Background
On August 6, 2016, at approximately 1145 eastern daylight time, a Piper PA-28R-201, registration N3783M, was substantially damaged during a forced landing following a partial loss of engine power near Northampton Airport (7B2) in Northampton, Massachusetts. The flight was an instructional flight conducted under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from 7B2 at about 1143.
Accident Sequence
The flight instructor reported that during a simulated soft field take-off, the airplane's climb performance deteriorated noticeably. When the airplane reached about 150 feet above ground level, the engine began to lose power. The instructor realized that continuing the climb was not possible, and any increase in pitch resulted in an immediate decrease in airspeed. He decided to perform an emergency off-airport landing in a corn field near the end of the departure runway. During the landing, the right wing and firewall were damaged. The flight instructor and the pilot receiving instruction were not injured.
Post-Accident Examination
A post-accident examination by a Federal Aviation Administration inspector revealed that the alternate air valve plate had separated from its mounting location and was lodged in the fuel servo air intake, blocking the fuel servo. Further examination of the alternate air valve plate showed that the hinge pin was worn completely through the plate assembly. A review of manufacturer engineering drawings indicated that the plate assembly had been modified with a spring attached to the plate. Examination of the aircraft logbooks did not reveal any entry documenting the modification or repair of the part.