Unusual Honeywell KLN94 aviation GPS failure - what could causethis?

On 09/11/06 13:54, Peter wrote:
Dave S wrote

How long were you in a static position on the ground? Less than 15 mins
or more than 15 mins?

In a static position, maybe 5 mins. Then another 10 mins before
getting airborne.

The issue is that *if* the box lost it's position (for whatever reason),
that unless it's sitting still for up to 15 minutes, it may take it
quite a while to determine it's position (I presume this is due to
problems it has in determining it's position while it's moving).


For whatever reason, if the box has "lost itself"
with regards to its last known position, or if the box is powered up
more than 50 or so miles away from its last known position, it can take
"a while" to find itself, and my understanding is that you need to be
still while this is happening. This process can be accelerated by
entering your current position into the box on one of the menu screens.

The thing is that I have done 600hrs behind this box, and have never
had this before.

Once in 600 hours qualifies as an intermittent problem. What he was
suggesting is that if there was a battery glitch (while the unit was
turned off), then it may have lost its *memory* of its position,
necessitating the longer start-up time.


Normally, you switch it on, and as reliable as clockwork it starts up
and is ready in a few minutes. Same during flight.

This assumes it remembers where it was when it was switched off. The
owner's manual talks about this issue (actually, this is true of all
GPS units, both aircraft and personal that I've ever used).


I've got two 89 series GPS's on my workbench, one of which will be used
for an upcoming experimental installation. My only references into this
matter are dealing with those two boxes, and the installation manual for
the 89 series.

You say the problem is fixed now, as in, not recurred?

That's correct.

Do you have any
user defined waypoints? If there are/were, and are not now, this might
point to a problem in the memory (powered by that little battery)..
maybe there is an intermittent break in the power supply. You indicated
the box was opened within the past few months - could be pertinent in
troubleshooting this item.

How would the loss of the battery power prevent the GPS getting a
satellite lock?

See above. It doesn't prevent it really ... but it can make it take
longer. Moving the GPS before it's done with this can make it take
even longer.


Unless somebody can find a clue in the data next to the individual
satellites, or the date+time+location, I suspect this is a rare bug in
the firmware.

That's possible regardless of what people find, I suspect.


Of course if it happens again then I have a duff unit...

okay.



--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA