Re: F-22 Raptor software problem

[Keith Thompson <kst-u@mib.org>]

Simon Wright <simon.j.wright@mac.com> writes:
> "peter koch" <peter.koch.larsen@gmail.com> writes:
>> On Feb 28, 8:44 am, Keith Thompson <k...@mib.org> wrote:
>>> I'm only guessing, but I doubt that the error was caused by using
>>> local time.  My suspicion is that the error occurred not when
>>> crossing the International Date Line (which is crooked, as you can
>>> see on a map), but when crossing the 180th meridian, when the
>>> longitude jumped from 179.909 to -179.990.
>
>> Yes - that makes far more sense. I had a very difficult time (!)
>> believe that the problem had anything to do with timezones.
>
> I could believe it if there were requirements to do something say
> every quarter-hour on the quarter-hour in local time. What seems hard
> to imagine in a military aircraft is the 'local time' part!

It would be easier to do something every quarter-hour in UTC; it will
be done at the sames, even in places with half-hour time zones.  And
an F-22 at top speed can cross a time zone in a few minutes.
Performing tasks that depend on local time wouldn't make much sense;
performing such tasks in a critical subsystem (which is what crashed)
makes even less sense.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center             <*>  <http://users.sdsc.edu/~kst>
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"