N776MC

HISTORY OF FLIGHTOn July 15, 2021, about 1129 eastern daylight time, a Piper PA-23, N776MC, was substantially damaged when it was involved in an accident near Easton, Maryland. The flight instructor and pilot receiving instruction were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.

The flight instructor stated that, after takeoff, the pilot receiving instruction, who was also a flight instructor, completed an approach to landing stall (flaps and gear down) and reported that the throttles felt “like bungee cords.” The flight instructor then executed the same maneuver and agreed, reporting that, during recovery, the left engine spooled up “slowly.”

The flight instructor told the pilot receiving instruction to perform the maneuver again, which began at 3,000 ft msl by lowering the nose while the airplane was operating at 70 mph to achieve a 500 fpm descent at 80 mph and 1,500 rpm. When the airplane was at an altitude of about 2,800 ft msl, the pilot receiving instruction initiated the stall maneuver by raising the nose and reducing engine power to idle. The airplane then descended about 100 ft before the stall buffet occurred at an airspeed of about 62 mph. During the subsequent recovery, full power was applied to both engines, but the left engine lost total power and the left propeller feathered uncommanded. At that time, the airspeed was about 57 mph, and the flight instructor stated that the airplane immediately rolled about 45° to the left into a Vmc [velocity minimum control airspeed] roll.

The flight instructor immediately took control of the airplane to recover, but, as he applied full right rudder, his seat slipped back, which released pressure on the right rudder pedal. The airplane entered a second VMC roll, from which he was able to recover, but the airplane was at an altitude of about 1,200 ft msl (or about 1,100 agl) and in a descent of about 800 fpm. The pilot receiving instruction was unable to restart the left engine, and the flaps and landing gear remained extended. The airplane was below 800 ft msl and descending fast when both pilots determined that the airplane would be unable to reach an airport. The flight instructor subsequently landed the airplane in a cornfield, which resulted in substantial damage to the left wing and fuselage. AIRCRAFT INFORMATIONThe airplane was equipped with hydraulically controlled flaps and a landing gear system that was primarily operated by an engine-driven hydraulic pump installed on the left engine. The airplane was also equipped with a hand pump in the cockpit. With an inoperative left engine, extension or retraction of the flaps and landing gear was done manually using the hand pump. According to the Owner’s Handbook for Operation and Maintenance of the Piper Apache Models PA-23 and PA-23-160 Airplanes, the landing gear required 30 to 40 pumps of the handle to be raised or lowered, and the flaps required 12 pumps of the handle to be raised or extended.

The airplane was also equipped with an engine monitor that recorded parameters for both engines, including cylinder head temperature (CHT) and exhaust gas temperature (EGT). A review of the downloaded engine monitor data revealed that the left and right engine EGT and CHT were normal and showed increasing and decreasing values for both engines, consistent with airwork. From 1125:04 to 1126:28, the left engine EGT began decreasing, and the CHT for all cylinders increased. From 1126:28 to the end of the recorded data at 1128:52, the left engine EGT showed a general increase with an occasional short-term decrease in temperature, and the CHT for all left engine cylinders showed slightly increasing or steady temperatures. The end of the recorded data for the flight showed the right engine EGT between 1,097°F and 1,200°F and the right engine CHT between 281°F and 326°F (the highest value recorded).

Supplemental Type Certificate (STC) SA1306SW, issued on May 4, 1971, to Apache Modification Aircraft Corporation, approved a change to the airplane type design of Piper PA-23 and Piper PA-23-160 airplanes involving the installation of 200horsepower Lycoming IO-360-C1C engines and Hartzell HC-C2YK-2 model propellers with counterweight-equipped C7666A-4 propeller blades that had a basic propeller diameter of 72 inches. With this STC, feathering of the propeller was accomplished by moving the propeller control in the cockpit to the feather position, which drained oil from the propeller back to the engine, thus allowing the air charge in the propeller cylinder and the counterweight on each blade to move the blades to the feather position. According to the airplane flight manual supplement associated with the STC, the CHT limitation was 500°F. According to the Federal Aviation Administration (FAA), the airplane was modified in May 2009 in accordance with STC SA1306SW.

According to maintenance records and work orders, after the airplane made a gear-up landing in September 2020, both engines were inspected and then reinstalled on the airplane, and Aeroshell 15W50 oil was added to both engines. Hartzell HCC2YK2RBF propellers, with F7666A-2 model propeller blades, were installed. A review of the left propeller logbook revealed that the propeller was overhauled on November 3, 2020. The propeller blades did not have the counterweights required by the STC and the basic propeller diameter of 74 inches was 2 inches longer than the STC-approved propeller.

According to the Propeller Owner’s Manual and Logbook, No. 115N, a note in the maintenance practices section indicated that propellers on certain aircraft and engine combinations have experienced inadvertent feathering that occurred either at the time of shutdown or at low engine rpm. The manual further stated that the feathering could be reduced or eliminated “by lowering the air charge within the propeller cylinder.” The manual showed that the air charge in the cylinder at 70°F was required to be 178 pounds per square inch (psi) ± 2 psi.

Further review of the maintenance records and work orders showed that, during the airplane’s last annual inspection (about 3 months before the accident), a technician inspected the seat hardware for condition, security, and operation. The records contained no written discrepancies related to the right front seat, and there was no entry in the airframe maintenance records regarding the right front seat. AIRPORT INFORMATIONThe airplane was equipped with hydraulically controlled flaps and a landing gear system that was primarily operated by an engine-driven hydraulic pump installed on the left engine. The airplane was also equipped with a hand pump in the cockpit. With an inoperative left engine, extension or retraction of the flaps and landing gear was done manually using the hand pump. According to the Owner’s Handbook for Operation and Maintenance of the Piper Apache Models PA-23 and PA-23-160 Airplanes, the landing gear required 30 to 40 pumps of the handle to be raised or lowered, and the flaps required 12 pumps of the handle to be raised or extended.

The airplane was also equipped with an engine monitor that recorded parameters for both engines, including cylinder head temperature (CHT) and exhaust gas temperature (EGT). A review of the downloaded engine monitor data revealed that the left and right engine EGT and CHT were normal and showed increasing and decreasing values for both engines, consistent with airwork. From 1125:04 to 1126:28, the left engine EGT began decreasing, and the CHT for all cylinders increased. From 1126:28 to the end of the recorded data at 1128:52, the left engine EGT showed a general increase with an occasional short-term decrease in temperature, and the CHT for all left engine cylinders showed slightly increasing or steady temperatures. The end of the recorded data for the flight showed the right engine EGT between 1,097°F and 1,200°F and the right engine CHT between 281°F and 326°F (the highest value recorded).

Supplemental Type Certificate (STC) SA1306SW, issued on May 4, 1971, to Apache Modification Aircraft Corporation, approved a change to the airplane type design of Piper PA-23 and Piper PA-23-160 airplanes involving the installation of 200horsepower Lycoming IO-360-C1C engines and Hartzell HC-C2YK-2 model propellers with counterweight-equipped C7666A-4 propeller blades that had a basic propeller diameter of 72 inches. With this STC, feathering of the propeller was accomplished by moving the propeller control in the cockpit to the feather position, which drained oil from the propeller back to the engine, thus allowing the air charge in the propeller cylinder and the counterweight on each blade to move the blades to the feather position. According to the airplane flight manual supplement associated with the STC, the CHT limitation was 500°F. According to the Federal Aviation Administration (FAA), the airplane was modified in May 2009 in accordance with STC SA1306SW.

According to maintenance records and work orders, after the airplane made a gear-up landing in September 2020, both engines were inspected and then reinstalled on the airplane, and Aeroshell 15W50 oil was added to both engines. Hartzell HCC2YK2RBF propellers, with F7666A-2 model propeller blades, were installed. A review of the left propeller logbook revealed that the propeller was overhauled on November 3, 2020. The propeller blades did not have the counterweights required by the STC and the basic propeller diameter of 74 inches was 2 inches longer than the STC-approved propeller.

According to the Propeller Owner’s Manual and Logbook, No. 115N, a note in the maintenance practices section indicated that propellers on certain aircraft and engine combinations have experienced inadvertent feathering that occurred either at the time of shutdown or at low engine rpm. The manual further stated that the feathering could be reduced or eliminated “by lowering the air charge within...