Augmentation & Assistance

Failure Imminent for WAAS GEO Satellite

April 15, 2010 By: Eric Gakstatter

The Federal Aviation Administration (FAA) announced that one of the two WAAS GEO satellites will drift out of usable orbit within two to four weeks. Earlier this week, Intelsat announced it had lost control of its Galaxy 15 satellite that hosts the WAAS SBAS transponder used by the FAA.

Intelsat Galaxy 15 satellite that has failed

The FAA says it is monitoring the satellite, but that failure is imminent. When G-15 is out of usuable orbit, WAAS will be disrupted for users in northwest Alaska. The rest of the WAAS service area — U.S., Canada, Mexico — will operate normally but will be reduced to a single point of failure with only one WAAS broadcasting satellite remaining (PRN 138).

The FAA is investigating at least two alternatives:

Utilize Inmarsat 3 (POR) that was previously used by WAAS before switching to Galaxy 15 in 2006. POR is located at 178°E.
Accelerate the testing of Inmarsat 4-F3 (PRN 133). Testing is already in progress and due to be complete in December 2010. The FAA stated that there is "potential to implement as an emergency release."

Neither of these two solutions is an immediate one. The FAA stated that integrating POR back into operational WAAS would take 12-16 months. The quickest solution is to accelerate the implementation of PRN 133, of which the FAA said they might be able to shave 1-2 months from the original target date.

The FAA also reported that with only a single WAAS GEO broadcasting satellite, users may experience a temporary loss of service 3-5 times this year for up to five minutes each while WAAS Uplink Station Switchovers occur.

It's fortunate for WAAS users that PRN 135 is the problem instead of PRN 138, which is more centrally located in the WAAS service area at 107°W. The following graphic depicts the coverage footprints for PRN 138 and PRN 135.