WASHINGTON — Images of the wreckage of the helicopter left behind at Osama bin Laden's compound by U.S. forces have prompted speculation that the chopper is a secret, highly-modified version of the military's iconic Black Hawk.
The stricken aircraft, which commandos blew up at the scene, appears to be a long-rumored stealth helicopter, NBC News reported; a Black Hawk modified to reduce rotor noise and make it more difficult to detect by radar.
Pentagon officials have declined to comment as did Sikorsky, the helicopter's manufacturer.
Aviation Week reported that the chopper's tail appears to be highly modified compared to a standard H-60 Black Hawk. The report noted that stealth features on a helicopter usually aim to dampen rotor noise and reduce infrared signals.
Noise reduction can be accomplished by adding blades to the rotors and changing the way the pilot flies the chopper, such as flying in a manner to reduce the rotor's rpm, the report said.
As for reducing the likelihood of the aircraft chopper giving off infrared signals, Aviation Week pointed to an earlier helicopter prototype that had a complex exhaust system and fresh air ejectors to lessen the aircraft's heat signals.
If the modifications did reduce the helicopter's sound, the raid still was noisy enough to attract attention. A computer programmer, Sohaib Athar , was startled by the noise and posted a note to Twitter: "Helicopter hovering above Abbotabad at 1AM (is a rare event)."
'Very unique appearance'
Citing a retired special operations aviator, Military Times reported that the helicopter's technology appeared similar to a F-117 Stealth Fighter. According to its manufacturer Lockheed Martin, the "startling, unconventional shape" of that aircraft, also known as the F-117 Nighthawk, ushered in the era of stealth technology with its "low-observable technology."
"It really didn’t look like a traditional Black Hawk," the retired aviator told the Times, noting that it had "hard edges, sort of like an … F-117, you know how they have those distinctive edges and angles — that’s what they had on this one." The U.S. Army began using the standard Black Hawk in 1979.
The source added that the helicopter's windshield might have been specially coated to help evade radar detection, making it "very plausible" that pilots wearing night-vision goggles would have a harder time with visibility.
The apparent modifications might have played a role in the chopper's hard landing as well, the retired aviator told the Times, because the additions could have added several hundred pounds to the weight of the craft.
Photos of the downed helicopter sparked a flurry of speculation about the design in the days after the raid, as the sections that survived the blast looked unlike anything the military has openly acknowledged, the Times report noted.
The downed chopper was one of two Black Hawks that transported the commandos who carried out the raid from Bagram Air Base in Afghanistan to the Abbottabad, Pakistan compound.
The original plan to place a rappelling team on the roof with a second team dropping into the courtyard was jettisoned when one of the helicopters, its blades clawing at hot, too-thin air, had to put down hard. Both choppers landed in the courtyard, behind one ring of walls with more to go.
'Had to blow the helicopter'
After the team sent word to Washington that bin Laden — code name "Geronimo" — was killed in action, commandos quickly swept the compound, retrieving possibly crucial records on the operations of al-Qaida.
The strong Pakistani military presence in Abbottabad, a garrison city with a military academy near the compound, provided a cover of sorts for the Americans. No one would be particularly surprised to hear choppers flying at night.
But the team needed to destroy the chopper that gave them trouble. This renewed worries that Pakistani authorities — who were not told of the mission in advance — would discover the mission prematurely. Neighbors certainly noticed.
"We had to blow the helicopter," CIA Director Leon Panetta said, "and that probably woke up a lot of people, including the Pakistanis."Slideshow: After the raid: Inside bin Laden's compound (on this page)
About 10 days before the raid, President Obama was briefed on the plan, NBC News reported. It included keeping two backup helicopters just outside Pakistani airspace in case something went wrong. But Obama felt that was risky. If the SEALs needed help, they couldn't afford to wait for backup.
He said the operation needed a plan in case the SEALs had to fight their way out. So two Chinooks were sent into Pakistani airspace, loaded with backup teams, just in case. One of those Chinooks landed in the compound after the Black Hawk became inoperable.
The raiders scrambled aboard the remaining Black Hawk and a Chinook, bin Laden's body with them, and flew to the USS Carl Vinson in the North Arabian Sea. The ground operation had taken about 40 minutes.
Only after the Americans left the area was Pakistan informed of what had happened on its territory.
Joint Chiefs Chairman Adm. Mike Mullen called Pakistani Army chief Ashfaq Kayani to tell him that an operation he had not known about was complete, a U.S. official told AP. Panetta called his Pakistani counterpart shortly afterward.
Mere hours after the operation, before most of the world knew bin Laden was found and killed, his body was buried at sea.
The Associated Press contributed to this report.