Why do airplane in-flight entertainment systems require an under-seat electronics box?

n-flight Entertainment Systems have been on board commercial airplanes long before tablet computers (or even before the very first IBM PC, which came out in August 1981). The need to provide entertainment on long-distance flights was real, and once the American carriers started doing it, the others simply followed. The airline business is a very competitive industry and you have to “keep up with the Joneses”!

Early systems were hard-wired, with one pair of wires bringing one channel of audio to your earphones. There were several audio channels, along with a movie audio channel. Movies were displayed on overhead screens or bulkhead screens, just like in a theatre. There was no seat-back video. All you could see on the seat-back was the drop table. Not very interesting!

With the Boeing 747 generation of aircraft entering service in 1969, Inflight Entertainment started using digital multiplexing. Now you had more choice of audio channels (In Air India: US Pop, US Rock, Western Classical, Indian Classical, Indian Popular, and some Regional Music); the wires were reduced because the same pair of wires carried several channels of audio; and several electronic boxes made their appearance to decode all this audio. The movie shows still remained the same: overhead projection onto a common screen.

Technology kept advancing; in the 90’s, servers replaced movie projectors, seat-backs started having individual screens, and now the passenger had a much larger choice of audio, video, and even computer games. Now you were not forced to watch the same movie which the others in your zone were watching; you had a choice, although a limited one.

Has Netflix come to the sky, where you can pay and watch any movie or TV serial of your choice? Not yet.

Although not really connected with the technology, In-flight Entertainment Systems caused a horrific crash which caused a total of 229 fatalities on Wednesday 2 September 1998. Read all about Swissair Flight Number 111 SR 111 McDonnell Douglas MD-11
accident, 9 km (5.6 mls) SW off Peggy’s Cove, Nova Scotia:

“At 21:10 the pilots detected an unusual odour in the cockpit and began to investigate. They determined that some smoke was present in the cockpit, but not in the passenger cabin. They assessed that the odour and smoke were related to the air conditioning system. A Pan Pan radio call was made to Moncton ACC. The aircraft was about 66 nm southwest of Halifax. The pilots reported that there was smoke in the cockpit and requested an immediate return to a convenient place. The flight crew discussed internally the dumping of fuel based on the aircraft’s gross weight, and on their perception of the cues regarding the aircraft condition, and agreed to dump fuel. The flight was vectored to the south to dump fuel. At 21:24, both pilots almost simultaneously declared an emergency. The co-pilot indicated to the controller that they were starting to dump fuel and that they had to land immediately. Last radio contact was one minute later when they again declared an emergency. By now the fire had propagated, causing severe disturbances of the electric system. In the last minutes of the flight, the electronic navigation equipment and communications radios stopped operating. The aircraft descended over the dark waters off the coast of Nova Scotia until it stuck the water in a 20 degrees nose down and 110 degrees right bank……”

All because the wires of the Inflight Entertainment system heated up and caused smoke and fire!

“A segment of in-flight entertainment network (IFEN) power supply unit cable (1-3791) exhibited a region of resolidified copper on one wire that was caused by an arcing event. This arc was likely associated with the fire initiation event; however, it could not be determined whether this arced wire was the lead event…”.

Moral: Even “unimportant” systems, like In-Flight Entertainment, if not designed with due care, can cause a crash!