What was found
UNSCHEDULED LANDING AT SAT DUE TO PRESSURIZATION FAILURE IN BOTH A/C PACKS WHEN USING ENGINES ANTI-ICE. ENGINES ANTI-ICE SET UP BOTH A/C PACKS CUT OUT. ACCOMPLISHED ABNORMAL PROCEDURE & OXYGEN MASKS DEPLOYED. MECHANIC PERFORMED PRESSURIZATION TESTS TO BOTH A/C PACKS, WORKED CORRECTLY. RELEASED TO SERVICE. FDR CHANGED IN ORDER TO ACCOMPLISH THE READ OUT AND TEST PROCEDURE. ACFT FERRIED TO MEX. FAILURE DID NOT PRESENT AGAIN DURING THE FT, THE A/C PACKS & PRESSURIZATION OPS CORRECTLY. DURING OVERNIGHT CHECK IN MEXICO, A/C PACKS TESTED IN AUTOMATIC & MANUAL MODE, ANTI-ICE SYS & A/C WERE TESTED IN MODE 1 & MODE 2. ENGINE ANTI-ICE TESTED IAW APPLICABLE MM. BEING ALL CORRECT. NOCOMPONENTS REPLACED.