Date: 201401
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: FBO
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Cruise
Airspace: Class B ZZZ; Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Reciprocating Engine Assembly
Component problem: Malfunctioning
Reporter organization: FBO
Reporter function: Pilot Not Flying; Instructor
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed As Precaution
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I departed towards the coast with a student to do airwork for a Biennial Flight Review. We were on a southerly heading when I requested that the student make a left turn back to the north. Passing through approximately 070 degrees heading; the engine burbled slightly. The student turned to me and asked 'Did you hear that?' to which I responded 'absolutely.' At that time; the engine began to roughly stumble and 'die' and lost a significant amount of power. We added power and increased the mixture to full rich; pitching up into an immediate climb. After about 4-5 seconds; the engine began to gradually run more smoothly; but still 'didn't seem quite right.' We continued our climb; there was a slight perceived roughness and what 'felt' like a subtle loss of power. I called up Approach 14 NM south of ZZZ at 5;200 FT and called pan-pan; requesting to remain as high as possible enroute to ZZZ if able; due to engine roughness. I didn't want to go across the ridge to head home as the engine was 'stumbling' now and again and I wasn't sure if it would continue running. The Controller issued me a squawk code and cleared me through the class bravo at or below 5;000 FT. According to the ZZZ AWOS; ZZZ was landing 12. In the vicinity of the airport; the Controller asked if we would be performing maneuvers or landing; to which I reiterated that we were landing with an urgent condition due to engine roughness. At that time; the Controller asked if we needed any further assistance. In our position; a successful landing was assured regardless of the state of the engine; so I replied in the negative and requested a change to advisory. We entered a high downwind at 2;800 FT MSL and called pan-pan on advisory frequency; advising traffic of our condition and intentions. Though the pattern was relatively busy; all the aircraft cleared to accommodate us. We turned an extended left base for 12 at 2;200 FT; then a long final at 1;800 FT; idle power. Performed S-turns and slipping S-turns down final to a successful landing. Power was available for taxi; and engine performed normally on the ground. The airport truck at ZZZ came out to meet us and render assistance if necessary. I opted not to do any troubleshooting in flight; as I didn't want to risk a total loss of power. Later evaluation by a Mechanic revealed no obvious abnormalities with operation of the engine; and to my knowledge the airplane was successfully flown back to home Airport. However; were I to experience the same symptoms on a future flight; I am forced to conclude that my response and actions would be identical. I do not know what caused the initial severe stumbling and roughness.




Synopsis: C172 instructor pilot experiences a rough engine during training and elects to divert to the nearest airport. Arriving overhead at 2;800 FT for a planned engine off landing the engine continues to run throughout and the instructor is able to taxi clear of the runway.