The FAA on Thursday issued an emergency airworthiness directive (2019-08-51) against the Cirrus SF50 Jet that grounds the entire fleet until specified maintenance is performed on the aircraft’s angle of attack indicators.
The AD was prompted by three incidents on Cirrus Model SF50 airplanes of the stall warning and protection system (SWPS) or electronic stability and protection (ESP) system engaging when not appropriate, with the first incident occurring in November and the latest this month.
The agency said, “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 potentially fatal consequences. The before-further-flight compliance time and need to replace the AOA sensors due to the potentially fatal consequences does not allow for prior notice and opportunity to comment for the public.”
The AD explained that the “SWPS or ESP systems may engage even when sufficient airspeed and proper angle of attack (AOA) exists for normal flight. The SWPS includes the stall warning alarm, stick shaker and stick pusher.
The Garmin-designed ESP includes under speed protection (USP). The SWPS system engaging inappropriately could potentially result in a stall warning crew alert message activation, accompanied by an audio alarm and stick shaker activation, followed possibly by either low-speed ESP/USP engaging and/or the stick pusher engaging. "The pilot will also observe the dynamic and color-coded.
This airworthiness directive supersedes an earlier service bulletin SB5X-34-03 issued on Tuesday that allowed for some limited flight of the aircraft pending AOA replacement.