Since the beginning of manned flight, it has been recognized that supplying the pilot with information about the aircraft and its operation could be useful and lead to safer flight. The Wright Brothers had very few instruments on their Wright Flyer, but they did have an engine tachometer, an anemometer (wind meter), and a stop watch. They were obviously concerned about the aircraft’s engine and the progress of their flight. From that simple beginning, a wide variety of instruments have been developed to inform flight crews of different parameters. Instrument systems now exist to provide information on the condition of the aircraft, engine, components, the aircraft’s attitude in the sky, weather, cabin environment, navigation, and communication. Figure 1 shows various instrument panels from the Wright Flyer to a modern jet airliner.
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| Figure 1. Top: instruments of the Wright Flyer, instruments on a World War I era aircraft, and a late 1950s/early. Bottom: 1960s Boeing 707 airliner flight deck, and an Airbus A380 glass flight deck |
The ability to capture and convey all of the information a pilot may want, in an accurate, easily understood manner, has been a challenge throughout the history of aviation. As the range of desired information has grown, so too have the size and complexity of modern aircraft, thus expanding even further the need to inform the flight crew without sensory overload or overcluttering the cockpit.
As a result, the old flat panel in the front of the cockpit with various individual instruments attached to it has evolved into a sophisticated computer-controlled digital interface with flat-panel display screens and prioritized messaging. A visual comparison between a conventional cockpit and a glass cockpit is shown in Figure 2.
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| Figure 2. A conventional instrument panel of the C-5A Galaxy (left) and the glass flight deck of the C-5B Galaxy (right) |
There are usually two parts to any instrument or instrument system. One part senses the situation and the other part displays it. In analog instruments, both of these functions often take place in a single unit or instrument (case). These are called direct-sensing instruments. Remote-sensing requires the information to be sensed, or captured, and then sent to a separate display unit in the cockpit. Both analog and digital instruments make use of this method. [Figure 3]
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| Figure 3. There are two parts to any instrument system—the sensing mechanism and the display mechanism |
The relaying of important bits of information can be done in various ways. Electricity is often used by way of wires that carry sensor information into the cockpit. Sometimes pneumatic lines are used. In complex, modern aircraft, this can lead to an enormous amount of tubing and wiring terminating behind the instrument display panel. More efficient information transfer has been accomplished via the use of digital data buses. Essentially, these are wires that share message carrying for many instruments by digitally encoding the signal for each. This reduces the number of wires and weight required to transfer remotely sensed information for the pilot’s use. Flat-panel computer display screens that can be controlled to show only the information desired are also lighter in weight than the numerous individual gauges it would take to display the same information simultaneously. An added bonus is the increased reliability inherent in these solid-state systems.
The following series introduces the fundamental aircraft instrument systems used in aviation, beginning with traditional analog instruments and progressing to modern electronic and digital flight display systems.
Instrument Systems Series
1. Classifying Instruments
Basic categories of aircraft instruments and their operational purposes.
View Topic →2. Pressure Measuring Instruments
Aircraft instruments that measure pressure for altitude and airspeed indications.
View Topic →3. Remote Sensing and Indication
Principles of sensing data remotely and displaying it in the cockpit.
View Topic →4. Mechanical Movement Indicators
Mechanical mechanisms used to convert sensor input into instrument display.
View Topic →5. Temperature Measuring Instruments
Systems used to measure and display temperature parameters in aircraft.
View Topic →6. Direction Indicating Instruments
Instruments used to determine and display aircraft directional heading.
View Topic →7. Sources of Power for Gyroscopic Instruments
Power systems used to operate aircraft gyroscopic instruments.
View Topic →8. Principles of Gyroscopic Instruments
Fundamental gyroscopic principles used in aircraft attitude and heading instruments.
View Topic →9. Common Gyroscopic Instruments
Overview of attitude indicators, heading indicators, and turn coordinators.
View Topic →10. Auto Pilot System
Introduction to automatic flight control systems used in aircraft.
View Topic →11. Autopilot Components
Major components and operation of aircraft autopilot systems.
View Topic →12. Automatic Flight Control System (AFCS)
Integrated systems used to automatically control aircraft flight.
View Topic →13. Flight Director Systems
Systems that provide visual flight guidance cues to the pilot.
View Topic →14. Electronic Instruments
Electronic instrument systems used in modern aircraft.
View Topic →15. Electronic Flight Information Systems
Integrated digital displays used in modern glass cockpits.
View Topic →16. Flight Management System (FMS)
Computer systems that manage navigation, performance, and flight planning.
View Topic →17. Warnings and Cautions
Aircraft systems designed to alert pilots of abnormal conditions.
View Topic →18. Clocks
Aircraft timing instruments used for navigation and operational tasks.
View Topic →19. Instrument Housings, Handling, Installations and Markings
Standards for instrument installation, handling, and identification.
View Topic →20. Maintenance of Instruments and Instrument Systems
Maintenance practices for aircraft instrument systems and components.
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