A perfect day, until the crash. Aviation Week has an evocative article about the crash of a Marine MV-22 Osprey in Hawaii on 17 May 2015. (A registration may be required, but no pay).
Despite the destruction of the airframe, only two of the Marine passengers on this combat-training mission, and none of the crew, were lost. But AW got hold of either a released Article 15-6 investigation report, or one hell of a leak from the actual accident board report (which is a closely held document, not releasable to the public).
It took about an hour for the Osprey to reach the Oahu coast from the Essex, arriving at about 11:30 a.m. Hawaii time. Outside, an 11-kt. wind topped off a 75F morning under slightly overcast skies as the pilots dealt with a slight glare. From the cockpit all was clear within 20 mi. of the beach. The pilots started their descent to 6,500 ft. and then to 1,500 ft. About three miles out, the pilots reduced power. The Osprey then began the riskiest stage of its flight—conversion to helicopter mode and preparation for landing, raising the nacelles and lowering the landing gear when it reached about 110 kt. a half mile before the beachline.
The Osprey crossed the beach at 80 kt. about 620 ft. above the sand, part of a formation of five MV-22s taking part in the exercise. In the cabin, some Marines would note the change in view from the vast blue Pacific to green fields and fences—a lot of fences. This would be a tight landing area.
The MV-22 began a right turn toward LZ Gull. That’s when the confusion started—the tiltrotor was following a flight path about 50 yards southeast of the intended landing point. One of the other formation Ospreys, Mayhem 12, radioed a warning: Mayhem 11 was in the wrong zone, it was too far to the right and off the range complex.
Fifty yards made all the difference, as did the failure to recon the DZ properly, and these errors would be compounded momentarily.
Inside the cabin, as they heard the change in the engine pitch announcing the switch from flight to imminent landing, the Marines strapped on their gear and unstrapped themselves from their safety harnesses. This had become common practice to allow them to exit the aircraft as quickly as possible. It was also a flagrant safety violation. They smacked themselves and each other on their plated chests. Officers held up two fingers—two minutes to landing and assault. Some again checked their magazines.
Using the nearby fence line as a reference point, the pilots started to creep their Osprey toward the LZ, with the large tree to their left. It did not look good, and they radioed the rest of the crews: “We’re going to wave this off …” The noise abatement area to the north severely constricted their ability to maneuver.
But a ragged flight formation was the least of their problems. As the aircraft descended to 25 ft., Mayhem 11 encountered brownout conditions that engulfed the Osprey—rotor downwash was kicking up a thick fog of sand and dust, obliterating points of visual reference.
“‘Brown out’ landings are one of the most difficult operations a helicopter or tiltrotor aircraft can conduct and require detailed planning for success,” investigators would later note. Those aboard Mayhem 11 were ill-prepared to perform one.
They waved off the first landing attempt, then came right back to the same place to try again.
Their next approach profile was exactly the same, producing another severe brownout. The aircraft became engulfed in dust about 25 ft. off the ground as the pilots struggled to get their bearings. It proved impossible to maintain a stable hover due to the unavailability of a clear, unobstructed view of the landing zone. The aircraft moved vertically and laterally off its mark, and the pilots realized they were climbing without meaning to. To reset and attempt another landing, the Osprey climbed to about 110 ft. to get out of the dust cloud as the pilots shifted controls, cued up a new hover page and hit the trim release button, so the aircraft wouldn’t drift from its spot in the sky.
The downwash of a V-22 has to be experienced to be believed. It is much stronger than the downwash of any other hovering rotorcraft — worse than the H-47, the H-53, the long-retired CH-54, and even the mighty Russian Mi-26. It’s very unpleasant to be under, and frightening to fast-rope from.
In addition, brownout not only ruins pilot (and crew chief) visibility, it also sluices a dry river of particulates into the engine intakes. The USMC and other Osprey operators were about to learn an expensive lesson about the plane’s ability to filter these particles.
Mayhem 11 had surpassed its limits for brownout exposure. Neither landing pass by itself had exceeded the 60-sec. brownout limit, and procedures said nothing about a combined limit within any certain period of time. The pilots were operating within accepted procedures. After this day, though, those procedures would be changed.
In the traditional story of Faust, the Devil requires the knowledge-seeking doctor to sign in blood. Flight manuals and operating limitations, also, are sometimes written in blood.
As the pilots tried to set the aircraft down for a third time, those watching the attempt from a nearby hill lost sight of the Osprey in the dust, but they heard a loud pop and saw three red flashes from the bottom exhaust of the port side engine nacelle, followed by black smoke. The pop also was heard within the V-22 itself, penetrating the hearing protection worn by the Marines. The left-hand engine had begun to clog with sand and dirt filled with reactive minerals—calcium, magnesium, aluminum and silicon—that had melted in the combustor and resolidified on the fixed first-state turbine vane. The engine surged, dipping the Osprey immediately left and rolling some of the passengers inside.
The aircraft was, perhaps, at 10 or 15 feet above the fence when the engine began to fail and the crew tried to power their way out of the imminent crash.
Inside the cockpit, time seemed to slow as the adrenaline flowed. The pilots felt the aircraft settling in its own downwash and they knew something was wrong. The Osprey started to fall. The crew chief yelled, “Power!” And then it seemed like the entire aircrew was yelling at once in unison: “Power! Power! Power!”
Both pilots slammed full forward the thrust control lever, which moves fore and aft like an airplane throttle, in an attempt to gain power and altitude. But there was nothing stopping the Osprey now—it plunged to the ground at a speed of about 36 ft. per second.
For comparison’s sake, the old MC1-1B/C parachute descended at about 18-22 feet per second with a normal load (150-300 lb.).
The crash destroyed the aircraft, killed two Marines, and injured 18 more. The casualty list would have been much worse if the Marines hadn’t self- and buddy-rescued before the noxious fumes from burning Osprey pieces could finish them.
Osprey mishaps get a lot of ink, but the aircraft is surprisingly safe, and surprisingly robust. The ship’s accident and fatal-accident rate is lower than some other combat types. One very expensive accident resulted when an Osprey tumbled off a flight deck and hit the water, getting partly submerged. The pilots never stopped fighting and they saved the aircraft, although one crewman bailed out after impact — and was not recovered by USS Boat. (Salt water corrosion meant that this would have been a Class A mishap even without the fatality, but that Osprey was repaired and flies on). The Marines are operating a couple hundred of the unique birds.
A similar “hard landing” in a Chinook or 53 would likely have caused more serious injuries and more fatalities. Unlike those aircraft, the airframe does burn (and release toxic fumes as it goes) which puts a premium on self-help after the parts are done bouncing.
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