Re: F-22 Raptor software problem

["Bob Spooner" <rls19@psu.edu>]

"peter koch" <peter.koch.larsen@gmail.com> wrote in message 
news:1172666017.141406.173400@v33g2000cwv.googlegroups.com...
> On Feb 28, 8:44 am, Keith Thompson <k...@mib.org> wrote:
>> "peter koch" <peter.koch.lar...@gmail.com> writes:
>> > On 26 Feb., 05:47, Hyman Rosen <hyro...@mail.com> wrote:
>> >> It's being reported (Slashdot, via CNN) that twelve of these
>> >> planes had their navigation and communications completely shut
>> >> down as they crossed the international date line while flying
>> >> from Hawaii to Japan. I believe much of the plane's software
>> >> is in Ada, but I have no details as to what caused the error.
>>
>> > It surprises me that the software had problems dealing with this
>> > problem in the first place. Why anyone uses "calender time" for
>> > anything but display purposes is simply beyond my comprehension.
>>
>> 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.
>>
>> I vaguely remember a similar problem with some air traffic control
>> software that was developed in the US, but wouldn't work in the UK,
>> because it couldn't handle a sign change in longitude.
>>
> Yes - that makes far more sense. I had a very difficult time (!)
> believe that the problem had anything to do with timezones.
>
> /Peter
>
If the navigation computer was calculating velocity as a change in position 
with respect to time and the time changed by a large (possibly negative) 
amount, something could have gotten out of range and caused a software 
crash.  Bob