(2008) Service Advisory 0838 Rev A: GPS/WAAS Loss of Reception in Alaska, Northwest Canada, and Eastern Russia

AFFECTED PRODUCTS

All G1000, Cirrus Perspective, G900X, GPS 400W/GNC 420W/GNS 430W/GPS 500W/GNS 530W and GNS 480 (CNX80) units with GPS/WAAS are affected.

DESCRIPTION

It has been reported to Garmin that operators using Garmin GPS/WAAS equipped units have been experiencing GPS/WAAS receiver resets, resulting in a temporary loss of navigation. The problem may occur only during certain satellite conditions and only in latitudes north of 60°N that include WAAS coverage. These occurrences are related to the receiver’s interaction with the newly expanded WAAS coverage in Alaska and Northern Canada.

During the reset of the GPS/WAAS receiver, the receiver will not provide a position for approximately two minutes. The unit will function in dead reckoning (DR) mode during those two minutes. The condition and type of operation are annunciated to alert the flight crew of the loss of GPS/WAAS position data. The byproduct result is only a reset of a GPS/WAAS receiver; the condition does not result in any erroneous or misleading information being displayed or otherwise used in the system.

ACTION RECOMMENDED

Operators in the area where the problem occurs can disable the WAAS functionality on their Garmin equipment as the GPS receiver is not affected (does not reset) when WAAS is disabled. This will limit the capability of the unit, but it will also ensure that there is no interruption of GPS position data.

In some installations, operators having two GPS/WAAS receivers may disable WAAS functionality on one unit to ensure there is no interruption in position service, while preserving the WAAS functionality at the aircraft level (outside of the potential two minute position interruption). In the G1000, Cirrus Perspective, and G900X systems there is no way to disable WAAS functionality on one GPS/WAAS receiver; if WAAS functionality is disabled in these systems then it is disabled for the entire system.

For G1000, Cirrus Perspective, G900X installations and installations with a single 400W/500W Series and GNS 480 (CNX80) unit:

Disabling WAAS functionality will result in the inability to perform LNAV/VNAV and LPV approach operations. LNAV approach operations, terminal operations (e.g., departures and arrivals), and en route operations are not affected with WAAS functionality disabled. Pre-flight planning should include a RAIM availability check at the destination airport when planning to use the GPS receiver without WAAS as the basis for an approach.

For installations with two 400W/500W Series or GNS 480 (CNX80) units that choose to disable WAAS functionality on only one unit:

To ensure continuity in position service if a reset occurs, operators should make appropriate adjustments to crew contingency procedures/training in case a WAAS receiver reset occurs (e.g., revert to receiver that has WAAS disabled and use LNAV minima).

Note: To ensure TAWS-B availability is unaffected by the potential GPS/WAAS receiver reset, it is recommended that WAAS functionality be disabled when operating in the affected geographic region.

INSTRUCTIONS FOR DISABLING WAAS FUNCTIONALITY

Service Advisory 0838 Rev A

RESOLUTION

A future software release for each product will correct this issue and will be made available once completed.