As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
D: GOGO REPORTS THE LEFT ATG ANTENNA V-POL IS SHOWING LOW PERFORMANCE. REPLACE LH ATG ANTENNA. AFTER INSTALLATION PERFORM A VSWR TEST ON THE LH ATG ANTENNA PER STC ST04216AT DOCUMENT 170-2365-02-1002 PARA 3. P/N P17204 - ANTENNA, P/N P17972 - GASKET (C-CHECK) RO:1/22/2020REMOVED AND REPLACED LEFT HAND ATG ANTENNA REF EMB STC DOC. OPERATIONAL CHECK GOOD REF EMB STC. VSWR TEST GOOD REF EMB STC.