Investigators probing the fatal crash on 6 July of the first Bell 525 Relentless prototype believe the main rotorblades struck both its nose and tail boom as it performed a high-speed simulated engine-out test in Texas.

Both experimental test pilots died in the accident which took place as the super-medium twin approached its never-exceed (Vne) speed. The tracking website FlightRadar24 suggests the Relentless was travelling at about 200kt (370km/h) at the time of the crash.

Confirming quotes originally reported on theRotor & Wingnews website, officials from the US National Transportation Safety Board (NTSB) say they saw signs consistent with blade strikes to the nose and tail boom of the 525 during simulated one-engine-inoperative trials.

Data from the helicopter indicates that main rotor RPM had also fallen significantly, the NTSB says, with some of its five composite main rotorblades appearing to drop from their normal plane.

However, the agency declines to speculate on any potential cause. “We have a great deal more work to do until we get into the analysis phase of the investigation where we will put all the data together to hone in on the factors that contributed to the crash,” it says.

The GE Aviation CT7-powered helicopter subsequently broke up and crashed around 30nm (56km) south of Bell’s facility in Arlington, Texas.

Although the majority of the wreckage was consumed by a post-crash fire, the 525’s flight-data recorder was recovered and data successfully downloaded, the NTSB says.

Bell declines to comment on the NTSB statements.

Flight tests using the remaining two prototypes of the fly-by-wire rotorcraft remain suspended, although the company continues to perform ground-based certification work.