A corroded blade that came loose on a Marine Corps KC-130T transport aircraft at 20,000 feet above Mississippi caused the deaths of 15 Marines and one Navy corpsman last year, according to a Marine Corps accident investigation released Thursday.
The propeller blade -- improperly maintained by Air Force maintenance crews in 2011 and later overlooked by the Navy, according to officials -- set off a series of cascading events that would cut the aircraft into three pieces before it fell to the ground on July 10, 2017, in a LeFlore County field, officials wrote in the investigation.
"Warner Robins Air Logistics Complex failed to remove existing and detectable corrosion pitting and [intergranular cracking] on [Propeller 2, Blade 4] in 2011, which ultimately resulted in its inflight liberation," investigators wrote. "This blade liberation was the root cause of the mishap."
The accident investigation was first reported in a joint Military Times and Defense News article Wednesday.
The aircraft, which belonged to Marine Aerial Refueling Squadron 452, out of Newburgh, New York, had been tasked with transporting six Marines and a sailor belonging to Marine Corps Forces Special Operations Command from Cherry Point, North Carolina, to Yuma, Arizona, for team-level pre-deployment training.
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Seven service members were from MARSOC's 2nd Marine Raider Battalion; nine Marine aircrew belonged to the squadron, VMGR-452. All 16 troops aboard the aircraft perished in the crash.
"I found that the deaths of Maj. Cain M. Goyette, Capt. Sean E. Elliott, Gunnery Sgt. Mark A. Hopkins, Gunnery Sgt. Brendan C. Johnson, Staff Sgt. Robert H. Cox, Staff Sgt. William J. Kundrat, Staff Sgt. Joshua M. Snowden, Petty Officer 1st Class Ryan M. Lohrey, Sgt. Chad E. Jenson, Sgt. Talon R. Leach, Sgt. Julian M. Kevianne, Sgt. Owen J. Lennon, Sgt. Joseph J. Murray, Sgt. Dietrich A. Schmieman, Cpl. Daniel I. Baldassare and Cpl. Collin J. Schaaff occurred in the line of duty and not due to their misconduct," an investigator said.
"Neither the aircrew nor anybody aboard the KC-130T could have prevented or altered the ultimate outcome after such a failure," officials said.
The crew had come over in two KC-130Ts from Stewart Air National Guard Base, New York. The two planes swapped missions, investigators said, "due to difficulties with cargo and embarkation" with one of the aircraft.
The destination of the flight, call sign "Yanky 72," was Naval Air Facility El Centro, California.
The KC-130T carried thousands of pounds in cargo, including "two internal slingable unit 90-inch (ISU-90) containers, one Polaris Defense all-terrain utility vehicle (MRZR), and one 463L pallet of ammunition," officials said. Also on board were 968 lithium-ion batteries, 22 cans of spray paint, one compressed oxygen cylinder, personal baggage and military kits, weighing about 2,800 pounds.
Propeller Two, including the corroded Blade Four, or P2B4, on the aircraft had flown 1,316.2 hours since its last major overhaul in September 2011, according to the documents. The aircraft had last flown missions May 24 through July 6, accumulating more than 73.3 hours within those two weeks.
The aircraft entered service in 1993. The propeller in question was made by UTC Aerospace Systems.
On the day of the accident, after it had detached from the rotating propeller, P2B4 sliced through the port side of the main fuselage, the 73-page investigation said.
The blade cut into the aircraft and then "passed unobstructed through the [mishap aircraft's] interior, and did not exit the airframe but rather impacted the interior starboard side of the cargo compartment where it remained until cargo compartment separation," it said. Its impact cut into the starboard interior support beam.
The violent force shook through the plane, causing the third propeller engine to separate from the aircraft. It bounced back into the aircraft, striking the right side of the fuselage and forcing a portion of one of the fuselage's longerons to buckle. Its impact also caused significant damage to the starboard horizontal stabilizer, causing "the stabilizer to separate from the aircraft," the investigation said.
Soon after, the aircraft's cockpit, center fuselage and rear fuselage would all break apart mid-air during its rapid descent.
The pilots and crew involved in the cataclysmic event likely experienced immediate disorientation and shock, rendering them immobile, officials said.
Investigators said an average of 5 percent of blades processed in the past nine years by Warner Robins (WR-ALC) were Navy or Marine Corps blades. The maintenance paperwork for the 2011 work on P2B4 no longer exists because, per Air Force regulations, work control documents are destroyed after a period of two years, the investigation noted.
During the quality control and quality assurance process, where items are inspected and approved or rejected based on their conditions, investigators said Warner Robins used ineffective practices and bypassed critical maintenance procedures.
Some of the other blades and propellers also were considered unsatisfactory, investigators said.
According to the report, the aircraft also missed an inspection in the spring. A 56-day conditional inspection is required when, within 56 days, the engine has not been run or the propeller has not been manually rotated "at least three consecutive times" on the aircraft, or a propeller has not "been flowed on a test stand at an intermediate level maintenance activity." Investigators said there was no supported evidence that a checkup was conducted.
The Navy also neglected to impose a check-and-balance system on the WR-ALC's work, investigators stated.
"Negligent practices, poor procedural compliance, lack of adherence to publications, an ineffective QC/QA program at WR-ALC, and insufficient oversight by the [U.S. Navy], resulted in deficient blades being released to the fleet for use on Navy and Marine Corps aircraft from before 2011 up until the recent blade overhaul suspension at WR-ALC occurring on 2 September 2017," officials said.
A Naval Air Systems Command (NAVAIR) liaison stationed at WR-ALC also did not check on the maintenance being done, according to Military Times and Defense News. Leaders at the base had "no record" of the liaison ever checking procedures, the report said.
Since the accident, multiple agencies -- including the Navy; Air Force; respective commands; UTC Aerospace, maker of the propeller; and officials from Lockheed Martin, the aircraft's manufacturer -- have convened to streamline practices and procedures to prevent any more similar catastrophic events, the documents said.
Investigators recommended the joint team's primary objective be to create a "uniform approach" to overhauling procedures for both Air Force and Navy C-130T blades.
"WR-ALC plans to upgrade and improve their ... process[es]," which will include the use of additional robotics, automation, and a wider scope of what's inspected, the investigation said.
That includes more refined paperwork filings into "one consolidated electronic document identifying all defects and corrective actions," it said.