only clues to what happened and was the basis for the accident report. It was ascertained that a malfunction involving an engine over-temperature and low fuel flow on the starboard engine had contributed to a catastrophic failure and subsequent aircraft break-up. 21 June 1968: Final A-12 flight to Palmdale, California. See SR-71 timeline for later SR-71 events. Variants Training variant The A-12 training variant (60-6927 "Titanium Goose") was a two-seat model with two cockpits in tandem with the rear cockpit raised and slightly offset. In case of emergency, the variant was designed to allow the flight instructor to take control. YF-12A The YF-12 program was a limited production variant of the A-12. Lockheed convinced the U.S. Air Force that an aircraft based on the A-12 would provide a less costly alternative to the recently canceled North American Aviation XF-108, since much of the design and development work on the YF-12 had already been done and paid for. Thus, in 1960 the Air Force agreed to take the seventh to ninth slots on the A-12 production line and have them completed in the YF-12A interceptor configuration. M-21 The M-21, a two-seat variant, carried and launched the Lockheed D-21, an unmanned, faster and higher-flying reconnaissance drone. The M-21 had a pylon on its back for mounting the drone and a second cockpit for a Launch Control Operator/Officer (LCO) in the place of the A-12's Q bay. The D-21 was autonomous; after launch, it would fly over the target, travel to a predetermined rendezvous point, eject its data package, and self-destruct. A C-130 Hercules would catch the package in midair. The M-21 program was canceled in 1966 after a drone collided with the mother ship at launch. The crew safely ejected, but LCO Ray Torick drowned when his flight suit filled with water after landing in the ocean. The D-21 lived on in the form of a B-model launched from a pylon under the wing of the B-52 bomber. The D-21B performed operational missions over China from 1969 to 1971, but was not particularly successful. Accidents and incidents Six of the 15 A-12s were lost in accidents, with the loss of two pilots and an engineer: 24 May 1963: 60-6926 (Article 123) crashed near Wendover, Utah. The aircraft was flying a subsonic engine test flight when it entered a cloud, pitched up, and went out of control; the CIA pilot ejected successfully. The