The FAA has issued an emergency Airworthiness Directive (AD) on the Cirrus SF50 Vision Jet, grounding the more than 110 in-service single-engine jets for immediate replacement of the aircraft’s angle of attack (AoA) vane. According to the emergency AD issued Thursday, Cirrus reported “the aircraft’s stall warning and protection system (SWPS) or Electronic Stability & Protection (ESP) System engag[ed] when not appropriate” in three incidents since November 2018, leading to a stall warning crew alert system (CAS) message and activation of the stick shaker and/or stick pusher despite the aircraft maintaining sufficient airspeed and AoA for normal flight.
Further, the FAA said unintended activation of the SF50’s stall protection systems could result in excessive nose-down attitude and difficulty in maintaining control of the aircraft. “The noted condition presents an immediate danger to pilots and passengers of Cirrus Design Corporation Model SF50 airplanes because an uncommanded pitch down may be difficult to recover from in some flight regimes with potential [sic] fatal consequences,” according to the agency.
The emergency AD came two days after Cirrus Aircraft issued a mandatory Service Bulletin (MSB) requiring immediate AoA vane replacement with a modified part from vane manufacturer Aerosonic, after originally-installed components were found with improper torquing and retention of two set screws mounting the potentiometer shaft to the AoA vane shaft.
While the Cirrus MSB mandated that SF50 operators have the replacement AoA vanes installed within the next five flight hours, the emergency AD “requires such replacement before further flight,” although operators are able to obtain a special flight permit to a location where the replacement can be performed.