Avionics Technology: Cabin Entertainment Systems

Aircraft entertainment systems currently in use can do it all. They provide music, videos, games, Internet access, and even display aircraft facts such as altitude and position.

Systems such as the Collins Airshow enable passengers to view information relative to the flight such as current aircraft position, speed, altitude, and time to destination. In addition the Airshow can also display various services like news, weather, and business reports.

Satellite television is also finding its way into numerous business and commercial aircraft and the subscription service is cheap insurance so company CEOs won’t miss the latest episodes of their favorite shows. This technology utilizes a steerable antenna that is driven by an onboard computer, which tracks the satellite constellation using information obtained from the aircraft navigation system. The computer will steer the antenna so that it is always pointing to the appropriate satellite.

The challenges of off-the-shelf

General aviation is still dependent on commercial off- the-shelf (COTS) equipment, much of which has been created for the automotive industry. Use of these devices often produces challenges for those installing and maintaining the units.

One such challenge is providing operating power. Most automotive systems require 12 to 14v DC while standard aircraft power is 24 to 28v DC. Much of today’s equipment will utilize an internal memory to either maintain a clock function or store preselected functions, and keeping power on the memory while the aircraft is parked has stymied many an installer.

One such system installed in a King Air by a refurbishment center used a relay that would energize anytime aircraft entertainment system power was available and would deliver the aircraft 28 volts to a power converter which in turn would deliver the 14 volts needed for the FM radio cassette player to operate. When the relay was deactivated a 9-volt battery was connected through a secondary contact to supply memory operating power. On one fateful day the relay developed an internal electrical short allowing 28 volts to be directed to the memory causing irreparable damage to the player plus producing smoke in the aircraft cabin. Like with other systems on the aircraft, a program of routine maintenance is advisable for cabin equipment and should include cleaning of media readers as well as replacement of backup batteries.

Audio quality in an aircraft cabin is often an area of frustration. The cabin size, orientation of furnishings, types of materials used, and prevalence of external noise are only some of the factors that will influence audio characteristics. Wiring used for speakers and headphones is another factor that can impact sound quality as electrical induction all too often will distort or disrupt the clarity. Close attention should be paid to wire routing when planning installations or troubleshooting audio malfunctions.

Video systems can be every bit as challenging to support as audio. Liquid crystal displays (LCD) are a common device to deliver the video image. The selection of monitors used in aircraft are pretty much a consumer’s preference. Of course there are the issues of what is considered suitable for installation in an aircraft.

Selection and certification

An organization known as the Radio Technical Commission for Aeronautics (RTCA) has established guidelines that provide standards for component selection and certification. Video displays for aircraft are available in a variety of sizes as well as means of attachment. In some cases large area monitors may be located on bulkheads, and with flat panel technology, variations in monitor size and mobile articulating arm positioning, passenger convenience is a nonissue.

Like with audio speakers, wiring for video systems is a major concern. Most of the information for display is transmitted in a digital format. This means digital busing requires adherence to proper impedance. The factors include resistance, capacitance, and inductance. In short, a digital bus is typically a pair of twisted insulated wires that are then shielded. The impedance of which can be affected by too tight a bend or even a wire tie that has been pulled excessively. Improperly terminated shields can also influence the buses’ ability to properly carry electronic data.

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