The destruction of the prototype delayed type certification of the Bell 525 for a year and a filter was added to the collective input control to avoid recurrence of the biomechanical feedback.
The accident involved the first Bell 525 Relentless prototype test vehicle (registration N525TA[4]), built in 2015 and assigned serial number 62001.
[7]: 13–14 At 11:48 AM, approximately 20.25 seconds into the test, the main rotor red blade[9] was flapping out-of-plane with a displacement sufficient to exceed the instrument's capacity; 0.5 seconds later, recorded airframe loads indicated the main rotor had struck the tail boom.
[10] The NTSB stated that a working CVDR would have helped to determine when the pilots first detected the severe vibration and a cockpit image recorder for test and experimental helicopters would have shown the actions they took to respond to it.
[6] In its preliminary report, the NTSB concluded that biomechanical feedback[11] to the collective control contributed to the aircraft's vibration.
[2][8] In addition, the prototype 525's attitude and heading reference system (AHRS) was designed to detect and respond to uncommanded accelerations to reduce their effects, such as external buffeting from winds.
[2] The NTSB noted that existing visual alerts to low rotor rotation speed may have been affected by the severe vertical vibration; because no distinctive aural warning tone was available and the increased collective control friction may not have been detected, the crew may not have realized the rotor rotation speed was low and did not respond accordingly, concluding that "the lack of an automated safeguard in the modified one-engine-inoperative software used during flight testing to exit at a critical [rotor rotation speed] threshold" and "the lack of distinct and unambiguous cues for low [rotor rotation speed]" further contributed to the inability to maintain control.
[2][8] After the accident, Bell amended the control paradigm, improving the filter on side-stick collective inputs to block transmission of stick vibrations to the rotor system.