Although the V-22 Osprey aircraft entered service more than a dozen years ago, Navy officials still can’t figure out how to keep dirt and sand from clogging the tiltrotor’s engines and causing potentially catastrophic mechanical failure, according to a report released this month by the Defense Department’s Office of the Inspector General.

Operated by the Marine Corps and Air Force but overseen by the Navy, Ospreys rely on innovative tiltrotor engines that allow them to take off and land like helicopters but fly like fixed-wing planes.

But keeping sand and soil from being sucked into the engines when the aircraft picks up or drops off personnel on natural terrain continues to bedevil the Naval Air Systems Command program office, according to the IG.

The Engine Air Particle Separator, or EAPS, was supposed to shield the Osprey’s engines from particulates, but NAVAIR officials have repeatedly failed to design an adequate EAPS since the aircraft first entered service in 2007, IG investigators wrote.

The EAPS is placed in front of the engine and is supposed to create a powerful vacuum to pull dirt away before it can enter the engine.

Without EAPS, too much soil can inhibit engine air flow, raising the risk of midair engine failure.

Ospreys suffered eight “rapid power loss events” in the engines due to EAPS failure between 2008 and 2015, according to the IG report.

“Although the eight engine rapid power loss events did not result in a catastrophic accident, the engines had degraded to a point where engine failure was possible,” IG determined.

“The V-22 remains at risk despite more than nine years of EAPS redesign attempts,” the IG report states.

NAVAIR undertook but aborted two EAPS redesign efforts over the past decade and is in the midst of a third try, which IG believes might not provide proper engine protection.

Officials with the V-22 Joint Program Office “could not provide analysis that demonstrated whether this redesign would adequately protect the engine,” according to the report.

Program officials also “stated that is it not technically feasible to meet the engine manufacturer’s specification for air quality in a desert environment,” IG found.

“Although the third EAPS redesign may remove more soil than the original EAPS, (program office officials) could not provide any analysis demonstrating the expected results…or whether the EAPS would remove enough soil to adequately protect the engine when operating in all desert environments,” according to IG.

While V-22 program officials told IG they could not test for every type of soil an Osprey may operate in, investigators noted in the report that the office is not taking advantage of the military’s ability to tailor soil samples for aircraft testing.

Program officials pushed back on the IG’s recommendation that the office review alternatives to help ensure the EAPS protects the Ospreys in all environments and argued that such a prescription fails to take into account the program office’s “multi-layered approach” to solving the EAPS problem.

But IG officials wrote that “It is not clear what impact this multi-layered approach may have on the reliability of the V-22 engine.”

“The Deputy Program Manager…stated that extensive research has led (the program office) to conclude that it is not technically possible to develop, integrate and field an EAPS that is fully capable of protecting the V-22 engine from all possible soil types and concentrations for unlimited durations,” according to the report.

Other program office efforts include an aircrew notification system, so that members on board can be made aware of “impending engine degradation,” IG indicated.

The program office initially confronted EAPS glitches in 2010. While operating in desert conditions, engines that were supposed to run for 500 hours before replacement could manage only 200 hours of service.

When the program office was developing the specification for the EAPS design, it didn’t require the system to meet the engine manufacturer’s performance specification, according to the IG report.

This month’s report is the latest to raise questions about the Osprey.

Data released by the Marine Corps earlier this year also revealed the Osprey fleet’s mission capable rate hovered at less than 60 percent due to maintenance problems and staffing shortages.