More than 100 Cirrus jets built in Duluth will need some work before they can safely return to the air. The Federal Aviation Administration has issued an emergency airworthiness directive requiring the immediate replacement of an angle-of-attack sensor on the Cirrus Vision SF50 jet.
The FAA said the directive "was prompted by Cirrus reporting three incidents" where the stall warning and protection system or electronic stability and protection inappropriately engaged in proper flight. The first incident occurred in November 2018 and the latest occurred earlier this month.
That most recent event involved Cirrus staff directly, according to a company statement issued Monday that said: "In early April of this year, one of our company pilots experienced the engagement of the stall warning and protection system when not appropriate during a flight at altitude. The pilot followed the published airplane flight manual (AFM) procedures and landed the aircraft safely. Out of an abundance of caution, we immediately began working with the FAA and our internal teams to determine the root cause and began our operator communication process."
The statement went on to say: "With the benefit of detailed feedback from our company pilot about the April event, we were able to identify service histories that pointed to a probable similar occurrence in November. We proactively and quickly issued two service advisories and one mandatory service bulletin to ensure our operators were up to speed on the issue and to remind them of the proper airplane flight manual (AFM) procedures to follow in case of an angle-of-attack (AOA)-related issue. We then quickly identified the root cause as an AOA sensor hardware issue; this is not a software issue."
Cirrus noted that a pilot can override the jet's stall warning and protection systems by pressing a single red button located on the control yoke.
"When this button is pressed, full and normal control is immediately available to the pilot without requiring any additional steps to restore normal flight control forces. Pilots are trained in this exact procedure and, in each of the isolated events, pilots followed the published airplane flight manual (AFM) and training procedures, which resulted in immediate disengagement of the stall warning and protection systems allowing them full and normal control of the aircraft. No accidents or mishaps have resulted from this condition and each pilot landed their aircraft without incident," the company noted.
In light of the incidents, the FAA is requiring the angle-of-attack sensor on all Cirrus jets to be replaced before further flight, essentially grounding the aircraft until the repair can be made. However, if necessary, pilots may obtain a special flight permit to get the jet to a service location where the sensor can be replaced.
The directive said: "The noted condition presents an immediate danger to pilots and passenger of Cirrus Design Corp. Model SF50 airplanes because an uncommanded pitch down may be difficult to recover from in some flight regimes with potential fatal consequences."
Cirrus and Aerosonic, the manufacturer of the faulty sensor, say they have identified the problem and are ready to address it.
Cirrus delivered its first jet in 2016, and 105 are currently in the field, with production expected to ramp up this year.
Ben Kowalski, senior vice president of sales and marketing, said: "Our AOA hardware supplier is now producing corrected AOA hardware sensors which are beginning to ship to operators now. These new, corrected AOA hardware sensors will be installed on fielded aircraft and new aircraft deliveries. Although jet production continues, our top priority is returning aircraft in the field to service."
The Cirrus Vision SF50, with a base price of $2.38 million, has come to represent a growing portion of the Duluth aircraft manufacturer's business. In 2018, the company delivered 63 jets, and it aims to boost that number this year.
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