B777 min. maneuving speed jump thru FL210
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Joined: May 2005
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From: Vancouver Island
B777 min. maneuving speed jump thru FL210
Hi all....
I have noticed that when climbing thru approximately FL210 when heavy, the minimum maneuvering speed (top of the amber tape) suddenly jumps up 20 or 30 knots. The other day we were climbing at 280 knots and the tape jumped up and touched our current speed. What causes this? Can't find anything in the books. Thanks Cropduster.
I have noticed that when climbing thru approximately FL210 when heavy, the minimum maneuvering speed (top of the amber tape) suddenly jumps up 20 or 30 knots. The other day we were climbing at 280 knots and the tape jumped up and touched our current speed. What causes this? Can't find anything in the books. Thanks Cropduster.
Joined: Sep 2003
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From: Sand pit
It does seem to change... I've seen where it has been 10 and other times 20 for essentially same weights? But it does grab your attention when you go from a comfortable margin of min man + 15 to all of a sudden in middle of yellow band
Joined: Feb 2001
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From: The Winchester
As has been been said the min maneuvering speed logic changes at 20,200 feet.
Try FCOM/systems descriptions/flight instruments/PDF reference speeds/minimum manevering speeds, or similar, it's 10.10 in ours.
FWIW:
Try FCOM/systems descriptions/flight instruments/PDF reference speeds/minimum manevering speeds, or similar, it's 10.10 in ours.
FWIW:
Minimum Maneuvering Speed
Indicates maneuver speed margin to stick shaker or low speed buffet. Top of the bar is the airspeed that provides:
1.3 g maneuver capability to stick shaker with flaps down.
1.3 g maneuver capability to stick shaker or VREF + 80, whichever is less, with flaps up at or below 20,200 FT.
1.3 g maneuver capability to low speed buffet (or an alternative approved maneuver capability as preset by maintenance), with flaps up above 20,200 FT.
Indicates maneuver speed margin to stick shaker or low speed buffet. Top of the bar is the airspeed that provides:
1.3 g maneuver capability to stick shaker with flaps down.
1.3 g maneuver capability to stick shaker or VREF + 80, whichever is less, with flaps up at or below 20,200 FT.
1.3 g maneuver capability to low speed buffet (or an alternative approved maneuver capability as preset by maintenance), with flaps up above 20,200 FT.
Joined: Feb 2001
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From: The Winchester
I'm afraid the above quote is pretty much all the FCOM says on the subject.
FWIW the Normal procedures section, climb and cruise procedure does have the following note:
FWIW the Normal procedures section, climb and cruise procedure does have the following note:
Maintain at least 15 knots above minimum maneuver speed when climbing through FL200 to prevent the EICAS caution message, “AIRSPEED LOW” from occurring.
Joined: Feb 2001
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From: The Winchester
Correct - Hence the comment in the FCOM: "1.3 g..........or an alternative approved maneuver capability as preset by maintenance, with flaps up above 20,200 FT."
As an aside we operated a solely -200 fleet for quite some time and this "gotcha" with the tape and airspeed low warnings didn't really become apparent until we started operating -300s at close to their RTOW on ultra long haul routes...at which stage one or two got caught out at 20,200 feet if they'd speed intervened in the climb, either for turbulence or to steepen the climb angle.
As an aside we operated a solely -200 fleet for quite some time and this "gotcha" with the tape and airspeed low warnings didn't really become apparent until we started operating -300s at close to their RTOW on ultra long haul routes...at which stage one or two got caught out at 20,200 feet if they'd speed intervened in the climb, either for turbulence or to steepen the climb angle.
Last edited by wiggy; 28th January 2017 at 08:02.
Joined: Feb 2001
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From: The Winchester
Yep, I gather going from 10-15 knots clear of the amber band to being instantly buried in it, with associated EICAS warnings can cause a few "WTFs" ....the company had so many reports about it when the issue first manifested itself with us that we actually ended up with a management newsletter re the whole "problem" which contained some interesting hints and tips ...I must see if I still have a copy:
Edit to add - found it - old article and I'll paraphrase: main prob was folks climbing out heavy weight and speed intervening at 270 knots due e.g moderate turbulence - they were then getting clobbered at 20200 by the "logic change". It was pointed out that Boeing don't actually recommend a best speed for light/mod turbulence so don't simply wind it back to 270kt 'cos it's a bit bumpy. Also recommended as a backstop maintaining FMC Climb MAX ANGLE speed + at least 15 knots.
HTH the OP.
Edit to add - found it - old article and I'll paraphrase: main prob was folks climbing out heavy weight and speed intervening at 270 knots due e.g moderate turbulence - they were then getting clobbered at 20200 by the "logic change". It was pointed out that Boeing don't actually recommend a best speed for light/mod turbulence so don't simply wind it back to 270kt 'cos it's a bit bumpy. Also recommended as a backstop maintaining FMC Climb MAX ANGLE speed + at least 15 knots.
HTH the OP.
Last edited by wiggy; 28th January 2017 at 09:09.
Joined: Apr 2008
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From: nowhere
"Minimum Maneuvering Speed
Indicates maneuver speed margin to stick shaker or low speed buffet. Top of the bar is the airspeed that provides:
1.3 g maneuver capability to stick shaker with flaps down.
1.3 g maneuver capability to stick shaker or VREF + 80, whichever is less, with flaps up at or below 20,200 FT.
1.3 g maneuver capability to low speed buffet (or an alternative approved maneuver capability as preset by maintenance), with flaps up above 20,200 FT."
I do remember this statement. That being said, I normally think of the 1.3 g margin as being to stickshaker of buffet. Is there a particular reason for the highlighted quote concerning flaps up below 20K. How close can one get to stickshaker if maneuver is based on the lower Vref+80 value instead?
Indicates maneuver speed margin to stick shaker or low speed buffet. Top of the bar is the airspeed that provides:
1.3 g maneuver capability to stick shaker with flaps down.
1.3 g maneuver capability to stick shaker or VREF + 80, whichever is less, with flaps up at or below 20,200 FT.
1.3 g maneuver capability to low speed buffet (or an alternative approved maneuver capability as preset by maintenance), with flaps up above 20,200 FT."
I do remember this statement. That being said, I normally think of the 1.3 g margin as being to stickshaker of buffet. Is there a particular reason for the highlighted quote concerning flaps up below 20K. How close can one get to stickshaker if maneuver is based on the lower Vref+80 value instead?
