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Instruments Flashcards

(43 cards)

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1
Q

What are the main advantages of a servo-assisted altimeter compared to a conventional aneroid altimeter

A

Higher accuracy
Less friction and hysteresis
Better response at high altitude and high speed
Allows electrical outputs (autopilot, TCAS, ADC)

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2
Q

What happens to indicated altitude when the altimeter subscale setting is increased or decreased

A

Pressure increased - Indicated altitude increases

Pressure reduced - Indicated altitude decreases

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3
Q

What happens to the altimeter reading at high speed, without position error correction and why

A

Indicated altitude is higher than true altitude

Static pressure is lower than ambient due to airflow acceleration around the fuselage

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4
Q

In an unpressurised aircraft with a single static port, what is the effect of a sideslip toward or away from the static port on the altimeter indication

A

Toward
Airflow impinges on the port
Static pressure sensed becomes higher than ambient
Altimeter interprets higher pressure as lower altitude
Altimeter reads lower than actual altitude

Away
Port sits in a low-pressure (suction) area
Static pressure sensed becomes lower than ambient
Altimeter interprets lower pressure as higher altitude
Altimeter reads higher than actual altitude

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5
Q

How does temperature deviation from ISA affect the relationship between indicated altitude and true altitude if warmer/colder than ISA air is below the aircraft

A

warmer-than-ISA air below:
Indicated altitude is higher than true altitude

colder-than-ISA air below:
Indicated altitude is lower than true altitude

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6
Q

What pressure exists inside the altimeter capsule and case

A

Capsule:
A sealed reference/vacuum pressure/atmospheric pressure

Case:
Static pressure from the static system

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7
Q

What does the blue line on a twin-engine ASI indicate

A

VYSE - best rate of climb speed with one engine inoperative

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8
Q

What does a second striped needle on the ASI indicate

A

VMO / Maximum Operating Speed

Some aircraft use a barber pole instead of a fixed red line

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9
Q

What do the following indicate:
1. VYSE
2. VFE
3. VNO
4. VMO
5. VNE
6. VS1
7. VSO
8. VLE
9. VLO
10. VA

A
  1. VYSE - Best rate of climb speed with one engine inoperative
  2. VFE - Maximum speed at which flaps may be extended
  3. VNO - Maximum normal operating speed
  4. VMO - Maximum operating speed
  5. VNE - Never exceed speed
  6. VS1 - Stall speed in clean configuration
  7. VS0 - Stall speed in landing configuration
  8. VLE - Maximum speed at which landing gear may remain extended
  9. VLO - Maximum speed at which landing gear may be extended or retracted
  10. VA - Maneuvering speed (full control deflection without structural damage)
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10
Q

What are IAS, CAS, EAS, and TAS mainly used for

A

IAS
Aircraft handling and limitations

CAS
Corrected IAS for instrument and position error

EAS
Structural loads and performance calculations

TAS
Navigation and flight planning

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11
Q

What pressure is inside the capsule and case of an ASI

What type of pressure does the ASI measure, and what is its formula

A

Capsule:
Pitot (total) pressure

Case:
Static pressure

Measures the difference between total and static pressure - (dynamic pressure)

Pdynamic = Ptotal - Pstatic

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12
Q

What happens to the readings on an ASI when:

  1. Pitot tube blocked, drain hole open
  2. Pitot tube and drain hole both blocked
  3. Static port blocked

Does the ASI overread/underread when:

  1. ASI errors at high altitude
  2. ASI errors at high speed
A
  1. ASI reads zero - Pitot pressure cannot build; diaphragm is equal to static - no dynamic pressure
  2. ASI behaves like an altimeter
    • Climb - ASI increases
    • Descent - ASI decreases
  3. ASI underreads in climb
    Overreads in descent
  4. ASI underreads due to low air density
  5. ASI overreads due to compressibility effects
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13
Q
  1. Why does ASI underread at altitude
  2. Why does ASI overread at high speed
A
  1. Air density decreases, reducing dynamic pressure for the same true speed
  2. Air becomes compressible, increasing sensed pressure
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14
Q
  1. What error are machmeters subject to
  2. Where is the machmeter reading obtained from
  3. What is the machmeter computed from
A
  1. Machmeters are subject to:
    Instrument and position error (same sources as ASI)
  2. Machmeter reading is obtained from: Pitot (total) pressure and static pressure
  3. Mach number is computed from:
    Speed ÷ Local Speed of Sound
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15
Q
  1. What is the VSI fed by
  2. What is the main limitation of a VSI
A
  1. The VSI is fed by static pressure only
  2. VSI has lag because it relies on a restricted flow into the capsule to detect rate of change of static pressure
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16
Q
  1. How do you calculate rate of descent using groundspeed and glide slope angle
  2. What is the rule of thumb for a 3° glide slope
A
  1. Rate of descent calculation:
    Rate of descent (fpm) = 5 × groundspeed(kts) × glideslope/3
  2. Rule of thumb for a 3° glide slope:
    Rate of descent = Groundspeed × 5
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17
Q

What happens to the VSI during a climb and descent

A

During a climb:
Static pressure in the case decreases immediately
Pressure in the capsule decreases slowly
Result: Climb indication

During a descent:
Static pressure in the case increases immediately
Pressure in the capsule increases slowly
Result: Descent indication

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18
Q

Gyroscopes
1. Where should the mass of a gyroscope be located to be most efficient

  1. Where are earth rate wander and transport wander equal to zero
  2. How does an air-driven gyroscope operate in an aircraft
  3. How do you calculate gyro drift due to earth rotation
  4. In which direction does gyro drift occur in each hemisphere
  5. What are the two main properties of a gyroscope
Study These Flashcards
A
  1. At the rim of the rotor to maximise moment of inertia
  2. At the equator
  3. Vacuum or pressure airflow spins the rotor; air jets both spin and stabilise the gyro
  4. Drift rate = 15° × sin(latitude) per hour
  5. Northern Hemisphere: apparent drift to the right
    Southern Hemisphere: apparent drift to the left
  6. Rigidity in space
    Precession
19
Q

What gyroscopic spin axis is used, and how many degrees of freedom apply to each instrument

Study These Flashcards
A

Attitude Indicator (AH)
Spin axis: Horizontal
Degrees of freedom: 2

Directional Indicator (DI)
Spin axis: Vertical
Degrees of freedom: 2

Turn Coordinator (TC)
Spin axis: Canted
Degrees of freedom: 1

Attitude and direction indicators use space-stabilised gyros, requiring two degrees of freedom to sense aircraft attitude or heading
Turn coordinator uses a rate gyro to sense angular velocity, so its gyro’s restricted to one degree of freedom, allowing deflection proportional to rate of turn

20
Q

What errors are associated with:
1. DI
2. AH

Study These Flashcards
A
  1. Earth rate wander
    Transport wander
    Bearing friction and precession
  2. Acceleration errors
    Turning errors
    Erection system errors
    Gimbal limit errors (tumbling)
21
Q
  1. What error can be expected on the attitude indicator during a constant-rate turn greater than 180°
  2. During a 270° turn to the right, what false indication may appear on the AH
Study These Flashcards
A
  1. The AH will indicate a climb and a turn opposite to the direction of turn
  2. The AH may indicate a climb and a turn to the left
22
Q
  1. What is EPR
  2. How is EPR computed
  3. Why is EPR preferred over RPM as a thrust indication
Study These Flashcards
A
  1. The ratio of turbine exhaust pressure to compressor inlet pressure
  2. EPR = Exhaust pressure / Inlet pressure
  3. Because EPR is less affected by temperature and altitude and better represents actual thrust
23
Q

What does the manifold pressure gauge measure

Study These Flashcards
A

The absolute pressure of the air-fuel mixture in the intake manifold

24
Q
  1. Where is EGT measured in a turbine engine
  2. What are the two main sources used to determine thrust in a turbine engine
Study These Flashcards
A
  1. In the exhaust gas stream, between the turbine stages or at the turbine outlet
  2. EPR
    RPM (N1 / N2)
25
What are the three types of tachometer and how do they operate
1. Mechanical Tachometer Driven directly from the engine by gears or a flexible shaft Shaft rotation acts on a centrifugal or drag mechanism inside the instrument Centrifugal force moves a needle against a spring Indication is directly proportional to RPM 2. Electrical Tachometer (Tachogenerator type) Engine drives a small generator Generator output (voltage or frequency) increases with engine speed Signal is sent electrically to the cockpit indicator Indicator converts the electrical signal into an RPM display 3. Electronic Tachometer Uses magnetic pickup or optical sensor to detect shaft rotation Each rotation produces a pulse Electronic circuitry counts pulses per unit time RPM is calculated and displayed (analogue or digital) No mechanical drive required - higher reliability
26
For powerplant systems, what are aneroid capsules, bellows, and bourbon tubes, and what are they used for
Aneroid capsule Used for measuring absolute or low pressure - Manifold pressure (MAP) - Altitude and Airspeed Instruments - Fuel Management: In turbocharger controllers (fixed datum controllers), aneroid capsule senses compressor discharge pressure and operates an oil bleed valve to control the wastegate Bellows Corrugated metal diaphrams stacked together to create a larger displacement Used for medium, or differential pressure systems - Carburettor intake/Fuel filter - Fuel Control Units - detect pressure changes and modulated Fuel flow - EPR Bourdon tube C shaped/helical flattened metal tube that straightens/uncoils when pressurized Measures high pressures - Oil Pressure - Hydraulic Pressure - Fuel Pressure
27
What are the 3 DME marker beacons and how far do they extend What amplitude modulation tones are used for marker beacons
Outer Marker: Blue, ~4–7 NM Middle Marker: Amber, ~0.5–0.8 NM Inner Marker: White, threshold (CAT II/III) Outer Marker: 400 Hz (continuous dashes) Middle Marker: 1300 Hz (alternating dots and dashes) Inner Marker: 3000 Hz (continuous dots)
28
What affects does the following have on the ASI: Pitot blockage, drain hole open Pitot blockage with closed drain hole Total pressure (pitot) leak in pressurized and non-pressurised aircraft
Pitot Blockage: No ram air enters Drain hole open - pitot line vents to atmosphere Pitot pressure = ambient static pressure ASI sees no pressure difference ASI reads zero Pitot blocked, drain hole closed: ASI acts like an altimeter: Climb - ASI increases Descend- ASI decreases Total Pressure Leak: Non-pressurised aircraft ASI underreads/drops to zero Pressurised aircraft Pitot system may be exposed to cabin pressure Cabin pressure ≠ ambient pressure Pressure relationships become unpredictable
29
What happens to the Altimeter when the static port is blocked during a climb/descent
Altimeter will continue to show the level at which the blockage occurred: Static port blocked during climb Altimeter under-reads Static port blocked during descent Altimeter over-reads
30
How does a gyromagnetic compass operate
Uses a free directional gyro for short-term stability Uses flux valves to sense Earth’s magnetic field - flux valve feeds error detector Slaving system compares gyro heading to magnetic heading Any drift is automatically corrected via torque motors Combines gyro stability with magnetic accuracy Primary coils fed AC voltage (487.5Hz) Accuracy on the magnetic field indicator < 0.5%
31
What information is displayed on the following navigation display modes: MAP ROSE VOR/ILS ROSE VOR ROSE ILS ARC
MAP Aircraft position, track, waypoints, routes, weather radar, terrain, and navigation aids ROSE Aircraft heading at the top, compass rose, selected navigation source, and deviation relative to aircraft heading VOR/ILS Selected VOR radial or ILS localizer and glide slope deviation, course deviation, and station information ROSE VOR Compass rose, selected VOR, course deviation, TO/FROM indication, bearing pointer(s) ROSE ILS Compass rose, ILS localizer deviation, glide slope deviation, runway alignment cues, no map or route display ARC Aircraft at the bottom of the display, forward-looking map, waypoints, track, and route, limited compass arc (usually 90°–120°)
32
What information is displayed on the Primary Flight Display
Attitude Airspeed Altitude Vertical speed Heading/track Flight director, and Basic navigation cues
33
What do the following flight warning system colours indicate: Red Amber/Yellow Green
Red - Immediate action required (warning) Amber/Yellow - Caution; prompt attention required Green - Normal operation or system status
34
What happens to the ASI when the static port is blocked during a climb/descent
When the static port is blocked: Static pressure becomes trapped at the value where it blocked Pitot pressure continues to change with airspeed and altitude During a climb: Actual static pressure decreases Trapped static pressure remains higher than ambient Pressure difference (Pt − Ps) is smaller than it should be ASI under-reads During a descent: Actual static pressure increases Trapped static pressure remains lower than ambient Pressure difference (Pt − Ps) is larger than it should be ASI over-reads
35
What information can be displayed on the Flight Mode Annunciator
The FMA shows the active and armed modes of the autoflight system, including: Autothrust/Autothrottle modes Vertical modes (e.g. climb, altitude hold, GS) Lateral modes (e.g. HDG, NAV, LOC) Engagement status of autopilot/flight director
36
How do the following thermometers operate, what ranges do they operate, and what are they used for: Mechanical/Bimetallic Thermometer Electrical Resistance Thermometer(RTD) Thermocouple Thermometer
Bimetallic Thermometer Operation: - 2 dissimilar metals bonded together, expanding at different rates when heated Range and Use: - -70°C to 600°C - OAT Electrical Resistance Thermometer Operation: - Electrical resistance varies with temperature Range and Use: - -70°C to 150°C - Carburettor air, Oil temp Thermocouple Thermometer Operation: - 2 dissimilar metal wires joined at one end(hot junction) and kept at a different temperature at the the other(cold junction), a small voltage is generated proportional to the temp difference Range and Use: - -200°C to 1200°C - EGT, CHT, TIT
37
How does selecting the alternate static source affect the altimeter in a non-pressurized, vs a pressurized aircraft, and why
Non-Pressurized Altimeter overreads (indicates higher than true altitude) Cabin pressure is lower than ambient due to airflow and venturi effects Lower sensed pressure - instrument thinks aircraft is higher Pressurized Altimeter underreads (indicates lower than true altitude) Cabin pressure is higher than outside air Higher sensed pressure - instrument thinks aircraft is lower
38
What inputs does the autopilot use
Attitude information (AH / IRS / ADIRU) Heading information (gyro / magnetometer) Navigation inputs (VOR, ILS, GPS, FMS) Air data (altitude, airspeed, vertical speed)
39
How does a slaved gyro compass system combine the advantages of a directional gyro and a magnetic compass How does the Slaving system correct for errors in the gyro heading
It uses a free directional gyro for short-term stability and a flux valve to sense Earth’s magnetic field for long-term accuracy The slaving system compares gyro heading with magnetic heading and uses torque motors to automatically correct any gyro drift
40
How does a slaved directional gyro correct gyro drift
A flux valve (flux gate magnetometer) senses the horizontal components of Earth’s magnetic field Its primary coil is energized with AC (≈487.5 Hz) The magnetic signal is sent to an error detector, which compares magnetic heading to gyro heading Any difference generates a correction signal that drives torque motors to precess the gyro back into alignment
41
Why is a slaved gyro compass more accurate than a standalone directional gyro
A standalone directional gyro drifts due to friction and Earth rate A slaved gyro system automatically corrects drift by continuously comparing the gyro heading to magnetic heading via a flux valve and applying corrections using torque motors
42
Why does true airspeed increase with altitude for a constant IAS
IAS measures dynamic pressure At altitude: - Air density decreases - You'd need a higher TAS to produce same dynamic pressure
43
How are QNH and QFE rounded to the nearest hPa
Rounded down to the nearest hPa
Instrument Rating
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