As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EMERGENCY DECLARED, EQUIP OVRHT MSG @ FL 390. DID QRH CHECKLIST YET MSG REMAINED. WENT AWAY @ 1200" AGL. ALSO REF 21-58-00-710-802-011 STEP D. AND STEP E. NO OVER HEAT NOTED. INSTALLED FWD AIR FILTER REF AMM 21-58-21-201 OPS CHECK GOOD SEE ATTACHED PICTURE FOR OLD FILTER.