me explain more. On all Boeing FMCs: 737,747,757,767,777 nothing needs to be entered into SPD TRANS, unless it needs to be different than 250/10000 on climb or 240/10000 on descent for a specific company/atc/performance reason. The question I'm asking is this: There's obviously no way to enter a speed restriction on the VNAV CRZ page, there is no box for SPD TRANS or SPD REST or anything. So, if the airplane changes to the CRZ phase, will it honor either the restriction from the climb, or the Descent, or none at all? If the real plane won't honor one (sounds crazy but I could see this being the case), then Captain sim got it right. That's what we're trying to figure out here. 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.


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Alex T Senior Member Offline Posts: 415 Location: Boston, MA Joined: Jun 21^st, 2015 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #5 - Apr 29^th, 2020 at 12:34am	Print Post
	logan3db wrote on Apr 29^th, 2020 at 12:08am: Alex T wrote on Apr 28^th, 2020 at 10:17pm: Aussiesix8 wrote on Apr 28^th, 2020 at 9:44pm: 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. Not quite the issue here, let me explain more. On all Boeing FMCs: 737,747,757,767,777 nothing needs to be entered into SPD TRANS, unless it needs to be different than 250/10000 on climb or 240/10000 on descent for a specific company/atc/performance reason. The question I'm asking is this: There's obviously no way to enter a speed restriction on the VNAV CRZ page, there is no box for SPD TRANS or SPD REST or anything. So, if the airplane changes to the CRZ phase, will it honor either the restriction from the climb, or the Descent, or none at all? If the real plane won't honor one (sounds crazy but I could see this being the case), then Captain sim got it right. That's what we're trying to figure out here. 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. Exactly what I was thinking! There's always a workaround haha. Thanks so much, please report back with some info, that would be cool!


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Captain Sim CS Team Offline Posts: 4357 Joined: Nov 7^th, 2005	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #6 - Apr 29^th, 2020 at 1:22am	Print Post
	You just lost me) Is there a bug or not?

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Alex T Senior Member Offline Posts: 415 Location: Boston, MA Joined: Jun 21^st, 2015 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #7 - Apr 29^th, 2020 at 1:25am	Print Post
	Captain Sim wrote on Apr 29^th, 2020 at 1:22am: You just lost me) Is there a bug or not? Not sure! it's never something we deal with in real life so it could just be a Boeing quirk, so our friend will have to do some investigation on the real airplane soon and report back.


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Markoz CS Team Offline Posts: 12445 Location: Victoria, Australia Joined: Apr 24^th, 2009 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #8 - Apr 29^th, 2020 at 1:28am	Print Post
	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.

	Mark Fletcher PC: i7 10700K @3.8/5.1GHz \| 64GB DDR4 3200 \| 12GB RTX 4070 Super \| 32" LCD Monitor \| 1TB SSD + 2TB SSD + 2TB HDD \| Win 11 Pro
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Alex T Senior Member Offline Posts: 415 Location: Boston, MA Joined: Jun 21^st, 2015 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #9 - Apr 29^th, 2020 at 1:29am	Print Post
	Markoz wrote on Apr 29^th, 2020 at 1:28am: 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. Exactly, you were in CLB mode, we're talking about CRZ mode; seems to be the time the plane accelerates to above 250 below 10,000.


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Markoz CS Team Offline Posts: 12445 Location: Victoria, Australia Joined: Apr 24^th, 2009 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #10 - Apr 29^th, 2020 at 1:34am	Print Post
	Alex T wrote on Apr 29^th, 2020 at 1:29am: you were in CLB mode I didn't think it was, but I'll check on the next flight that that happens on.

	Mark Fletcher PC: i7 10700K @3.8/5.1GHz \| 64GB DDR4 3200 \| 12GB RTX 4070 Super \| 32" LCD Monitor \| 1TB SSD + 2TB SSD + 2TB HDD \| Win 11 Pro
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Captain Sim CS Team Offline Posts: 4357 Joined: Nov 7^th, 2005	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #11 - Apr 29^th, 2020 at 1:59am	Print Post
	Alex T wrote on Apr 29^th, 2020 at 1:25am: it could just be a Boeing quirk Most likely

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logan3db Full Member Offline Posts: 32 Joined: Jun 21^st, 2018	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #12 - Apr 29^th, 2020 at 2:09am	Print Post
	Markoz wrote on Apr 29^th, 2020 at 1:28am: 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. 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!


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Markoz CS Team Offline Posts: 12445 Location: Victoria, Australia Joined: Apr 24^th, 2009 Gender:	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #13 - Apr 29^th, 2020 at 2:31am	Print Post
	I have done flights where I've cruised at 9000'-10000' before, but that's usually when I'm testing something else, and have no need for the flight to exceed 10000'. I haven't done that in the 767 II yet, but that's easy enough to do.

	Mark Fletcher PC: i7 10700K @3.8/5.1GHz \| 64GB DDR4 3200 \| 12GB RTX 4070 Super \| 32" LCD Monitor \| 1TB SSD + 2TB SSD + 2TB HDD \| Win 11 Pro
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logan3db Full Member Offline Posts: 32 Joined: Jun 21^st, 2018	Re: Possible 250kts below 10k bug (Any chime-ins?) Reply #14 - Apr 29^th, 2020 at 2:54am	Print Post
	Do you remember if your Cruise page gave you 250, or another number above that?


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