My Latest Engine Failure

The engine failure didn’t happen suddenly…. I was flying a Mooney M20C in clear, cool air, 7500 feet above the Kansas/Oklahoma border.  I’d flown the 1962 speedster from Augusta, Kansas (just easy of Wichita) to Oklahoma City, picked up a passenger and flew to a meeting in southeast Oklahoma, and was now, on the solo leg of my trip homeward.  My first clue of impending trouble, however, appeared much earlier that day.

Climbing southeast out of OKC that morning the engine was running abnormally rough.  Most of my flight time is in Beech airplanes with six-cylinder engines.  Going back to a four-banger like this Mooney is, among other things, a return to a less smooth-running engine than the tuned-injection IO-520s and -550s I’m used to flying.  I rationalized some of the engine roughness as simply my lack of recent experience with more economical airplane engines.  This particular Mooney is fitted with a three-bladed propeller.  In my experience very often a retrofit propeller (the Mooney’s O-360 engine was originally fitted with a two-blade prop) will introduce some vibration unless the propeller is painstakingly balanced, something uncommon in the world of rental airplanes such as this.  I further rationalized the roughness as being related to the prop installation.

I had a passenger on board, a gentleman I greatly respect but. Despite a long career in aviation management, this was his first flight in a single-engine airplane.  Even though I was seriously considering putting down at Norman, Oklahoma, just under the right wing as we climbed out of OKC I was tempted to press on.  This leg was only about 20 minutes long, and I rationalized that by climbing high I could increase our options if the roughness got worse.  The engine smoothed down once I set power for cruise.  Surely those tiny creatures of aviation myth, the gremlins that eat away at airplanes in flight, had been driven overboard by my superior systems knowledge and my timely adjustment of power and pitch.

Head North, While Things Went South
Later in the afternoon, again lofting out of OKC solo and headed north, toward home, the climb-power roughness resumed.  By this time the engine had run all day—occasionally rough like this, but always smoothing out—and again an easy rationalization came, the feeling that nothing bad had happened so far, so it could not happen at all.  This time the engine did not completely smooth out when I set cruise power and leaned the mixture, despite steady readings on all engine instruments.  I tried different propeller speeds and played around with the carburetor heat to see if I could find a setting that eliminated the intermittent, but persistent roughness.  I was fairly high and my route of flight took me over several airports I know well.  I was in radar contact with ATC, participating in VFR Flight Following.  The sky was completely clear and a gentle tailwind rushed me homeward.

The roughness increased despite normal engine indications, but I decided to call it a day.  Winfield, Kansas, was about eight miles off the nose, 30 miles short of my destination but home to a former military field with lots of open runway.  I angled slightly right of course toward Winfield when I noticed the airspeed dropping.  My first glance went to the engine gauges—the oil temperature and pressure were okay, EGT (exhaust gas temperature) hadn’t changed, but the lone CHT (cylinder head temperature) had dropped 100 degrees.  Full throttle and 2500 rpm was only netting 120 miles per hour indicated airspeed.  Even in a total engine failure the EGT would have dropped off the bottom of the scale as soon as combustion creased, but the CHT would have held its value at least for a while, with only a gradual reduction.  This rapid drop in CHT suggested to me that the intake valve in the cylinder containing the CHT probe was stuck open, allowing a rush of air into the cylinder that cooled the probe.  This would also account for the loss of performance, as power would be significantly affected.

Then the Engine Quit
I called ATC and advised I had a power loss and was gliding to Winfield as I switched fuel tanks, the first step in almost all engine failure checklists.  No change.  Fielding the controller’s questions about souls on board and fuel remaining, I applied carb heat, again with no response, as I completed checks of mixture, boost pump, and magnetos.  From this altitude I had the airport made; in fact, I was a little high and began a slight slip to lose more altitude.  I asked the controller for the frequency for Winfield so I could call ahead into the traffic pattern and received the reply.

Down at about 2500 feet, with no specific action from me, the engine lit back up.  Was the valve unstuck?  Was it really carb ice in this warm, dry air, that had melted out at a lower altitude?  Suddenly I found myself with a smooth-running engine on a three-mile final but only 30 miles from home…and I was extremely temped to turn around and head north.  I even began the turn when I remembered just how many mishaps I’ve read (and written) about where a similar decision led to a serious accident later on.  I had the airport made, but I no longer had the luxury of altitude if the engine died again as swiftly and mysteriously as power had returned.  I reversed my bank and continued my landing under normal power.

Lessons Learned
• Altitude truly is your friend.  Cruise as high as conditions make safe and practical, to provide more time and options.
• If it feels wrong, it’s probably wrong.  Don’t ignore inner feelings that something isn’t quite right.
• Studying mishap history positively affects in-flight decision-making.  Learn from the experiences of others.
• Flight Following can be very helpful in an emergency.
• Everyone’s in danger of rationalizing away hints before they become problems.  Don’t let theorizing about a problem distract you from dealing with it.

I’ve had four engine failures over a 3400-hour career: an engine-drive fuel pump failure in a Baron twin, easily countered by activating the auxiliary pump; a cracked cylinder on takeoff in a Cessna 120, resulting in an abort on the remaining runway; a fuel injector pulled loose from the nozzle in an A36 Bonanza while being vectored for an instrument approach in IMC, with massive power loss but a successful limp to the airport; and this Mooney incident.  That’s one failure for every 850 flight hours, testimony that we can’t ever let our guard down, and must always be prepared to deal with an engine failure.

BOTTOM LINE:  Are you a high-time pilot, comfortable and knowledgeable with your airplane type?  Remember that your very knowledge and experience may conspire to explain away the gremlins until they strike their final blow.