747-400 GPWS/EGPWS upgrade question
We have some pre 2000-build -400s which had factory fitted Honeywell GPWS. Operator upgraded to EGPWS through local airworthiness authority-approved EO based on Boeing's factory installation. We now need to get FAA approval and have been told that we need an STC but all the searches we have done do not appear to show there has ever been an STC for this upgrade. There must be many -400s out there that have had to have similar upgrades so how was this accomplished and certificated? Can anybody shed some light?
Cheers
Torque