Re: F-22 Raptor software problem

[Markus E Leypold <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>]

"Bob Spooner" <rls19@psu.edu> writes:

> "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 


On would think that internal time keeping would always done in GMT or
with a counter with a fixed offset to GMT, esp. since GPS works with
GMT anyway.

Regards -- Markus