B777 min. maneuving speed jump thru FL210

[Cropduster]

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.

[777300ER]

This actually occurs at around FL202 and generally presents as an amber band increase of 10-15kts due to the Minimum Maneuvering Speed changing from low altitude to high altitude logic.

[casablanca]

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

[Cropduster]

Thanks.What is the low and high altitude logic? What else changes? Again, can't find it in our books. Thanks.

[Cropduster]

Thanks.What is the low and high altitude logic? What else changes? Again, can't find it in our books. Thanks.

[wiggy]

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:

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.

[Cropduster]

Wow, that explains it all, it is referencing a different limitimg speed. Thanks so much.

[Cropduster]

Hi...we have a company AOM and not the FCOM. This info doesn't appear to have been included. Could anyone post a copy of the FCOM section dealing with this? Thanks eh.

[wiggy]

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:


Maintain at least 15 knots above minimum maneuver speed when climbing through FL200 to prevent the EICAS caution message, “AIRSPEED LOW” from occurring.

[zlin77]

I think the margin above 20,000' can be specified by the operator, 1.4 v 1.3...

[wiggy]

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.

[FullWings]

Yes, although it’s a non-event aerodynamically (Mr Navier and Mr Stokes are still in charge), it can be somewhat startling if you were unaware: “It was fine just a second ago?!..."

[wiggy]

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.

[JammedStab]

"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?