Date: 201510
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 20
Light: Night
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
Aircraft component: Engine
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Commercial
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Procedure
Primary problem: Ambiguous

Narrative: I experienced a partial loss of engine power; followed by a full loss of engine power; followed by a resurgence of power. I performed a precautionary landing. No anomalies were noted upon inspection of the engine. The likely cause of loss of engine power was determined to be due to induction icing. The event occurred about one hour into the flight at 11;000ft. While the flight was in VMC; visible moisture was apparent at my altitude. There were no anomalies noted during the flight up to the point to the point where the loss of power occurred. I had been applying carb heat when visible moisture was present and removing it when it was not present. At the time of the event; a ~50rpm drop in engine rpm was noted; and carb heat was applied. The engine rpms continued to drop; and the engine lost power. I turned to the nearest airport; began [the] engine failure in flight checklist and contacted ATC to let them know that I had lost power; could not maintain altitude; and requested vectors to the nearest airport; which ATC confirmed was to the west.  When it was apparent that carb heat did not help I performed an abbreviated engine failure in flight checklist again. I arrived over the airport and began circling while turning on the runway lights and checking winds. The engine regained power at about 7;000ft MSL and I adjusted power; mixture; carb heat to confirm full engine power. I then proceeded to make a precautionary landing and notified ATC that I regained engine power and my intention to land.After landing I performed an engine runup and noted no anomalies. I inspected the oil; engine compartment and induction system. I noted no anomalies. I called ATC on my cell phone to give them a report and let them know that my initial diagnosis was that I had temporarily lost engine power to carb ice or induction ice.After taking time to thoroughly inspection the rest of the airplane and allow time to cool down; I then continued with my trip; starting with a good run up on the ground and circling [the airport] while climbing. There were no anomalies for the rest of the trip; which was flown at a lower altitude.Once at my destination a review of service bulletins for the Air Box installed showed that continuous carb heat is recommended to avoid induction icing. Later when preparing the aircraft for sale it was noted that the pitot-static inspection had elapsed. There were no indications that the pitot-static system contributed to the loss of engine power; or gave any erroneous information. Both altimeters read airport elevation on the ground. Both altimeters agreed with each other and our encoding altimeter output in flight. Both airspeed indicators agreed with each other in flight. The key takeaway from this incident is to use carb heat all the time around visible moisture with the [designated] Air Box.




Synopsis: The pilot of an experimental aircraft reported fluctuations in engine power due to suspected induction icing. He later discovered that the installed air box has a recommendation for continuous carb heat to be used when operating in visible moisture.