The Bell Helicopter 525 Relentless that crashed earlier this month during a test flight broke up in midair, the National Transportation Safety Board said Wednesday.
Although NTSB investigators have not released their preliminary findings of the July 6 crash in Ellis County that killed two pilots, it appears the main rotor struck the front and back of the helicopter, causing the helicopter to break up in mid-flight, said NTSB spokesman Peter Knudson.
“The signatures indicate that the main rotor struck both the tailboom and the nose,” Knudson said. “The probable cause of the inflight break-up is still under investigation.”
No cause has been ruled out yet and investigators are still looking at all systems in the helicopter, Knudson said. The preliminary report is usually issued within 30 days of the crash and should be available in early August.
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According to FlightRadar24, the helicopter was traveling 199 knots (about 229 mph) at an altitude of 1,975 feet immediately before the crash. Throughout its one-hour test flight, radar data shows the helicopter increased and decreased speed several times.
To help investigators determine the cause of the crash, Bell Helicopter employees are using an engineering simulator to evaluate the data and providing test results to the NTSB, Knudson said.
In an interview with Rotor & Wing International this week, NTSB investigator John Lovell said the “data indicates that main rotor [rotations per minute] dropped significantly” and the main rotor blades “appeared to have dropped from their normal plane of rotation.”
Bell is testing computer-controlled flight controls, known as fly-by-wire, on the 525 Relentless, a large aircraft that can seat up to 20 people. Since it is the first commercial helicopter with the system in the U.S., the Federal Aviation Administration issued a notice proposing special conditions to establish safety levels for the helicopter design.
Bell Helicopter had hoped to complete the certification process for the 525 in 2017, but the crash has delayed certification as well as first deliveries to customers.
“We do remain committed to the 525 program and will work to ensure the aircraft will be a safe, reliable and high-performance helicopter,” said Textron chief executive Scott Donnelly last week. Textron owns Bell Helicopter.