Cessna 170
Flight Crew Private
Flight Crew Last 90 Days 20; Flight Crew Total 200; Flight Crew Type 80
Aircraft Equipment Problem Critical; Airspace Violation All Types
Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition
Aircraft
I was enroute at 1800 ft MSL. I experienced sudden moderate engine roughness with about a 100 RPM drop. The issue continued despite applying carburetor heat; setting the mixture to full rich; and reducing throttle. I decided to make a precautionary landing [at a nearby alternate]. Because the airport was beyond gliding distance; I also decided to begin a climb while the engine was still making enough power to do so. During the climb; I climbed into the 1900 ft shelf of the Class B airspace; stopping around 2500 ft MSL. I was already on the CTAF and didn't want to be messing around with the radio; so broadcast on frequency my position; that I had an emergency; and that I was proceeding directly to the airport. I also broadcast that I was climbing into the Class B and requested anybody on frequency who was talking to [ATC] to inform them. Once reaching the airport was assured I descended out of the Class B and landed uneventfully.Because I was in an emergency situation; I had a right to climb into the Class B if necessary for the safety of the flight. I didn't want to add the distraction of getting out a chart and messing with the radios; so I elected to not attempt to contact [ATC] to inform them of my intentions. I also only have one radio; so to do so I would have had to stop monitoring the CTAF at my destination. Only after I had already descended out of the Class B did [I] realize that I should have squawked 7700.
C170 pilot reported entering Class B airspace without clearance after experiencing engine roughness.