# Avionics Questions and Answers – Air Data Equations

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This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Air Data Equations”.

1. Which of the following is used to obtain the altitude from the static pressure?
a) International atmospheric data
b) Standard atmospheric model
c) International atmospheric tables
d) Standard atmospheric tables

Explanation: To determine the altitude from the measured static pressure, the standard atmospheric model has been established. The standard model gives the relation between a height and the properties of the atmosphere as the solution to a differential equation relating the difference in pressure.

2. What is the height called when the standard temperatures are used?
a) Standard altitude
b) Constant altitude
c) Pressure altitude
d) Total altitude

Explanation: The altitude at which the standard temperatures are used is called the pressure altitude. Pressure altitude is the altitude of the aircraft above sea level. It always takes it’s reference as sea level.

3. Which of the following altitude is measured by the pitot-static tube?
a) Standard altitude
b) Constant altitude
c) Pressure altitude
d) Total altitude

Explanation: Pressure altitude, as the name suggests, is the altitude derived from pressure measurements. It is measured from the static port of the pitot-static probe. The static pressure of air varies with altitude with approximately 101Kpa at sea level.

4. Why is it dangerous to fly over hilly areas with pressure altitude?
a) Affected by temperature
b) Not reliable
c) Costly
d) Not the true altitude

Explanation: Pressure altitude is always referenced from the sea level. When flying over hilly areas, the actual altitude of the aircraft from the ground is definitely lesser than the pressure altitude, thus showing erroneous altitude readings.

5. What does the altitude rate essentially tell us?
a) Vertical speed
b) Rate of climb
c) Rate of glide
d) Rate of decent

Explanation: Air data computers usually provide an output identified as altitude rate which is an outgrowth of the early pneumatic vertical speed indicators which suffer from undesirable lags. Altitude rate combines accelerometer readings and pneumatic readings.

6. Which are the factors that mach number does not depend on?
a) Static pressure
b) Stagnation pressure
c) Static temperature
d) Thrust produced by the aircraft

Explanation: The mach number is computed from the corrected values of static and stagnation pressures. Mach number is comparatively easier to calculate than airspeed in supersonic speeds due to the compression shocks that form in the pitot tube.

7. Why are retractable pitot tubes used in stealth planes?
a) Aerodynamically efficient
b) Stealth configuration
c) Error values in supersonic speeds
d) Use GPS for speed and altitude

Explanation: Stealth planes, such as the B2 spirit stealth bomber, use retractable pitot tubes to maintain their stealth. When not in stealth mode they extend the probes for air data measurements.

8. Why is heating necessary in pitot-static tube?
a) Ice formation
b) Force the flow away from tube
c) Force the flow towards the flow
d) Increase the sensitivity

Explanation: Pitot-static tubes are generally placed with heating elements to stop the formation of ice in the orifice of the probe. Formation of ice on the probes causes erroneous readings and has lead to fatal air crashes.

9. Calibrated speed is the actual speed of the aircraft relative to the wind.
a) True
b) False

Explanation: Calibrated speed is the speed under sea level conditions which would give the same impact pressure. True airspeed is the velocity of the aircraft relative to the local wind.

10. Where will the measurements of static pressure be most accurate?
a) Nose of the aircraft
b) Tail of the aircraft
c) Wing tips of the aircraft
d) Trailing cone

Explanation: The most accurate value of static pressure is when the flow is least affected by the presence of the aircraft itself. In a trailing cone configuration, the probe is far behind the aircraft and is least affected by the flow.

11. What is the speed of the aircraft relative to the ground called as?
a) Relative speed
b) Inertial speed
c) Ground speed
d) True airspeed

Explanation: When you stand on the ground with a radar speed gun pointing at the aircraft, the speed measured is called the ground speed and is measured relative to the ground. True airspeed is measured relative to the wind.

12. Density altitude is the standard parameter for vertical navigation.
a) True
b) False 