Two Marine pilots killed in a January Marine helicopter crash in California last winter were just a few hundred yards from their final destination when the transmission of their aircraft UH-1Y helo their aircraft’s transmission seized, stopping its main rotor and causing it to plummet, according to a lengthy investigation into the crashcrash and burn.Two pilots killed by a Marine helicopter crash in California last winter were just a few hundred yards from their final destination when their aircraft’s transmission seized, stopping its main rotor and causing it to plummet.

Improper aircraft maintenance and pilot misjudgment contributed to the fatal Jan. 23 UH-1Y Venom helicopter crash near Marine Corps Air Ground Combat Center Twentynine Palms accident, investigators wrote in the an accident report. The report was obtained by Marine Corps Times through a Freedom of Information Act request.

The pilot, Maj. Elizabeth Kealey, and co-pilot, Capt. Adam Satterfield, were killed in the crash. Both were assigned to Marine Light Attack Squadron 169, and were concluding a short flight from Marine Corps Air Station Camp Pendleton, their home base, to participate in an exercise with the rest of their squadron. Kealey was a captain at the time and Satterfield a first lieutenant — the pair was posthumously promoted during a February ceremony.

At the heart of the tragedy was an improperly installed filter cover, which allowed the transmission to dump all its oil during flight. Ultimately, investigators found that the aircraft Kealey and Satterfield plummeted 200 feet, just 400 yards away from the Marines' ir intended landing point. 

Investigators would find that a confluence of missteps, oversights and miscalculations led would lead to the fatal accident, but stopped short of finding wrongdoing. 

Maj. Gen. Michael Rocco, the commanding general of 3rd Marine Aircraft Wing, wrote in his endorsement of the investigation that the deaths of Kealey and Satterfield were "in the line of duty and were not due to their own misconduct."

"There are two errors that contributed to this tragic event. The improper installation of the [main rotor gear box] 40-micron filter cover and the decision by the aircrew to continue flying to the destination instead of landing at a closer suitable area," investigators wrote in an accident report obtained by Marine Corps Times through a Freedom of Information Act request.

Sensor troubles 

"There are two errors that contributed to this tragic event. The improper installation of the [main rotor gear box] 40-micron filter cover and the decision by the aircrew to continue flying to the destination instead of landing at a closer suitable area," investigators wrote.

About 34 minutes into the 49-minute flight, the pilots noticed that their oil pressure gauge fluctuated and then plummeted to zero. Suspecting an instrument malfunction, the pilots ignored warning lights indicating that the transmission failure could occur within 15 minutes. 

While the warning lights typically indicate an emergency, the pilots likely assumed the problem was due to a faulty  Normally, that would be considered a significant emergency. But the pilots may not have thought they were facing impending catastrophe, likely assuming that the problem was a faulty gauge, not actual fluid loss, because of recent maintenance issues. About a week prior, On Jan. 18 and 19, their aircraft had undergone maintenance because of a faulty reading, which included replacing oil pressure sensors.

With They decided to continue to Twentynine Palms, which was more than 15 minutes away, the pilots decided to continue flying. They passeding two airports where they could have landed safely before — prior to the transmission froze, the investigators found.

"The [pilots] chose not to divert to either Palm Springs or Yucca Valley airports, both of which would have put them on the deck in about six to seven minutes after initial indications of loss of [mMain rRotor gGear bBox] oil pressure," the investigator wrote. "This would have provided them eight to nine minutes of time remaining until the designed failure limit ... on the MRGB was reached."

Instead of putting the aircraft down, they calmly called to have avionics trouble shooters standing by on the flight line.

"This is indicative of a pilot who thinks they have an instrument indication problem, not one that has a full-blown emergency on their hands," the investigating officer wrote.

According to Navy aviation publications, zero oil pressure should trigger pilots to execute "impending [main rotor gear box] failure procedures," under the assumption that the aircraft will soon become inoperable. That means landing as soon as possible.

"Loss of MRGB oil pressure will render the helicopter unflyable within 15 minutes," according to the aircraft’s Naval Air Training and Operating Procedures Standardization manual states.

"At the moment that the MRGB lost oil pressure, the [Marine aircraft] had at most approximately 15 minutes of flight remaining according to the [manual] NATOPS," the investigation states. "The [Marine aircraft commander’s] decision to continue on to Twentynine Palms, which was over 15 minutes away, was directly causal to this mishap." the investigating officer wrote. "The MAC chose not to divert to either Palm Springs or Yucca Valley airports, both of which would have put them on the deck in about six to seven minutes after initial indications of loss of MRGB oil pressure. This would have provided them eight to nine minutes of time remaining until the designed failure limit on the MRGB was reached.""...I believe the fact that the [Marine aircraft] had recently had the MRGB pressure sensor and packing on the pressure transducer replaced in the days prior to the [Marine flight] greatly influenced this decision." according to the investigating officer.

A maintenance error 

A In fact, the tragedy stemmed from the fact that the new filter cover improperly installed three days before Kealey and Satterfield were killed the flight Jan. 20, was not seated properly and leaked or came off in flight.

The root cause of the trouble with the filter was a maintenance error made long before the accident. The filter housing must be uninstalled to change the filter. But at some point, an unapproved epoxy was used to seal the filter body, preventing Marines from removing it.

Two pilots killed by a Marine helicopter crash in California last winter were just a few hundred yards from their final destination when their aircraftÕs transmission seized, stopping its main rotor and causing it to plummet.
Two pilots killed by a Marine helicopter crash in California last winter were just a few hundred yards from their final destination when their aircraftÕs transmission seized, stopping its main rotor and causing it to plummet.

After falling vertically and slamming into the ground right-side-up, the aircraft rolled to its right side. Members of Marine Unmanned Aerial Vehicle Squadron 1, working in a hangar about 1,000 feet away, ran to the site and pulled Kealey and Satterfield from the wreckage.

Photo Credit: DoD

As a result, three waivers were issued over months to forgo a filter change. It was deemed unlikely that the filter was dirty, an assumption supported by the post-crash investigation, meaning the filter itself was not a contributing factor.

However, during one failed attempt to change the filter while it was still installed in the aircraft, the cover was damaged. That required that a new one be installed on Jan. 20. Three Marines worked to accomplish the task, which was later inspected and approved by a superior.

But because the filter housing was contained in a small space, they did not realize that a retaining ring that holds the cover on was not seated properly.

That ultimately led ntimely lead to massive fluid loss during flight three days later and then the crash.

Shortly after impact, Kealey and Satterfield were pulled from the aircraft by nearby Marines from Marine Unmanned Aerial Vehicle Squadron 1 who were working in a hangar about 1,000 feet away.

After falling vertically and slamming into the ground right-side-up, the aircraft rolled to its right side. Members of Marine Unmanned Aerial Vehicle Squadron 1, who were working in a hangar about 1,000 feet away, sprang into action.

They pulled Satterfield from the aircraft. A Marine, whose name was redacted, directed others to try to put out a 3- to 4-foot fire when he One Marine, whose name was redacted, directed others Marines to begin fighting a three- to four-foot fire when he noticed Kealey was still in the helo. They aboard. He rallied Marines to extracted her.

The same Marine whose name was redacted from the report then noticed and then noticing Satterfield was not being tended to in the chaos, so moved to aid him. They cleared his airway, got him onto a backboard and cut away clothing to check for additional injuries. The continued to aid the pilots until medical personnel arrived on scene.

Kealey was transported to the Desert Regional Medical Center in Palm Springs and passed away 45 minutes later during surgery. Satterfield was transported to Naval Hospital Twentynine Palms where he died in the emergency room ER an hour later. Both died of "multiple blunt force trauma."

The seats in their helicopter worked as designed to absorb the impact, but the fall was too far for them to be effective both the seats or human tolerance, according to the investigation.

Ultimately, investigators found "oversights in judgment in various areas that do need to be addressed through mentoring and leadership," however they did not find any negligence.

The investigator recommended did recommend changes to the focusing on the filter housing maintenance that caused the leak as the culprit. Those include: 

  • Ensuring proper supervision of flightline maintainers removing the 40-micron filter housing.
  • Update naval air NAVAIR publications with detailed instructions for removal, disassembly, inspection, reassembly and installation of the filter housing.
  • Ensure all members of the UH-1 helicopter community learn pertinent information from the accident and begin training with it pending publication updates.
  • Prohibit the installation of the filter cover without removing the entire filter housing.

Beyond that no action was recommended.

"I do not believe there should be any punitive action taken against any members of HMLA-169," the investigating officer wrote.