1337Delta764 From United States of America, joined Oct 2005, 6423 posts, RR: 2 Posted (2 years 7 months 3 weeks 21 hours ago) and read 3046 times:
I have heard some stories about reading lights on particular aircraft randomy flashing like disco lights. It especially seems to be reported more often on widebodies, especially the 767.
I was wondering, what would be the cause of this? I know that on most widebodies, reading lights are controlled by in-seat buttons or through the IFE system, rather than having buttons directly on the PSU. However, why does it seem to occur more often on 767s (espcially non-Signature Interior) than any other aircraft?
The Pink Delta 767-400ER - The most beautiful aircraft in the sky
767eng From United Kingdom, joined Oct 2010, 49 posts, RR: 0
Reply 1, posted (2 years 7 months 3 weeks 20 hours ago) and read 3022 times:
It's because the system is run on a multiplex basis which saves on wiring , all the signals are sent down the same wires but seperated into chunks of data.
This data is timed by something called a column timer decoder which in laymans terms is a clock based unit which takes each portion of data and decides which seat it came from and what that seat has asked for.
As each piece of data is generated by a box underneath your seat (called an SEB or Seat Electronics Box) this chunk of data needs to be timed to perfection so the CTD at the other end knows where the signal came from.
Unfortunately as the system gets older, the SEBs become less tolerant to temperature changes and in general become cranky old men and start getting their timing and signals all messed up.
The CTD gets all these messed up out of time signals and starts firing off commands to the reading light and call lights hence the disco light effect.
It's normally cured when the aircraft has warmed up a bit, just like an old CRT television which comes good when warmed up. If not you have to track down the cranky old man SEB and replace him with a nice new one. Sometimes it's several at once and can be a bit of a pig to track down.
High resistance joints, or faulty end of seat column terminating resistors can also be the culprit.