Investigators with the National Transportation Safety Board have issued their findings on the cause of an accident that took the lives of two aviators near Italy in 2016.

At approximately 11:50 a.m. on July 6, 2016, Ellis County 911 received a call for emergency services regarding an aircraft crash near Farm-to-Market Road 876 and Bell Branch Road. It was found that a Bell 525 Helicopter crashed in a field off the roadway. The helicopter was undergoing flight-testing at the time of the accident.

“The accident helicopter was undergoing developmental flight tests before type certification. On the day of the accident, the helicopter test crew was performing a series of one engine inoperative tests at increasing airspeeds with a heavy, forward center-of-gravity configuration,” the NTSB report stated. “For the OEI tests, the pilots used OEI special training mode software to reduce the power of both engines to a level that simulated the loss of one engine. The crew initiated the final planned OEI test at 185 knots.”

The report noted that once the particular training mode was engaged, the helicopter’s rotation speed decayed from 100 percent to 91 percent. The crew began to stop the decay, increasing rotation speed to 103 percent, which is the target speed to recover the aircraft from a stall. The crew was only able to recover the speed to 92 percent. This caused a vibration to take place and was evident the main rotor, tail rotor, airframe, in the pilots' seats, and the with control inputs.

“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,” the report read. “As an experimental research and development helicopter configured to carry two pilots and with no passenger seating, the accident helicopter was not required to be equipped with either a flight data recorder or cockpit voice recorder.”

The report continued, stating when certified as a transport-category rotorcraft it would be equipped with these recording capabilities.

According to the Bell Helicopter website, the 525 Relentless has standard seating for the helicopter — two flight crewmembers and 16 passengers with a maximum range of 570. The FAA's website lists the helicopter’s classification as experimental.

“The accident helicopter was heavily instrumented with airborne and ground-based recording systems, including a streaming telemetry system,” the report noted. “A combination cockpit voice recorder and flight data recorder was installed in the flight test helicopter but was not operational at the time of the accident.”

It stated there was also no communications between the crew and either the ground station or the chase helicopter after the test had started.

The NTSB wrote that Bell Helicopter independently addressed this deficiency before the return to flight of the 525-program. The 525-helicopter cockpit audio is being recorded by an onboard cockpit voice recorder and flight data recorder as well as at the ground station along with the telemetry systems during all flights. Cockpit video is recorded by the instrumentation system and archived at the ground station.

“Additionally, Bell Helicopter issued a company-wide business directive to ensure that cockpit audio is recorded during all telemetered flight test activities across their flight test sites,” the document stated. “The NTSB concludes that flight test safety would be enhanced if manufacturers and flight test industry groups had knowledge of the lessons learned from this accident specific to the use of recorders during experimental flight test activities.”

The NTSB recommends the lessons learned from this accident—specific to having recording devices for parametric data, cockpit audio, and cockpit images during experimental flight test activities — be shared with interested manufactures, fight test industry groups and other appropriate parties. The board also stated that recorded cockpit audio and images from experimental flight test aircraft would help manufacturers and investigators better understand the circumstances of an accident. These steps could help to make improvements to the aircraft and procedures.

Phone calls made to Bell Helicopter for comment on the NTSB's report were left unreturned as of Friday evening.

In a statement released at the time of the accident, Bell stated that “This is a devastating day for Bell Helicopter. We are deeply saddened by the loss of our teammates and have reached out to their families to offer support.”