The pilot wasn’t surprised to see them there because a Coast Guard helicopter had already tried to intercept the aircraft.

The short but stressful flight began when the pilot, who had flown to another area airport on business, decided to take the airplane up locally to check the engine. Tachometer indications had been fluctuating recently, so the pilot took off and flew away from the populated area, planning to level off at 2,000 feet and monitor engine behavior.

“I checked the FAA TFR site for TFR restrictions and did not see any listed,” the pilot noted in a narrative submitted to the Aviation Safety Reporting System to explain how the flight fell apart.

About 10 minutes after takeoff “my engine began surging wildly, and the tach followed,” the pilot wrote. Fearing imminent engine failure, “I decided to get the airplane on the ground immediately and hit my ‘NRST’ button on my GPS.”

The pilot saw the TFR displayed and was “fully aware” that it would be penetrated, “but this was an emergency and I decided to proceed” to the airport displayed on the GPS.

The report noted that the interception had failed because the Piper pilot had attempted to communicate­ with it not on the emergency frequency 121.5 MHz, as procedure prescribes, but on the frequency of the airport to which the flight had diverted.

A prior misstep, the pilot acknowledged, was “in NOT calling FSS for a TFR report/briefing” as an additional precaution beyond checking the FAA’s online TFR information.

That leaves the matter of the tachometer fluctuations: After giving the engine a full-power runup, a mechanic gave the airplane a clean bill of health, suggesting that the engine’s surging behavior might have been caused by water in the fuel. Although the pilot reported having sampled the fuel and pronounced it clean before the test flight, the mechanic’s theory “made sense because I believe the airplane was refueled in a hard rain, and no other likely cause was determined.”

Flight planning, airspace, intercept procedures, emergency management, situational awareness, and fuel contamination are just some of the topics that suggest themselves for review when extracting lessons from this brief but eventful flight.