Instruments Flashcards
What are Va, Vb, Vso and Vd ?
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
When do we need to adjust temperature when operating an altimeter ?
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.
What are the Indicated Altitude, Pressure Altitude, Density Altitude, True Altitude and Absolute Altitude ?
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.
Name 4 errors that affect airspeed indicator.
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.
What are the IAS, CAS,EAS and TAS ?
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.
What is a radar altimeter ?
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.
What is a decision height ?
The decision height is the altitude for which the pilot is deciding whether he has sufficient visibility to land or not.
What is EFIS ?
The Electronic Flight Instrument System is a cockpit instrumentation system that uses electronic rather than electromechanical technology.
When can we use tablets or smartphones in the cockpit ?
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.
What is the ISA standard atmosphere ?
29.92 ‘‘Hg
15°C
No humidity
What is the max allowable altimeter error ?
+-50 feet
What are the main errors of the altimeter ?
Mountain effect : A strong valley wind create venturi effect ( pressure decreases ).
Pressure errors ( temperature variation , pressure variation).
What happen to the altimeter if there is a blocked static port ?
Indicated altitude remain constant.
What happen to the altimeter if the pitot tube is blocked ?
Nothing
What happen to the altimeter if the static port is partially blocked ?
It will underestimate in climb and overestimate in descent.
Explain briefly how works the altimeter.
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.
Explain briefly how works the Vertical Speed Indicator.
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.
Why there is a delay of indication ?What is the average delay in indication of the Vertical Speed Indicator ?
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.
What happens to the Vertical Speed Indicator if the static port is blocked ?
The VSI freezes at zero.
What happens to the Vertical speed Indicator if the static port is partially blocked ?
There is a very slow response.
What is the max permissible error for the Vertical Speed Indicator ?
+-200 ft / min
Explain briefly how works the Airspeed indicator.
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.
What are the white arc, green arc and yellow arc on the Airspeed Indicator ? What is the red line ?
White arc : flaps range.
Green arc : Normal operation range.
Yellow arc : Precaution range.
Red line : never exceed speed.
When the aircraft have a static port on the left what are the impact on the Airpseed Indicator and the risks during sideslips ?
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.
What happens to the Airspeed Indicator if the Pitot Tube is blocked ?
It will overestimate in climb and underestimate in descent.
What happens to the Airspeed Indicator if the static port is blocked.
It will underestimate in climb and overestimate in descent.
What is a gyroscope ?
A spinning wheel rotating at high speed ( usually around 20 000 RPM ) in a mounting called gimbal. ( discovered by Foucault in 1852 ).
What are the two fundamentals characteristics of a Gyroscope ?
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.
Whar are the errors that we can encounter in the gyroscopic instruments ?
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 )
Explain briefly how works the attitude indicator.
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.
What are the errors we can encounter on an attitude indicator ?
Following an acceleration it will show a climb.
Following a deceleration it will show a descent.
Explain briefly how works a directional gyro.
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.
Explain briefly how works a turn coordinator.
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.
What is rate one turn ?
It correspond to a rate of turn of 360° in 2 min ( 180° in 1 min ) which would be 3° per second.
What can you say about the earth magnetic field ?
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 ).
What is the compass regulation ?
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)
Explain briefly how works a magnetic compass.
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.
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What is the magnetic dip ? How can we reduced it in the design of the magnetic compass ?
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.
What are the errors due to the magnetic dip ?
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.
What are the VOR frequencies ?What are the maximum permissible errors on a VOR ?
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°
What is the angle of bank at rate one turn corresponding to a certain true airspeed ?
Angle (in degree ) = 10% TAS + 7 ( 5 when MPH )
