WAAS Upgrade Not Yet Working Well With PFDs

On Friday, Avidyne issued a mandatory service bulletin detailing information on known incompatibilities between Garmin 400W/500W series navigators and Avidyne Primary Flight Displays. It includes mandatory operational limitations for aircraft with certain combinations of equipment and recommends against new or updated installations in affected configurations.

Avidyne tells ANN the bulletin communicates important safety information concerning aircraft equipped with Avidyne EXP5000 Primary Flight Displays ("Avidyne PFDs") and Garmin 400W/500W-series navigators with WAAS ("Garmin WAAS navigators").

As Aero-News reported, Garmin recently introduced upgrades to its 400/500-series GPS navigators to incorporate support for the Wide Area Augmentation System (WAAS). The new models are designated the 400W/500W-series, and is available both as new production and as upgrades to previously purchased 400/500-series navigators.

Avidyne states many Garmin 400/500-series navigators are installed in airplanes equipped with Avidyne PFDs. When operators of those planes -- hoping to take advantage of the improved accuracy and added features of WAAS -- install the upgrade, however, it has caused serious incompatibility issues between the Garmin WAAS navigators, and the Avidyne PFDs.

The Garmin WAAS navigators make use of extended precision in transmitting course deviation data while on GPS approaches -- an extended precision that was not anticipated in the development of the Avidyne PFD, according to the company. As a result, the PFD may erroneously display a centered HDI/CDI needle on final approach... when an off-center indication is appropriate.

As of this date, there is no information in either Garmin’s installation data or Avidyne's installation data to indicate compatibility of this equipment, nor is there any approval basis in an STC held by Garmin or Avidyne or any TC held by any airplane manufacturer. Nevertheless, it has come to Avidyne's attention that upgrades of existing installations from 400/500-series navigators to 400W/500W-series navigators in airplanes equipped with Avidyne PFDs may have been performed via some form of field approval.

Avidyne says it is preparing a modification to the PFD that will correct the incompatibility. Until a compatible configuration of Avidyne PFD and Garmin WAAS navigators is installed, however, no GPS approaches of any type may be flown in affected aircraft. Only LOC, ILS and VOR approaches (by means of VOR, not by means of GPS) may be flown.

Avidyne also strongly recommends against upgrades of Garmin 400/500-series navigators to 400W/500W-series in affected airplanes until a compatible Avidyne PFD software version is available and installed.

Note: Avidyne IS hard at work on a significant upgrade to the software that powers the Entegra system, which will incorporate the necessary WAAS support. Availability is expected in 3Q/07. Additional info is now available at www.avidyne.com/products/release7.shtm.

FMI: www.avidyne.com, call 888-723-7592 for more information