A cascade of aviation readiness problems followed 12 Hawaii Marines into two helicopters that collided at sea off Oahu on Jan. 14, killing all aboard, the crash investigation shows.

Pilot error was faulted. However, the investigation notes that a 2015 Marine Corps study found that readiness within the entire CH-53E Super Stallion fleet was “appalling” due to inadequate inventory, too many aircraft in maintenance, a lack of designated resources and no fleetwide “reset” following heavy use in Iraq and Afghanistan.

Inadequate flight time contributed to the crash, the Marine Corps said. The flight included some of Marine Heavy Helicopter squadron 463’s most experienced aircrew. “However, currency, experience, proficiency and qualifications do not compensate for inadequate pilot flight time,” the report said.

In the 30 days preceding the crash, the four Hawaii pilots had only flown four, five, four and 13 hours, according to the investigation. The required average flight hours per month for CH-53E pilots is 15.1 hours to maintain readiness and proficiency, Capt. Sarah Burns, a Marine Corps spokeswoman, said in an email.

Lisa and Mike De La Cruz, the parents of 24-year-old crew chief Sgt. Dillon Semolina, who was among those killed, said the litany of problems with HMH-463 included the squadron commander being relieved of duty just three days before the crash. The Minnesota couple said there should have been an “operational pause” to regroup from serious problems, but that didn’t happen.

“Lisa and I do not blame any of the pilots for anything whatsover. We know that they did the best that they absolutely could under the conditions,” Mike De La Cruz said in a phone interview. “But we do blame the Marine Corps and we absolutely blame the command.”

If the helicopter squadron had stopped operations at the time of the command change, their son “would be sitting in this living room right now,” Mike De La Cruz said. “He would have been out (of the Marine Corps).” Semolina was going to get out of the Marine Corps in September, De La Cruz said.

The investigating officer said a flight stoppage “would have mitigated many of the risks that contributed to the mishap.”

Pegasus 31, one of two CH-53Es flying the night training mission, accelerated to catch up to Pegasus 32 just as the lead aircraft turned suddenly to the left and into the trailing helicopter’s path.

After the blades of the two big choppers impacted, the fuselage of Pegasus 31 drove into the fuselage of Pegasus 32 near its left window, causing a violent explosion at 1,500 feet altitude, according to the Marine Corps investigation.

“A tactical lead is obligated to remain predictable, and a wingman is obligated to maintain a safe distance from the tactical lead. In this case, neither occurred,” the investigating officer wrote.

The Marine Corps recently released part of the investigation into the crash 1.7 miles off the North Shore. The violence of the ocean impact, “with energy estimated at hundreds of times the force of gravity, instantaneously killed all 12 Marines.”

The Marines took the unusual step of withholding from public release key portions of the investigation, including the investigating officer’s findings, recommendations and command endorsements.

In an email, a spokesman said Marine Corps Forces Pacific redacted the investigation “in accordance with the (federal) Freedom of Information Act” and with guidance provided by the Marine Corps headquarters FOIA office.

The Honolulu Star-Advertiser obtained some of the missing report, which includes a damning statement from Lt. Gen. David Berger, the commander of Marine Corps Forces Pacific.

“This heartbreaking mishap was avoidable,” he said. “The aircrews of Pegasus 31 and 32 were not set up for success.” The risks associated with the night training mission “were not adequately identified nor mitigated,” Berger said.

Two of the pilots were not “adequately proficient” in the use of night-vision goggles, the investigation said. One pilot had only flown 2.8 hours using a night-vision device in the last 90 days, with two of those hours flown the night before the crash. Another of the pilots had not flown with night-vision goggles in over three months.

In the months preceding the crash, HMH-463 copilots averaged approximately two flight hours each month. Inadequate pilot flight hours resulted from HMH-463’s inability to maintain an adequate number of flyable aircraft.

Low numbers of ready aircraft in 2015 conflicted with higher command orders to improve, and HMH-463 had to work multiple weekends and was directed on multiple occasions to work 12 hours on and 12 hours off, leading to poor morale.

“Low morale plagued the HMH-463 maintenance department in 2015,” the investigation said.

An “inadequate” flight brief before the crash was indicative of the “general complacency” that existed within HMH-463. “Pilots resorted to canned briefs because they anticipated frequent flight cancellations” due to a long-term lack of flyable aircraft, according to the report.

From 2013 to January 2016, HMH-463 had as many as 15 helicopters, but sometimes only had two or fewer mission-capable “ready basic aircraft.” Fleet-wide repair directives and the need to support an Australia deployment added significant burdens to maintenance requirements.

In September 2015, flight operations ceased for more than a month after HMH-463 failed a maintenance inspection. A “get well” plan was formulated, but squadron commander Lt. Col. Edward Pavelka was relieved of command on Jan. 11 — three days before the crash — due to his “inadequate improvement” in readiness rates, the investigation said.

The report said that by January 2016, “many pilots in HMH-463 believed they were not ready for combat as they felt they would not be able to safely execute certain tasks, like safely landing a helicopter at night.” Aviators used a simulator to make up for a lack of real flying time.

After the crash, the squadron stopped all flight operations for 12 days and then only conducted functional check-flights required in support of maintenance-related operations, with no training or operational support flights flown for a total of 19 days, the Marine Corps said.

In February, HMH-463 increased the frequency of shorter training flights and increased simulator usage and then progressed to night-vision device training once pilots demonstrated proficiency in daytime flying, the Corps said.

Multiple training flights and participation in the Rim of the Pacific maritime exercise enabled HMH-463 pilots to exceed the 15.1 flying hours requirement, 1st Lt. Joseph Butterfield, a 1st Marine Aircraft Wing spokesman, said in an email.

In August, Naval Air Systems Command announced that the Marine Corps had begun a “full reset” of its CH-53E helicopters “aimed at significantly increasing the number of operationally fit aircraft and addressing systemic issues.”

One Hawaii helicopter is in reset, which involves, on average, a 110-day process of stripping the aircraft down completely and rebuilding it, with all of the Marine helicopters expected to be completed in three to four years.

Asked if anyone in the command chain was disciplined as a result of the crash, Lt. Col. Curtis Hill, a Marine Corps Forces spokesman, said the purpose of the command investigation was, in part, to make a “line of duty” determination, and that “it would be inappropriate to speculate as to any future adverse administrative or punitive actions.”