FAA Proposes Special Conditions for Skyryse Fly-By-Wire System on Robinson R66 Helicopter

Background and Application

On April 10, 2023, Skyryse applied for a supplemental type certificate (STC) to install its SkyOS fly-by-wire (FBW) flight control system (FCS) in the Robinson Helicopter Company Model R66 helicopter. The Robinson Model R66 is currently approved under Type Certificate No. R00015LA and is a single-engine, normal category rotorcraft with a maximum takeoff weight of 2,700 pounds and a maximum seating capacity of five passengers. Because the modified helicopter will incorporate a novel or unusual design feature — replacing mechanical flight controls with a digital FBW system — the FAA has determined that the applicable airworthiness regulations under 14 CFR part 27 do not contain adequate or appropriate safety standards for this feature, and has proposed special conditions to fill that gap.

The Regulatory Gap and Its Mechanism

The FAA explains that the airworthiness standards for controllability and maneuverability of rotorcraft are contained in 14 CFR § 27.143. According to the document, these controllability requirements are compatible with most FBW systems, while most maneuverability requirements are not affected by FBW systems — except for control margins. The rule states that one purpose of § 27.143 is to ensure that control margins at the rotor and anti-torque system level are sufficient within the defined flight envelope to avoid loss of control, meaning the rotorcraft has adequate control power for the pilot to exit potentially hazardous flight conditions.

The FAA further explains that § 27.143 was written to address hydro-mechanical flight control systems, through which pilot awareness of control margins is provided by cyclic and pedal position relative to cockpit control stops. In a FBW system, however, there is no mechanical link between the inceptor and the receptor. Without a constant correlation between cockpit control and main or tail rotor actuator positions, the FCS may not provide tactile control margin feedback to the pilot through cockpit control position relative to the control position physical stop or limit, for all flight conditions. The agency states this renders the existing rule inadequate for certification of a FBW FCS.

The Proposed Special Conditions

To establish a level of safety equivalent to that established by the existing airworthiness standards, the FAA is proposing special conditions under 14 CFR § 21.16. These special conditions would require, as a minimum safety standard, that awareness of proximity to control limits at the main rotor and tail rotor be provided to pilots of the helicopter. Under 14 CFR 21.101, Skyryse must show that the Robinson Model R66, as changed, continues to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. R00015LA, or the applicable regulations in effect on the date of application for the change.

What to Watch

The FAA has invited public comment on the proposed special conditions, with written comments, data, or views due on or before October 13, 2026. The agency states it will consider all comments received by the closing date and will consider late comments if doing so will not incur delay. The FAA notes it may change the special conditions based on comments received. Comments are to be submitted to www.regulations.gov, except for Confidential Business Information (CBI), which must be clearly designated as such and marked "PROPIN" on each page, and sent directly to the relevant FAA contact rather than posted to the public docket.

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