ATPL - performance and loading question
 

When calculating a SAR or SGR.

How do you convert mach to TAS using the whizz wheel or BASIC rule of thumb arithmetic?


ie
"what is the SAR for a 727 that weighs 72,000Kg cruising at FL350 @ Mach .82 and ISA temp?"

SAR = TAS/FF*1000

TAS = ??
FF = 4410KG/h(normal cruise at mach .82)

If you have a CR-2/3

Find the ISA temperature at FL350 = -55

Go to the Mach Index window on your CR-3 and line up -55.

On the Gray outer scale of your CR-2/3 (which you would normally use for minutes in a fuel flow calculation) line up 82 (which is Mach 0.82) The outer scale will show a TAS of 470kts

SAR = 470/4410*1000

SARs are pretty useless, SGRs are used everyday and something you will be using a lot in Flight Planning.

Good Luck.

TAS = Mach No x (39 x SQRT (Temp in Kelvin))

0 deg C = 273 deg K