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  • Did Degraded Engines Down USAF V-22?
    Posted by Bill Sweetman 8:31 PM on Dec 17, 2010

    USAF officers disagreed over the cause of the first combat loss of a V-22 Osprey tilt-rotor, according to a report in the Fort Worth Star-Telegram, with a senior general ultimately overruling the investigation team and declaring the cause to be pilot error. The April 9 accident killed four people, including the pilot, and injured 16. The full report is here.

    A major complicating factor was that the CV-22B wreckage was bombed hours after the accident to prevent sensitive equipment from being removed, and the flight incident recorder was never recovered.

    The CV-22B unit had ferried its aircraft into Afghanistan eight days before the accident, which took place on its first operational mission, infiltrating a special operations team into an unprepared site. The report notes that the three-aircraft formation encountered unexpected tailwinds on the approach.

    Following a low-visibility approach that the investigators described as "poorly executed" and a rapid rate of descent, the aircraft landed with a 75-knot forward speed. The nosewheel bounced, then collapsed, and the aircraft slid forwards until it struck an irrigation ditch, separating the cockpit from the forward fuselage and causing the aircraft to flip over and break up.

    blog post photo
    Tire tracks show the start of the V-22's landing run (USAF)

    Brig Gen Donald Harvel, president of the board, determined "from the preponderance of the evidence" that the Osprey had experienced power loss on the approach, leading to a high rate of descent and making it impossible to go around. Video of the accident and of strike marks on the ground showed that the proprotor speed was 78-80 per cent of nominal RPM, which could only be caused by substantial power loss.

    Engine power had been measured on April 6, but Harvel finds it possible that after four subsequent austere landings, including one where the engine air particle separator (EAPS) failed, "one or both of the mishap aircraft's engines was degraded below acceptable standards". Harvel believes that the accident crew recognized an excessive descent, found a go-around impossible due to lack of power, and attempted a "near perfect roll-on landing".

    However, Lt. Gen. Kurt Cichowski, vice commander of Air Force Special Operations Command, the convening authority for the investigation board, ruled that engine power loss could not be considered as a major factor in the accident.

    Harvel notes that had the nose gear not collapsed and if the aircraft had not struck the ditch, damage and injuries would have been much less severe. Separate testing by the Navy has shown that the V-22's STOL performance is limited by the nose landing gear, which early trials showed cannot clear a 2-inch bump at more than 25 knots.

    Tags: ar99, v-22

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