Deadly 2015 Fort Campbell helicopter crash: What we now know

CORRECTION: An earlier version of this article mischaracterized the pilot's performance standards. Kevin Weiss met the standards.

The training mission was halfway through when something startled the two pilots of an AH-64E Apache helicopter as it flew over the Cumberland River in Montgomery County.

For the next 24 seconds, more than 50 warnings, cautions and advisories alerted them that their Army aircraft was in serious trouble. A crew from a second helicopter watched helplessly as Kevin Weiss, 32, and Alex Caraballo-Leon, 35, struggled to do the impossible.

"At approximately (6:48 p.m.), the accident aircraft was observed by the (air mission commander) aircraft as it pitched up abruptly, yawed and rolled left as the tail boom and main rotor hub separated from the aircraft," according to a U.S. Army Safety Accident Investigation Report obtained by USA TODAY NETWORK-Tennessee. "The aircraft then impacted the ground and burst into flames."

More: Two pilots killed in Fort Campbell helicopter crash

The report on the Dec. 2, 2015, crash is more than 300 pages long, and the damage to the new Apache helicopter was recorded in painstaking detail.

It comes down to this: The problem that caused the $25.2 million Apache to crash could not be avoided once a small piece malfunctioned — or didn't function at all — because it was not properly installed.

The AH-64E Apache Guardian was delivered to the 2-17th Heavy Attack Reconnaissance Squadron at Fort Campbell on Aug. 18, 2015.

It underwent an inspection on Nov. 19, 2015, and two bearings that would later prove critical — the numbers 1 and 3 pitch change link road end bearings — were replaced with ceramic-coated bearings the same day.

The helicopter had only 50 hours on it when Weiss and Caraballo-Leon reported for training on Dec. 2, 2015, at 11 a.m.

More: Pilots from Apache helicopter crash identified

The training mission

The two were scheduled to conduct team training with a second AH-64E on day and nighttime vision. Weiss was in command of the first helicopter, and Caraballo-Leon was in the back seat.

They were supposed to do field exercises at Range 75 on post, but because the ground was saturated by rain, the crew and the air mission commander's aircrew were taken by ground to the Sabre Army Heliport.

The team evaluated the forecast and were briefed on the training mission.

The two helicopters took off at 4:15 p.m.

The team practiced movement techniques around the Suckchon Drop Zone and then went east. After stopping to refuel at 5:30 p.m., Weiss and Caraballo-Leon assumed the lead position for the second half of the training mission.

The team flew to the Lake Kyle area — still on Fort Campbell property — but saw a UH-60 Black Hawk operating in the same vicinity.

The air mission commander directed the pilots to depart the Fort Campbell reservation for Whifferdill Airfield in Chapmansboro, Cheatham County, southeast of Clarksville. While en route, the helicopter passed over the Cumberland River and then flew south.

Rotor and tail

At 6:48 p.m., while flying 120 knots at 700 feet above ground level, "the aircraft encountered an anomaly which caused it to pitch up and roll left."

According to the report, a main rotor pitch housing with an attached composite main rotor blade separated from the main rotor head.

The tail boom separated from the fuselage, and the remaining main rotor system separated from the main transmission.

Essentially, the Apache came apart in mid-air.

The main fuselage, which is the body of the helicopter where the pilots were sitting, hit the ground and burst into flames.

As the other helicopter kept track of the wreckage, an emergency crew landed adjacent to the crash site to check for survivors. None were found.

The next day, the investigation began. It took more than a year and a half for the Army to release its findings this month.

The investigation

Shortly before the crash, something startled Weiss and Caraballo-Leon.

About 30 seconds of audio were recovered that shows one of the men responding to a slew of warnings, cautions and advisories that appeared on a display panel.

Because the fire damaged so much of the helicopter, not all its pieces were found. But the parts that were painted a picture of what went wrong.

An examination of the Number 3 lower bearing outer ring revealed "undisputable evidence" that the bearing was not staked onto the Number 3 lower rod end, according to the accident report.

"The root cause for the displacement of the lower rod end and bearing was the bearing not being staked," the report said. "Once the displaced rod end made contact with the rotating swashplate, lug fatigue ensued, causing the No. 3 lower rod end to fracture," the report said. "All other damage to the aircraft is secondary."

The No. 3 pitch housing was found about 297 yards from the fuselage of the helicopter. The tail boom was found about 215 yards away. The main rotor hub and attached parts were found about 39 yards away. The debris surrounded those items and the fuselage, which suffered "intense fire damage."

The blaze was confined to the main fuselage. Because there was no fire damage to the items that broke apart before the crash, investigators knew the blaze didn't start until the helicopter, which was full of fuel, hit the ground.

According to the report, the crash was not survivable.

Who's at fault?

The report found fault with work performed by three soldiers tasked with installing parts on the helicopter in November 2015. It said standards were not met because of the deficient staking procedures. The report also indicated an inspector did not meet standards.

The names of those four soldiers were redacted from the report, as were the specific explanations for what they did wrong.

"The safety of our soldiers is paramount," said Capt. Kristoffer L. Sibbaluca, 101st Combat Aviation Brigade spokesperson, when asked for comment on the investigation and its findings. "This was a tragic accident and our thoughts and prayers remain with all those affected.

"We have since implemented all recommendations from the U.S Army Safety Accident Investigation report to ensure we do everything in our power to prevent an accident of this nature."

The final report recommends that an inspection of the staking process be implemented in the future.

All other recommendations were redacted.

The pilots

Chief Warrant Officer 2 Weiss entered the Army on March 26, 2003. He had 777 flight hours, 389 of which were in combat. He was 32 and a native of McHenry, Illinois.

Weiss served as an Apache attack helicopter pilot with Company C, 3rd Battalion, and Troop C, 2nd Squadron, 17th Cavalry Regiment, 101st Combat Aviation Brigade.

More: Pilot was always 'life of the conversation'

Chief Warrant Officer 2 Caraballo-Leon entered the Army on April 30, 2003. He had a total of 897 flight hours, 460 of which were in combat. He was 35 and a native of Patillas, Puerto Rico.

Caraballo-Leon served as an Apache attack helicopter pilot with Company B, 1st Battalion, and 2nd Squadron, 17th Cavalry Regiment, 101st Combat Aviation Brigade.

Reach Reporter Stephanie Ingersoll at singersoll@theleafchronicle.com or 931-245-0267 and on Twitter @StephLeaf