Shifting Cargo May Have Doomed Plane That Crashed Near Kabul KABUL, Afghanistan - Crash investigators in Afghanistan said Monday that quickly shifting cargo of heavy military vehicles contributed to the crash of a civilian cargo plane on April 29 in which all seven people aboard were killed. Officials said that as the Boeing 747 began to take off from the Bagram Air Base, the vehicles slammed into the back of the cargo space so hard that parts of the plane broke off and were left on the runway. With the center of gravity pushed too far backward, the nose rose too high for the plane to be able to fly. The cockpit voice recorder did not indicate that the pilots knew what was happening, but wiring at the back of the plane showed damage from the shifting cargo, according to Nangialai Qalatwal, a spokesman for the Ministry of Transportation and Civil Aviation. The crash was caught on video by a dashboard camera on a vehicle at the air base. The accident may cast new attention on the quality of Defense Department oversight of its contractors. The safety of civilian flights is usually regulated by the Federal Aviation Administration, but after a 2004 crash in Afghanistan of an American civilian cargo plane under contract to the American military, the F.A.A., which had no personnel in the country, delegated the Defense Department to oversee safety. With the American military pullout from Afghanistan in full swing, a vast network of transportation contractors has been employed to ship heavy equipment out of the country. Although most of the cargo traffic is expected to go through Pakistani seaports via road hauling, a huge uptick in outbound cargo flights is also under way. On May 17, the F.A.A. issued a reminder to cargo carriers with heavy vehicles on board to ensure that their loads were tightly fastened, an indication that American safety officials suspected a cargo shift in the April crash. But on Monday, Afghan officials cautioned that it was too early to determine the exact cause of the accident, which remains under investigation. The cockpit voice recorder, which was recovered from the wreckage, has offered few clues, Mr. Qalatwal said. "The only thing that was recorded by the black box right before the crash was a pilot's voice, who was shouting, "Wait! Wait!" " he told a news conference in Kabul. The plane, operated by National Air Cargo, a Michigan-based carrier, was loaded with three armored vehicles and two mine sweepers, almost 80 tons of equipment in all, for a flight from Afghanistan to Dubai, Mr. Qalatwal said. He said the plane was checked twice before takeoff, once two hours before departure and again just before it left, and that neither review revealed any technical problems. Aviation experts had speculated earlier that there had been a mechanical problem with the plane's pitch control, and that a part might have fallen off during takeoff. The charred remains of the cargo straps were recovered from the site and appear to have been cut, but Mr. Qalatwal said it was unclear whether the damage occurred before or after takeoff. The plane, consumed by a huge fire from the crash, yielded little else in the wreckage, he said. Under treaties governing aviation, the responsibility for investigating a crash lies with the host country, although other parties, including safety officials from the country where the plane was registered, must be involved. The National Transportation Safety Board sent technical experts to Kabul to assist with the investigation. If the problem were shifting cargo, it would be "a freak accident," said Mark V. Rosenker, a retired Air Force general who led the N.T.S.B. in the 1990s. But, he said, "it could be that one broke loose and flipped into the others." In that case, he said, there would be "a domino effect" inside the plane. Azam Ahmed reported from Kabul, Afghanistan, and Matthew L. Wald from Washington. Habib Zahori contributed reporting from Kabul.