Friday Update, February 10, 2012

[Varrattu]

Originally Posted by Richie

How many Kms slower is a 109 speedometer at sea level than actual true airspeed?

It depends on ...

True airspeed, or TAS, is a measure of the physical speed of the aircraft in relation to the air around it. Just as differences in wind velocity affect groundspeed, differences in air density affect true airspeed. At the same engine power setting, e.g., 75 percent power, an airplane can move faster through air that is less dense. That’s why higher altitudes can
translate to higher true airspeeds.
Like aircraft groundspeed, TAS cannot be measured directly. Rather, the pilot uses outside air temperature (OAT), pressure altitude, and calibrated airspeed CAS to calculate
this value.

Regards Varrattu