N459TARobinson Helicopter R44 · 2005

On July 21, 2019, about 0845 central daylight time, a Robinson R-44 (Raven I), N459TA, sustained substantial damage when it was involved in an accident near Ida Grove, Iowa. The commercial pilot sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.

The pilot reported the purpose of the flight was to apply fungicide to a field. The pilot was spraying the field with north to south and south to north swath runs. Due to the location of various obstacles near the field, the pilot was conducting teardrop turns to safely facilitate the swath runs. The obstacles near the field included trees, power line poles, and power lines.

At the end of his second north to south swath run, the helicopter came out of the field and executed a "gentle" tear drop turn to the left going about 25 kts. The pilot estimated his altitude at the time to be about one and half to two "telephone pole" lengths high. Once the turn was completed and the pilot was approaching the target field, the helicopter yawed "hard" to the left. The pilot attempted to correct the yaw with right tail rotor pedal input and the low rotor rpm light and horn activated. The pilot observed the engine rpm below "half" and dropping, along with the main rotor rpm, which had a "good split." The pilot reduced the collective and attempted a high hovering autorotation. Due to the lack of airspeed and altitude, the pilot reported the helicopter impacted a bean field "very hard." The pilot reported the engine was not operating when the helicopter came to rest on its left side. The pilot was able to egress from the helicopter without further incident.

At the time of the accident, the pilot reported the temperature was about 64° F and the wind condition originated from about 030°, at 6 kts. He reported he was paying close attention to the carburetor heat temperature during the flight, as he had the carburetor heat lever pulled out "a little over half" and he kept the needle out of the yellow arc depicted on the carburetor temperature gauge. For the engine power settings with the collective for the swath runs, he reported he was below 15 inches of manifold pressure as he would come out of the field, and once he would level out, he would never exceed 21 inches of manifold pressure.

About 15 minutes prior to the accident, a loader from the operator reported that he loaded the helicopter with 30 gallons of water, 105 ounces (0.82 gallons) of AFrame fungicide, and 5 gallons of 100 low lead fuel.

The helicopter sustained substantial damage to the main rotor system, the fuselage, the tail boom, and the tail rotor system. A postaccident examination of the airframe and engine by a Federal Aviation Administration (FAA) aviation safety inspector (ASI) found no preimpact mechanical malfunctions or failures that would have precluded normal operation. The FAA ASI additionally reported that photographs from law enforcement officials at the accident site showed the carburetor heat was on at the time of the impact.

The reported temperature and dewpoint at the time of the accident indicated a probability of serious icing conditions at glide power settings per the carburetor icing probability graph from the FAA Special Airworthiness Information Bulletin CE-09-35 Carburetor Icing Prevention. The helicopter was equipped with a carburetor heat assist device. The Robinson R-44 Pilot's Operating Handbook discusses this device and states in part:

The carburetor heat assist correlates application of carburetor heat with changes in collective setting to reduce pilot workload. Lowering collective mechanically adds heat and raising collective reduces heat. A friction clutch allows the pilot to override the system and increase or decrease heat as required.