A friend of mine has a turbocharged, single-engine airplane. Part of the appeal of the turbo is the ability it provides to “overfly the weather.” He and his wife were happily cruising at Flight Level 200 (20,000 feet) when something happened…and manifold pressure dropped in half. Where seconds before they were racing above a bank of clouds 15,000 feet thick, now they were sliding down into the deck with but a fraction of their available power…and the clouds were full of ice.
Night, over mountains. The pilot of a piston twin cruises in visual conditions above dark and forbidding peaks. He’d flown this route once or twice before in a high-performance single, but was always worried about the possibility of an engine failure, so much that he made a significant investment in a multiengine airplane and the training (and expense) to fly it. Now, with one engine ready should the other one fail, he was completely at ease…until the night one engine did fail, after all. He maintains control and correctly troubleshoots the problem, but the engine won’t restart so he has to feather the propeller. Not to worry, eh? Not so fast. This airplane, like most piston twins, has a single-engine service ceiling of about 5000 feet at maximum aircraft weight. Flying solo and well into a trip this airplane is a good bit lighter, but even so flight with one prop feathered and at “blue line” (least drag) airspeed the best he can do is hold a slight descent as the plane slides down to its weight-adjusted single-engine ceiling—whatever that might be. The second engine gives our pilot some choices of where to aim as the shadowy peaks grow in the dark, but the airplane won’t be able to avoid impact for long.
“I have plenty of fuel,” the VFR-only pilot of a retractable single-engine airplane may have thought when the forecast was for extensive, low IFR conditions for a large part of his route. The cloud tops were low—it was more fog than cloud—and it was “severe clear” both on the departure and arrival ends of the flight. When a fuel vent plugged en route and he could no longer get fuel from his right wing tank, however, his easy overflight turned to an emergency letdown into the abysmal weather. He was neither certified nor trained for flight by reference to instruments, however, and he lost control while maneuvering for a descent.
Wisdom from the Dawn of Flight None less than Wilbur Wright gave us perhaps our first look at aeronautical risk management, saying “carelessness and overconfidence are usually more dangerous than deliberately accepted risks.” He said this two years before his first powered flight—which was successful not because he and his brother Orville avoided risk, but because they carefully managed the risk and took as many precautions as they could. They didn’t do anything stupid. Of course, at the speeds and altitudes the Wright Brothers flew, it was less likely that any miscalculation of the risk would be catastrophic, or that any aircraft anomaly would drive it into an environment in which it could not fly. Even then, the wrights were careful to fly only under carefully considered conditions that would keep them (and their Flyer) within a predictable flight envelope.
Relative Risk So where does this leave our pilots whose airplanes are capable of overflying hazardous weather or terrain under normal circumstances, but not when an anomaly forces the aircraft or the pilot into the environment it was designed to avoid? For very few piston airplanes are designed to handle any airframe icing, and physics dictate the capability of a multiengine airplane with an engine shut down. Instrument flight takes training and practice, and won’t come naturally if you’re “VFR only” or if your instrument currency is long out of date.
Overflight may at times be a acceptably risky practice, but merely hoping nothing will go wrong does not replace the need to plan for possibilities and have a safe way out of trouble. Flying over conditions you or your airplane can’t handle is on the same level of risk as the pilot who “scud runs” because he or the airplane can’t handle the instrument conditions above. Just as sometimes a scud-running flight can be safely planned and executed, so also may a hazard overflight be orchestrated to minimize risk by limiting the “overflight” portion of the trip as much as possible. Always consider the possibility that you may have to descend into that thick layer of ice or fog you’re trying to overfly, and plan that multiengine mountain trip to stay over the lowest terrain wherever possible. It’s the pilot who fails to plan for trouble (as Wilbur Wright would have told us more than a century ago) who will likely find it.
BOTTOM LINE: I’m not telling you to avoid overflying hazards all the time. I am advising, however, that you not blindly overfly without a contingency plan for that rare day (or night) when your airplane can’t hold the altitude you’re asking of it.