Airspeed, Mach & Vertical Speed

B. 0.81

ISA at FL330 = -51 C, so -36 C = 237 K. LSS = 38.95 x sqrt(237) = 600 kt. M = 487 / 600 = 0.81.

The question was recalled without its options; these options were written to it.

B. static pressure in the capsule with static pressure in the case fed through a calibrated leak (metering unit)

The capsule receives static directly; the case receives it through a restriction, so in a climb or descent the case lags and the difference shows the rate. No pitot input - a blocked pitot does not affect it.

The question was recalled without its options; these options were written to it.

A. Upper limit VNE, lower limit VNO

The yellow (caution) arc starts at VNO, the top of the green arc, and ends at VNE, the red line. So the upper limit is VNE and the lower limit is VNO.

The question was recalled without its options; these options were written to it.

C. 614 kt

LSS = 38.95 x sqrt(T in kelvin) = 38.95 x sqrt(248) = 614 kt. (661 kt is the sea-level ISA value at +15 C.)

The question was recalled without its options; these options were written to it.

B. progressively under-read

Trapped static stays at the higher (lower-altitude) pressure while real static falls; the capsule sees pitot - trapped static, which is too small: the ASI under-reads. In a DESCENT it over-reads.

The question was recalled without its options; these options were written to it.

B. TAT - ram rise

Air brought to rest on the probe heats up (ram rise): TAT = SAT + ram rise, so SAT = TAT - ram rise. ISA deviation uses SAT.

A. white, green, yellow, then the red line

White arc: flap operating range (VS0-VFE). Green: normal range (VS1-VNO). Yellow: caution range (VNO-VNE). Red line: VNE.

The question was recalled without its options; these options were written to it.

C. the Machmeter reading is independent of temperature

The Machmeter works only from pitot and static pressure (Mach depends on (Pt - Ps)/Ps), so temperature never enters. At constant CAS the Mach number INCREASES in a climb and decreases in a descent - both other statements are reversed.

C. instrument error and position error

CAS (also called RAS) is IAS corrected for both instrument error and position error.

The question was recalled without its options; these options were written to it.

B. decrease

Pitot pressure is trapped; static increases as you descend, so pitot - static shrinks and the ASI falls, whatever the real speed. It now behaves like an altimeter: rising in a climb, falling in a descent.

The question was recalled without its options; these options were written to it.

A. the ASI (and Machmeter) only

Only the ASI and Machmeter use pitot pressure. The altimeter and VSI use static alone, so a blocked STATIC source affects all of them.

The question was recalled without its options; these options were written to it.

C. total pressure (static + dynamic)

The air brought to rest in the tube gives total (pitot) pressure = static + dynamic. The ASI subtracts static to leave the dynamic part.

The question was recalled without its options; these options were written to it.

A. increase, and the margin to low-speed buffet increases

Descending at constant Mach, the air gets denser and warmer: IAS (CAS) rises, moving the aircraft away from low-speed buffet and towards VMO - which is why the changeover from Mach to IAS is made in the descent.

The question was recalled without its options; these options were written to it.

C. Mach number increases; TAS increases

Climbing at constant CAS the Mach number and TAS both increase.

A. increases

TAS = CAS / sqrt(relative density). Higher density altitude means thinner air, so for the same CAS the TAS is higher.

B. may cause errors during the take-off run

A VSI is fooled only while the position error is changing - e.g. as speed builds rapidly on the take-off run. It also lags for a few seconds when a climb or descent starts or stops (lag + manoeuvre error).

The question was recalled without its options; these options were written to it.

A. over-read

In a right sideslip the right side meets the airflow (high pressure) and the left is in its lee (low pressure). With the right vent blocked, only the low left-side pressure is sensed: static too LOW - the altimeter over-reads and the ASI over-reads.

The question was recalled without its options; these options were written to it.

A. over-reads, showing the aircraft further from the stall than it really is

Static trapped at a lower (higher-altitude) pressure makes pitot - static too large as you descend: over-reading. The real speed is lower than shown - the stall is closer than you think.

The question was recalled without its options; these options were written to it.

A. the same as TAS

CAS equals TAS only at ISA sea level, where density is 1.225 kg/m3.

B. increase steadily

Trapped pitot pressure against a falling static pressure: the indicated speed climbs steadily with altitude, regardless of the real speed.

The question was recalled without its options; these options were written to it.

B. 27.1

Descent 7,500 to 1,000 ft = 6,500 ft at 800 ft/min = 8.1 min; at 156 kt that is 21.1 NM. Add the 6 NM still to run: start the descent 27.1 NM before the beacon.

As recalled, this question depended on a chart or table that is not reproduced here; the key is the recalled paper's answer.

A. Increase

With the pitot blocked (and its drain closed) the trapped pressure stays constant while static pressure falls in the climb, so the ASI over-reads and increases.

C. TAS remains constant

In an isothermal layer the speed of sound is constant, so at constant Mach the TAS is constant.

B. VS1 to VNO

Green = normal operating range: lower end VS1 (stall, clean, max weight), upper end VNO (max structural cruising speed).

The question was recalled without its options; these options were written to it.

B. instrument, position and manoeuvre-induced

The Machmeter uses a pressure RATIO, so it has no density or temperature error, and compressibility is built into its calibration. That leaves instrument, position and manoeuvre-induced errors.

The question was recalled without its options; these options were written to it.

A. TAS decreases

Descending at constant CAS the air gets denser, so TAS falls (and the Mach number falls).

B. IAS - CAS - EAS - TAS

IAS + instrument and position error = CAS; CAS + compressibility = EAS; EAS + density error = TAS.

The question was recalled without its options; these options were written to it.

A. CAS and TAS both decrease

Temperature falls in the climb, so the speed of sound falls: same Mach = lower TAS. Air also gets thinner, so CAS falls even faster.

B. position (pressure) error

Position error is the error from the static vent sensing a pressure different from the true ambient pressure because of the local airflow - ice or debris round the vent changes exactly that.

The question was recalled without its options; these options were written to it.

C. stays constant

Mach = TAS / speed of sound, and the speed of sound depends only on temperature. Constant temperature + constant TAS = constant Mach.

The question was recalled without its options; these options were written to it.

D. under-read

In an unpressurised cabin the leak lets pitot pressure escape to roughly static pressure, so the difference sensed is too small: the ASI under-reads.

The question was recalled without its options; these options were written to it.

A. CAS increases, TAS decreases

CAS rises in any descent at constant Mach (denser air). TAS = Mach x speed of sound, and the speed of sound falls with the colder air in the inversion, so TAS falls.

B. pitot (total) pressure; static pressure

Total (pitot) pressure inside the capsule, static around it: the capsule expands with the difference, the dynamic pressure 1/2 rho V^2.

The question was recalled without its options; these options were written to it.

C. gradually fall to zero

With the drain open, the pressure in the pitot line leaks away to atmospheric (static) pressure, so pitot - static becomes zero. If the drain is ALSO blocked, pressure is trapped and the ASI acts like an altimeter.

The question was recalled without its options; these options were written to it.

C. react like an altimeter

Trapped pitot pressure is compared with a changing static pressure: in a climb the static falls and the ASI rises; in a descent it falls - just like an altimeter.

The question was recalled without its options; these options were written to it.

C. the VSI will return to zero..

Static pressure trapped at the blocked level while the aircraft climbs: the VSI returns to zero.

A. 499 kt

ISA at FL300 = -44.4 C, so OAT = -29.4 C = 243.8 K. Local speed of sound = 38.95 x sqrt(243.8) = 608 kt; TAS = 0.82 x 608 = 499 kt.

B. thermocouples

A thermocouple (two dissimilar metals) generates a voltage proportional to the hot-junction temperature with no external power - used for CHT (on the hottest cylinder) and EGT.

A. 540 kt

ISA at FL330 = -51 C; + 15 gives -36 C = 237 K. Speed of sound = 38.95 x sqrt(237) = 600 kt; TAS = 0.9 x 600 = 540 kt.

The question was recalled without its options; these options were written to it.

B. 254 cm/s

1 ft = 30.48 cm, so 500 ft/min = 15,240 cm/min = 15,240 / 60 = 254 cm/s.

A. pitot pressure, static pressure and total air temperature

From pitot, static and TAT (and often AoA) the ADC computes altitude, vertical speed, IAS/CAS, Mach, TAS and SAT.

The question was recalled without its options; these options were written to it.

A. initially by MMO, then by VMO below a certain flight level

At high level the Mach limit (MMO) is reached first; below the crossover altitude the airspeed limit VMO becomes the limit.

C. CAS

VMO is a calibrated airspeed limit.

A. 1650 ft/min

Height to lose = 37,000 - 12,000 = 25,000 ft. Time = 100 / 396 h = 15.15 min. Rate = 25,000 / 15.15 = 1,650 ft/min.

B. reduce the error caused by sideslip or yaw

Averaging the two sides cancels the pressure difference created by sideslip/yaw. The alternate static source is the backup for blockage.

The question was recalled without its options; these options were written to it.

B. 6500 FT/MIN

540 kt = 54,700 ft/min of ground distance; 12% of that = 6,560 ft/min, about 6,500 ft/min.

C. Cannot rely on its readings, especially when a change of pitch Attitude is occurring

The VSI lags and gives wrong readings during pitch changes.

A. 1800 ft/min

Height to lose = 35,000 - 8,000 = 27,000 ft. Time = 85 / 340 h = 15 min. Rate = 27,000 / 15 = 1,800 ft/min.

A. 97 kt

ISA at 8000 ft is -1 C, so ISA + 11. Air density ratio gives TAS = 84 x 1.15 = 97 kt (rule of thumb: +2 % per 1000 ft = 97 kt).

The question was recalled without its options; these options were written to it.

C. ASI, altimeter, VSI and Machmeter

Static feeds the altimeter, VSI, ASI and Machmeter; pitot feeds the ASI and Machmeter. Block both and every pressure instrument is wrong.

The question was recalled without its options; these options were written to it.

A. under-read

Slipping left, the left side faces the airflow, so the open left vent senses a pressure ABOVE true static. Pitot - static is too small: the ASI (and Machmeter) under-read.

The question was recalled without its options; these options were written to it.

A. Increase

In a constant-Mach descent the speed of sound rises, so CAS and IAS increase.

B. conditions of the ISA at mean sea level

The ASI is calibrated to read TAS only in ISA sea-level air (1.225 kg/m3, 1013.25 hPa, +15 C). Anywhere else density error makes IAS differ from TAS.

The question was recalled without its options; these options were written to it.

A. 0.67

Mach depends only on the ratio of dynamic to static pressure, i.e. on CAS and pressure altitude - not on temperature. At FL290, 255 kt CAS gives M 0.67. The ISA deviation changes the TAS (here about 390 kt), not the Mach.

The question was recalled without its options; these options were written to it.

B. turbine (jet pipe) outlet pressure / compressor inlet pressure

EPR = exhaust (turbine outlet) total pressure divided by compressor inlet total pressure - a direct measure of thrust on many jets.

The question was recalled without its options; these options were written to it.

A. Breaking the rate-of climb indicator glass window.

In an unpressurised aeroplane, breaking the VSI glass admits cabin (ambient) pressure to the static system as an emergency static source.

B. 75 Nm

Time = 14,000 ft / 500 ft/min = 28 min. Ground speed with the 20 kt headwind = 160 kt: 160 x 28/60 = 75 NM.

A. select the alternate static source

Select the alternate static source (usually inside the cabin; it may make the instruments over-read slightly). Breaking the VSI glass is the last-resort way to vent the system to cabin pressure if there is no alternate.

A. -51 C

ISA: +15 C at sea level, falling about 2 C per 1000 ft: 15 - 66 = -51 C (-50.3 with 1.98). -56.5 C is the tropopause value, reached at 36,090 ft.

The question was recalled without its options; these options were written to it.

A. 30,400 ft

First remove the ram rise: SAT = TAT / (1 + 0.2 M^2) = 263 / 1.134 = 232 K = -41 C. ISA at 30,000 ft is -44.4 C, so ISA + 3. Density altitude = 30,000 + 3 x 120 = about 30,400 ft.

The question was recalled without its options; these options were written to it.

B. MMO first, then VMO

Up high the Mach limit (MMO) governs; descending at constant Mach the IAS rises until VMO is reached, after which the crew flies IAS.

The question was recalled without its options; these options were written to it.

B. 19 deg

tan(bank) = V x rate / g = 61.7 m/s x 0.0524 rad/s / 9.81 = 0.33, bank = 18 deg. Rule of thumb: TAS/10 + 7 = 19 deg.

The question was recalled without its options; these options were written to it.

B. K x sqrt(temperature in kelvin) knots

The correct answer is: K x sqrt(temperature in kelvin) knots.

The question was recalled without its options; these options were written to it.

A. VS0 to VFE

White = flap operating range: VS0 (stall with full flap) to VFE (maximum flap-extended speed).

The question was recalled without its options; these options were written to it.

B. Mach number decreases.

In an isothermal layer the speed of sound is constant; at constant CAS the TAS and hence the Mach number fall in the descent.

A. 141 kt

At FL80 with +20 C (ISA +21): density ratio = 0.743 / 1.017 = 0.730, so TAS = 120 / sqrt 0.730 = 140-141 kt.

The question was recalled without its options; these options were written to it.

B. an accelerometer (dashpot) that reacts at once to vertical acceleration

A small spring-loaded piston (dashpot) moves with vertical acceleration and produces an immediate pressure difference, so the needle responds at once while the normal metering takes over.

A. 16 C

Ram rise = (TAS/100)^2 = (400/100)^2 = 16 C, so TAT is about 16 C warmer than SAT.

A. increases

Warmer air is less dense; the same IAS needs a higher TAS (roughly +1 % per 5 C).

A. static air temperature plus the ram rise

Air brought to rest on the probe is heated by compression: TAT = SAT + ram rise. The ram rise grows with the square of TAS (about 1 deg C at 100 kt, about 9 deg C at 300 kt in round figures).