***This report was modified on March 8, 2018. Please see the docket for this accident to view the original report.*** On August 4, 2017, about 0900 central daylight time, a Cessna A188B airplane, N3047J, was substantially damaged when it settled into a bean field after takeoff from runway 18 (5,006 feet by 75 feet, concrete) at the Marshall Memorial Municipal Airport (MHL), Marshall, Missouri. The pilot was not injured. The airplane was registered to and operated by private individuals as a 14 Code of Federal Regulations Part 137 flight. Visual meteorological conditions prevailed. The flight was not operated on a flight plan. The local aerial application flight was originating at the time of the accident. The pilot stated that the airplane was loaded with about 120 gallons of fertilizer and 54 gallons of fuel at the time of the accident takeoff. The pretakeoff run-up was normal. After takeoff, he reduced engine power for climb. When he did so, the engine "surged." He responded by increasing the throttle "a little," but the engine "surged" again. He subsequently applied full throttle, but was unable to maintain a positive rate of climb. The airplane settled into a bean field and encountered a fence before coming to rest in the adjoining corn field. The pilot informed a Federal Aviation Administration (FAA) inspector that the airplane seemed to be "sagging" after takeoff. The engine indications appeared to be normal before the accident. The airplane had a full load of fertilizer and fuel at the time of the accident takeoff. The pilot also informed the inspector that the airspeed indicator had been inoperative for some time. A postaccident engine examination conducted by FAA inspectors did not reveal any anomalies consistent with a preimpact loss of engine power. The wing flaps were positioned at 20 degrees deflection at the time of the exam. The airplane flight manual noted that the recommended takeoff wing flap setting for restricted category airplanes was 10 degrees. The approved takeoff range for normal category airplanes was 0 to 20 degrees. The information manual indicated that optimum takeoff performance at heavy weights is obtained using 10 degrees wing flaps. FAA regulations (14 CFR 91.205) require an operational airspeed indicator for civil aircraft operating under a standard airworthiness certificate. The accident airplane was operating under a restricted category airworthiness certificate and was not required to comply with that regulation.