Gyroscopic Instruments: Critical Flight Instrument

There are several basic flight instruments located in the cockpit - they may be traditional physical instruments, or digitized. When a pilot gets their Instrument Flight Rules (IFR) rating, they are required to pilot the aircraft based on the information displayed on these instruments. Some of the indispensable instruments are the airspeed indicator, altimeter, attitude indicator, heading indicator, turn coordinator, and vertical speed indicator. They can be categorized based on corresponding systems that relay proper information to the instruments: the pitot-static system, the vacuum system, gyroscopic instruments, and the magnetic compass.

The International Standard Atmosphere (ISA) is a set of established “typical” atmospheric conditions which are used to standardize aircraft instruments - however, the reality is that atmospheric conditions vary greatly. As described by the ISA, as altitude increases, pressure and temperature decrease. With a decrease in altitude, the resulting effects are the opposite. It is pertinent to understand differences in these conditions and how to make the proper corrections - otherwise the pilot may think they’re at an altitude that they are not, or an airspeed that they are not.

The pitot-static system utilizes the static air pressure and dynamic pressure due to the motion of the aircraft through the air. The pressures are used to relay information to the airspeed indicator (ASI), altimeter, and the vertical speed indicator (VSI). An ASI utilizes both the static and pitot system in order to display the airspeed. Because the airspeed is measured based on the air density, the indicated airspeed may be false and need to be corrected. The altimeter displays the altitude, which is determined by measuring the air pressure outside the aircraft. Due to variations, corrections are made so that the altimeter displays an accurate reading. The VSI, also referred to as a vertical velocity indicator (VVI), shows the rate of climb or descent, which is displayed in feet per minute (fpm). If this instrument is calibrated properly, then it will be zero during level flight.

Gyroscopic instruments include the turn coordinator, heading indicator, and the attitude indicator. There are two types of turn indicators: the slip-and-slip indicator and the turn coordinator. The turn coordinator is the most common turn indicator used in training aircraft. It displays the rate and direction of a turn. The miniature aircraft printed on the instrument should meet the turn index because it indicates that the aircraft is following the standard-rate turn— 3° per second— and is used to avoid banking at steep angles.  A magnetic compass is accurate when the aircraft is still, but it becomes very difficult to read during flight. The heading indicator is used during flight because it’s not affected by the same forces as a magnetic compass during flight. It should be adjusted to match the magnetic compass before the aircraft starts moving. An attitude indicator contains a miniature aircraft and a horizon line— it shows the relationship between the aircraft's position relative to the horizon.

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1. alex marsh
2. Posted on April 4, 2019
aerospace

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