GEOFF BENNETT: The U.S. military announced earlier this week that it would ground its entire fleet of V-22 Osprey aircraft.
That's while they investigate the cause of last week's crash off the coast of Japan that killed all eight service members on board.
The military took the extraordinary step of grounding the fleet after an initial investigation found something wrong with the aircraft itself that led to the crash, and not errors by the crew.
The crash last week was just the latest for the Osprey with a near-century-long checkered and deadly record.
SABRINA SINGH, Pentagon Deputy Press Secretary: This action is being taken out of abundance of caution while the AFSOC investigation is conducted.
As each service conducts operational safety reviews within their fleets, each will reevaluate their respective grounding bulletins and then determine timelines for resuming flight operations.
GEOFF BENNETT: No other American military aircraft does what the V-22 Osprey can, take off and land just about anywhere, lifting off like a helicopter.
But when its rotors are tilted forward, it can fly fast and far like an airplane.
Almost all of the military services rely on Ospreys.
For the Marine Corps, it's their workhorse.
The Navy flies people and supplies to aircraft carriers.
And Air Force Special Operations uses it to rescue crews shot down over enemy lines.
All told, there are about 400 Ospreys in the U.S. military, and there have been 10 fatal crashes, killing 57 people, over the past 23 years.
An investigation of two crashes in the year 2000 during test flights found the Marines had cut corners during the trials.
This week's grounding is not the first.
Ospreys were grounded in February due to ongoing issues with the tilt rotator's clutch.
Last year, the Air Force grounded its fleet for the same reason.
BRIAN ALEXANDER, Aviation Attorney, Kreindler & Kreindler: It is so challenging and complicated from a mechanical standpoint to create this platform.
You're going to have issues from time to time.
GEOFF BENNETT: Brian Alexander is a former army helicopter pilot.
He's now a lawyer who has represented family members with loved ones killed in Osprey accidents.
He says, unlike other aircraft, the Osprey is much harder to land safely when there's a major failure.
And it can't auto-rotate well like normal helicopters when the pilot uses the lift provided by the spinning propeller to land.
BRIAN ALEXANDER: If something goes wrong, it is unlike an airplane, where you're usually at tremendous altitude with a lot of options maybe to get to a safe landing area, or even a helicopter, which is much more challenging and risky, but you have got auto-rotation capabilities.
That's really not the case for the Osprey.
REX RIVOLO, Former Pentagon V-22 Program Analyst: The utility that this aircraft brings through the military is enormous.
It really gives you a complete new operating world.
But we're paying the price for it.
GEOFF BENNETT: Rex Rivolo was a fighter bomber aircraft pilot during the Vietnam War.
And, after, he flew helicopters.
He later worked for the Pentagon and evaluated the Osprey as it was being developed.
He says the most recent crash was likely due to problems with the clutch.
REX RIVOLO: Given the eyewitness accounts of seeing the aircraft tumbling and spinning, the only way you can explain that is if an engine was lost or was surging and the interconnecting driveshafts were severed.
GEOFF BENNETT: In 2003, Rivolo wrote a memo called "Lingering Safety Concerns of the V-22."
And he noted that the side-by-side engines made the aircraft prone to roll at times.
High vibrations from the engines would cause parts to fail and the high downwash from the rotors would kick up dirt, making it hard to see.
REX RIVOLO: That was 2003.
Here we are in 2023, and we basically have seen a spate of accidents all linked to these five or six items that I outlined in that memorandum.
GEOFF BENNETT: We asked the Marines to respond to what both Alexander and Rivolo told us.
In a written statement, they said the Osprey has a 10-year average mishap rate of 3.28 per 100,000 flight hours, and that the 10-year total Marine Corps average mishap rate is 3.36 per 100,000 flight hours.
They said there's no evidence that last week's crash was caused by a clutch problem, but they theorize that clutches that have been installed for a lengthy period of time need to be replaced.
In the meantime, as the military tries to get to the bottom of what caused the most recent crash and find a solution, the Ospreys will remain grounded.