Heavily Modified Gulfstreams
Among some of the weirder modifications done to Gulfstream planes were the changes for Shuttle Training Aircraft, a G-II that was used to simulate landings before astronauts jumped into the Shuttle itself.
Shuttle approaches were so steep — 20 degrees! — that the jets had to be operated with the main landing gear down and both Spey engines running in reverse at 92% N2.
N2 is a measure of the rotational speed of the high-compression stage of the engine, so 92% reverse N2 is almost full throttle in the opposite direction!