Helicopter Carrying SEALs Downed by Vortex, Not Mechanical Flaw or Gunfire
A United Technologies Corp. (UTX) 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 U.S. government officials, a lawmaker and congressional staff briefed yesterday 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 yesterday briefed the Senate and House armed services and intelligence committees.
Rappelling Mission Ditched
The aviation unit is based at Fort Campbell, Kentucky. President Barack Obama is scheduled to visit the base on Friday and see members of the 160th, said an Army official who spoke on condition of anonymity because he wasn’t authorized to discuss the trip.
Twenty-five Navy SEALS were flown to the bin Laden home by two Black Hawks, CIA Director Leon Panetta told the PBS “News Hour” May 3.
The helicopter that crash-landed was supposed to hover over the compound’s courtyard so that the SEALS would rappel, or “fast rope,” to the ground, Panetta said.
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.
Hard Landing
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 Representative Adam Smith told reporters after a McRaven briefing.
Asked if there was a mechanical failure in the United Technologies’ Sikorsky aircraft, Smith said, “I don’t believe that is what happened.
‘‘As was explained to me, with the temperature and the setting, it came down faster than they anticipated so I don’t believe there was some sort of mechanical failure. It’s just those were tough conditions to land in,” Smith said.
House Armed Services Committee Chairman Representative Howard McKeon of California reiterated in Washington yesterday that “it was not a mechanical failure.”
Wreckage Destroyed
He also said he had “no sense from the military that they had any concerns about” leaving wreckage of the modified Black Hawk, said McKeon.
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.
Night Stalkers
Once known as the secret Task Force 160, the aviation regiment was formed in 1981 and has participated in most major U.S. military operations since the 1983 invasion of Grenada. Its pilots are known as the “Night Stalkers.”
Five of its personnel were lost and eight aircraft, including two Black Hawks, were either destroyed or damaged during the October 1993 battle in Mogadishu, Somalia.
The unit’s Black Hawks and the mission to rescue the air crews were the basis of the book and movie “Black Hawk Down.”
The unit flies the Sikorsky MH-60 Black Hawk, Boeing Co. (BA) MH-47E heavy assault chopper, and the Boeing A/H-6M Little Bird, used to ferry Army Delta Force commandos during a raid in the invasion of Panama to free a jailed American businessman, Kurt Muse.
What makes the experts think the aircraft that crashed in Abbottabad was a secret "stealth helicopter?"
• "The first thing that stood out, and it may seem like a small thing, is the color scheme. Whereas most Black Hawk Army helicopters are painted olive green, this particular one is gray. Not just any gray; it's infrared-suppressant gray, and the purpose of the IR gray, as it's known, is to help reduce the vulnerability of the helicopter to ground-launched heat-seeking missile systems," Jennings told CNN Pentagon Correspondent Chris Lawrence.
• Photos from Abbottabad show that the chopper had a five-bladed tail rotor. "On a conventional Black Hawk, you have four blades. The addition of the extra rotor blades on the tail rotor hub reduces the acoustic signature of the helicopter there by making it hard to hear, giving the SEALs that extra few minutes to get over the compound before anyone on the ground quite knows what's going on," according to Jennings.
• Those five tail rotor blades are partially covered by a disk-like object that Jennings called a "hub-mounted vibration suppression system." He believes it provides more noise suppression and some possible protection for the tail rotor from bullets of shrapnel. And it's not typical on military helicopters. "No, I've never seen that on an operational helicopter before," Jennings said. But he added that a similar system was part of the Comanche helicopter design.
• The blades on that tail rotor also appear to be shorter and thinner than typical Black Hawk helicopter's blades. One former Army Black Hawk pilot, who asked not to be identified, said, "More blades and shorter blades means the helicopter would make less noise in flight."
It's not just the tail rotor blades that are different. "On the main rotor assembly that was actually destroyed by the SEAL team on the ground the blades themselves are threaded, which signify that these are carbon composite rotor blades as opposed to conventional ****l rotor blades, which again signifies aspects of stealth technology that have been incorporated into this particular helicopter," Jennings said.
• Some photos show parts of the helicopter appear similar to non-secret stealth aircraft. "What's left of the tail section of that helicopter, the shape of the fuselage, it's canted. It's angled. It's a shape that's synonymous with fixed-wing stealth fighters such as the F-22, the F-35. Essentially, it's designed to defeat radar. If you eliminate right angles in an aircraft design, radar waves can't bounce back," Jennings said.
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7th May 2011, 06:14 PM
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