Intrument flying review

Instrument flying


Flight-instrument systems

  • There are two flight-instrument systems, producing two types of flight instruments:
    • Pitot-static instruments
    • Gyro instruments.

Pitot-Static instruments

  • The pitot-static system records static and dynamic air pressure, providing the pilot with information related to airspeed and altitude.
    • The airspeed indicator (ASI).
    • The vertical speed indicator (VSI).
    • The altimeter (ALT).
  • Only the ASI is connected to both pressure sources.
  • Static port:
    • Measures pressure that is static (not moving), the ambient air.
  • Pitot tube (dynamic tube):
    • Measures impact, or dynamic, pressure (ram air).
Intrument flying review
Aispeed Indicator
  • Measure the speed at which the aircraft is moving through the air.
  • Connected to both the static and pitot (dynamic) ports.
  • ASI records the pressure difference between the two ports.
  • Report the height above sea level.
  • The ALT is an instrument case connected only to the static port.
  • As an aircraft increases in altitude the aneroid capsules expand due to decreasing ambient air pressure, this expansion is registered on the instrument face.
Vertical speed Indicator
  • Indicates the vertical speed of the aircraft (climb or descent).
  • Connected to static port only.
  • Has a few second lag.
  • As pressure drops, the aneroid compresses, indicating a climb.
  • As the pressure increases, the aneroid expands, indicating a descent.
  • As the aircraft levels off, pressure no longer changes and the pointer returns to its zero position.

Static port blocked

  • Airspeed Indicator:
    • Under-read in climb.
    • Over read in descent.
  • Vercical speed indicator:
    • Constant zero indication.
  • Altimeter:
    • Frozen.

Pitot static blocked

  • Affects airspeed indicator only.
  • ASI act like an altimeter.
    • Over-read in climb.
    • Under-read in descent.
  • Pitot tube partially blocked:
  • Airspeed Indicator:
    • Decrases to Zero.

Alternate static source

  • Can be selected if the outside sources become clogged with ice.
  • The instrument relying on the static pressure may operate slightly differently.
  • Altimeter:
    • May indicate a higher-than-actual altitude.
  • VSI:
    • Will momentarily indicate a climb.
  • ASI:
    • Will indicate greater-than-normal speed.

Gyroscopic instruments

  • Heading indicator (HI)
  • Attitude indicator (AI)
  • Turn and slip indicator or turn co-ordinator.
  • May be powered by:
    • Vacuum/ pressure system.
    • Electrically.
Gyroscope properties:
  • Rigidity:
    • Regardless of the position of its base, a gyro remains rigid in space, with its axis of rotation pointed in a constant direction.
  • Precession:
    • If an external force is applied to the gyroscope to change the direction of the rotor axis, the gyro resists the angular movement and moves in a plane at a right angle to that of the applied force, the resulting movement being called precession.

Turn coordinator Vs Turn and Bank Indicator

  • The purpose of these two intruments is to indicate:
    • Rate of turn.
    • Quality of turn (coordinated or not).
  • Turn and bank indicator (turn and slip Indicator) can only identifying:
    • Yaw.
  • Turn coordinator will identify both:
    • Yawing motion.
    • Rolling motion.
  • Inclinometer:
    • Shows slip and skid.
    • Shows quality of a turn.
  • In a standard rate turn the aircraft moves through 3° every second. It takes 2 minutes to turn 360°.
Turn coordinator
Turn and Bank Indicator

Review questions

  • What is the main difference between a turn coordinator and a turn and bank indicator?
  • Which flight instruments are part of the pitot-static system?
  • Which instruments are driven by a vacuum pump?
  • How do the gyroscopic instruments work?
  • The pitot system provides impact pressure for which instrument?
Study flight
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