ANC05LA128 · Gardner SR3500

The airline transport pilot was concluding a personal flight under Title 14, CFR Part 91. He reported that as he turned final approach to land, he added power, and the airplane decelerated and violently pitched nose down. He said he applied additional power to raise the nose and arrest the rate of descent, but the nose pitched down further. He indicated the airplane was low on final approach, in a level attitude, and descending rapidly. He applied power again, but the airplane pitched down again. The airplane continued to descend until it struck a curb, dirt berm, and an unoccupied vehicle in a parking lot near the approach end of the runway. The pilot said there were no known mechanical anomalies with the airplane prior to the accident. The airplane is equipped with a propeller that is capable of changing its pitch angle to provide reverse thrust for ground operations. The airframe mounted anti-reverse safety devices, intended to prevent the propeller from reversing in-flight, were tested on the ground and found to function properly. A third anti-reverse device, fly-weights in the propeller governor, could not be tested. The propeller governor was removed and disassembled. The electric propeller pitch change solenoid functioned properly, however the reversing valve, which is located in a valve body to which the solenoid is attached, was found stuck in what, according to schematics provided by the manufacturer, was consistent with the reverse pitch position. The reversing valve is intended to move freely within the valve body, but had to be forcefully removed. The interior of the reversing valve body had a coating of carbon-like material around the interior.

Verbatim NTSB analysis and probable cause from the NTSB dataset