On February 1, 2015, about 0030 Pacific standard time, a Robinson R44 II, N510KJ, force landed following a partial loss of engine power approximately 5 miles east of Calexico, California. The commercial pilot was not injured, and the helicopter was substantially damaged. The helicopter was registered and operated by John Reed Aviation as a 14 Code of Federal Regulations Part 137 aerial application flight. Night, visual meteorological conditions prevailed and no flight plan was filed. The local flight originated at Calexico International Airport, Calexico, California, about 0025. The pilot reported in a written statement to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), that the pilot who flew the helicopter on the previous flight stated to him prior to the accident flight that there was a "feeling and increasing vibration on the pedals." A subsequent examination of the helicopter revealed no anomalies. He further stated, "I started it [the accident helicopter], and did a hover control check to make sure everything was working properly, after that I took off to do the high recon of the field. There were power lines to the north, after the recon I set up for my first practice pass (south to north) wind was out of the west so the turns where going to be to the west." After reaching the field and during the first turn, the engine experienced a partial loss of power. He further stated "I started my pull, to perform a 'P' turn [A turning maneuver where at the conclusion of the spray pass, the helicopter pulls up, initially turns to the right, and then makes a left turn until it is lined up for the next pass], with the same inputs on the controls as I've done plenty of times in the past, and as the aircraft started to gain altitude and lose airspeed, the RPMs went down, it felt like the governor was not able to keep them on the green, I lowered collective and rolled throttle on, also I turned to the west to avoid the power lines, I flared as I got close to the ground…" The helicopter landed hard and rolled onto its right side, resulting in substantial damage to the forward fuselage and tailboom. The pilot reported to the NTSB that he accumulated a total time of 583 hours in rotorcraft, and 40 hours in the last 90 days. He also accumulated a total night flying experience of 85 hours. The United States Naval Observatory data indicated that the sunset and end of civil twilight at the accident site were at 1714 and 1740, respectively. The moon was in a waxing gibbous phase, with 96% of the moon's visible disk illuminated. Examination of the helicopter was performed by the NTSB and a Federal Aviation Administration (FAA) inspector. The agricultural sprayer assembly was removed from the fuselage prior to the examination of the wreckage. The main rotor blades, tail boom sections, drive shaft, tail rotor assembly and four transmission drive belts were removed from the helicopter prior to the examination and found with the main wreckage. The four transmission drive belts were cut to facilitate their removal and revealed normal wear. A section of the tail rotor pitch control rod, about 3 feet in length, separated from the aft control rod end, and was not found during the examination. Examination of the fuselage revealed that the windshield separated from both left and right sides and was buckled in several locations. The main rotor blades remained intact and were buckled in several locations. The tail rotor assembly was intact and the stinger separated near the aft attachment. The tail rotor blade pitch movement moved freely by hand. The engine cowling and fan shroud was undamaged. The instrument panel was undamaged. Control continuity was established from the cabin controls to the swashplate and damaged tail rotor control rod. Examination of the Lycoming IO-520-AE1AA engine revealed no anomalies. The helicopter was setup for a test run and the engine started with little hesitation. The engine ran smoothly for several minutes and a magneto check was performed. Several throttle bursts were applied and the engine was shut down normally.