Hi Suntracker,
>310ias at 30,000 feet is 496mph. Pretty fast!
Hm, that calculator apparently uses a rule of thumb to calculate true air speed.
According to my calculation, 310 mph IAS at 30000 feet is 506 mph TAS, or Mach 0.75.
That's neglecting both calibration and compressibility error - I'd expect the true air speed to have been considerably lower than Mach 0.75 at that IAS reading.
Regards,
Henning (HoHun)