Atmosfer ve Hız mülakat soruları

Height is the vertical distance of an aircraft (or object) above a specified datum, normally the ground or aerodrome; on the altimeter it is read with QFE set.

Altitude is the vertical distance of a level, point or object above mean sea level; the altimeter indicates it when the local QNH is set.

A flight level is a surface of constant atmospheric pressure related to the standard datum of 1013.25 hPa (29.92 inHg), named in hundreds of feet, e.g. FL350 = 35,000 ft on the standard setting.

ISA is the International Standard Atmosphere: an ICAO reference model of the atmosphere's temperature, pressure and density with height, used for altimeter calibration and aircraft performance.

Temperature +15 °C, pressure 1013.25 hPa (29.92 inHg), density 1.225 kg/m³; temperature decreases by about 2 °C (1.98 °C) per 1000 ft up to the tropopause at 36,090 ft, where it is −56.5 °C.

Air pressure is the force per unit area exerted by the weight of the air column above a point; it decreases with height and is measured in hectopascals (ICAO standard), millibars (same value) or inches of mercury.

It varies with altitude and temperature: about 27 ft per hPa at sea level in ISA, increasing to about 50 ft at 18,000 ft and 80–100 ft above 35,000 ft; 30 ft per hPa is the common rule of thumb in the lower levels.

1 hPa (millibar) ≈ 0.0295 inHg; conversely 1 inHg ≈ 33.86 hPa, and 29.92 inHg = 1013.25 hPa.

Pressure altitude is the altitude in the ISA that corresponds to the measured air pressure; it is what the altimeter reads with 1013.25 hPa (29.92 inHg) set.

Find the difference between the regional QNH and 1013 hPa, convert it at about 30 ft per hPa, and add it to the pressure altitude if QNH is above 1013 or subtract it if QNH is below 1013.

A flight level is referenced to the 1013 hPa / 29.92 inHg standard datum, so it differs from true altitude whenever real sea-level pressure (and temperature) differ from ISA. You need true height for terrain clearance and for performance calculations.

Barometric error. If you fly from higher into lower sea-level pressure without resetting the subscale, the altimeter overreads and you are lower than indicated: "high to low, beware below". Flying into higher pressure has the opposite effect.

SAT (static air temperature) is the temperature of the undisturbed air and is the same as OAT. TAT (total air temperature) is the higher reading from a probe that brings the air to rest, so TAT = SAT + ram rise.

It is the actual temperature minus the ISA temperature for the same pressure altitude. It is written as ISA +X or ISA −X (for example ISA +6) and is the standard way to describe temperature in performance work.

ISA at 33,000 ft is about 15 − (33 × 2) = −51°C. The actual temperature is −45°C, so the deviation is −45 − (−51) = +6°C, written ISA +6.

Density is mass per unit volume (ρ = m / V). For air it falls with altitude and with higher temperature. ISA sea-level air density is 1.225 kg/m³.

Density altitude is the altitude in the standard atmosphere that has the same air density as the air you are actually in. It is pressure altitude corrected for the non-standard temperature (ISA deviation).

Temperature, pressure and humidity. Higher temperature, lower pressure (higher altitude) and more moisture all reduce density. At a given pressure altitude, temperature is the dominant factor.

Warmer than ISA means less dense air, which reduces engine thrust and aerodynamic performance: longer take-off runs, poorer climb and lower limiting weights. Colder than ISA has the opposite effect and improves performance.

Two: altimeter temperature (density) error and airspeed density error. In cold air the altimeter overreads, so you are lower than indicated. The ASI matches TAS only at ISA sea-level density.

Static pressure is the ambient atmospheric pressure at a point, caused by the weight of the air above it and acting equally in all directions. It is independent of the aircraft's motion and is sensed by static ports.

Dynamic pressure is the extra pressure, above static, produced by the air's motion relative to the aircraft: q = ½ρV². It depends on air density and true airspeed.

IAS is the speed read directly from the airspeed indicator. It is dynamic pressure (pitot minus static) shown in knots, using ISA sea-level calibration, so it equals TAS only at ISA sea-level density.

CAS (called RAS in older UK usage) is IAS corrected for instrument error and position (pressure) error. It is what a perfect ASI system would show.

EAS is CAS corrected for compressibility error. It is the sea-level speed that would give the same dynamic pressure. The correction matters mainly at high speed and high altitude, and always reduces the figure (EAS ≤ CAS).

TAS is the aircraft's actual speed through the air mass. At a constant IAS or CAS, TAS rises as density falls, so it increases with altitude and with warmer temperature.

Ground speed is the aircraft's speed over the ground: TAS combined with the wind. A tailwind makes it higher than TAS, a headwind lower, and in still air the two are equal.

LSS is the speed of sound in the air at the aircraft's position. It depends only on temperature: LSS ≈ 38.94 × √T knots (T in kelvin), about 661 kt at ISA sea level and falling as the air gets colder with altitude.

The speed of sound is proportional to the square root of absolute temperature. Colder air gives a lower LSS and warmer air a higher one: LSS ≈ 38.94 × √(273 + °C) knots.

Mach number is TAS divided by the local speed of sound (M = TAS / LSS). In a constant-IAS climb it keeps rising, so above the crossover altitude (often around FL260–FL310) the Mach limit takes over from the IAS limit and the aircraft is flown at constant Mach.

M = TAS / LSS. For example, 470 kt TAS where the LSS is 590 kt gives about M0.80.

Temperature, because it alone sets the local speed of sound. At a constant TAS, colder air lowers the LSS and so raises the Mach number (M = TAS / LSS).

It decreases. As weight falls, less lift is needed, so the optimum (long-range cruise) speed schedule calls for a lower Mach number at the same level.

CAS (IAS) increases. Air density rises as you descend, and with a fixed TAS the dynamic pressure ½ρV², which the ASI reads, therefore increases.

TAS increases. Density falls with altitude, so keeping the same dynamic pressure (constant CAS) needs a higher true airspeed.

Mach number increases, for two reasons: TAS rises because density falls, and the speed of sound falls because temperature drops. M = TAS / LSS therefore climbs quickly.

CAS (IAS) stays what you are holding, while TAS increases. Warmer air is less dense, so a higher true airspeed is needed to produce the same dynamic pressure.

In the troposphere, the lower aircraft has both the higher TAS and the higher CAS. The air there is warmer, so the speed of sound, and therefore TAS for the same Mach, is higher, and the denser air gives a higher CAS too.

Mach number stays constant because temperature, and so the speed of sound, does not change. CAS (IAS) decreases because density falls with height.

CAS (IAS) increases. Even with constant temperature, pressure, and therefore density, rises as you descend, so the dynamic pressure at a fixed TAS goes up.

CAS (IAS) falls faster than usual, and the Mach number decreases. Temperature rises with height in an inversion, so density drops more quickly and the speed of sound increases.