Cross Over Altitude

[George Yogi]

Cross Over Altitude : Altitude at which a/c speed limited by Vmo changes to Mmo (at .76 Mach) .A320 FCOM limitation states cross over Altitude as 25000' , But is Cross over Altitude constant ? It could change at any time right ? since it is a Function of TAS and Temp , Please explain.

[flyboyike]

It is constant, because the aircraft is programmed that way. What changes is the actual Mach number based on TAS and Temp, as you have suggested, but the "crossover" altitude stays the same only because that's what the manufacturer chose.

[john_tullamarine]

Sonic velocity has a temperature consideration ...

Mach has naught to do with OAT.

Suggest a search on the topic as it regularly gets done to death. Typical discussion here (http://www.pprune.org/tech-log/146658-mach-transition.html)

[Natstrackalpha]

Ah, yes. Tis indeed the Local Speed of Sound, which is thus determined from temperature and not the Machno.


Mach is Dynamic over Static. D/S (enuf said big time)