Atmosphere and Speed

What is the aviation definition of altitude?

Altitude is the measured distance above the local pressure setting (i.e., QNH, Query: Nautical Height) or altitude above mean sea level (MSL).

What is the aviation definition of a flight level?

measured pressure level above the 29.92-in/1013- millibar datum.

What are the ICAO ISA conditions at sea level? Temperature:

Temperature: + 15°C [environmental lapserate (ELR), -2°C per 1000 ft)

What are the ICAO ISA conditions at sea level? Pressure:

29.92 inches of mercury or 1013 hectopascals (millibars) (decreases with altitude)

What are the ICAO ISA conditions at sea level? Density:

1225 g/m3 (density is influenced by temperature and pressure)

What is pressure altitude?

international standard atmosphere (ISA) height above the 29.92-inl1013 millibar pressure datum,

How do you calculate the pressure altitude's actual height?

Then convert this pressure difference into a height, which you then add or subtract from the pressure altitude depending on whether the region QNH is above or below the 29.92-in

Assume that 0.0295 inch of mercury!l millibar - 30 ft

Why do you need to calculate the actual height of a pressure altitude?

1. Ground clearance
2. Calculating the performance capabilities of the aircraft

What is ISA temperature deviation?

measurement of the actual temperature against the ISA temperature for the corresponding altitude

If you were at 33,000 ft with an outside air temperature (OAT) of -45°C, what is the temperature deviation from international standard atmosphere (lAS)?

ISA temperature is + 15°C at mean sea level (MSL), with a 2°C per 1000 ft lapse rate. Therefore ISA temperature at 33,000 ft is
+15 + (33 X -2) = -5°C
Actual temperature minus ISA temperature at 33,000 ft is Therefore, temperature deviation at 33,000 ft
= lAS + 6°C.

What is density altitude?

pressure altitude corrected for nonstandard temperature

What are the main influences on air density?

1. Temperature 2. Pressure 3. Humidity

How does the variation of air density due to temperature affect an aircraft's performance?

decrease in the perfonnance level of the aircraft's engines and a decrease in aerodynamic perfonnance because the aircraft's perfonnance is based around air density.

What is static pressure?

Static pressure is the equal weight of all the air molecules at anyone point in the atmosphere.

What is dynamic pressure?

There are two main components that determine the amount of dynamic pressure experienced:
1. The speed ofthe body relative to the air 2. The density of the air

Dynamic pressure = ½ R (rho) X V² (TAS)

Describe lAS.

measure of dynamic pressure translated to a speed

Describe RAS/CAS. Calibrated airspeed

corrected for instrument error and pressure errors

Describe TAS.

calibrated airspeed corrected for temperature and pressure

actual speed of an aircraft through the air mass in which it is flying.

Describe ground speed

speed of an aircraft relative to the ground.

Describe LSS.

LSS is the local speed of sound.

speed of sound, Mach 1.0, does not remain a constant value of knots per hour because it is influenced by temperature;

decreases with a decrease in temperature.

Describe Mach number

Mach number is the true airspeed (TAS) of an aircraft, given as a percentage relative to the local speed of sound (LSS)

What happens to your calculated airspeed (CAS) or indicated airspeed (lAS) if you descend at a constant true airspeed (TAS)?

he CAS (lAS) will increase. This is so because pressure increases with a decrease in altitude