Enhancing situational awareness has long been a desirable circumstance in the world of aviation while providing the flight crew with necessary and wanted information has been a constant challenge for designers. Available space for equipment and instruments is almost always at a premium.
Minimum requirements are most often dictated depending on the basis for airworthiness. The majority of small single engine aircraft, at a minimum, will have an airspeed indicator, altimeter, and a compass. Living in the information age causes many to strive for more data and given technological advancements in recent times provides availability of precision navigation along with enhancements to protect against controlled flight into terrain (CFIT) as well as in-flight collisions.
Throughout the first 70 years in aviation anytime new technology was to be made available for flight deck viewing, an evaluation had to be conducted to assess available real-estate to locate the new instrument. In some situations it became necessary to combine displays in one device.
A well-equipped vintage machine may have every square inch of instrument panel occupied by some type of gauge or switching device and in the world of transport category aircraft, redundancy has always been an important facet requiring duplication. In an electro- mechanical environment swapping inputs to flight deck instruments requires significant engineering and finesse to accommodate the wide array of analog gizmos and gadgets.
The past 30 years has yielded significant technological breakthroughs in the realm of avionics. Electronic flight instrument systems started to appear and were fed digital data. It was realized early on they would revolutionize the flight crew’s ability to increase awareness plus reduce wiring along with ancillary components.
The concept enables flight crews to not only view required information but to also choose what supplemental data can be highlighted. Information transfer capability can provide immediate relief in the event of a single display failure. When reversionary modes are used it is often possible to transfer information from a failed indicator to a second display where the operator can choose to observe multiple or composite indications.
Cathode ray tube
A cathode ray tube (CRT) is a vacuum tube which consists of one or more electron guns, possibly internal electrostatic deflection plates, and a phosphor target. The entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a “raster.” An image is produced by controlling the intensity of each of the three electron beams, one for each primary color (red, green, and blue) with a reference signal.
In all modern CRT displays as well as televisions, the beams are deflected using varying electric fields produced by coils and driven by electronic circuits within the case. The brightness, color, and persistence of the illumination depends upon the type of phosphor used on the CRT screen. Phosphors are available with persistence ranging from less than one microsecond to several seconds. For visual observation of brief transient events, a long persistence phosphor may be desirable. For events which are fast and repetitive, or high frequency, a short-persistence phosphor is generally preferable.
Color tubes use three different phosphors which emit red, green, and blue light and are packed together in stripes or clusters called “triads.” Color CRTs have three electron guns, one for each primary color, arranged either in a straight line or in a triangular configuration (the guns are usually constructed as a single unit). A grille or mask absorbs the electrons that would otherwise hit the wrong phosphor. This type of display does have a tendency to degrade with age and over time will loose luminescence resulting in costly replacement. Display intensity can be controlled either by an external dimming circuit or by an ambient light sensor.
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