THE BAD NEWS AND GOOD NEWS ABOUT ENGINE FAILURES
Acknowledgements: AIR FACTS (John Zimmerman)
(Ed. Note: The following is condensed from an article by John, which can be read in full on the AIR FACTS site. Thankyou John!)
“You’ve probably said it to a nervous passenger: “Don’t worry, airplane engines almost never quit” .... This is mostly true for turbine engines, but it’s far less true for piston engines.
THE BAD NEWS
According to the NTSB and FAA, there are somewhere between 150 and 200 accidents per year that are caused by power loss. Roughly a quarter of these are fatal, which makes this the second leading cause of fatal accidents. Such events seem to be holding steady, even though overall accidents have declined somewhat in recent years. Data from AOPA paints a similar picture. An interesting study from the Australian Transportation Safety Board (which does some first-rate safety research), offers more supporting evidence: There were 322 engine failures or malfunctions between 2009 and 2014.
It’s worth pointing out that all these statistics almost certainly under-count the actual number of engine failures, since they only appear in these reports the result is an accident.
THE GOOD NEWS
The good news is that “System Malfunction (Powerplant)” hides an awful lot of important details. That NTSB phrase merely defines the event, not the root cause. 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.
Pilots will probably always find ways to run out of fuel, but it bears repeating that a few good habits can dramatically reduce your chances of such an engine failure.
· Having a hard one-hour minimum is a great place to start – under no circumstances can you still be flying with less than one hour of fuel in the tanks.
· Next, spend some time understanding the fuel systemso you can always get that fuel to the engine, especially in twins and older airplanes with complicated fuel systems.
· Take a little time away from practicing a rare emergency and instead discuss different fuel scenariosthat might pop up.
· Finally, always know how much fuel was in the tanks at engine start and know your real-world fuel burn rate. Depending on those, and not as much on the gauges, will lead to more realistic decision-making.
THE ENGINE QUIT. BUT WHY?
The list of causes includes:
· Pilot mistakes, generally preventable
· Fuel contamination. It does happen and it can have serious consequences. Again, this is almost totally preventable, by performing a thorough pre-flight every time and staying with the airplane whenever it’s fuelled to verify you get the right type.
· Next comes carburettor icing, which is either impossible (fuel injected engines) or preventable(by using the carb heat). The penalty for pulling that knob is fairly small in most airplanes, so when in doubt you should use it – even if the conditions seem inhospitable for icing. A carburettor temperature gauge is a good idea too, especially for some Continental models.
· By the time you get to real mechanical failures such as a failed magneto or a broken connecting rod, the numbers are fairly small – less than 20% of all powerplant problems. Some of these are simply bad luck, but a decent number were due to faulty maintenance, typically soon after major repair work or overhaul. This argues for high quality maintenance, but it also supports Mike Busch’s theory of Reliability Centred Maintenance, where overhauls are completed on-condition, not based on an arbitrary time limit.
THE RIGHT HABITS
First, the easy stuff: Develop good habits regarding fuel management and maintain the discipline to follow them every time:
· Sample fuel before every flight
· Buy from reputable FBOs
· Make sure your fuel caps seal tightly
· Use carb heat (if applicable) on every flight to prevent icing, not just when the engine starts to run rough.
Beyond those everyday basics:
· Seek out high quality maintenance, but perhaps only when it’s really needed. The right balance will keep the engine under close supervision, with regular oil analysis and borescopes, but avoid added riskfrom doing invasive part replacement too often.
· When maintenance is performed, pilots should be scepticalon the first flight after overhaul or parts replacement. In other words, don’t make that first trip a hard IFR trip over the mountains.
Of course some traditional advice also helps a lot:
· Fly the airplane regularly
· Avoidcold starts
· Operate the engine conservatively (especially with respect to CHT)
The biggest payoff from these habits is in longevity, especially when it comes to preventing corrosion, but there is certainly some improvement in reliability to be had as well.
Following these rules can reduce your chances of an engine failure by over 75%, which should make you feel a lot more comfortable on your next flight over remote terrain. But that still means the fan out front can stop turning. In that situation, all you have to fall back on is good training and realistic planning.
Based on the numbers above, practising engine failure scenarios as a part of your regular training is time well spent, and continuously thinking about forced landing sites in flight doesn’t hurt either.
Engines can and do fail, but a little preparation and a little paranoia should keep you from adding to those statistics”.