B - The Mach Meter (18-05-18) Flashcards
What is Mach?
The local speed of sound.
What is the equation for LSS?
LSS = 38.95 x root(T(A))
T(A) - Absolute temperature (Kelvin)
What is the JSA and how does it differ from ISA?
The Jet Standard Atmosphere
The only difference is that it ignores the tropopause and so Temperature continues to decline at 1.98degC/1000ft.
What is the equation for Mach no?
M = TAS/LSS = (PT - PS) / PS
How does a Mach meter work?
It combines the workings of an ASI and an altimeter.
It has 2 capsules, one that is fed with total pressure (The ASI capsule) and another than is partially evacuated (The altimeter capsule)
The ASI capsule essentially measures PT-PS, while the altimeter essentially measures Ps and so Mach is determined.
What errors are associated with the Mach meter?
Instrument error
Maneouvre error
Position/pressure error.
Only C & D if it is combined with an ASI.
What happens if there is a blockage in the Mach meter?
PUDSOD
POCSUC
Same as ASI.
What happens if there is a pitot leak in a Mach meter?
It will cause under reading due to some of the total pressure leaking out.
What happens if there is a leak in the static line of a Mach meter in pressurised/unpressurised aircraft?
The static pressure measured becomes cabin pressure and so will significantly under read and be pretty much useless.
Unpressurised aircraft don’t travel fast enough to warrant having a Mach meter.
Where is Mach number displayed on an EFIS display?
Below the CAS speed tape.
How is Mach number displayed on older aircraft systems?
On the ASI with the barbers pole.
At constant FL and CAS, when flying into colder air, what happens to Temperature, TAS and True altitude?
They all go down
3 T’s:
Temperature
TAS
True alt
all go the same way
What is the change over altitude?
The point which you switch between MMO and VMO to avoid exceeding them in a climb or descent.
