Story ID: 313
Bell 525 Flight-test Program Makes Progress
By: Mark Huber
Caption: Two Bell 525 flight-test vehicles have accumulated an additional 200 flight test hours since returning to the air last July.
Word Count: 472
Since the Bell 525 returned to the air in July, Bell (Booth C5122) has flown both of its remaining super-medium twins nearly an additional 200 flight-test hours. But its two flight-test vehicles—FTV2 and FTV3—have now accumulated approximately 290 total flight test hours between them. FTV4 is scheduled to make its maiden flight in the fourth quarter.

The program continues to progress on multiple fronts. Bell completed a four-day, 12-flight-hour cross-country ferry flight to deploy the aircraft for cold-weather testing. This included a cold soak test to -35 degrees C. Other trials have involved a super drive system loss-of-lubrication test and initial coupled-flight-guidance testing. Bell further had completed return to flight with software addressing more than 300 problem reports, installed and tested production version of GE engine software, and executed and passed the boosted controls and cockpit controls proofload test for FAA credit.

Other reported progress includes initial navcom avionics system development testing, finalizing upper cowling configuration, and gathering preliminary noise survey data and passing those certification requirements.

Bell has yet to set a formal price for the 525, nor will it confirm a certification timeline goal. When asked about the latter, a company spokeswoman told AIN, “We are working actively to quantify the schedule impact resulting from the pause in our flight operations and will update as we assess the impact.” The 525 program had stood down for a year following the fatal crash of FTV1 in July 2016.

Likewise, Bell declined to comment on the 525 order book but said it might do so in the future now that the NTSB accident report on FTV1 has been released. The report was released in January and found that the accident was caused by “severe vibration of the helicopter that led to the crew's inability to maintain sufficient rotor rotation speed (Nr), leading to excessive main rotor blade flapping, subsequent main rotor blade contact with the tailboom, and the resultant in-flight breakup.”

In addition, the NTSB noted, "Contributing to the severity and sustainment of the vibration, which was not predicted during development, were (1) the collective biomechanical feedback and (2) the attitude and heading reference system response, both of which occurred due to the lack of protections in the flight control laws against the sustainment and growth of adverse feedback loops when the 6-hertz airframe vibration initiated. Contributing to the crew's inability to maintain sufficient Nr in the severe-vibration environment were (1) the lack of an automated safeguard in the modified one-engine-inoperative software used during flight testing to exit at a critical Nr threshold and (2) the lack of distinct and unambiguous cues for low Nr.”

Following the accident, Bell implemented several design changes to the 525, including filtering of the biomechanical and sensor feedback by the control system to prevent amplification of vibrations in specific flight conditions.