Cessna 170
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 84; Flight Crew Total 8200; Flight Crew Type 100
Aircraft Equipment Problem Critical; Airspace Violation All Types
Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Diverted; General Declared Emergency
Aircraft
Departing ZZZ1 VFR at 1200 MSL across the [the water] staying clear of the Class B airspace and navigating in the VFR corridor. Then heading toward ZZZ Check point staying clear of the Class D airspace. When heading toward the checkpoint following the VFR map on my Fore flight IPAD that's when my attention was detracted just inside the shoreline to a slight vibration of the engine. As I did my emergency checklist (checking fuel; mags; oil pressure) the engine continue to get more severe as we proceeded? Then it happen; a loud bang and engine sounded like it was coming apart. My first reaction to the extreme vibration was I thought a cylinder was coming apart. I glance outside to see my landing options and I was right over downtown. Freeway was not an option because of the heavy traffic and a high-density resident and business area; my next option was to declare an emergency into ZZZ; which in turn the tower gave me priority. With a high level of pucker factor I once again tried to figure what was the problem. Flying the airplane was my first priority and getting down safely. I did not bust the Class D airspace intentionally but for survival. Upon reaching the ground and having the power to the parking area and opening the cowling; it was discovered a spark plug had blow out the left rear cylinder. The aircraft has a low time engine and just had the annual done two weeks prior and met all torque requirements.
An instructor pilot describes an engine problem and successful diversion to the closest airport.