The U.S. Air Force Tuesday blamed a German military plane for a mid-air collision with a U.S. C-141 that killed 33 people off the coast of Africa last September.

But the chief Air Force accident investigator said the mishap could have been avoided if either plane had been equipped with a Traffic Alert and Collision Avoidance System, known as TCAS."In my opinion the absence of TCAS was not a cause or substantial contributing factor, but the presence of a fully operational TCAS could have prevented the accident, " said Air Force Col. William Schell Jr., who headed the accident investigation board.

The German and the U.S. air forces both concluded the primary cause of the Sept. 13 accident was that the German Tupolev 154 was flying at the wrong cruise altitude over the Atlantic off the coast of Namibia.

The German plane, with 24 people on board, was flying from Niger to Windhoek in Namibia at 35,000 feet after filing a flight plan for a cruise altitude of 39,000 feet .

The U.S. C-141, with nine people on board, was en route from Windhoek to the Azores.

Schell's report also criticized a weak Luanda air traffic control agency in Angola whose flight following procedures failed to comply with the standards of the international civil aviation organization.

Poor regional ground communication, including unreliable telecommunications lines, accounted for Windhoek air traffic control agency in Namibia not to receive the German aircraft's flight plan.

Earlier Tuesday in Bonn, the German air force issued a report reaching many of the same conclusions.

"What decision process led to the (German) aircraft not leaving the (35,000 feet) altitude could not be established," a report by German air force investigators said.