Instruments – part 1

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Magnetic compass

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Magnetic Northpole

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North Magnetic Pole (2005) 82.7° N 114.4°

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

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VARIATION WEST, MAGNETIC BEST, VARIATION EAST, MAGNETIC LEAST

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

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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.

Northerly Turning Errors:The result is a false northerly turn indication

Southerly Turning Errors:The result is a false southerly turn indication

Pressure instruments

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ADC: Air Data Computer

ASI: Airspeed Indicator

VSI: Vertical Speed Indicator

Machmeter

Altimeter

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

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The Airspeed Indicator is calibrated to ICAO ISA atmosphere

Pressure: 1013,25 hPa

Temp: +15C

Density: Standard MSL

Speed definitions

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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)

VSI Vertical Speed Indicator

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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

Machmeter

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

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

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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).

Attitude indicator

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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

Heading indicator

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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".

Gyro drift

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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.

Flux gate

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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.

Non Precission Approach

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NDB – Non Directional Beacon

VOR – VHF Omni-directional Radio range

TACAN - TACtical Air Navigation

MDH / MDA

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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.

NDB

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Non-directional beacon

NDBs typically operate in the frenquency range from 190 kHz to 535 kHz.

NDB

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Other information transmitted by an NDB

Automatic Terminal Information Service or ATIS

Meteorological Information Broadcast or VOLMET

ADF

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Automatic Direction Finder

ADF receiver

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VOR

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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

VOR receiver

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VOR

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VHF Omni-directional Radio Range

VOR

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DME

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Distance Measuring Equipment

Aircraft control pedestal

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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.

TACAN

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TACtical Air NavigationTACAN 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.

VORTAC

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At VORTAC facilities, the DME portion of the TACAN system is available for civil use.