The NASA Mishap Investigation Board, headed by Vance D. Brand of NASA's Dryden Flight Research Center, concluded that the primary cause of the accident was that the brake line on the helium pneumatic system for landing gear 2 was not connected. This unconnected brake line prevented the brake mechanism from becoming pressurized. The brake mechanism needed to be pressurized in order for it to release the brake. The result was that landing gear 2 did not extend, and the vehicle became unstable when it landed. The DC-XA then toppled onto its side, exploded, and burned.

A number of causes contributed to the failure, according to the NASA Mishap Investigation Board. These included the design of the system for stowing the gear, which required technicians to violate the integrity of the helium brake line after integrity had been verified previously. No other check was conducted to verify again the integrity of the system after disconnection and reconnection of the line. Landing gear stowage was never identified as a critical process, and no special steps were taken to ensure the readiness of that system for flight. The Board also found that, during the gear stowage process, no record of checking off steps was made, and there was no evidence of cross-checking of work by another person. Moreover, distraction or interruption of the technician during gear stowage operations may have contributed to the brake line not be connected.

In short, the NASA Mishap Investigation Board largely blamed human error for the demise of the Clipper Graham. Moreover, the failure to connect the landing gear brake line was not an isolated incident. While preparing the DC-XA for its third flight, a hydraulics technician discovered the same failure to connect the landing gear brake line. The technician brought the matter to the attention of the other technicians, and the problem was corrected before flight. However, the incident was never documented, and no changes were made to the procedure to highlight the issue. "This appears," NASA Mishap Investigation Board concluded, "to have been a missed opportunity to tighten up the controls of this critical process."

The Board also found fault with the way the project had been managed. Because the design and operational procedures of the DC-XA "were driven by rapid development and low cost," a number of imprudent practices resulted. "Accordingly, a minimum number of personnel were involved in operations. Also, design was single string, and there was just one flight test vehicle. There was strong reliance on good people but not a lot of margin for human error afforded by the vehicle preparation process. The McDonnell Douglas Rapid Prototyping Guidelines or implementation thereof for the DC-XA may have gone too far in the direction of sacrificing quality and reliability. This rapid prototyping concept should be revisited from an operations perspective."

Many fans of the DC-X and the DC-XA had hoped to see the vehicle standing at the National Air and Space Museum one day. Others wanted to fly it until, well, it crashed. The Clipper Graham's demise ended all such discussion. Now the friends of the vehicle and the ideas for which it stood wanted NASA to build another one and keep flying. Would that be the best use of limited NASA funding for launcher technology development?

The answer to that question was up to Gary Payton, formerly with the Air Force and the Strategic Defense Initiative Organization, but now head of reusable launch vehicle technology development at NASA Headquarters. There was just not enough money to build another ship, the price tag for which was probably $120 million, and by now, the DC-XA was not the only vehicle in the NASA program to develop single-stage-to-orbit and other advanced launch technologies. Consequently, Payton decided to not build another DC-XA.

The demise of the Clipper Graham did not bring the curtain down on NASA's development of reusable launch technology. NASA had two more "X" vehicles in the works. The next fact sheet will take up the story of one of those, the X-34.