The Federal Aviation Administration has grounded a small jet made by Duluth-based Cirrus Aircraft, citing problems with a sensor similar to those found in Boeing 737 Max models that crashed in Ethiopia and Indonesia.
The FAA issued an emergency directive last week after Cirrus reported three incidents on its Model SF50 jets in which protective systems engaged when they were not supposed to. The problems involved either the "stall warning and protection system" (SWPS) or the "electronic stability and protection system," FAA officials said.
"The SWPS or ESP systems may engage even when sufficient airspeed and proper angle of attack [AOA] exists for normal flight," the FAA said.
Cirrus reported the first incident to the FAA in November and the most recent on April 16. Cirrus notified owners of the seven-seater, single-engine jets late last week of the need to get the planes repaired.
"To the best of our knowledge, we utilize both different hardware and software than Boeing," Cirrus officials said in a statement. "We are not experts on their aircraft or systems, so what we can do is describe how our aircraft works and what we have done [and] are doing related to our issue."
Cirrus said its pilots have always been able to immediately override its automated warning and protection systems by pressing a special red button 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," the statement said.
Still, the company's reports to the FAA noted that its first incident occurred in November while the SF50 airplane was under manual pilot control. In that case, the airplane activated several downward pitch commands along with stall warning, stick shaker and several associated alerts.
The pilot was able to stop the automatic pitch commands by pressing and holding an autopilot disconnect button and was able to safely land at the intended destination, the report said.
In the second case, the pilot reported a stall warning and stick pusher failure in flight. In the third case, the airspeed indicator went red and the stall warning and stick shaker were heard and felt while on descent.
The autopilot was disengaged and the pilot was able to land without incident.
The FAA noted that Cirrus and Aerosonic, the Florida company that manufactures the sensor in question, have identified the probable root cause of all three flying incidents: a malfunction in the AOA sensor because of a quality control problem on the assembly line.
The quality problem was narrowed down to two sets of sensor screws having improper torque and threading issues. The FAA has ordered that all AOA sensors on the SF50 models be replaced. Shipments from Aerosonic are starting to be distributed to all fielded aircraft, said Cirrus spokesman Ben Kowalski in an e-mail.
There are about 105 Cirrus SF50 aircraft that have been grounded, Kowalski said.
Cirrus delivered the first of its SF50 jets in December 2016.
