WASHINGTON — A Black Hawk helicopter carrying U.S. Navy SEALs to Osama Bin Laden’s hideout was downed by an air vortex caused by unexpectedly warm air and the effect of a high wall surrounding the compound, not mechanical failure or gunfire, according to U.S. officials and a lawmaker.

The Army pilot from the service’s most elite aviation unit executed a hard but controlled landing — clipping a corner wall — after the chopper lost lift. The 12 heavily armed SEALs exited the aircraft unharmed.

Senior government officials briefing reporters by telephone on May 1, the day bin Laden was killed, gave conflicting accounts, first saying the chopper experienced a mechanical “malfunction” and then backtracking without an explanation.

The initial administration explanation wasn’t accurate, according to government officials, a lawmaker and congressional staff briefed Thursday by Vice Admiral William McRaven, leader of the Joint Special Operations Command.

The command includes the Army’s 160th Special Operations Aviation Regiment, which piloted the SEALs of the Navy’s Special Warfare Development Group to the house in Abbottabad, Pakistan. McRaven Thursday briefed the Senate and House armed services and intelligence committees. The aviation unit is based at Fort Campbell, Ky.

According to two U.S. officials, who praised the skill of the pilot, the chopper lost the lift necessary to hover because it entered a “vortex” condition. At least two factors were at play — hotter than expected air temperature and the compound’s 18-foot-high walls, they said.

The wall blocked rotor blade downwash from moving down and away as it normally would. This caused disturbed airflow to move in a circular, upward and then downward path back through the top of the rotor, causing insufficient lift for the aircraft.

The pilot, realizing he had lost lift, landed quickly in a maneuver practiced by pilots to deal with helicopter flight conditions known as “settling with power,” one official said.

Another explained that if a helicopter hovers next to a large enough building at just the right distance, moving air created by the rotors won’t be able to exit freely. Instead, it will hit the wall and have nowhere to go except back into the rotor, robbing lift.

The pilot executed a “hard landing” as a result, House Armed Services Committee ranking Democrat Rep. Adam Smith told reporters after a McRaven briefing.

Asked if there was a mechanical failure in the United Technologies’ Sikorsky aircraft, Smith, D-Wash., said, “I don’t believe that is what happened.

The commandos detonated an explosive to destroy the helicopter, which the Army Times reports was a specially configured stealth model Black Hawk.

Two 160th additional MH-47 special operations Chinook helicopters provided back-up and assisted in flying out the raiders.

Sikorsky Aircraft spokesman Paul Jackson said the company hasn’t been contacted about any aspect of the raid.