aircraft instrumentation

aircraft instrumentation

Aircraft instrumentation

A coordinated group of instruments that provide the flight crew with information about the aircraft and its subsystems. These instruments provide flight data, navigation, power plant performance, and aircraft auxiliary equipment operating information to the flight crew, air-traffic controllers, and maintenance personnel. While not considered as instrumentation, communication equipment is, however, directly concerned with the instrumentation and overall indirect control of the aircraft.

Situation information on the operating environment, such as weather reports and traffic advisories, has become a necessity for effective flight planning and decision making. The prolific growth and multiplicity of instruments in the modern cockpit and the growing need for knowledge about the aircraft's situation are leading to the introduction of computers and advanced electronic displays as a means for the pilot to better organize and assimilate this body of information.

Instrumentation complexity and accuracy are dictated by the aircraft's performance capabilities and the conditions under which it is intended to operate. Light aircraft may carry only a minimum set of instruments; an airspeed indicator, an altimeter, an engine tachometer and oil pressure gage, a fuel quantity indicator, and a magnetic compass. These instruments allow operation by a pilotage technique.

Operation under low visibility and under Instrument Flight Rules (IFR) requires this same information in a more precise form and also requires attitude and navigation data. An attitude-director indicator (ADI) presents an artificial horizon, bank angle, and turn coordination data for attitude control without external visual reference. The attitude-director indicator may contain a vertical gyro within the indicator, or a gyro may be remotely located as a part of a flight director or navigational system. Flying through a large speed range at a variety of altitudes is simplified if the indicated airspeed is corrected to true airspeed for navigation purposes and the Mach number (M) is also shown on the ADI for flight control and performance purposes. Rate-of-climb is provided by an instantaneous vertical-speed indicator (IVSI). Heading data are provided by a directional gyro or data derived from an inertial reference system.

Navigation aids include: very-high-frequency omnidirectional radio ranges (VOR) that transmit azimuth information for navigation at specified Earth locations; distance-measuring equipment (DME) that indicates the distance to radio aids on or near airports or to VORs; automatic direction finders (ADF) that give the bearing of other radio stations (generally low-frequency); low-range radio altimeters (LRRA) which by radar determine the height of the aircraft above the terrain at low altitudes; and instrument landing systems (ILS) that show vertical and lateral deviation from a radio-generated glide-path signal for landing at appropriately equipped runways. Some inertial navigation systems include special-purpose computers that provide precise Earth latitude and longitude, ground speed, course, and heading.

Engines require specific instruments to indicate limits and efficiency of operation. For reciprocating engines, instruments may display intake and exhaust manifold pressures, cylinder head and oil temperature, oil pressure, and engine speed. For jet engines, instruments display engine pressure ratio (EPR), exhaust gas temperature (EGT), engine rotor speed, oil temperature and pressure, and fuel flow. Vibration monitors on both types of engines indicate unbalance and potential trouble.

Depending on the complexity of the aircraft and the facilities that are provided, there is also an assortment of instruments and controls for the auxiliary systems.

Electronic technology developments include: ring laser gyros, strap-down inertial reference systems, microprocessor digital computers, color cathode-ray tubes (CRT), liquid crystal displays (LCD), light-emitting diodes (LED), and digital data buses. Application of this technology allows a new era of system integration and situation information on the aircraft flight deck and instrument panels. Commercial jet transports will use digital electronics to improve safety, performance, economics, and passenger service. The concept of an integrated flight management system (FMS) includes automatic flight control, electronic flight instrument displays, communications, navigation, guidance, performance management, and crew alerting to satisfy the requirements of the current and future air-traffic and energy-intensive environment.

Effective flight management is closely tied to providing accurate and timely information to the pilot. The nature of the pilot's various tasks determines the general types of data which must be available. The key is to provide these data in a form best suited for use. If the pilot is not required to accomplish extensive mental processing before information can be used, then more information can be presented and less effort, fewer errors, and lower training requirements can be expected. Computer-generated displays offer significant advances in this direction.

The electronic horizontal-situation indicator (EHSI) provides an integrated multicolor map display of the airplane's position, plus a color weather radar (WXR) display. The scale for the radar and map can be selected by the pilots.