I was in a 787 @ M.85 behind a 757 @ M.85, we were on the same flt plan, accordinng to your own info max mach for 757 is M.83. The 787 info says you can do mach .90 max but you get a speed warning at m.90 so why is 757 not getting a speed warning for exceeding mach .83? Im not saying m.90 is a realistic cruise, but i never could pass the 757 even at m.89, what the heck?
Sometimes people use the ground speed as mach and depending on the winds you got you can get results as far as 0.90M. But iirc mach speed does not refer normally on GS.
I guess/think the mach speed of the 787 should be between 0.84-85M.
The B757 should not go faster than 0.80M
(everything over 0.85M is too fast for commercial aircrafts, people going 0.90M are going insanely overboard with their speed. And it’s unrealistic)
The actual speed numbers for the 757 from Boeing for your dissemination!
Normal Cruise: Mach .8 (461 kn; 854 km/h; 531 mph),
Max.: Mach .86 (496 kn; 918 km/h; 571 mph)
Ceiling: 42000
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I just flew back from Newark on a UA 757-200 @ 38k. He was running just shy of .89mach with a tail wind. Is that speeding?
Not when the plane says it’s running at .85mach.
Made the trip to the home base in 3.1hours which is usually 3.45hrs. It’s all in the wind as they say!
The displayed Mach speed is a measure of TAS (true airspeed)*. I assume your displayed Mach speed was .85, and if so, where were you measuring .89?
*edit: however, while the Mach limit is a fixed number for each aircraft type, the speed of sound changes somewhat with temperature (and temperature changes with altitude)…so, the actual relationship between Mach and TAS does change somewhat: As temperature increases sound travels faster through the air…
So, the particular aircraft’s Mach limit will be at a a somewhat higher TAS as temperature increases.
@Kjet797
As far as aircraft alarms going off when hitting the exact published Mach limit, there is some question of whether the Mach-TAS dependence on temperature is modelled or not, and whether that has any bearing on where you see the max Mach speed warning going off .
Actually, the speed was IRL and not the Game/SIM! I merely asked the pilot what the aircraft’s true speed was coming west and as we all know is usually lower across the continental US, which sparked my interest as to why the speed increase. He slowed way down the last 25min. of the flight due to the gate we were destined to - still had a plane in it. So there you are!
Not necessarily related to the op’s question, but no, I didn’t know that tbh (I presume I should have). But I’m a bit confused why the pilot quoted you a GS in terms of a precise Mach number. But, that’s ok, I not infrequently miss things:)
(tangential reference admittedly, but super cool, precise rapid answers, to aerospace/aeronautical engineering related questions in everyday language, published roughly a week ago: Aerospace Engineer Answers Airplane Questions From Twitter | Tech Support | WIRED (youtube.com))
Anyway, as to the op’s question, refer to my prior comment for the best I can come up with at the moment given the limits of my understanding…
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