The following information is derived from the FAA's Service Difficulty Reports and Aviation Maintenance Alerts.


p>Beechcraft C90 King Air

Antenna Blockage

Troubleshot both #1 and #2 GPS systems due to failures. The #2 antenna resistance checked okay, but any time the #2 GPS system was turned on, it blocked all GPS signals to aircraft. With the #2 GPS system turned off, the #1 GPS system operated with no problems. Installed new #2 antenna and both systems tested okay with no problems noted.

Part total time: Unknown


Cessna 172S Skyhawk SP

GPS Antenna Failure

The #2 GPS lost signal during RNAV approach with a warning message on the Garmin G1000 display. The antenna’s BNC connectors were found not crimped onto extender cables and the antenna was not properly sealed around its perimeter or fastener(s) at OEM installation. This allowed for water intrusion, corrosion and antenna failure. Replaced #2 antenna; ops checks were satisfactory.

Part total time: 4236.0 hours


Cessna 182T Skylane

Separated ELT Antennas

Operator reported four-plus failures of the whip ELT antenna. These antennas were installed under STC at the factory. One antenna became lodged between the left horizontal stabilizer and elevator. No control issues were noted.

Part total time: 500.0 hours


Piaggio P.180 Avanti

Faulty ADF Antenna Mount

Cabin pressurization was operating normally in manual mode until reaching 20,000 feet; then it began an uncontrolled climb. It did not respond to remedial actions; crew requested a descent. Crew was able to get control of pressurization descending through 15,000 feet msl. Inspection revealed the ADF antenna seal was leaking air. Removed, cleaned, reinstalled and resealed ADF antenna. Checked good on the ground.

Part total time: Unknown


Pilatus PC-12

Total GPS Failure

Aircraft suffered en route failure of four GPS devices, including a GTN 750 and 650, a portable WAAS GPS receiver and a Spidertracks flight tracker. The GTN 750 displayed an error message referencing antenna coax cable. The GTN 750 pilot guides offer no procedure referencing antenna coax message or total loss of independent GTN units.

The pilot radioed the company’s base and a help desk advised that this was likely caused by one of the two GTN units’ WAAS GPS antennas failing in a mode causing a “GPS oscillation signal” that will jam GPS reception. After securing the GTN 750, GPS satellite reception was restored on the remaining three devices, including the GTN 650. Recommend promulgating abnormal procedure guidance and redesigning antennas to eliminate this failure mode.

Part total time: 2675.0 hours


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