The FAA is planning to issue an airworthiness directive mandating a software upgrade for certain GX-series GPS units from UPS Aviation Technologies, now a division of Garmin, known as Garmin AT. Software versions 3.0 through 3.4 for the units can give pilots momentarily inaccurate readings on their course deviation indicators. That could cause a slaved autopilot to begin an inappropriate turn.

"This is a known problem that UPSAT, and now Garmin, have been working with aircraft owners to correct for more than two years," said AOPA Senior Director of Advanced Technology Randy Kenagy. "UPSAT issued a service bulletin more than two years ago offering the necessary software upgrade for free. The FAA is now proposing to require the upgrade with the AD."

The AD would give GX-series owners six months to have their units' software upgraded.

Since Garmin purchased UPSAT, the company has committed to honoring UPSAT's promise of a free software upgrade for all GX-series owners, regardless of age. Garmin reports that as many as half of the nearly 1,200 affected units have already received the upgrade.

According to Garmin, the CDI may display incorrect course deviation indications for two to six seconds. The incorrect information is displayed only after a pilot has instructed the GPS to go "direct to" a waypoint. The GPS position or navigation information is never lost despite the momentary incorrect display.

Both the original UPSAT service bulletin and the proposed airworthiness directive are available online, or owners may contact Garmin AT at 800-525-6726.

FMI: www.faa.gov, www.garmin.com