Were airlines appropriately cautious they would park them for a few days while the initial readback of the FDR and CVRs was done. They should not wait for a government order to do so.
I see there was also another time problem / counter rollover identified on 787 that fits the symptoms very well:
"More trouble for Dreamliner as Federal Aviation Administration warns glitch in control unit causes generators to shut down if left powered on for 248 days"
"The US air safety authority has issued a warning and maintenance order over a software bug that causes a complete electric shutdown of Boeing’s 787 and potentially “loss of control” of the aircraft.
In the latest of a long line of problems plaguing Boeing’s 787 Dreamliner, which saw the company’s fleet grounded over battery issues and concerns raised over possible hacking vulnerabilities, the new software bug was found in plane’s generator-control units.
The plane’s electrical generators fall into a failsafe mode if kept continuously powered on for 248 days. The 787 has four such main generator-control units that, if powered on at the same time, could fail simultaneously and cause a complete electrical shutdown.
We are issuing this AD [airworthiness directive] to prevent loss of all AC electrical power, which could result in loss of control of the aeroplane,” said the Federal Aviation Administration directive. “If the four main generator control units (associated with the engine-mounted generators) were powered up at the same time, after 248 days of continuous power, all four GCUs will go into failsafe mode at the same time, resulting in a loss of all AC electrical power regardless of flight phase.”
https://www.theguardian.com/business...oss-of-control
Per the AD:
We have been advised by Boeing of an issue identified during laboratory testing.
The software counter internal to the generator control units (GCUs) will overflow after
248 days of continuous power, causing that GCU to go into failsafe mode. If the four
main GCUs (associated with the engine mounted generators) were powered up at the
same time, after 248 days of continuous power, all four GCUs will go into failsafe mode
at the same time, resulting in a loss of all AC electrical power regardless of flight phase.
https://s3.amazonaws.com/public-insp...2015-10066.pdf
This is superseded by AD 2018-20-15 to install new software. See
https://ad.easa.europa.eu/ad/US-2018-20-15 et al.
SUMMARY: We are superseding Airworthiness Directive (AD) 2015-09-07, which applied to all
The Boeing Company Model 787 airplanes. AD 2015-09-07 required a repetitive maintenance task
for electrical power deactivation. This AD requires installing new software for the generator control
unit (GCU). This AD also removes certain airplanes from the applicability. This AD was prompted
by the determination that a Model 787 airplane that has been powered continuously for 248 days can
lose all alternating current (AC) electrical power due to the GCUs simultaneously going into failsafe
mode. We are issuing this AD to address the unsafe condition on these products.
The 22 day version refers to a similar counter bug in the computers for flight controls.