Flown limited edition commemorative cover, 9.5 x 4.25, number 926/1500, with a cachet honoring the twelve X-15 pilots, signed on the front in pencil by five of the pilots: Scott Crossfield, Robert M. White, Bill Dana, William J. Knight and Joe Engle. Cover was flown by Engle on the 50th Anniversary of the plane. In fine condition. RRAuction COA.
