(Bloomberg) -- The two top House lawmakers overseeing US military readiness want a formal review of the $56 billion V-22 Osprey program following a Nov. 29 crash off the coast of Japan that killed eight airmen and prompted a worldwide grounding of the fleet. 

The crash off the southwestern Japanese island of Yakushima, along with three prior crashes in recent years prompted the request from Representative Mike Waltz, a Florida Republican who chairs the House Armed Services readiness panel, and Democrat counterpart John Garamendi of California.

“In the last two years, four fatal Osprey crashes have claimed the lives of at least 13 American service members,” the lawmakers wrote in a letter to US Comptroller General Gene Dodaro. “Nonfatal accidents involving the Osprey also occurred during this time, which resulted in injuries, fatalities, and costly damage to aircraft.” 

The lawmakers called on Dodaro — who heads the US Government Accountability Office — to respond to their request within 30 days. US military officials said they were grounding the entire fleet to investigate a possible equipment problem that may have caused the deadly crash in Japan.

That incident returned scrutiny to the Osprey, a tilt-rotor aircraft that can take off and land like a helicopter and fly like an airplane. After early years of setbacks and accidents — especially in 2000, when two crashes killed 23 Marines, triggered a major Pentagon review, and subsequent design changes — the aircraft built by a unit of Boeing Co. and the Bell Helicopter unit of Textron Inc. served in Iraq and Afghanistan.

Read More: US Military Grounds Osprey Aircraft After Deadly Crash

Possibly its most famous mission was flying the body of Osama bin Laden to the USS Carl Vinson aircraft carrier after he was killed in the May 2011 commando raid in Pakistan. 

Among the questions the lawmakers want the GAO to probe:

* What are the trends in accidents involving the Osprey and what causes have been associated with these accidents?

* What are the trends in maintenance and supply issues that negatively impact the availability rates of Ospreys and to what extent have the rates met fleetwide goals? 

*  What steps have the V-22 Joint Program Office, Navy and Marine Corps “taken to reduce or prevent accidents involving the Osprey and to what extent are additional actions warranted to enhance the safe operation of the aircraft?”

This week’s grounding of the V-22 affects as many as 348 aircraft for the Marines, 51 for the Air Force and 29 for the Navy, according Naval Air Systems Command and Air Force Special Operations Command statistics.


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