Private plane by NetJets tracked Flight UA93 on September 11

"Additional recordings would be played from the cockpit of an executive jet that tracked Flight 93 on Sept. 11… An official for NetJets, a company that sells shares in private business aircraft, confirmed that the plane tracking Flight 93 belonged to the company.
The official, who asked not to be identified by name, said the company was asked not to comment on the Sept. 11 flight but would not say who made the request." -Holland Sentinel/AP (8/09/02)