Find the calibrated airspeed

Find the calibrated airspeed (KCAS). Given information: Pressure Altitude = 20,000 ft Indicated Airspeed = 250 KIAS Atmosphere Table 2.1 Compressibility Correction Fig. 2.12 Position error correction chart provided ? 248 KCAS ? 240 KCAS ? 252 KCAS ? 260 KCAS

The Correct Answer and Explanation is:

To determine the calibrated airspeed (KCAS), you need to consider the following steps, based on the given information:

1. Indicated Airspeed (KIAS): This is the speed shown on the airspeed indicator. In this case, it is 250 KIAS.
2. Pressure Altitude: The altitude provided is 20,000 feet. At this altitude, corrections are needed because indicated airspeed does not account for temperature and pressure changes that affect the aircraft’s true airspeed.
3. Compressibility Correction (Table 2.1): Compressibility effects become more significant at higher speeds and altitudes. At 20,000 feet and 250 KIAS, the aircraft may experience changes in air density, so you need to apply a compressibility correction. This correction accounts for the changes in airspeed due to the compressibility of air as you approach or exceed the speed of sound.
4. Position Error Correction (Fig. 2.12): Airspeed indicators often have a position error due to the location of the pitot tube, which can lead to discrepancies in airspeed readings. The correction for this is typically provided by the manufacturer or a chart like Fig. 2.12, which will give a correction factor based on the altitude and airspeed.

Steps to calculate KCAS:

• Step 1: Apply compressibility correction: Using Table 2.1, determine if any compressibility correction needs to be applied at 20,000 feet and 250 KIAS. Based on the altitude and speed, this correction may be a small value added to the indicated airspeed.
• Step 2: Apply position error correction: Refer to Fig. 2.12 to determine the position error correction. This might be a small subtraction from the indicated airspeed, as the pitot tube may overestimate the actual speed.

Now, calculate the calibrated airspeed (KCAS):

• After applying both corrections, you’ll get a calibrated airspeed that compensates for altitude, compressibility, and position errors. In this case, given the indicated airspeed of 250 KIAS and after corrections, you would likely end up with one of the following values for KCAS:
  • 248 KCAS
  • 240 KCAS
  • 252 KCAS
  • 260 KCAS

Conclusion:

Given the nature of the corrections and the typical magnitude of changes at this altitude, the calibrated airspeed is most likely 248 KCAS based on the options provided. However, the exact value depends on the specific compressibility and position error corrections used.