Piper PA-28-140 (Modified) Cherokee, G-EEKY
Before descending from 2,000 ft the pilot selected the carburettor heat to HOT. At 1,200 ft agl she found the throttle was stuck at 1,500 rpm. Unable to maintain level flight she flew a forced landing into a field. After touchdown the pilot and her passenger vacated the aircraft uninjured. Two hours later the CFI of the local flying club examined the aircraft and encountered a throttle restriction which prevented him from closing the throttle but he was able to advance the throttle to full travel. Two maintenance organisations found nothing that might have caused a throttle restriction. The temperature and dew point for the time of the accident fell in the Serious Icing - Cruise Power region of the CAA’s chart. Despite the use of carburettor heat in the descent, icing could have formed downstream of the accelerator pump in the vicinity of the discharge valve and discharge nozzle inside the carburettor. In this situation the throttle is likely behave as if it has some form of restriction and the engine may continue to run smoothly. However, the true cause of the restriction could not be identified.