My handheld GPS Pilot III has lost sight of the satellite constellation
several times but only while I was cross country. The outages ranged
from several minutes to an hour. In several years of flying locally,
it has never failed to lock on and work perfectly. Even on cross
country flights it has only lost track a very small percentage of the
time. On one of those flights I suspect an antenna farm on the ground
was causing some interference but the other times I have no clue what
could have caused the loss of track.