The only two aircraft that I am aware of is his lowtime Gulfstream II-SP N492JT, and his Boeing 707 N707JT.
I’ve heard rumours that he purchased a Convair 990 Airliner N8357C. John also purchased a Connie L-749 N494TW but has since sold it. He also sold his Jetstar N155TJ, along with a Citation ISP. He sold his Jet Commander N9023W which ended up donated at a aviation school in Norway. Unconfirmed is a previous ownership of a DH125 and a MS760 Paris Jet.
The Vampire Jet was sold N6878D and is registered in NY State but is in Canada. His Canadair Tutor CL-41 Jet Trainer N401AG was donated to Embry-Riddle. The Lear 24B he sold afew years ago, I can’t seem to find the registration, but it used to be owned by Paul Anka, and is the Lear Howard Hughes reportedly died aboard. At that time I recall it was owned by Robert J Graf Jets in Fort Lauderdale and I think was N744W.
From CBS News Interview, “Today he has logged close to 5,000 hours since earning his wings in 1974. He is qualified to fly as a captain in the Gulfstream II, Lear Jet 24, Hawker 1A, Citation 1 and 2, Tebuan, and Vampire Jet, and as first officer in the Boeing 707. He says what he likes to fly best is the 707 and the ultralights, which he says are very much like the Wrights’ first aircraft.”