Subject: V-22 Settling Problem Disclosed, Navy Claims It's Unrelated ToMishap
Inside The Navy
August 21, 2000
V-22 Settling Problem Disclosed, Navy Claims It's Unrelated To Mishap
An audit of the V-22 Osprey program by the Pentagon's inspector general reveals officials knew a year ago the tiltrotor had a problem with "settling due to loss of interim power" but decided the deficiency was not important enough to immediately spend money correcting it.
The report discloses for the first time that military testers identified a specific settling deficiency associated with the V-22 last September, and Osprey program officials labeled the problem "nonmajor" and not worth fixing before the start of operational testing and evaluation, the phase in which Marines were participating at the time of an April 8 crash that killed 19 Marines. Such deficiencies are valid but do not restrict the V-22 from meeting its mission, the audit report says.
V-22 program officials told Inside the Navy last week the problem is minor and not related to the phenomenon called power settling that is believed to have contributed to the fatal April 8 Osprey crash.
The Marine Corps and the Defense Department have a lot riding on the V-22, which operates like a helicopter for takeoffs and landings and, once airborne, converts to a turboprop plane. The Marine Corps is buying 360 of the aircraft and the Air Force is buying 50. Defense Secretary William Cohen has predicted all of the military services will one day rely on tiltrotor technology. A team of Bell Helicopter and Boeing builds the high-profile V-22.
At press time, the V-22 program office told ITN in brief comments the settling deficiency is not related to vortex ring state, nor related in any way to the mishap, even though the words used in the DOD IG report to describe the problem echo terms used to explain the fatal April 8 crash.
"Interim power is selectable by the pilot and provides for additional rotor thrust and power margin up to mast torque values of 109 percent at a rotor speed of 103.8 percent Nr," the program office said in a written statement to ITN. "By design, interim power is deactivated at nacelle angles less than 80 degrees or airspeeds greater than 50 knots."
ITN has learned that V-22 pilots who fail to observe certain airspeed and rotor-angle rules can lose interim power, causing the aircraft to settle without warning. While this concern was noted by military testers, Rear Adm. John Nathman, then the Navy's top aviation requirements official, said last September the program could proceed to operational evaluation without immediately fixing the problem. Officials maintain this issue is not a serious safety concern. The Navy's response to the DOD IG report,
published with the audit on Aug. 15, claims the deficiencies described are "in no way safety related."
For months, the Marine Corps has publicly dismissed the possibility that the V-22 might be especially susceptible to the vortex ring state.
"No, absolutely not," Lt. Gen. Fred McCorkle told reporters on May 9 when asked if there was is any evidence to suggest the V-22 is more susceptible than other rotorcraft to power settling or settling with power. McCorkle, the assistant commandant for aviation, said he believes the V-22 is less susceptible to such conditions when compared to other helicopters. "In fact, I would say [the V-22 is] less [susceptible] because of the amount of power that it's got." That day, McCorkle also said the mishap investigation was "concentrating on flight characteristics which are not peculiar or unique to the V-22 but can be experienced in all our helicopters . . . or any others in the world."
The Marine Corps concluded the mishap aircraft was piloted into a descent that was too rapid and steep. That flight induced the "vortex ring state" or rotor blade stall, which caused an asymmetric loss of lift of the rotors, the service announced. The pilots of the two aircraft involved were deemed responsible for the mishap and those from the surviving aircraft were disciplined.
When the Marine Corps Judge Advocate General investigated the recent Osprey tragedy, it concluded the mishap did not appear to be a result of any design, material, or maintenance factors specific to tiltrotors, but the JAG noted it is relatively unusual for the contributing factors in this mishap to cause the loss of a helicopter.
"It's primary cause, that of a MV-22 entering a Vortex Ring State and/or blade stall condition is not peculiar to tiltrotors," the JAG report states. The contributing factors to the mishap -- a steep approach with a high rate of descent and slow airspeed, poor aircrew coordination, and diminished situational awareness -- are also not peculiar to tiltrotors, the report continues. "However, the end result, departure form controlled flight, is more extreme than results experienced in most rotorcraft to date," the JAG report concludes.
When the service released copies of the JAG report, the opinions and recommendations sections were deliberately omitted, leaving unresolved key questions about their contents.
It is well documented that the vortex ring state is powerful and dangerous enough that pilots of rotorcraft caught in the unstable flight condition can lose control of aircraft if they fail to take proper action. Rotorcraft caught in the state require an unusual amount of power to maintain rotor thrust. The term "power settling" comes from pilots' observations that in some cases a helicopter keeps coming down even though full engine power is applied, according to "Practical Helicopter Aerodynamics" by R. W. Prouty.
The V-22's settling problem is one of the "nonmajor" deficiencies referenced in the Naval Air Warfare Center's integrated operational assessment, which was completed on Sept. 20, 1999. The NAWC report, which said major tests planned for the V-22 were not completed, identified limitations in major operational effectiveness. Additional testing would be needed to resolve certain critical operational issues, the NAWC concluded. However, fixes would not be in place to support operational evaluation testing. NAWC recommended various flight envelope and mission limitations, and prohibited maneuvers and operations for operational evaluation testing. However, despite the limitations, that report recommended the V-22 proceed to operational evaluation testing.
Some key Osprey problems -- such as those concerning the cargo handling system and protection from nuclear, chemical and biological agents -- were given high priority and the program office made plans to correct them during operational testing, the report indicates. Other deficiencies, including the settling problem, were dismissed by the program office as lesser issues, according to the DOD IG report.
The V-22 program office believed it "did not need to delay operational test and evaluation or to commit scarce program resources" to correct the settling deficiency before operational test and evaluation, the report states.
Pentagon spokesman Rear Adm. Craig Quigley spoke generally about the V-22 audit on Aug. 17.
"Let me just say everybody wants this system to work properly," Quigley said. "It is in everybody's interest that a good, tough review of the program at all levels be conducted. But as with any other new aircraft development program, there are going to be bugs in it."
Quigley said the Pentagon looks forward to rigorous testing and reviews of the V-22 program to find bugs, "so that those responsible for the program can work out a plan to correct them and come to an aircraft that will serve our military well for many years to come."
The admiral said reviewing and fixing problems with the V-22 is not something officials are shying away from. "We welcome the closest possible scrutiny of the program at all levels, so that we can all work towards a good aircraft that's safe and reliable and affordable and meets all of our criteria by the time it's put into the field," he said.
-- Christopher J. Castelli