B787-9 Not keeping altitude, stalls every time

[Captain_JR]

I set to M 0.87

A bit too high…

M0.85 or less.

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The B787-family cruises typically at M0.85, but the economical speed, which is basically to save a little bit of time and fuel too then M0.87 is used. When Which Airline and What Reasons are behind for a 787 to fly at .87 is unknown to me, as that can depend on various factors from weather to delayed flight to airline operations.

But the B787 does not fly any slower than .85 as that speed is what you’re supposed to aim at and fly at basically every time though 0.87 is not wrong, but I don’t know in which situations a pilot would choose to fly that little but faster.

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Source: DeerCrusher! 🦌

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Overspeeding

M.85 is cruise, M.89 is max cruise

Overspeeding

So what is the M0.87 you mentioned? When the cruise normally is .85 and not .87?

Overspeeding

I’ve found it to be an economy cruise speed. Its a bit closer to the sweet spot. When comparing .85 to .87, you get to your destination a bit quicker while using slightly less fuel in regards to the ratio of flight time to fuel used.

Overspeeding

So the fuel consumption is ever-so-slightly lower by flying M.87? With other words, it is a little more efficient to fly at .87?

Overspeeding

Yes. Let me see if I can simplify it. When comparing M.85 to M.87 you are:

Flying faster and you get to the destination in a shorter amount of time. Now, the nose of the aircraft is a bit more level to the horizon and fuel burn is slightly lower at this higher speed than a slower speed.

When at M.85, the opposite is true. The nose is slightly higher, which requires a slight amount more thrust (extra fuel burn). And it takes slightly longer because you’re flying slower. Again, the difference in minimal for a 3hr flight or shorter. But when flying from say LAX to SYD then you’ll see a difference. Hope that makes a little sense.

Overspeeding

1. Do airlines usually fly at M.85 or .87 when flying these Long Hauls from for an example: US to AUS and/or Asia?
2. Flying at .87, it that something pilots do when the flight is delayed and are perhaps trying to recover lost time?

Overspeeding

1. I’m not sure. It depends on what the dispatchers planned on. But I’d assume slightly faster. It all depends on if the aircraft is capable of flying those speeds.
2. Sometimes. They may also check with ATC and/or company to see if pilots are giving ride reports. The pilots can talk with their company to find out where the better winds are at in terms of stronger tailwinds or headwinds that are not as strong.

But still, even if you flying at .87, a certain altitude, with a certain load factor, you will still stall, thats’s this earth’s physics for you ;)

[Cameron_Stone]

The one in the picture could be really light. I see more -8s do it than -9s and -10s, and usually with about ~3 hours or less left in a long haul. I’m not sure what TUI’s load factors on that route are. It could be a 787 because it is the only plane that can both fly the route and make it profitable with a small load.

[David_Gallardo]

Wasn’t discussing weight, was just trying to show him that 787s do cruise at FL43.

[Ironman_Ballets]

I gotta say that’s actually a really cool feature.

[BennyBoy_Alpha]

Yes I have seen that but they climb at like 1000fpm maximum

[David_Gallardo]

All the way through? Thanks will try it out like that usually climbed about 1800fpm

[Tep_NEMO]

I personally rarely fly that high but when I do, I lower the VS gradualy, from 2600 initially to 2000 up to FL 100 then 1400, then 1000, then 800 from FL 320 to the ceiling. It never failed me yet!