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

In-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:

ASN Aircraft accident McDonnell Douglas MD-11 HB-IWF Peggy’s Cove, NS

 “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!

It’s only the old ones. If you look for instance at the A340-600 from LH they changed to a new system without the box and with a very decent screen – even in economy.