Instruments

Question 1

What are Va, Vb, Vso and Vd ?

Answer 1

Va : Manoeuvrable speed ( full deflections of controls still possible without exceeding the design limit load factor/ usually operated during turbulences ) Vb : Design speed for maximum gust intensity. Vso : Stall speed in landing configuration ( gears down , flaps down ) Vd : Design diving speed

Question 2

When do we need to adjust temperature when operating an altimeter ?

Answer 2

Whenever the plane goes in an air mass which have a different temperature than standard air. The reading of the altimeter is then not indicating the true altitude.

Question 3

What are the Indicated Altitude, Pressure Altitude, Density Altitude, True Altitude and Absolute Altitude ?

Answer 3

Indicated Altitude : The reading on the altimeter when it is set to the current barometric pressure. Pressure Altitude : The reading on the altimeter when it is set to standard barometric pressure. Density Altitude: Pressure altitude corrected for temperature. True Altitude : Exact height above mean sea level. Absolute Altitude : Exact height above the earth’s surface.

Question 4

Name 4 errors that affect airspeed indicator.

Answer 4

Position error : Eddies that are formed as the air passes over the wing and struts are responsible for position error. Lag error : A mechanical error due to the friction in the instrument parts. Icing error : Ice formation , blocking the pitot or static pressure sources. Density error : The density of the air decreases as the altitude increase.

Question 5

What are the IAS, CAS,EAS and TAS ?

Answer 5

Indicated Airspeed : read on the instrument. Calibrated Airspeed : IAS corrected for instrument and installation error. Equivalent Airspeed : CAS corrected for compressibility factor. ( relevant for high speed aircraft ) True Airspeed : the actual speed of the airplane through the air mass.

Question 6

What is a radar altimeter ?

Answer 6

The radar altimeter indicates the actual height of the airplane above the earth, or above any object on the earth over which the airplane is passing.

Question 7

What is a decision height ?

Answer 7

The decision height is the altitude for which the pilot is deciding whether he has sufficient visibility to land or not.

Question 8

What is EFIS ?

Answer 8

The Electronic Flight Instrument System is a cockpit instrumentation system that uses electronic rather than electromechanical technology.

Question 9

When can we use tablets or smartphones in the cockpit ?

Answer 9

The smartphones or Tablets can only be considered as a backup system. The plane must be sufficiently equipped so that it is possible to pilot and navigate without them even if they are handy.

Question 10

What is the ISA standard atmosphere ?

Answer 10

29.92 ‘‘Hg
15°C
No humidity

Question 11

What is the max allowable altimeter error ?

Answer 11

+-50 feet

Question 12

What are the main errors of the altimeter ?

Answer 12

Mountain effect : A strong valley wind create venturi effect ( pressure decreases ).

Pressure errors ( temperature variation , pressure variation).

Question 13

What happen to the altimeter if there is a blocked static port ?

Answer 13

Indicated altitude remain constant.

Question 14

What happen to the altimeter if the pitot tube is blocked ?

Answer 14

Nothing

Question 15

What happen to the altimeter if the static port is partially blocked ?

Answer 15

It will underestimate in climb and overestimate in descent.

Question 16

Explain briefly how works the altimeter.

Answer 16

The Altimeter consist in a box connected to the static source. In this box there is wafer ( calibrated to ISA ) which expands with the decrease of the pressure when the plane is gaining altitude. The wafer expansion make the needle to move through a mechanism.

Question 17

Explain briefly how works the Vertical Speed Indicator.

Answer 17

The Vertical Speed Indicator consist in a box connected to the static source but with a calibrated orifice. In this box there is awafer ( directly connected to the static source ) which expands with the decrease of the pressure when the plane is gaining altitude . The wafer expansion is damped by the calibrated air static orifice. So that the difference between the static pressure in the wafer and the one in the box ( calibrated ) will enable to give an indication of the vertical speed. This indication is given thanks to a needle connected to the wafer via a mechanism.

Question 18

Why there is a delay of indication ?What is the average delay in indication of the Vertical Speed Indicator ?

Answer 18

The delay of indication is due to the delay of the pressure in the box. The delay of indication can range from 6 to 9 seconds.

Question 19

What happens to the Vertical Speed Indicator if the static port is blocked ?

Answer 19

The VSI freezes at zero.

Question 20

What happens to the Vertical speed Indicator if the static port is partially blocked ?

Answer 20

There is a very slow response.

Question 21

What is the max permissible error for the Vertical Speed Indicator ?

Answer 21

+-200 ft / min

Question 22

Explain briefly how works the Airspeed indicator.

Answer 22

The Airspeed indicator consist in a box connected to the static source. In this box there is a wafer which is connected to the pitot tube.
The ram air from the pitot tube is providing total pressure. As the box is connected to the static port hence static pressure, it is possible to know the dynamic pressure by knowing the difference between the total and the static pressure.
The movement of the wafer actually give the indication of this difference. Afterwards it provides the information by moving a needle via a mechanism.

Question 23

What are the white arc, green arc and yellow arc on the Airspeed Indicator ? What is the red line ?

Answer 23

White arc : flaps range.
Green arc : Normal operation range.
Yellow arc : Precaution range.
Red line : never exceed speed.

Question 24

When the aircraft have a static port on the left what are the impact on the Airpseed Indicator and the risks during sideslips ?

Answer 24

If the airplane do a side slip to the Left, the Airspeed Indicator under estimates and there is a risk of spiral.

If the airplane do a side slip to the Right, the Airspeed Indicator over estimates and there is a risk of stall or spin.

Question 25

What happens to the Airspeed Indicator if the Pitot Tube is blocked ?

Answer 25

It will overestimate in climb and underestimate in descent.

Question 26

What happens to the Airspeed Indicator if the static port is blocked.

Answer 26

It will underestimate in climb and overestimate in descent.

Question 27

What is a gyroscope ?

Answer 27

A spinning wheel rotating at high speed ( usually around 20 000 RPM ) in a mounting called gimbal. ( discovered by Foucault in 1852 ).

Question 28

What are the two fundamentals characteristics of a Gyroscope ?

Answer 28

Rigidity in space ( Gyroscopic inertia ) : A rotating body will resist any forced applied to modify its axis of rotation, its keeps the same position.

Precession : Once rotation is established a force applied to modify the axis will be felt 90° away from the point where it is applied in the direction of the rotation.

Question 29

Whar are the errors that we can encounter in the gyroscopic instruments ?

Answer 29

Apparent precession : The aircrafts moves over a rotating earth, the pilot must readjust the gyro for more precision . ( 15 ° per hour at the north pole and 0° at the equator)

Deviation : The friction between rotating parts will cause a precession error too. ( 3° to 4° every 15 min )

Question 30

Explain briefly how works the attitude indicator.

Answer 30

The Attittude indicator consist in a Gyro mounted horizontally onto a pitch gimbal which is itself mounted onto a roll gimbal.
The roll gimbal is bond to the horizontal reference arm which gives the information of attitude.
The Gyro will remains always parallel to the surface of the earth.

Question 31

What are the errors we can encounter on an attitude indicator ?

Answer 31

Following an acceleration it will show a climb.

Following a deceleration it will show a descent.

Question 32

Explain briefly how works a directional gyro.

Answer 32

The Directional gyro consist in a Gyro mounted vertically onto two gimbals.
The bigger gimbal is linked to the compass card heading indicator via a mechanism .
The Gyro will remains always perpendicular to the surface of the earth.

Question 33

Explain briefly how works a turn coordinator.

Answer 33

The Turn Coordinator consit in a gyro mounted vertically on a 35° canted gimbal. This gimbal is bond to the turn indicator.
Both roll and yaw causes a turn indication.

Question 34

What is rate one turn ?

Answer 34

It correspond to a rate of turn of 360° in 2 min ( 180° in 1 min ) which would be 3° per second.

Question 35

What can you say about the earth magnetic field ?

Answer 35

It is tilted at an angle of 11.5 degrees with respect to the rotational axis of the earth.
It is composed by Isogonic lines and Agonic lines ( 0° Deviation lines ).

Question 36

What is the compass regulation ?

Answer 36

It is the operation which consists in correcting the indication of the compass. ( If the compass is too much deviated the plane is not able to take off)

Question 37

Explain briefly how works a magnetic compass.

Answer 37

The magnetic compass consists in a magnetised bar bond to a compass card mounted onto a pivot in a box full of kerosene. As the plane change of heading the compass card will move to indicate the currrent heading.
.

Question 38

What is the magnetic dip ? How can we reduced it in the design of the magnetic compass ?

Answer 38

The earth’s lines of force are horizontal at the equator but become vertical toward the poles. This cause the compass card to tilt because of the increased force pointing towards the ground as we approach the poles. To limit this phenomenon the CoG of the compass card is lowered.

Question 39

What are the errors due to the magnetic dip ?

Answer 39

In Turns :
Turn From South, the compass will Lead.
Turn from North, the compass will Lag

When heading East or West :
If the plane Accelerate, the compass will indicate a Turn to the North.
If the plane Decelerate the compass will indicate a Turn to the South.

Question 40

What are the VOR frequencies ?What are the maximum permissible errors on a VOR ?

Answer 40

Frequencies : From 108 Hz to 117.95 Hz
Maximum allowable error for an Inflight check : 4°
Maximum allowable error for a visual check on a radial : 6°

Question 41

What is the angle of bank at rate one turn corresponding to a certain true airspeed ?

Answer 41

Angle (in degree ) = 10% TAS + 7 ( 5 when MPH )