Why it quits—and what to do about it

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?

SR-20 crash site
This is not good fuel planning.

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.

Garmin engine gauges
A full engine monitor is a good investment in your engine’s longevity.

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.

22 Comments

  • The author makes some excellent points in this article. I would like to add that an emergency could happen any time even if you follow the author’s recommendations to the letter. I have had 2 engines fail in 1,000 hours of flight time. Neither was from fuel starvation or exhaustion. That’s why single engine pilots need to train for gliding to a safe place for an emergency landing, or to use their ballistic recovery parachute if so equipped and a dead stick landing seems impossible.

  • A great reminder to apply common sense to our fuel planning and always have and brief (even when flying solo) a practiced plan for engine stoppage. “…fly with $200 of fuel when only a $100 amount is required saves 90% of these engine stoppage events.” Indeed, it really is that simple. Thanks!

  • Expect your engine to quit, and you’ll never be disappointed.

    An engine out in a small aircraft should very very rarely result in a fatality, and they wouldn’t- IF we trained and flew those aircraft properly in the first place.

    At no point in an approach should you be below an altitude that allows for you to glide to the airport (if not the runway). Read that again, it’s important.

    That doesn’t mean enough altitude to make the full pattern & approach – but sufficient altitude that a turn towards the field will result in landing on the airport, anywhere on the airport, safely.

    Regardless of what the PAPI/VASI or other visual indicators say, if you can’t make the field power off from where you are, you are too low for the conditions present. The low, flat, power on approach works great in a jet aircraft, which they were originally designed for, and they do work in recip powered aircraft as well, as long as everything is OK. But once things are not OK – your options on that type of approach are often picking the place to crash, and not much else.

    A stable approach does not need to be made at a shallow angle – it should be made at the appropriate angle, for the conditions at the time.

    It’s been proven time and time again that under duress we will default to the pattern of action that we have performed the most often. We’ll default to our most practiced muscle memory – so if we’ve only ever made power off gliding approaches to landings during flight reviews or check rides, then we’ll never be able to execute when the stress is on.

    Flying a power off approach to a full stop is good a good practice – and should be something done frequently to maintain proficiency.

    Knowing the glide slope of our aircraft in various conditions is essential – most power failure fatalities result from loss of control/stall spin – pilots tried to glide and either got too low & slow, because the only glide slope they followed for years was a shallow 3 degree approach with power and they couldn’t fly another under stress, or they went for the perfect field, a little too far away, and spun in when they stalled.

    This has to be practiced, to be learned. Understanding what a head wind will do to your approach when you can’t compensate with power is a critical piece of information for you to have.

    Lastly – it is better to land, in control, and damaged the plane than to try to save the airplane and lose control and crash. This is impossible to practice, but should be foremost in our minds. A gear up landing is the best short field procedure, and they are eminently survivable. A deliberate ground loop for a fixed gear aircraft has the same result. We walk away from the bent airplane, and let the insurance company figure it out.

  • Good article BUT… tell me more about the 14 pounds per square inch of gravitational pull? That’s a new one for me. Kind of detracts from what is otherwise a very credible and well written article.

    • Good catch Dave, the error : should be 1 mega pascal or 14,500 pounds per square inch compressive pressure at sea level. Missed the digits. The gravitational pull is at 32 f/s or 9.81 m/s. My apologies on the transposed branches of thought in the fog of writing.
      Glad the rest worked out.
      Best

      • Actually, the acceleration of gravity is 32 ft/sec/sec, not 32 ft/sec

        Also, water also gets into fuel tanks as normal moist air (especially in tanks that are not full of fuel). Air temperature changes from day to night will cause air to move in and out of the overflow tubes, pulling in a little more damp air every evening.

  • 30 degrees lean of peak seems a conservative number for running an engine that is set up correctly and has a good engine monitor. It is very easy to run 50 to 70 degrees lean of peak if the ignition system is up to snuff and the fuel flow to all cylinders is mostly equal. I consistently run a Cessna 340 seventy degrees lean of peak at all altitudes from 1,000 ASL up to FL 250 burning 6 gallons per NM versus rich of peak of 4.8 gallons per NM at higher flight elevations.

  • Don’t know how failure to safety wire the oil filter could cause engine failure on take off on the first flight after annual.

  • Presumably, engine vibration caused the filter to back off enough that it leaked, which starved the engine of oil.

  • “14lbs/sq.in. gravitational force” is air pressure
    gravitational acceleration is ~ 9.9 m / sec2, g
    “gravitational force” is weight (mass x g)

  • I fly a Cessna 182 RG with the extended range 80 gallons of fuel. I always make sure the aircraft is full before i take off. As well as if there is any water in the fuel samples. That said, i use my bladder method of flying. 2-3 hours airborne, and i need a bathroom break. Good time to refuel the plane. There is no way i am ever going to burn off 80 gallons in 2-3 hours of flying. Especially when i lean out the mixture to save fuel.)

  • Of course most of us fly planes which give us a choice of full fuel or full seats, but not both. I always add my “personal” range to the equation which mostly works out to three hours max. So I fly with four hours of fuel at take-off, and a preselected alternate at about the two hour range of my bird. That closer alternate also works well for weather, too.

  • I found a pair of gloves, a screw driver, and a pair of pliers tucked tightly inside the closed tail cone in my inspection after an annual – totally beyond belief!!!

  • @Parvez: <> Not sure where you got that number, but let’s think about it. Those failures are broken crankshafts, camshafts, connecting rods etc. — catastrophic failures from which there is no recovery of power. When that happens to a single engine aircraft shortly after takeoff at a urban airport it’s a “miracle on the Hudson” kind of moment with miracles in short supply.

    13 failures per 100,000 flight hours is 1.3 failures per 10,000 flight hours, or .65 failures per 5,000 hours. That implies that if you fly 2500 hours you have about a 1 out of 3 chance of experiencing a catastrophic engine failure!! (not rigorous probability math, but it gives you the idea…)

    This is not particularly great reliability when lives are at stake. What would you think about an automobile manufacture where 1/3 of their cars suffered a catastrophic engine failure in the first 150,000 miles? (2500 hrs @ 60mph)

    Full Disclosure: I’ve had an engine failure in a single engine aircraft during takeoff on 17L at KAUS –engine ran strong on runup, and then QUIT/kaput at 300-400 AGL. Fortunately, KAUS is a former SAC base with Looooong runways built for heavily loaded B52s, and I had elected to taxi all the way to the end instead of taking the midway. If the wind had been from the North that day, and I’d taken the midway, I’d have been down on the freeway, a street, or a house.

    This is serious stuff. Names and faces of people I used to know come into my mind whenever the subject of aircraft engine reliability comes up. There used to be a video of a PA32 trying to land on a freeway shortly after takeoff taken from the dashcam of a police car on the internet. It ends in a fireball. There were 5 on board. No survivors.

    Different subject: <> Reality with most single engine airplanes is that you have to trade off fuel load against passengers and baggage. The real issue with fuel exhaustion accidents is that the pilot neglected to calculate how long the engine(s) would run on the fuel that was available at takeoff. If they had realized at some point that they had 30 minutes of fuel remaining, they would have put it down before the prop stopped. This is a concept that should be taught early in a student pilots training — gallons = minutes. The problems occur when the “minutes of power” required for the flight are greater than the “minutes of fuel” onboard.

    Thanks for writing a thought provoking article.

    • The quotes within the s were: “…The traditional Continental and Lycoming engines have a failure rate of about 13 failures per 100,000 flight hours.”

      and “…So 30%-90% of these unfortunate accidents can be avoided by filling up the tanks.”

    • “1 out of 3 chance of experiencing a catastrophic engine failure” is absolute nonsense, based on obviously incorrect math. You mixed up numbers with percentage. 13 out of 100,000 is a failure rate of 0.013% (which most would agree is pretty good for anything in this world). Therefore, at the 2,500 hours you chose, that would mean .325 “failures” which is one third of one. Certainly not the “1 out of 3 chance of experiencing a catastrophic engine failure!!” hysterically and erroneously mentioned. The error the commenter made was in confusing the .325 with percentage, then calling that “1 in 3”.

      This erroneous conclusion is a defamation upon aviation which the uninformed will inaccurately employ to wrongly scare themselves and others out of flying in our aircraft — therefore the correction I’m making is much needed.

      (Also, Don W., you need to be careful about the “gallons = minutes.” Depends on power setting and fuel mixture, which obviously greatly affect fuel burn per minute. You are setting yourself up for trouble making a generalization you may fall back upon one day, to your peril.)

  • This is how my brand new R44 ran out of fuel on its 80th flight hour. The air induction tube collapsed no air to engine and you’re out of engine noise. The rest of the story. I auto rotated successfully with no damage. Turned defective helicopter over to the dealer and factory they crashed and totaled helicopter on initial test flight with same problem. I am now out of aviation 4246 j Brentmutton at g mail dot com

  • You write: “The traditional Continental and Lycoming engines have a failure rate of about 13 failures per 100,000 flight hours.”
    Where did you find that information?
    And: Does this include full overhauls? Or will a overhaul reset this counter to 0 hours?

    • There is no reliable database of piston engine failures either at the FAA or NTSB. If the engine failure ends with a successful forced landing without the damage or injury required to meet the NTSB definition of an accident there is no record.
      We hope that’s how most engine failures/power loss events end.
      The mechanics who work on the failed engine could file a service difficulty report but, even if they do, that information doesn’t migrate to any unified database.
      The situation is similar to gear-up landings which seldom cause enough damage to be classified as an accident and thus enter the NTSB database.
      The NTSB counts the power loss events that end very badly but how many successful forced landings occur can only be a guess.
      Mac Mc

  • One thing that needs to be repeated over and over, “Check your fuel setting switches” Especially in a twin engine plane and one you may not be totally familiar with. Do not inadvertently leave either of the switches in take-off check position. Most important is not leaving either fuel selector switch in the wrong position,i.e. ‘X Feed’. This will consume all the fuel in only one wing,letting both engines starve and die,all this with a full tank on the side with X Feed selected .

    NTSB Findings for just such a fatality event:

    The commercial pilot departed on a cross-country flight in night instrument meteorological conditions with the airplane’s fuel tanks full, providing an estimated fuel endurance of 4 hours 50 minutes. Two hours 50 minutes into the flight, the pilot reported a loss of engine power on the right engine, which was followed by a loss of engine power on the left engine. The pilot attempted to land at a nearby airport; however, the airplane impacted trees about 8 miles short of the airport. A review of weather information revealed no evidence of in-flight icing or other weather conditions that may have contributed to the accident. Post-accident examination of the air frame and engines revealed no pre-impact failures or malfunctions that would have precluded normal operation. All fuel tanks were compromised; however, an undetermined amount of fuel spilled from the left fuel tank during recovery of the wreckage. The left engine fuel selector valve was found in the “X-FEED” (crossfeed) position, and the corresponding cockpit fuel selector switch was found in an intermediate position, which was likely the result of impact damage. The right engine fuel selector valve and the corresponding cockpit fuel selector switch were found in the “ON” position. With the valves in these positions, both the left and right engines would have consumed fuel from the right fuel tank. Review of performance charts and fueling records indicated that if the flight was conducted with the valves in the as-found positions, exhaustion of the fuel in the airplane’s right fuel tank would have occurred about the time the pilot reported the dual engine failure. In addition, the yaw trim was found in the full nose-right position. It is possible that the pilot used nose-right yaw trim to counteract an increasing left-turning tendency during the flight as fuel was burned from only the right wing’s fuel tank making it relatively lighter than the left wing. According to the expanded checklist in the pilot’s operating handbook for the airplane, during taxi, the pilot was to move each fuel selector to “X-FEED” for a short time, while the other selector was in the “ON” position, before returning both fuel selectors to the “ON” position before takeoff. According to a checklist found in the airplane, the fuel selectors were to be set to “X-FEED” during taxi and then to “ON” during engine run up. GPS data recovered from onboard devices indicated that the pilot taxied from the ramp and onto the active runway without stopping in about 3 minutes, indicating that it is unlikely he performed a complete run up of both engines before takeoff. He likely failed to return the left engine fuel selector from the “X-FEED” to the “ON” position, where it remained throughout the flight and resulted in fuel starvation and a loss of engine power on both engines. ”

    I hope this post may help someone avoid a situation such as this.

Leave a Reply

Your email address will not be published. Required fields are marked *