The Bell 525 on display with Bristow livery at Heli-Expo 2018 in Las Vegas.
The FAA has issued a final set of special conditions that Bell Flight must satisfy toward achieving type certification on its 525 Relentless. According to the agency, the special conditions address current 14 CFR 29 standards that do not provide adequate standards for pilot situational awareness of certain flight control modes while flying the 525.
Bell resumed flight testing on the 525 in July 2017, and the NTSB issued its full report on the fatal 2016 crash of the fly-by-wire utility helicopter in January. Now, the FAA’s rotorcraft standards branch has established new conditions that address the 525’s unique four-axis full authority digital fly-by-wire flight control system.
The FAA is focusing on its current set of regulations that do not entirely evaluate pilot awareness of flight control modes while operating the 525. The helicopter’s fly-by-wire system is configured to allow for pilot inputs and coupled flight director modes. Bell designed the 525 so that pilot inputs are transmitted electrically to each of the aircraft’s three flight control computers. The inputs are then processed and transmitted to the hydraulic flight control actuators, which allow manipulation of the main and tail rotors, according to the FAA.
“The proposed special condition will require that suitable mode annunciation be provided to the flight crew for events that significantly change the operating mode of the system, but do not merit the traditional warnings, cautions and advisories,” the FAA noted in the newly published special conditions.
By requiring a suitable mode annunciation to flight crews for changes in flight control modes, the agency is focusing on events that can significantly change the operating mode of the system. It is not including the special conditions as a requirement for traditional cockpit warnings, cautions and advisories.
The agency first proposed the special conditions for the 525 in December 2017. A comment on the proposal from Sikorsky helped to establish the special conditions in the final format. Sikorsky’s comment sought to establish the special conditions so that the mode annunciation would be placed within the pilot's immediate field of view.
The FAA’s rotorcraft standards branch also revised the special conditions to address Sikorsky’s request to provide more clarification in the special conditions. The Lockheed Martin subsidiary requested that the special conditions require mode annunciation to indicate that the operating mode is changing “in such a way as to alter the pilots primary control strategy.”
As noted in 14 CFR 11.19 of the Federal Aviation Regulations, special conditions issued by the FAA become a requirement of the type-certification criteria for the aircraft type against which they're issued. Bell will be required to achieve the special conditions on the 525 and any future model helicopters that incorporate the same type of fly-by-wire configuration.
“In addition to the applicable airworthiness regulations and special conditions, the [Bell 525] helicopter must comply with the noise certification requirements of 14 CFR part 36,” the FAA said in the special conditions notice.
During the recent Textron quarterly earnings call, Textron CEO Scott Donnelly told analysts that the 525 is in “full flight test operations,” and he expects that program (along with the V-280) to lead to increased research and development spending for Bell.