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Flight Instruments

Airspeed Indicator (ASI)

Flight Instruments

The ASI is a sensitive, differential pressure gauge which measures and promptly indicates the difference between pitot (impact/dynamic pressure) and static pressure. These two pressures are equal when the aircraft is parked on the ground in calm air. When the aircraft moves through the air, the pressure on the pitot line becomes greater than the […]

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Vertical Speed Indicator (VSI)

Flight Instruments

The VSI, which is sometimes called a vertical velocity indicator (VVI), indicates whether the aircraft is climbing, descending, or in level flight. The rate of climb or descent is indicated in feet per minute (fpm). If properly calibrated, the VSI indicates zero in level flight. [Figure 7-5] Although the VSI operates solely from static pressure, […]

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Altimeters (Part Six) Types of Altitude

Flight Instruments

Altitude in itself is a relevant term only when it is specifically stated to which type of altitude a pilot is referring to. Normally when the term altitude is used, it is referring to altitude above sea level since this is the altitude which is used to depict obstacles and airspace, as well as to […]

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Altimeters (Part Five) Altimeter Operation

Flight Instruments

There are two means by which the altimeter pointers can be moved. The first is a change in air pressure, while the other is an adjustment to the barometric scale. When the aircraft climbs or descends, changing pressure within the altimeter case expands or contracts the aneroid barometer. This movement is transmitted through mechanical linkage […]

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Altimeters (Part Four) Setting the Altimeter

Flight Instruments

Most altimeters are equipped with a barometric pressure setting window (or Kollsman window) providing a means to adjust the altimeter. A knob is located at the bottom of the instrument for this adjustment. To adjust the altimeter for variation in atmospheric pressure, the pressure scale in the altimeter setting window, calibrated in inches of mercury […]

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Altimeters (Part Three) Non Standard Pressure and Temperature

Flight Instruments

It is easy to maintain a consistent height above ground if the barometric pressure and temperature remain constant, but this is rarely the case. The pressure temperature can change between takeoff and landing even on a local flight. If these changes are not taken into consideration, flight becomes dangerous. If altimeters could not be adjusted […]

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Altimeters (Part Two) Principles of Operation

Flight Instruments

The pressure altimeter is an aneroid barometer that measures the pressure of the atmosphere at the level where the altimeter is located, and presents an altitude indication in feet. The altimeter uses static pressure as its source of operation. Air is denser at sea level than aloft—as altitude increases, atmospheric pressure decreases. This difference in […]

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Altimeters (Part One)

Flight Instruments

The altimeter is an instrument that measures the height of an aircraft above a given pressure level. Pressure levels are discussed later in detail. Since the altimeter is the only instrument that is capable of indicating altitude, this is one of the most vital instruments installed in the aircraft. To use the altimeter effectively, the […]

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Static Pressure Chamber and Lines

Flight Instruments

The static chamber is vented through small holes to the free undisturbed air on the side(s) of the aircraft. As the atmospheric pressure changes, the pressure is able to move freely in and out of the instruments through the small lines which connect the instruments into the static system. An alternate static source is provided […]

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