119
edits
Changes
From CUGC Wiki
m
→Errors: TAS & IAS
Most of the times the instrument designers are not completely stupid, so the constant density hard coded into the ASI is not a random number. It is actually the average density of air at sea level, which the airfields and airports are usually not far away from. Therefore, at low levels where the density is quite close to the sea level density, the ASI is reasonably accurate. The problem most commonly arises when aeroplanes are flown at high altitudes: as we have discussed in the atmosphere section, the density of the air decreases with altitude. Therefore, the higher the altitude, the larger the difference between the IAS and the TAS. For example, a jet airliner that operates at FL360 can read an IAS of 280kts, but the TAS is actually around 450kts. For flying in wave lift which can take a glider to high altitudes, this is an important point to understand: you will travel faster than the ASI tells you.
A rule of thumb for calculating TAS corrections is, for every 1000ft above mean sea level, the TAS is 2% higher than the IAS. For example, if you fly at QNH 5000ft, your TAS will be 10% higher than your IAS.
==== Stall speed and \(V_{NE}\) ====
