By   / September 29, 2003

As flight testing of the V-22 Osprey continued this month, the program encountered a hydraulic failure in Osprey No. 22, while another aircraft, Osprey No. 21, twice suffered broken windscreens.

The first incident damaged the left-hand windscreen on Osprey No. 21 when the aircraft was on the ground at Patuxent River, MD. A few days later, on Sept. 5, another crack caused by a foreign object was detected in the right-hand side windscreen of the same aircraft while it was flying.

After detecting the crack 90 minutes into a flight, the crew landed Osprey No. 21 at Patuxent River without incident, said Ward Carroll, the Navy's V-22 spokesman.

Also on the afternoon of Sept. 5, Osprey No. 22 suffered a hydraulic failure but landed without incident, he said. In each case, the pilots landed as soon as practicable but did not have to execute emergency landings, he said. Neither the windscreen cracks nor the hydraulic leak constituted safety concerns or major problems, according to Carroll.

The Osprey program is engaged in a flight test program aimed at addressing all concerns raised following two fatal V-22 crashes in 2000. Bell Helicopter Textron and Boeing manufacture the aircraft. At the Pentagon, the program has had strong support lately. The Marine Corps Osprey plan includes three stages -- Blocks A, B and C -- each of which is associated with particular improvements. Block A production is ongoing and delivery of those aircraft is scheduled to continue until 2006.

The cracked windscreen incidents are manifestations of a known deficiency (a weakness of the glass outer layer). Nine windscreens cracked during the last operational evaluation due to thermal stress and impact damage, said Carroll. What caused the cracks in Osprey No. 21's windscreens is not clear, though rocks kicked up in the air might have been responsible, he said.

New windscreens with an acrylic outer layer will be available in Block A aircraft, starting with Osprey No. 56 (rather than No. 50, as the program office initially told defense officials this month), said Carroll. He also said existing Ospreys slated to participate in the program's next operational evaluation may be fitted with the improved windscreens before that testing begins.

After the cracked windscreen detected Sept. 5 was replaced, Osprey No. 21 flew again on Sept. 9 and has been flying without incident since, said Carroll. He also said Osprey No. 22 had a 34-hour inspection following the Sept. 5 hydraulic leak and has flown "a lot" since resuming flights Sept. 8.

Philip Coyle, a former head of the Pentagon's operational testing directorate, said the program office appears to be taking the right approach by replacing the deficient windscreens. And he acknowledged it sounded as though the back-up hydraulic systems worked when Osprey No. 22 had its leak. But beyond these individual incidents, he said, the program and Bell-Boeing must focus on the overall reliability and maintainability of the aircraft.

"It's the accumulation of all of these little things" that could become a concern, he said.

In the Osprey, hydraulic power is provided by three onboard independent systems, with power and control components located in each nacelle and the midwing area. The No. 1 and No. 2 hydraulic systems, located in the left and right nacelle, respectively, are identical and dedicated flight control systems. The No. 3 hydraulic system is located in the midwing area and serves as a backup to certain flight control systems; it also provides pressure to power utility systems like the landing gear, ramp, wing stow, and nose wheel steering.

The No. 3 system was affected when a leak occurred in the nose gear wheel well of Osprey No. 22 during a flight near Patuxent River on Sept. 5.

At fault, according to program officials, was a loose "B-nut" that normally connects the power steering pressure hose to the power steering pressure hydraulic line. Air Force Col. Craig Olson, the new Osprey program manager, briefly discussed the incident with Inside the Navy on Sept. 17 at the Air Force Association's annual conference in Washington, DC. He cited the loose B-nut and said the incident was not a safety issue. The B-nut came loose, he said, because part of the aircraft in the nose did not have "an optimum design." He said he expects a design change will be needed and added that the change would be incorporated in Block A aircraft to help keep the hydraulic line from moving.

Carroll said the problem has been a "known issue" for some time, though the possibility of such a leak was considered a "very low" risk. The design change was planned long before the unexpected Sept. 5 leak occurred, he said. And Osprey No. 34, the first Block A aircraft, which was recently delivered to Patuxent River, already incorporates the design change, Carroll said.

Though the latest hydraulic leak is not good news for the Osprey, the program office is pleased the triply redundant hydraulics functioned as intended, isolating the problem. The pilots did not encounter flight control system problems during the incident and instead found warning systems and the No. 3 hydraulic system functioned as designed, according to the program office.

The first sign of trouble was when someone aboard Osprey No. 22 smelled hydraulic fluid as the aircraft lowered its landing gear during a precision approach maneuver. Almost instantly, the crew received a warning that the utility systems were inoperable. The pilots observed the No. 3 hydraulic system reservoir fluid level go down to approximately 138 cubic inches and observed the No. 3 system isolate utility system functions, as designed. These utility functions included the normal landing gear, ramp door, engine starters, the Engine Air Particle Separator (EAPS), nose wheel steering, cargo winch, rotor brake and normal wheel brake operation (back-up brakes were still available). The pilots conducted an uneventful vertical landing on the runway, but received a warning that nose wheel steering was unavailable. Then, the pilots took off vertically and landed the aircraft near its hangar. -- Christopher J. Castelli