Avionics Technology: Cabin Entertainment Systems

I can remember back as a kid flying on the airlines, the unusual noises, wonderful sights, and sensations associated with the motions of powered flight were an endless source of amusement. When the initial excitement wore off there was the colorful collection of switches and knobs within easy reach of the cabin seat and I found out at an early age, if you pushed the little button enough times that made the funny chiming noise the stewardess would almost always appear with crayons and an airplane coloring book or a deck of cards. As I grew older I noticed many of the adult passengers writing reports and letters or reading books and magazines. Being a male teenager in the 1960s, simply watching the stewardess was all the entertainment I needed. So why is it any different today?

The fundamentals of life

It is of course the media availability; cell phones, laptops, Ipods, and even DVDs are terms that have only in recent times become a trademark of life in this day and age.

Air travel today has changed significantly; we now transport hundreds of passengers thousands of miles. So how do you deprive all of these people of the fundamentals of life when they are commuting the 18 hours from Houston to Tokyo? The answer is simple, give them what they want! 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. Power ports can be installed in accessible locations to the passengers providing ample energy to use laptop computers along with other personal electronic equipment. Noise-canceling headsets block airplane noise while delivering audio with acoustic qualities on the level of the finest performance halls.

Lighting

Lighting methods are a crucial part of passenger comfort and in some systems cabin lights are integrated within the same control network as audiovisual and even temperature control. Cabin reading lights can be finely tuned to meet the requirements of the most optically critical user.

Selecting and maintaining reading light systems can become quite challenging. Lamps are often broadly classified as spot and flood. Choosing an appropriate light involves more than just proper wattage, it can involve factoring in the primary target distance from the lamp, area of coverage and intensity, and in some cases diffusers are used to provide specific filtration of the light beam. One recent event involving scheduled replacement of reading lamps in a specific business aircraft revealed the original part number lamp was no longer available and the aircraft manufacturer suggested what it considered to be a suitable replacement. The technician noted the wattage stamped on the bulb housing was the same as the original and proceeded to install the recommended replacement.

During the operational test, it was noted that when more than two-thirds of the lamps were operating the circuit breaker would pop. It made no difference which lamps were turned on. Investigation soon revealed the wattage on the replacement lamp was for operation in a 24-volt circuit while the original was rated at 28 volts.

Music, news, and television

It used to be if you wanted to listen to music in an aircraft, you had to tune the Automatic Direction Finder (ADF) to the frequency of a local commercial broadcast AM radio station and then figure out how to couple it to the aircraft Public Address (PA) system.

Now music options are not so limited as many commercial stations are broadcast on a satellite network, compact discs and even audio cassettes can be obtained and transported easily. In the case of the commercial airlines on many flights of long duration, enormous audio files can be accessed through control panels available to each passenger and individual headsets eliminate the need for majority rule in deciding what type of music will be played.

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.

Information available to the video monitor may be from several sources. DVD players are becoming as common in aircraft as in the family car. One consideration when installing a DVD is to consider its interface both mechanically and electrically to the aircraft and to also consider the average commercial life of most consumer electronics is about two years. If extensive modification will be required to replace the device after several years in service, perhaps purchase of a spare unit should be considered as part of the initial installation.

Cabin management systems computers

Cabin management systems are being utilized by many manufacturers of transport aircraft as a means of tying together most of the systems that effect passenger comfort.

Giving passengers individual control of what they see and hear is one of the main objectives along with automating certain safety briefings and in-flight messages. Some manufacturers of this type of equipment use a central computer as the brains for managing cabin functions. When a passenger dons a headset and makes an audio selection it is this computer that makes it all possible. In addition to switching functions it is not unusual for a device such as this to include an audio equalizer for each passenger position, so each output can be individually pre-selected. The adjustments are made by installing an external laptop computer and running a system specific software program. Once all the adjustments are made they are saved in the cabin management computer, but also need to be saved either within the laptop or on some other type of external information storage media.

In the event the cabin management computer is replaced, the unit being installed is loaded with only the factory settings and it may take close to a full day to reprogram each of the passenger positions with the specifics of that position. Having a software backup of the aircraft’s specific settings will greatly facilitate the computer replacement as the data reload may now take only minutes.

Considering computer technology, when working with a personal computer and a glitch occurs, often the only option left if CTRL + ALT + DEL is not effective is to re-boot. This is a condition where the computer power is removed for a short time followed by a re-start.

This is an infrequent but sometimes necessary requirement for computerized cabin management systems. The means of interacting with cabin management computers may involve using touch screens, actuating switches, or remote control devices. Remote units are identified as either infrared (IR) or radio frequency (RF). Both kinds typically work equally as well but the pros and cons should be considered prior to selecting one over the other. When using IR equipment the location of the sensor is very important. If the light beam is interrupted so is the information path. A sensor that is located where it is readily exposed to direct sunlight may also hamper the operation by making the command signal from the handheld device unreadable.

RF technology on the other hand does not care if the sending unit is aligned with the sensor, as it is transmitting radio signals in all directions. A common concern with this type device is if other wireless systems are in use the data stream may be corrupt. As an example a certain business aircraft using a wireless RF mouse has a condition where the mouse is not usable when the aircraft is in the hangar. When the aircraft is moved out on the ramp, the mouse works. The hangar is wired for a wireless computer network which distorts the mouse signal.

Personal electronic equipment concerns

Using personal electronic equipment onboard an aircraft is something that has gotten the attention of Airworthiness officials. Recent advisories have been issued that significantly impact outfitting cabins in transport aircraft with COTS devices. Among other things being addressed are outlets for AC power. The concern of course is that passengers won’t realize the outlet power in the aircraft is not exactly like what they have at home. One of the new requirements is that the FAA is limiting individual outlets to a maximum of 200 watts and the outlet has to be self-disabling. In addition modifying an existing AC power system by adding outlets may require a Supplemental Type Certificate (STC).

I guess entertainment is really a personal choice and where some people are easily amused others require complex devices to hold their attention. It seems everything is relative; 40 years ago the airlines were providing passengers many of the comforts that were appropriate for that point in time. I have now been forced to succumb to sleeping while winging my way to the next destination. I sometimes wonder if that choice is resentment to new technology or perhaps just an effect of age. Must be technology!

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