Date: 201406
Local time of day: 0601-1200
Location: ZZZ.TRACON, US
Flight conditions: VMC
Light: Daylight
Aircraft: PA-24 Comanche
Operator: Personal
Operating under: Part 91
Flight plan: SVFR
Mission: Personal
Flight phase: Cruise
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ; Tower ZZZ
Aircraft component: Engine
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Private; Flight Crew Instrument
Human factors: Troubleshooting; Time Pressure; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Diverted; General Declared Emergency; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While flying a brief flight through the SFRA at approximately 1;400 FT MSL; the aircraft's engine began to run extremely rough. Flight through the SFRA in this area requires navigation around the Class B SFC airspace while remaining below 1;500 MSL. Within several seconds of the beginning of engine roughness airspeed began decreasing with engine performance. The limited altitude of the flight left very little time for decision making and the runways at a major airport were clearly visible and definitely the closest runways. After trying to resolve the engine roughness through the application of appropriate controls (fuel pump; mixture; carb heat; and power changes); I made the decision to declare an emergency and divert to and land at the nearby airport. This was the safest course of action given the issues as understood at the time. Due to the early morning time of the flight; no other traffic was observed or heard over the radio during the entire period. ATC passed us to Tower which cleared us to land on any runway. We made an uneventful landing. Upon landing; we were cleared by the fire crew and met and interacted with security. We then attempted to understand what had gone wrong and ran the engine for an extended duration on the ground and were unable to replicate the issue. Following this; we filed a flight plan and were cleared to depart for our original destination. Upon landing; we tried again to replicate the problem on the ground and were unsuccessful. A Mechanic was asked to review the plane and perform an aircraft run-up. This was accomplished and an entry in the aircraft log was procured as a result. Later in the day we attempted a flight to return the aircraft to its home airport for a thorough review by the aircraft's primary Mechanic. Shortly after takeoff; the problem reappeared less than 5 miles from the airport prompting an immediate return and uneventful landing back the departure airport. The aircraft will remain the distant airport until a thorough mechanical review is complete and the problem has been identified.




Synopsis: A PA-24 at 1;400 FT in the ZZZ SFRA made an emergency landing at a major Class B airport because of a rough running engine. The engine appeared normal; so he continued to his filed destination where a Mechanic cleared the aircraft. On the next departure; the problem appeared again forcing a return to land.