Date: 201909
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: Cessna Single Piston Undifferentiated or Other Model
Operator: FBO
Operating under: Part 91
Mission: Training
Flight phase: Climb
ATC / advisory: Tower ZZZ
Aircraft component: Spark Plug
Component problem: Malfunctioning
Reporter organization: FBO
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Commercial
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: With two students on board flying a cross country flight the following events occurred. While climbing though 2;000 feet on a 050 assigned heading with Departure we encountered a repeated momentary loss in power. The engine would stumble and run rough then surge back to full power. The first two times the power loss was momentary; not more than one second. The following 3 or 4 occurred with less time between the power loss events and lasted for a second or two and getting longer for each occurrence. All the engine instrumentation was in the green; the mixture was full in; fuel cutoff full in; fuel valve on both and mags on both. I took the flight controls and tried to radio departure to request a return to the field. After the second request was unanswered I turned to a 180 heading and reduced the power to maintain altitude. I was unable to get my request to the controller due to frequency congestion after four attempts. At this point I went back to the tower frequency without departure's approval. I requested an immediate return to the field on runway XX; I was northeast of the field at this point at 2100 feet within gliding distance. The tower instructed me to continue 180 heading and maintain altitude. I maintained separation from the traffic I saw in the pattern below us. As we passed abeam mid field we heard the go-around calls for both a [twin-engine GA aircraft] landing on XX and a business jet landing XY (intersecting runways). The two planes approached midfield at about the same time and same altitude. We witnessed the business jet make a significant turn to the right and immediate climb as they approached the intersection of the runways to avoid the [GA plane]. We continued south and tower called out regional jet traffic ahead and about 1000 feet below. We were instructed to follow the regional jet traffic cleared to land XY. The approach to the runway was uneventful. We were very high but with full flaps and a full forward slip through the descent I was able to land. Member of management asked if I would take the plane around the pattern to further troubleshoot the issue; I declined and requested to have the engine looked at before further flight.The repeated power loss caused the heading deviation in order to return to the field. The frequency change to tower without departure's approval was due to frequency congestion and being unable to reach the controller when needed. I chose a heading and altitude that would keep our flight within gliding distance and not conflict with traffic in the pattern. The conflicting aircraft over the field more than 1500 feet below our flight was due to poor sequencing and spacing by the controllers.Issue turned out to be a fouled plug. Lesson learned to lean the mixture even during climb if engine power issue occurs.




Synopsis: Cessna pilot reported rough-running engine after takeoff due to fouled spark plug.