US Naval Air Systems Command confirms today that a fifth MV-22 -- and the first US-based aircraft – is afflicted with the same “loose bolts” problem that caused the fleet to be grounded earlier this week

This discovery means all “high-time” V-22 airframes may have a safety-critical design problem, and is not isolated to the four Iraq-based MV-22s previously found with the problem.

The bolts are used to attach a swashplate that controls the pitch of the propeller blade. If the swashplate comes loose during flight, the aircraft could crash.

“You would essentially lose control of the aircraft,” Col Matt Mulhern, V-22 programme manager, told

While a root-cause investigation is ongoing, NAVAIR officials believe a design change will likely be required to ensure bolts in the proprotor cannot come loose, which if left unchecked would cause the aircraft to spin out of control.

Mulhern notes that investigators have not ruled out potential defects in maintenance or manufacturing either. But the new fact that both aircraft in Iraq and the US are affected suggests that poor maintenance is not a driving factor.

“We’re going to eventually need a material fix for this” problem, Mulhern said.

The problem was discovered on Saturday after an MV-22 landed at Al-Asad Air Base, Iraq. The crew heard strange noises, and the inspection found the bolts rattling loose inside one of the MV-22’s two engine nacelles. The bolts appear to have shaken loose after the aircraft landed, which could offer a clue to investigators.

“That has raised questions about what happens [to the bolts] when you take the load off of [the prop-rotor],” Mulhern said.

Two days after the first discovery, the USMC grounded all 73 MV-22s and 11 CV-22s for inspections as a safety precaution. Immediately, the inspections identified three more MV-22s at Al-Asad with loose bolts on the same component, although the bolts had not fallen completely from their holes.

Programme officials had hoped the problem was contained to the MV-22s deployed to Iraq, which could have suggested that the more intense operations were a contributing factor.

Instead, the discovery of the MV-22 based at New River, North Carolina, on Wednesday, changed the focus of the investigation. All five MV-22s shared a common trait as among the most “high-time” airframes in the fleet.

The “loose bolts” problem comes at a sensitive time for the programme. The Pentagon is preparing the final version of the Fiscal 2010 budget request. The US Special Operations Command is interested in accelerating purchases of CV-22s over the next five years.

“This is an event that aircraft go through, and it was a precautionary grounding,” Mulhern said. “But you’re always worried about how the politics play out.”