Instruments

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Instruments part 1
www.lrn.dk/arnop.htm
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Magnetic compass
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Magnetic Northpole
North Magnetic Pole (2005) 82.7 N 114.4
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Magnetic Northpole

• It wanders in an elliptical path each day, and
  moves, on the average, more than forty meters
  northward each day

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Earth magnetism
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Magnetic dip
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Magnetic variation
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Magnetic variation
VARIATION WEST, MAGNETIC BEST, VARIATION EAST,
MAGNETIC LEAST
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Magnetic deviation
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Deviation table
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Magnetic compass

• Magnectic compass
• for an aircraft

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Magnetic compass
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Compass errors
Northerly Turning Errors The result is a false
northerly turn indication
Southerly Turning Errors The result is a false
southerly turn indication
Acceleration error When accelerating on either
an east or west heading , the error appears as a
turn indication toward north. When decelerating
on either of these headings, the compass
indicates a turn toward south.
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Pressure instruments
ADC Air Data Computer
ASI Airspeed Indicator
VSI Vertical Speed Indicator
Machmeter
Altimeter
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Pitot / static system
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Static port
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Pitot tube
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Pitot / static ports
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Pitot / static ports
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ASI Airspeed Indicator
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ASI errors
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ASI calibration
The Airspeed Indicator is calibrated to ICAO ISA
atmosphere Pressure 1013,25 hPa Temp
15C Density Standard MSL
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Speed definitions

• IAS Indicated Air Speed
• CAS Calibrated Air Speed (IAS
  corrected for installation and position error)
• EAS Equivalent Air Speed
• (CAS corrected for compressibility
  error)
• TAS True Air Speed
• (EAS corrected for density)

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VSI Vertical Speed Indicator

• The vertical airspeed specifically shows the rate
  of climb or the rate of descent, which is
  measured in feet per minute or meters per second

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Machmeter

• An aircraft flying at the speed of sound is
  flying at a Mach number of one, expressed as
  "Mach 1.0".

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Altimeter
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QFE / QNH

• The regional or local air pressure at mean sea
  level (MSL) is called the QNH or "altimeter
  setting", and the pressure which will calibrate
  the altimeter to show the height above ground at
  a given airfield is called the QFE of the field.
  An altimeter cannot, however, be adjusted for
  variations in air temperature. Differences in
  temperature from the ISA model will, therefore,
  cause errors in indicated altitude.

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QFE / QNH

• QFE Aerodrome elevation pressure
  (Altimeter indicate 0 ft height)
• QNH QFE reduced to MSL according ISA
• (Altimeter indicate aerodrome
  elevation)
• 1 hPa 27 ft

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QFE / QNH
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Height / Altitude

• Indicated height QFE as datum
• Indicated altitude QNH as datum
• True altitude corrected for temp and
• pressure

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Transition level / altitude
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ADC Air Data Computer

• Modern aircraft use air data computers (ADC) to
  calculate airspeed, rate of climb, altitude and
  mach number. Two ADCs receive total and static
  pressure from independent pitot tubes and static
  ports, and the aircraft's flight data computer
  compares the information from both computers and
  checks one against the other.

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Gyro
A gyroscope is a device for measuring or
maintaining orientation. This orientation
changes much less in response to a given external
torque than it would without the large angular
momentum associated with the gyroscope's high
rate of spin. Since external torque is minimized
by mounting the device in gimbals, its
orientation remains nearly fixed, regardless of
any motion of the platform on which it is
mounted. This stability increases if the rotor
has great mass and speed. Thus, the gyros in
aircraft instruments are constructed of heavy
materials and designed to spin rapidly
(approximately 10,000 rpm to 70,000 rpm).
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Attitude indicator
The purpose of the attitude indicator is to
present the pilot with a continuous picture of
the aircraft's attitude in relation to the
surface of the earth. The figure to the right
shows the face of a typical attitude indicator
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Heading indicator
HEADING INDICATOR The heading indicator, shown
in the figure to the right, formerly called the
directional gyro, uses the principle of
gyroscopic rigidity to provide a stable heading
reference. The pilot should remember that real
precession, caused by maneuvers and internal
instrument errors, as well as apparent precession
caused by aircraft movement and earth rotation,
may cause the heading indicator to "drift".
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Gyro drift
Because the earth rotates (apparent drift) and
because of small accumulated errors caused by
friction and imperfect balancing of the gyro
(real drift), the Heading Indicator will drift
over time, and must be reset from the compass
periodically. The HI cannot sense North like a
compass. The HI must be realigned with the
compass about every 10 minutes. You might say to
yourself, "Why don't I just use the compass?".
The compass can be very difficult to read because
it wobbles around. The HI is more stable and
easier to read, but it must constantly be
realigned.
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Flux gate
Some more expensive heading indicators are
'slaved' to a sensor (called a 'flux gate'). The
flux gate continuously senses the earth's
magnetic field, and a servo mechanism constantly
corrects the heading indicator. These 'slaved
gyros' reduce pilot workload by eliminating the
need for manual realignment every ten to fifteen
minutes.
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Non Precission Approach

• NDB Non Directional Beacon
• VOR VHF Omni-directional Radio range
• TACAN - TACtical Air Navigation

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MDH / MDA

• A minimum descent height (MDH) or minimum descent
  altitude (MDA) is the equivalent of the DA for
  non-precision approaches, however there are some
  significant differences. It is the level below
  which a pilot making such an approach must not
  allow his or her aircraft to descend unless the
  required visual reference to continue the
  approach has been established. Unlike a DA, a
  missed approach need not be initiated once the
  aircraft has descended to the MDH, that decision
  can be deferred to the missed approach point
  (MAP). So a pilot flying a non-precision approach
  may descend to the minimum descent altitude and
  maintain it until reaching the MAP, then initiate
  a missed approach if the required visual
  reference was not obtained.

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NDB

• Non-directional beacon
• NDBs typically operate in the frenquency range
  from 190 kHz to 535 kHz.

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NDB

• Other information transmitted by an NDB
• Automatic Terminal Information Service or ATIS
• Meteorological Information Broadcast or VOLMET

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ADF

• Automatic Direction Finder

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ADF receiver
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VOR

• VHF Omni-directional Radio Range

VORs are assigned radio channels between 108.0
MHz (megahertz) and 117.95 MHz (with 50 kHz
spacing) this is in the VHF (very high
frequency) range
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VOR receiver
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VOR

• VHF Omni-directional Radio Range

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VOR
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DME

• Distance Measuring Equipment

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Aircraft control pedestal
1. VHF COM 1. The frequency is on the STANDBY
(right) side and then transferred to the ACTIVE
(left) side with the TFR button in between. 2.
VHF COM 2. 3. ADF 1. The frequency can be set
on both sides. The TRF switch is used to select
the active side. 4. ADF 2. 5. SELCAL. 6.
Transponder and TCAS control panel. 7. Center
instrument and pedestal light switches.
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TACAN

• TACtical Air Navigation

TACAN in general can be described as the military
version of the VOR/DME system. It operates in the
frequency band 960-1215 MHz. The bearing unit of
TACAN is more accurate than a standard VOR.
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VORTAC
At VORTAC facilities, the DME portion of the
TACAN system is available for civil use.
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