Stefan Mileschin

This will stop catastrophes

The US Federal Aviation Administration has ordered Boeing 787 operators to switch their aircraft off and on every 51 days to prevent what it called several potential catastrophes.

Apparently, this includes the onboard network switches crashing which we assume would be followed by the aircraft.

The airworthiness directive, due to be enforced from later this month, orders airlines to power-cycle their B787s before the aircraft reaches the specified days of continuous power-on operation.

Power cycling is needed to prevent stale data from populating the aircraft's systems, where it sits around and makes a nuisance of itself. This has happened before on different 787 systems in the past but no one has actually thought of writing a bit of code to get rid of it.

According to the directive itself, if the aircraft is powered on for more than 51 days this can lead to "display of misleading data" to the pilots, with that data including airspeed, attitude, altitude, and engine operating indications. The stall warning horn and overspeed horn stop working which means that, unless the aircraft has a backup brass section it is good night Vienna.

The 787's common core system (CCS) is a Wind River VxWorks realtime OS product loses the will to filter out stale data from key flight control displays. That stale data-monitoring function going down in turn "could lead to undetected or unannunciated loss of common data network (CDN) message age validation, combined with a CDN switch failure".

It is easy to fix if you power the aircraft down completely before reaching 51 days nothing bad can happen. But it is usual for commercial airliners to spend weeks or more continuously powered on so it means that someone has to remember to do it.
https://fudzilla.com/news/50598-boei...f-and-on-again