CEN23FA045 · Cirrus Design Corp SF50

The pilot reported that he engaged the autopilot (AP) and autothrottle (AT) just after takeoff. Shortly thereafter, he received landing gear up warnings, and the airplane pitched up and engine thrust reduced uncommanded. He stated that he unsuccessfully attempted to disconnect the autopilot and manually override the nose-up pitch and throttle position, but he felt resistance in the control yoke, and the throttle returned to the idle position when he released it. After receiving a stall warning, he chose to activate the airframe parachute system (CAPS). The CAPS deployed and the airplane descended under canopy, coming to rest in a retention pond. Data recovered from the airplane indicated that the CAPS AP mode activated just after takeoff about 226 ft above ground level (agl). CAPS AP mode is designed to slow the airplane by commanding idle thrust with AT, leveling the wings, and increasing the airplane’s pitch attitude in order to bring the airspeed within CAPS deployment parameters. The landing gear warnings the pilot received were due to the airplane’s low altitude and reduced engine power. Although the pilot reported that he pressed the AP disconnect button on the yoke, recorded data showed that the pilot attempted to override the AP and AT servos with manual inputs to the control yoke and throttle lever, and did not press the AP disconnect button until about 27 seconds after CAPS AP mode activated. By this time, the airplane’s pitch trim was in the full nose-up position, and some aileron trim would have been applied in order to level the wings; this is consistent with the pilot’s statement that the airplane pitched up and rolled, which he interpreted as a stall, and resulted in his decision to activate the CAPS at an altitude about 570 ft above ground level. In CAPS AP mode, manual throttle inputs would not decouple AT, and the AP disconnect button was required to disengage AT. Examination and testing of modules from the CAPS activation system showed corrosion on electronic components. Further testing revealed that a momentary interruption of electrical power or ground to the electronic modules in the CAPS would result in the generation of a “CAPS Activated” signal, even if power was restored to the modules. It is likely that the corrosion of electrical components in the CAPS activation system resulted in a transient power or ground interruption, which resulted in generation of the “CAPS Activated” signal and subsequent uncommanded activation of the CAPS AP mode. The pilot likely did not recognize the situation, even though the autopilot status bar indicated the autopilot was in CAPS mode and believed that the airplane was in an unrecoverable flight condition, which resulted in his decision to deploy the CAPS.

Verbatim NTSB analysis and probable cause from the NTSB dataset