If you are into the sort of thing that warrants full tanks of fuel for every flight, then you are already in the realm of those who live to read these tales. Otherwise, this one is for you. You see, flying with a half tank of gas when the trip requires more is asking for a prayer at some time before you reach your destination.
Imagine if you will, over rocky terrain or a congested area or an uninhabited wooded lot, the last drip has dripped and the fumes run out and the engine coughs and coughs and cannot seem to quench its thirst and finally out of sheer exhaustion, it quits. What to do? What will you do? While in an armchair next to the warm glow of a fireplace and a cup of tea, you might say, “I will do this or that.” True enough, but then there is that time when it actually happens, and your life is on the line. What then?
If you happen to be flying one of those aircraft with a BRS chute, you might say, “No problem, I will exert my 45 pounds of force and pull on the overhead handle and come down safely with the parachute.” Umm, yes, that is possible but there is always that 14lbs/sq.in. gravitational force that on impact might claim a few linear compression fractures of the spinal vertebrae, among other things. And if your aircraft is not equipped with the BRS system then there is only the wind-hushed glide and a loud prayer.
Landing in a field is fraught with some danger of terrain and rocks and bushes that can cartwheel the best of the best. On a road there is always the landlubber crowd driving their four-wheelers around, messing up a perfectly great landing strip of a straight road, along with the power lines and the road signs, oh my! Add the murkiness of the dark of a moonless night and the complexities abound. The black holes suddenly emerge everywhere, and the mind wills itself to see spots of lights where none exist. You frantically press the NRST button and find that the closest airport is just out of reach and gravity has a date with the aircraft at that time. And you were only going for a dinner with some friends that night. What a shame! Isn’t it?
So, it behooves us as pilots to always have a trick up our sleeve: situational awareness and anticipation. As Shakespeare eloquently (when was he ineloquent?) said, “There’s a special providence in the fall of a sparrow. If it be now, ’tis not to come. If it be not to come, it will be now. If it be not now, yet it will come—the readiness is all.”
NTSB data from various aircraft sources tell a bit different for each aircraft. As John Zimmerman has pointed out, “And by far the most common reason piston engines quit is because they don’t receive fuel, either due to fuel starvation (the airplane has fuel but it doesn’t make it to the engine) or fuel exhaustion (the airplane truly ran out of it). These two causes account for over one-third of engine failure accidents, but they are completely under the control of the pilot.” NTSB data on Beechcraft piston engine aircraft point to fuel starvation/exhaustion/contamination as causal in 90% of engine failures.
One such unlucky pilot a long time ago had fuel starvation happen to him on a two-mile final at an airport and he tried to stretch the glide. As the yoke shuddered and then the airframe responded with equal vigor to the shudder, all went black as the wing dropped and the aircraft followed suit from only 200 feet into a ditch; a huge momentum-stopper. The other wing had plenty to fly another 200 miles.
So 30%-90% of these unfortunate accidents can be avoided by filling up the tanks. After all, if you fly for personal or business reasons, either way, fuel is the cheapest insurance. Isn’t it? There is just one more hiccup that we might face on takeoff and that is fuel contamination. It behooves us to drain the fuel on each tank and the lowest sump site to make sure there is no water or other contaminants. Water can accumulate from a rainfall while the aircraft sits idly outside, due to leaky O-rings. So, sump the tanks well and smell, look and confirm, “Clear of water and contaminants!”
Fuel starvation by its very nature is a fuel mismanagement issue either due to distraction, not following checklists for timed switch between tanks, inappropriate switching to the wrong tank, or unfamiliarity with the fuel system in the aircraft. In some twin aircraft, cross-feeding from auxiliary tanks on takeoff instead of the main tanks while in others switching the lever partially in between the two tanks can lead to engine failures at precisely the wrong time. All these errors of distraction and improper actions by the pilot have been known to cause grave harm. One of my habits on long cross-country flights is to change fuel tanks near an airport along the flight path. Just some dumb thinking involved here, without any stats to support but it gives me some added comfort.
The above graphic, from the ATSB, depicts the mindset in fuel exhaustion and starvation: preflight miscues, decisions in flight, and technical factors (although not specified, they probably include partial turn of the lever or switching to the wrong tank.
Fuel exhaustion, on the other hand, is mostly a miscalculation blunder in the face of a strong headwind and trying to reach a destination or at times in saving a penny for less fuel to lose a pound of flesh in a mishap. Planning for an alternate airport in a cross-country flight is both a comfort and a pain but it forces us to calculate the extra fuel to fly the 30 minutes or 45 minutes after the alternate, giving us extra bit of cushion from a propeller flailing in the air silently. And sometimes it is a matter of a wrongly placed decimal in the navigation log (rare, yet it happens). Sadly, human behavior is circumspect at times, and no amount of guessing and assuming followed by hoping will change the hard fact in the air.
Then there are the 10%. The traditional Continental and Lycoming engines have a failure rate of about 13 failures per 100,000 flight hours. However, it does seem that there is such a thing as “infant mortality,” when brand new or recently overhauled engines give up their compressions. Rare events, these, but if you are following along, the possibilities are there, based on statistics. Mostly these engines have some metallurgic anomalies or installation errors, and the weakest parts give up their hold and the whole system gets unglued and unbolted metal gets ingested and then after the biggest shudder and a riotous clanging, all is silence. There we have little to do or can do.
But if even 100 hours have passed and you are listening to the engine by doing oil analysis, looking for metal in the filter and the oil, you might catch it. In more seasoned engines the reliability is good once the engine achieves adulthood. If you treat that engine well and are not a power jockey with the candle burning at both ends, the engine will take you to the promised land of the TBO and perhaps beyond. Failed valves from unseating or asymmetrical seating, on the other hand, can be determined by compression tests and borescopes.
A short write-up from AOPA here will help in the understanding: The EGT and CHT supervision on a good engine analyzer can give a reasonable clinical diagnosis for the sharp-eyed aviator. Every pilot perhaps should strive to have one of these multi-probe engine analyzers in their aircraft. Monitoring the trend is how one can keep an eye on subtleties of mechanical failures along with the oil analyses and the gold standard of borescoping the pistons and valves. Remember, the top of the engine (pistons, cylinders, valves and valve guides) has more risk than the bottom part of the engine (crankshaft, crankcase, and in Continentals, camshaft as well).
Top-overhauled cylinders face a common enemy of early failures if the through-bolts are not torqued or lubricated to specs, according to data gleaned from various engine sites. So, a reputable shop has to be given the pilot’s authority to use new through-bolts when an engine is torn down for cylinder repair or grafting a new one. A little short-term extra expense but it is definitely a long-term safety profile. An improperly set bearing that loses oil supply is a precursor to a sudden prop stillness. And that virtue of safety belongs to a seasoned mechanic with plenty of hours under his or her belt.
Another likely scenario that might become an issue is after an annual is where the mechanic was distracted from putting the right pieces together, as with the ailerons or safety wiring parts. A family friend, a retired airline pilot, flew his Cessna off the airfield after an annual and the engine failed on takeoff. His experience in handling the emergency helped minimize injuries to scratches and a temporary limp, but the cause was the mechanic’s failure to secure the oil filter with safety wire. Small changes can have large effects. The saying goes, the butterfly flaps its wings and creates a hurricane somewhere. I don’t mean to disparage the mechanics, but simply bring to light the possibilities that exist, and it is the pilot’s responsibility to do a thorough preflight test and then on first post-annual inspection takeoff, perhaps fly in a climbing spiral over the airport before departing elsewhere.
Engines are very reliable nowadays. They go kerplunk from aforementioned reasons and from misuse or abuse of the engine by the pilot. Flying rich of peak at 100 degrees F from the leanest cylinder (or the first cylinder to peak) or 20-30 degrees lean of peak (from the richest cylinder or the last cylinder to peak) is fine. What is not good is to fly the engine at peak (unless the power is set below 65%), where the combustion timing and peak intra-cylinder pressures are the highest and create significant damage to the cylinder compartment and to the piston heads.
Treat the engine well and it will serve you for a long time. Sometimes too much is demanded of the engine in advance, and too little is promised in its support and care. One friend is on his third engine in 6500 hours, while an acquaintance is on his third engine in 2000 hours. It matters!
If you have followed along thus far, you will come to the same conclusion that I have: fly with $200 of fuel when only a $100 amount is required saves 90% of these engine stoppage events. Monitor the engine’s performance for trends and treat it with respect, and preflight thoroughly before each flight and especially after a mechanic has had it in the shop.
One more thing, although not the realm of this discussion but has to be mentioned: practice engine out scenarios with an instructor periodically to get the feel and flow of thought and action in assuming command of such a potential eventuality.