The US Federal Aviation Administration (FAA) has grounded the worldwide fleet of Cirrus SF50 Vision Jets, following several reported issues with the aircraft’s angle of attack (AoA) sensors.
The AoA sensors on an aircraft measure the angle that an aircraft is flying at, and give warnings based upon what phase of flight the aircraft is in. This includes stall warnings if the relative airspeed is slower than the climb of the aircraft. It works by rotating in line with the airflow, then calculates the angle of attack based on a reference point on the aircraft’s wing or fuselage.
According to an emergency airworthiness directive issued by the FAA on April 18, three separate incidents involving the SF50s stall warning and protection system (SWPS) or Electronic Stability & Protection (ESP) System, were automatically triggered at the wrong time, causing the aircraft to pitch downwards.
The incidents all occurred between November 2018 and April 2019. In each of the three reported cases, the FAA says that the pilots flying the aircraft during the time of the incidents received stall warnings, as well as stick shaker and other associated alerts.
In all cases, the pilots had to fly the approach manually without the VREF indicator but were able to land safely.
“We are issuing this AD because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.” Says the FAA in its emergency AD. “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 grounding of all SF50 Vision Jets became immediate, as soon as the AD was received by aircraft operators.
Aerosonic, the manufacturer of the AoA sensors, alongside Cirrus have identified the possible cause of the malfunction, saying that two sets of screws could be at fault.
The FAA says that until the AoA sensors are replaced with improved AoA sensors, all SF50s are grounded. Operators that need to fly their aircraft to be repaired will need to apply for a special flight permit.
In 2018 the SF50 Vision Jet was the most-delivered business jet, with a total of 63 new aircraft deliveries. There are now over 100 aircraft in service, with the majority of aircraft registered on the US N register, although aircraft are also registered in Brazil, Guernsey, and San Marino.