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IWETHEY Home / IWETHEY Board / News Picks Forum / Time for break from COVID-19...
Post #433,350
by scoenye
4/2/20 5:55:07 PM
4/2/20 5:55:07 PM
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New Time for break from COVID-19...
... we haven't heard from Boeing for a while
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 potentially catastrophic failure scenarios"
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. On top of all that, the stall warning horn and overspeed horn also stop working.

For some reason, we had to postpone our May trip to Belgium. Does anyone have a copy of the blueprints to the Titanic?
Post #433,353
by a6l6e6x
Picture of a6l6e6x
4/2/20 9:35:42 PM
4/2/20 10:52:18 PM
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New I bet there is a 32 bit counter for time in milliseconds that is used to timestep events.
On day 51 it overflows.

[edit add]

Did the math and overflow is on 49th or 50th day depending on when exactly in the day it was turned on.
Alex

"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."

-- Isaac Asimov
Expand Edited by a6l6e6x April 2, 2020, 10:52:18 PM EDT
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Post #433,383
by scoenye
4/4/20 10:19:21 AM
4/4/20 10:19:21 AM
Reply
New That is the general thought
Maybe they got a good deal on a load of "extended lifetime" timer chips, where each ms lasts 1.024 real ms.
Post #433,384
by drook
Picture of drook
4/4/20 10:47:47 AM
4/4/20 10:47:47 AM
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New Someone did the math, suggested 40(?) bit microseconds
32 bit milliseconds overflows at 49.7 days so rebooting every 51 wouldn't help. Because of their high speed planes might use microseconds for more accurate positioning.
--

Drew
Post #433,395
by a6l6e6x
Picture of a6l6e6x
4/4/20 9:59:20 PM
4/4/20 9:59:20 PM
Reply
New It must depend on what part of the many subsystems are monitored.
Summary information for pilot instruments is probably OK with milliseconds.

You are right that some subsystems need more precise resolution. GPS is down at the nanosecond level.
Alex

"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."

-- Isaac Asimov
Post #433,396
by pwhysall
Picture of pwhysall
4/5/20 5:25:57 AM
4/5/20 5:25:57 AM
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New Having seen bespoke industrial software up close...
...I hypothesise that there is a fixed-sized data structure with a number of event slots or similar, that can hold 52 days worth of data, and which is supposed to be overwritten in a circular manner.

Only the overwrite code is shit, so you end up with old data presented as current.

This data structure is not persistent between powercycles, hence the instruction to turn the plane off and on again every 51 days.

Or something.
Post #434,186
by CRConrad
5/27/20 7:54:25 AM
5/27/20 7:54:25 AM
Reply
New And it was originally planned as weeks, to hold a year's worth of data -- hence the 52?
Either that, or they took it from the B-52.
     Time for break from COVID-19... - (scoenye) - (6) - April 2, 2020, 05:55:07 PM EDT
         I bet there is a 32 bit counter for time in milliseconds that is used to timestep events. - (a6l6e6x) - (5) - April 2, 2020, 10:52:18 PM EDT
             That is the general thought - (scoenye) - (4) - April 4, 2020, 10:19:21 AM EDT
                 Someone did the math, suggested 40(?) bit microseconds - (drook) - (3) - April 4, 2020, 10:47:47 AM EDT
                     It must depend on what part of the many subsystems are monitored. - (a6l6e6x) - April 4, 2020, 09:59:20 PM EDT
                     Having seen bespoke industrial software up close... - (pwhysall) - (1) - April 5, 2020, 05:25:57 AM EDT
                         And it was originally planned as weeks, to hold a year's worth of data -- hence the 52? -NT - (CRConrad) - May 27, 2020, 07:54:25 AM EDT

But calm down, don't wet yourself over spotting one!
55 ms