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Thoughts from the Western Slope

Worried About an Engine Failure?
By Bill Marvel
Posted on 3/27/2020 6:53 PM


In an earlier article, I wrote about night flying out here in the west where ground lights are few, dark is really dark, terrain ranges from rough to vertical and for those reasons, many pilots with single engine airplanes tend not to fly.  That’s the norm and is fully understandable given human nature.  It is also one of the reasons night flight is so enjoyable – you own the sky, it is generally smooth and you can see any traffic far away.  But in the back of your mind (or maybe in the front of it!) lurks that nagging, gut wrenching, emotion driven question, “what if the engine quits?” 


I will never forget the first time that gut wrenching question crossed my mind.  An American pilot I met in Sydney, Australia had just ferried a new Cessna 172 there from the factory in Wichita.  I was fascinated he could even do that and we talked all night about his adventures while on the 747 headed back to the states. 

Not long afterwards he called me from his home in Vacaville, CA, near Nut Tree Airport where he was based.  He had just won a contract to ferry a Britten Norman Islander from the U.S. to Formosa Airlines in Taipei, Taiwan.  With three large fuselage ferry tanks needed in addition to standard wing tank fuel, only the right front seat remained and it was mine if I wanted it.  I did. 

Long story short, we took off at 9 PM from Nut Tree, cruised at 6000 feet all the way to Honolulu in that 110-knot airplane and landed 20 hours and 15 minutes later.  There was no autopilot so we traded off flying in pitch black with no moon.  It took the first 8 hours of flying with both engines running to allow us to burn off enough fuel just to be down to full certified gross weight.  There was no possibility of maintaining flight if one engine quit until we were most of the way across because of the heavy weight.

Sixty flying hours and several days later we delivered the airplane to the customer and I just stood there looking at those two Lycoming O-540 engines that never missed a beat all the way across the Pacific.  (Actually, they both quit every time we burned out a ferry tank but then started again once they got fuel.  You can’t blame the engines for that).

Denny and I flew many more ferry trips all over the world for the next several years and he’s still out there doing it.  That flying was one of the highlights of my life.  But to the point of this article, the trip to Taipei changed my view of engines.  And that and subsequent trips taught me a lot about fuel management.         


Most have heard the expression "the slow boat to China" at one time
or another.  Above is the slow airplane version
of that idiom.

An aircraft engine is not a human being with a brain and emotions.  It has no idea whether outside the cowling is day or night, land or water, a 10,000 foot runway or a rugged mountain range.  It just runs.  Why does it run?   What causes it not to run?  What influence do you have in preventing it from failing?  Let’s take a moment to think about it.  In this analysis, I am assuming a genuine aircraft engine and not an experimental auto conversion, a two-cycle snow mobile engine or some other power plant with little proven history in an aviation application.  Those have their role, but high reliability has not been one of their attributes.    


It takes a little thought, but in doing so I came up with six things an air-cooled aircraft engine needs in order to operate.  In no particular order they are fuel, combustion air, ignition, cooling air, lubricating oil and structural integrity.  The first five of those are either totally or largely within your control.  The sixth is partially within your control if you own the airplane you are flying and especially so if you are the one doing some of the maintenance on it.  More on that later.  But now, let’s look further into all six of them and see if your concerns about engine reliability can be allayed. 

1.  Fuel.  Without researching any statistics, I am certain the majority of engine failures in GA aircraft are simply due to pilots running out of fuel.  I would say “enough said” is the appropriate comment here but it isn’t.

More needs to be said.  First, forget the 30 minute and 45 minute rules for fuel remaining at destination and go for a full hour.  That’s an easy number to remember.  Pay attention to your fuel gauges and your fuel totalizer and install the latter if you don’t have one. Periodically in flight, compare what each says as they should closely agree. 

Always know where your fuel is.  In my RV-14A or any other airplane when I am doing a very long flight, I’ll manage fuel so as to burn one tank out because I then know for certain where all of my remaining fuel is – in the other one!  How many times have you read of an airplane crashing short of the runway out of fuel when another tank still had 15 gallons in it?  I’ll go out on a limb here and even recommend you do something few will suggest.  In cruise flight, turn the fuel valve to OFF and let the engine quit.  Then turn the fuel valve on and note how long it takes to restore power.  It won't be more than a few seconds and will give you the confidence to use all available fuel if you need to.  Landing with each tank on 1/8 without knowing how accurate your fuel gauges are is scary. Just how close is that 1/8 to 0/8? 

With experimental aircraft in Phase 1 testing, I always burn each tank dry (but not on the same flight!) and then refuel it to see how much usable fuel there actually is. 
I note what the fuel level says before burnout occurs, whether I get a low fuel level or low fuel pressure annunciation from installed equipment and note whether the engine quits abruptly or coughs and sputters first.  In ferry flying it was standard practice to burn a ferry tank dry, as in the engine quitting, to know you had used all the fuel in it.  If you see you’re going to be into that last hour of fuel before you arrive due to head winds or any other reason, stop and refuel.  You’d feel very foolish if you didn’t, arrived at your destination with minimal fuel on board and found the airport closed because of a gear up landing on the only runway 10 minutes previously.  LAND with one-hour fuel remaining and with the fuel selector on a tank that you positively know has fuel in it.  Do this and you will never have a fuel exhaustion event.  Unless someone is shooting holes in your tanks in flight, a fuel cap comes off, or a fuel line is significantly leaking, that one hour is going to prevent you from arriving at ground level prior to the runway.  Comparing fuel tank quantity with totalizer quantity will assure that all of the fuel you should have on board is still there.  Now, that’s enough said and it will prevent your having a fuel problem of your own making.  Doing so is both inexcusable and avoidable.         

2.  Ignition.  There are two independent ignition systems in every piston aircraft engine.  Turbines are a different beast but few of us operate them.  You check both systems during runup prior to each flight and you don’t go if either one has a problem.  Either system will get you to an airport if the other one fails.  Checking both prior to each departure, plus doing whatever periodic inspections are required, will eliminate this concern. 


The beach towel is optional but opening up your mags every few hundred hours just for a look and
some basic health checks will do wonders for reliability.  If you cannot legally do this yourself, find an A&P
who will do it for you while you watch and learn.  There are many indications of an internal problem
if you have one, and most of them are easily seen.

3.  Combustion Air.  The engine needs air to mix with fuel prior to ignition taking place.  Each engine has two sources of this combustion air – primary and secondary.  Primary air comes through a filtration system prior to becoming mixed with fuel.  This flow path (air inlets) is checked visually during pre-flight.  You control the application of secondary combustion air via either a carb heat or alternate air system.   Neither one of those is needed routinely but each is available to you as a backup if necessary.   Between the primary and secondary flow paths, you control combustion air.


4.  Cooling Air.  Cooling air is ram air coming in over the cylinders and continuing past them and through the oil cooler, or vice versa in some airframes.  If this path is clear during a pre-flight inspection, it is almost impossible for it to become restricted during flight unless you happen to hit a large bird in exactly the right place on the cowling so as to block flow – a daunting task even if you tried.  This applies whether the engine is entirely air cooled or if it has some component of liquid cooling.  Even liquid cooling transfers heat to an air stream eventually.  It is virtually impossible to block cooling air if the flow path is clear before takeoff.     


5.  Lubricating Oil.  Oil provides both lubrication and cooling since it carries a good deal of engine heat with it.  Oil transfers that heat to the passing air stream via the oil cooler discussed above.  You check oil quantity prior to each engine start and you know there is little change in quantity from one start to the next.  If there is, you see it on the dipstick and can stay on the ground to find out why.  In flight, oil is consumed at a low rate in normal operation.  But even if there is unusually high consumption, say from a broken piston ring, the chance you will run out of oil prior to running out of fuel is remote.  You would see increasing oil temperature and decreasing oil pressure well before the engine seizes.  In short, if you have sufficient oil at the start of a flight (and remember to replace the dipstick…), there is nothing you can do during flight to exhaust it.    


                                                              Don't ignore the air inlets behind the propeller.  These seemingly simple holes provide fully 50% of the items critical to your engine's  operation.  Those are engine cooling air, filtered combustion air and oil cooling air in most airframes.  Take away any one of those, let alone all three, and you're doing down...    


6.  Structural Integrity.  The one thing somewhat out of your control is structural integrity.  If the engine’s crankshaft breaks in two or a piston rod goes through the case, you’re simply out of luck and in an emergency situation.  Handle it as best you can.   But if you failed to pay attention to oil quantity and oil consumption, you may have actually missed an opportunity to prevent that crank break or rod throw from occurring.


I said earlier in this article we’d come back to maintenance and we’re now there.  Some of this structural integrity category is in your control if you perform even the most basic of owner maintenance as allowed by the FARs.  Just removing the cowling every 25 hours and inspecting the engine with a flashlight and mirror is very helpful.  This alone will allow you to look for something as insidious as chafing of fuel and oil hoses as well as ignition leads.  It is surprising how often chafing issues occur under the cowling.  By changing the oil, monitoring oil consumption rate, opening and inspecting oil filters, having oil samples done and watching for evidence of case or cylinder cracks like oil seeps and exhaust stains, you might avoid even this last failure cause of the six I pointed out.  And don't forget that big fan bolted to the engine.  Without it the engine is worthless except for weight and balance.  Any appearance of cracks, dents, nicks, grease, oil and the like on the prop blades or prop hub are all caution flags that warrant further investigation.  The more you know about your aircraft and the more you see, the better you will be in helping your A&P maintain it.  Even if you are in a joint ownership situation (and maybe especially so!) take the time to do this.  Rest assured not all owners are hands on and thus something you find that is a potential problem likely will not be found or even noticed by another owner/partner.  

And please -- don't do any of this with a radio or TV on, people talking with you or with any other distractions nearby.  Making sure you have a reliable engine is serious business and you need to focus your full attention and all your senses on what you are doing.  Want to chit chat with a buddy?  Go out and have lunch or coffee, talk all you want and then come back to continue...alone.  


Have an A&P take you on a tour of your engine compartment.  Knowing what is there, where it is
and what it does will give you a great deal of insight about what is normal and what is not. 

There you have it, blow by blow.  When I got to Taiwan in the Islander, I wondered why I was at all concerned about flying over the mountains day or night provided killer issues like ice and high winds aloft were not present.  I realized that the biggest threat of all was not the engine in the cowling but the imagination between the ears. 


When engine reliability is broken down like this, you realize the odds of having a complete engine failure just when you happen to be flying at night or over bad terrain are near zero.  But you can increase them considerably by your own negligence or failure to pay attention to obvious risks like running out of fuel or oil.


Now develop some renewed confidence by fueling up and heading out over the high country for lunch somewhere.  Flying is the best thing you can do for your engine even though it has no idea what you are doing or why.  And be sure to mark your aircraft maintenance calendar starting right now for an every 25 hour cowling removal and engine inspection.