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InsideDefense.com NewsStand | Christopher J. Castelli | April 10, 2006


As the investigation into the V-22 Osprey program's recent mishap on the ground in North Carolina continues, officials are reviewing an unexplained, previously unpublicized incident in November 2005 that also involved an uncommanded engine acceleration, according to Osprey program manager Marine Corps Col. Bill Taylor.

Though the November 2005 incident involved similar symptoms compared to the March 27 mishap, the two events are dissimilar in terms of the consequences because last year's event happened in flight during a visit aboard an amphibious ship and did not result in a mishap, he told Inside the Navy in a brief interview.

The engineering investigation into last November's incident never revealed any root cause, so that has not provided officials any clues as to whether the two incidents share the same root cause, Taylor indicated.

When an uncommanded engine acceleration happens in flight, it turns out to be a non-event, said Taylor, referring to last November's incident. “You have pitch on the blades already, so you're containing [rotations per minute] from the get go,” he said.

Taylor shed new light on the March 27 mishap when he briefed reporters last week at the Navy League's annual conference in Washington. The mishap occurred during a post-maintenance check flight at the Marine air base in New River, NC.

He said officials believe the inadvertent takeoff happened as pilots were switching between two sets of full authority digital engine controls (FADECs) that govern the engine function. There are two identical FADECs for each engine, one acting as a primary and one as a backup. When a pilot switched between FADECs as part of routine check, the V-22 rapidly ascended. Taylor clarified it is not accurate to say the pilot switched between automatic and manual control of the FADEC, as some Pentagon sources initially indicated to Inside the Navy.

A leading theory is that when FADECs were switched, the newly selected FADEC malfunctioned and caused a dramatic boost in power to one engine, according to program officials. This scenario -- called a high-side failure -- can happen in a wide variety of aircraft, not simply the V-22, program officials maintain.

Maj. Shawn Haney, a spokeswoman for the 2nd Marine Air Wing at Cherry Point, NC, previously said the V-22 rose about 30 feet in the air before making a hard landing on the flight line at New River. Taylor said that figure came from eyewitnesses, noting the flight data has since revealed the Osprey rose only about six feet in the air.

After about two or three seconds, the system detected the failure and automatically switched back to the working FADEC. That FADEC reduced the excess power on the engine back to the level commanded by the pilot, according to the presentation the program office provided to reporters.

“Because the thrust control lever had not been advanced as it would be for flight, this reversion to a ‘normal' on-the-ground power condition caused loss of lift and rapid descent to earth,” the presentation states.

The aircraft then dropped to the ground with sufficient force to crack the starboard wing at the wing root, Taylor confirmed. In crash situations, the Osprey is designed to shed the weight of the wing and nacelle, to protect the cabin and its occupants.

The V-22 landed on its wheels, almost level. The nacelle did not hit the ground first, but the aircraft came to rest with the right nacelle on the ground.

Program officials are still determining if it is worth repairing the aircraft or whether it will be scrapped. If it is scrapped, it probably will not be replaced, Taylor indicated. The cost of the class A mishap is expected to exceed $1 million, but no total cost estimate has been released.

The root cause of FADEC failure and/or high-side failure remains under investigation, according to the program office.

Asked whether there is any connection between the mishap and the fact that V-22 personnel removed and replaced a FADEC in the same aircraft prior to the mishap, Taylor said, “I don't believe there is any link but we don't know root cause.”

He added, “They are investigating everything -- wiring harnesses, FADECs, the fuel pump metering unit. I don't want to speculate as to why it happened.”

Lt. Gen. Emerson Gardner, deputy commandant for programs and resources, told a Senate panel last month that investigators would examine the maintenance work performed on the aircraft prior to the mishap.

“Please don't ask me to speculate on that,” Taylor told ITN, noting the incident remains under investigation.

Following the March 27 mishap, the system safety working group completed an extensive risk analysis, and determined no flight restrictions are warranted. But Taylor said officials have added a warning to the V-22 flight manual so pilots will understand the proper emergency procedures if a high-side failure and/or uncommanded acceleration occurs while on the ground. If the aircraft is on the ground, the pilot should shut down the engines. If the aircraft is flying, the pilot is supposed to stay in the air by increasing proprotor pitch and stabilizing flight, according to the presentation provided to reporters.

Taylor said the program has also developed a simulator syllabus to recreate the event and train pilots in these procedures.

A long-term solution is for V-22 engine manufacturer Rolls-Royce to accelerate the delivery of a software improvement for the FADEC. The new software is supposed to dramatically speed automatic switching time from a malfunctioning FADEC to the backup. “Had this aircraft responded as rapidly as the new software will allow, the high-side failure would have been headed off, or corrected before the aircraft ever left the ground,” according to the presentation provided to reporters.