On Tue, 02 Jun 2020 21:50:39 -0500, Mitchell Holman
wrote:

Airworthiness certificates for cargo planes
are far less....demanding....than for passenger
equipment. I remember when DC-10's were all
pulled from passenger service after the Chicago
crash where an engine fell off kiling everyone
on board. The military snapped them up as
refueling tankers, and they are still in use as
firefighting drop planes.

Pretty sure all USAF KC-10s were new-build by McDD. The Royal
Netherlands Air Force did convert two ex-airliners to KDC-10s.