The day before the accident, the pilot had removed the airplane’s induction air filter but had inadvertently forgotten to reinstall it. On the day of the accident flight, he had also inadvertently forgotten to remove the engine cowling plugs. After takeoff, the pilot turned onto the downwind leg of the airport traffic pattern and the engine output immediately reduced to idle power and the engine would not respond to throttle input. The pilot then executed a forced landing in a gravel lot, during which the airplane bounced, the nose landing gear separated, and the airplane came to rest inverted. The airplane sustained substantial damage to the right wing and fuselage. Postaccident examination of the wreckage confirmed that the left cowling plug was partially ingested into the end of the intake filter duct, completely obstructing it. No evidence of any preimpact mechanical malfunctions or failures of the airframe or engine were otherwise found. Based on this information, it is likely that the restricted flow of intake air to the engine resulted in the partial loss of engine power.