Next time you have "struggled" to FL410 have a look at your airspeeds once stabilised in the cruise. I would hazard a guess that you will be indicating M0.78~M0.80, or about 250KIAS.
(These are approximate figures to illustrate a point. In real life your numbers may be slightly different depending on your operation, your aeroplane, and the prevailing ambient atmospheric conditions)
At FL410 setting 280Kts will put you into an overspeed condition.
It's been about 3 years since I've gone up to 410, but I do remember that the coffin corner starts to get pretty tight.
But back to the point, the recommended speed is 280/M.76
whichever is less. At 410, one should be setting M.76. I think that's about 230kias.
At FL410 setting M0.76 will have you very close to Minimum Maneuver Speed.
For some reason, the tables I'm looking at only go to FL390, but at 390, it says:
Vb = M0.76. The lower and upper limits for .3G is 223kias and 252kias for a 737-9 at 150,000lbs. It looks like M0.76 puts you closer to the bottom than the top. But, that's Boeing's
Vb.
Whereas setting 280Kts/M0.76 is fine at lower cruise levels it doesn't necessarily work for higher levels. Setting Turbulence N1 (which is usually somewhere about 1% less than your cruise N1) will usually ensure you neither overspeed, or underspeed. Boeing don't differentiate between cruising flight levels, and so don't provide recommended airspeeds.
I'd say they do. That's why Boeing has a table called "FLIGHT WITH UNRELIABLE AIRSPEED / TURBULENT AIR PENETRATION Cruise (.76/280)" They then go on to provide N1 and pitch for various altitudes. Eg. At FL400 and 140,000lbs, N1 91.0% and +3.5 pitch.
ps. Don't forget that if you are in RVSM and the turbulence is so severe that you cannot maintain your Flight Level within tolerance you need to advise ATC. Thankfully genuine "Severe Turbulence" is comparatively rare.
Agreed!
Regardless of whether the speed should be M0.76 or some other, the goal is a safe airspeed.
My greater concern is pilots using the MCP to command the autothrottle to set an N1 which a power setting for a desired speed. (Whatever speed it may be.) Convoluted!
Either set the MCP to the speed you want, or turn off the autothrottle and set an N1 that you want.