Severe vibration caused the crash of a Bell helicopter that killed two pilots during testing in 2016 in rural Ellis County, according to a final NTSB report published this week.
Officials at Fort Worth-based Bell Helicopter Textron say the company has made changes to the configuration of the pilot controls in response to the crash of the 525 Relentless, which occurred July 6, 2016, after the aircraft broke up in midflight near the town of Italy.
“Bell and the NTSB have carefully studied the cause of the vibration, which had never been encountered before,” company officials said Wednesday in a statement. “The vibration was the result of an unanticipated combination of very high airspeed with a sustained low rotor RPM condition.”
The crash killed pilots Jason Grogan, who lived in Burleson with his wife and two children, and Erik Boyse. Both were members of the Select Marine Corps Reserve and had served multiple times in Iraq, according to Military Times.
The pilots were conducting routine tests that included shutting off one of the aircraft’s two engines to see how the helicopter would perform if one engine failed, company officials said.
About 11 seconds into the test, the crew experienced unexpected vibration in the cabin.
“Vibration at the pilot seat led to unintentional control inputs that rapidly amplified the vibration as the crew attempted to respond,” company officials said. “Approximately 20 seconds into the test, rotor RPM slowed significantly and the ship broke up in flight.”
The helicopter was traveling 199 knots (about 230 mph) at an altitude of 1,975 feet immediately before the crash. The 525 Relentless had been in the air for an hour and eight minutes.
Radar data show before that the helicopter slowed down and sped up several times, from 190 knots at an altitude of 2,650 feet down to 150 knots.
In its promotional material, Bell said the helicopter’s maximum cruising speed is 162 knots (about 185 mph).
“The NTSB determined that the probable cause of the accident was a severe vibration of the helicopter that led to the crew’s inability to maintain sufficient rotor rotation speed, leading to excessive main rotor blade flapping, subsequent main rotor blade contact with the tail boom, and the resultant in-flight breakup,” NTSB wrote in its report. “About 21 seconds into the test, the main rotor blades flapped low enough to impact the tail boom, severing it and causing the in-flight breakup of the helicopter.”
Testing resumed last year
Since the crash, Bell has enhanced its filtering system on the pilot’s side-stick controller, so vibrations of the pilot stick are not passed onto the rotor system. Also, filtering was added to the control system to stabilize the aircraft during gusts and maneuvers.
The NTSB has also recommended changes in the way test flights are recorded.
Testing of the 525 Relentless, a civilian helicopter designed to carry up to 20 passengers, resumed last July.
The aircraft was originally scheduled to be placed on the market last year, but sales were postponed while the crash investigation was underway. Bell officials have not disclosed when the aircraft might be available for sale.
“We remain committed to the 525 program,” spokeswoman Lindsey Hughes said in an email. “The continued work of the program team will result in a reliable, innovative helicopter with advanced rotorcraft safety features when it comes to market.”
‘Somebody has to test those limits’
In the hours after the 2016 crash, Grogan’s widow, Lynn, recalled the advice another military wife had given her shortly after her 2005 marriage about preparing for the possibility her husband could die.
“She told me that as long as he’s flying, I need to wake up every day prepared that will be the day he won’t come home,” she told the Star-Telegram at the time.
As a test pilot, she said, “somebody has to test those limits, and that’s what he did.”
Jason Grogan was survived by two children, Katelyn, who was 8 at the time, and Aaron, who was 5.
Grogan flew the 525 Relentless three to four times a week as a test pilot.
Before working for Bell, he served two tours of duty in Iraq and worked as a test pilot in California.
Boyse was from Spokane, Wash., and was survived by a wife and infant daughter, television station KREM reported.
Big Bell investment
Bell has invested hundreds of millions of dollars as it shifts to commercial sales because orders of its military aircraft have slowed.
In 2016, Scott Donnelly, chief executive officer of Bell’s Rhode Island-based parent, Textron, said the company had built two 525 helicopters for flight testing with a third expected soon.
The 525 Relentless is the first commercial helicopter in the U.S. to have computer-controlled flight controls, known as fly by wire. In 2016, the Federal Aviation Administration issued a notice proposing special conditions to establish safety levels for the new helicopter design.
“This helicopter will have a novel or unusual design feature associated with fly-by-wire flight control system functions that affect the structural integrity of the rotorcraft,” the FAA said. “These proposed special conditions contain the additional safety standards that the administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.”
This report includes information from the Star-Telegram archives.