Intrigued by the potential benefits of turbocharging and pressurization, but scared by the bad reputation and horror stories of reduced TBO and high maintenance costs? Don't believe everything you hear! AVweb editor Mike Busch (who has owned, flown and maintained a variety of piston-powered aircraft — normally- aspirated and turbocharged — over the past 30 years) offers a frank and detailed analysis of the costs and benefits.
August 13, 1996
When I learned to fly on the East Coast thirty-something years
ago, turbocharging was a dirty word. Everybody said turbos were
expensive, inefficient, maintenance-intensive, problem-prone,
shortens TBO drastically, and makes sense only for folks based
in the Colorado Rockies. As a young, impressionable airman, I
bought it...lock, stock and intercooler.
I bought my first airplane in 1968, a nice conservative normally-aspirated
Cessna 182. After flying the Skylane for four years and 1,000
hours, I traded up to a higher-performance retractable, a Bellanca
Super Viking, which was also normally-aspirated. Following the
Bellanca, I flew a succession of retractable singles including
a Bonanza and a Cessna 210. All normally-aspirated.
My turbo initiation
And then nine years ago, I bought my first turbocharged airplane.
Not just any turbocharged airplane, mind you. A turbocharged twin.
My first twin. A 1979 Cessna Turbo 310, to be exact, with a pair
of turbocharged TCM TSIO-520 engines.
I was scared to death that this twin-turboed machine would eat
me out of house and home. In fact, I promised myself that if the
310 started showing signs of being a lemon or a hangar queen,
I'd sell it in a heartbeat...and buy some nice conservative normally-aspirated
Well, here I am nine years and nearly 2,000 hours later. I still
own the T310R. Astonishingly, it has proven to be the most reliable
and trouble-free airplane I've ever owned. And a truly wonderful
As a result, my attitude toward turbocharging has made a complete
one-eighty. My next airplane may not be a twin, but it certainly
will be turbocharged. I'd never again consider purchasing a normally-aspirated
airplane. That's how strongly I feel about the many benefits of
By the way, most of the discussion that follows really isn't limited
to twins: it is equally applicable to singles.
Turbos and ice
If I had to pick one benefit of turbocharging above all others,
I guess it would have to be ice avoidance. Prior to buying the
T310, most of my scariest flying experiences had been due to airframe
icing. Flying a normally-aspirated aircraft in IMC when the freezing
level is below the MEA is no fun at all. Even if the tops are
below the airplane's service ceiling, trying to top an icing layer
in an bird with anemic climb performance is seldom a winning proposition.
Trust me, I've been there and tried that.
So when I first got my twin, you can imagine how excited I was
about having all that fancy known-icing paraphernalia: boots,
hot props, windshield hot plate, heated static and fuel vents,
But in nine years of flying my T310, much of it coast-to-coast
trips in all sorts of weather, I can't recall a single flight
in which having the boots and other deicing gear offered a decisive
You know why? Because the airplane is turbocharged!
With turbocharging, there's always some ice-free altitude available...either
below the freezing level, on-top, or up where it's cold enough
that icing isn't a problem. And with full takeoff power available
up to 20,000 feet, getting above the ice becomes do-able.
If I had to make a trip in icing conditions and was given the
choice of turbocharging or deicing boots (but not both), it would
be no contest. I'd pick the turbo every time.
Of course, having both a turbo and boots is even nicer.
Avoiding the bumps
Thunderstorms are the other great producer of sweaty palms and
stained underwear, and turbocharging offers some significant benefits
Being able to cruise in the high teens and low twenties won't
let you top a line of frontal thunderstorms. But when penetrating
a field of air mass thunderstorms, FL200 is often high enough
to offer a good visual perspective and let you circumnavigate
the buildups visually. And personally, I'd much rather use eyeball
avoidance than rely on a Stormscope or weather radar.
Even when icing and thunderstorms are not a factor, turbocharging
often makes it possible to find smooth air when normally-aspirated
aircraft are being badly beaten up by bumps. While turbulence
is usually considered more of an annoyance than a serious threat,
it can be a major cause of discomfort and fatigue, especially
on the long trips I often fly. I'll happily give up 10 or 15 knots
of groundspeed to get out of rough air.
Speed and climb
Turbocharging is often touted as a "speed mod" and sometimes
it is. I've had the pleasure of catching a few 100-knot tailwinds
up in the lower Flight Levels that treated me to 300 knots on
the groundspeed readout and enabled me to make it more than halfway
across the country nonstop...and boy is that ever fun! But frankly,
this sort of scenario doesn't happen often enough to justify turbocharging.
Ignoring winds (which always hurt more than help over the long
run), turbocharging offers modest speed benefits. A normally-aspirated
Cessna 310 cruises at about 180 knots at 6,000 feet and 75% power.
At the same power setting, my T310 will do 195K at 12,000 feet
(where supplemental oxygen isn't required) and 215K at 20,000
But I don't fly it that fast because doing so would shorten engine
life and burn a lot of fuel (more on this later). I prefer to
throttle back to 65% power or less and cruise at 185K down low
or 205K up high. Flown that way, the turbo gives me a small speed
advantage, but nothing that gets me too excited. That's why speed
rates rather low on my list of turbocharging advantages.
Ironically, improved takeoff and climb performance in high density-altitude
situations is perhaps the benefit most often cited for turbocharging,
but it comes at the very bottom of my list. This might be a big
deal for folks who live at higher elevations or who do a lot of
flying into mountain airports. I just don't happen to be one of
them. When I fly to Colorado or Wyoming, my destination is usually
a big airport with a 10,000+ runway. So takeoff and climb performance
isn't usually a major issue.
Come to think of it, I do recall a few "exciting" takeoffs
in the Bellanca at full gross on hot summer days from South Lake
Tahoe or Albuquerque or Santa Fe, despite the generous runway
lengths. That doesn't happen anymore now that I fly a turbo.
Reduced TBO is and increased engine maintenance is probably the
most frequently cited disadvantage of turbocharging. For example,
the published TBO for the IO-520-MB in a normally-aspirated Cessna
310 is 1700 hours, while the TSIO-520-BB in my T310 is rated at
only 1400 hours.
But what does published TBO really mean? Damned little, actually.
Some TCM engines virtually never make it to TBO, while other engines
often make it well past TBO.
Take my T310, for example. When my engines reached their 1400
hour TBO, they were still running beautifully and showed every
indication of good health. So I continued flying and checking.
And flying and checking. Finally, at 1900 hours, the #6 cylinder
in the left engine started losing compression due to an exhaust
valve leak. So I pulled both engines and had them majored.
The inspection reports from the engine shop were quite interesting.
Except for worn exhaust valve guides, all twelve cylinders from
the two engines at 500 hours past TBO were still within new limits!
The cranks, cams, bearings and gears all looked like new, too.
With the benefit of hindsight from the teardown inspection, those
engines could have been re-valved and run for another 1000 hours.
So much for published TBOs.
What does it cost?
How about the increased maintenance costs associated with turbocharging?
Even if you accept the reduced TBO theory (which I don't, based
on experience), the costs really aren't as high as many think.
Let's try to quantify them.
A normally-aspirated IO-520-MB factory reman has a street price
(exchange) of about $17,000 and has a published TBO of 1700 hours;
this computes out as a reserve-for-overhaul of $10 per hour. A
turbocharged TSIO-520-BB reman sells for about $21,000 and has
a TBO of 1400 hours; reserve-for-overhaul is $15 per hour. So
figure the overhaul cost penalty for turbocharging at $5 per hour
Now let's be pessimistic and say that you don't fly your turbocharged
engine at reduced cruise power settings (the way I do), and therefore
assume that the turbo engine burns an extra gallon-per-hour more
than its normally-aspirated sister. That adds $2 per hour (per
engine) to operating costs.
Now let's be even more pessimistic and assume that because you
run your engine so hard, the turbocharger, wastegate and controller
all need mid-TBO overhauls (mine didn't). That costs about $2,800,
so adds another $2 per hour (based on a 1400-hour TBO). What the
heck, let's even toss in an extra $1 per hour for exhaust system
.Using this worst-case analysis, the additional cost of turbocharging
comes to $10 per hour (per engine). It certainly isn't more than
that, and very likely is less.
If we're talking about an airplane in the Bonanza or 210 class
(which costs $100 to $150 per hour to fly), the additional $10/hour
cost of turbocharging is chump change. The same is true of the
$20/hour cost for a twin (which costs $200 or $300 per hour to
How about the poor fuel economy that critics of turbocharging
Well, it's true that most normally-aspirated engines have a 8.5-to-1
compression ratio and most turbocharged engines have only a 7.5-to-1
ratio. The turbocharged engine is a bit less fuel-efficient (which
is why we tossed in that extra 1 GPH in our cost analysis).
But looking at engine efficiency doesn't tell the whole story,
because it ignores the fact that airframes are much more efficient
up at the higher altitudes that turbocharging allows. By throttling
back from 75% to 65% power and climbing from 6,000' to 12,000',
my T310 can fly 5 knots faster than a normally-aspirated 310,
and do it at lower fuel flow. If I'm willing to put on a cannula,
I can climb to FL200 and beat the non-turboed 310 by 25 knots
with no fuel flow penalty.
The normally-aspirated airplane is more efficient than the turbo
only if you force both airplanes to fly at the same low altitude.
And that's simply unrealistic.
Why the bad rep?
If turbocharging is such a panacea, why does it have such a lousy
reputation? There are some good reasons.
For one thing, turbocharged engines are far more vulnerable to
abuse in the hands of a ham-fisted pilot. You know, the kind that
slams the throttle in and out, doesn't bother to lean accurately,
runs tanks dry, etc. A normally-aspirated engine can tolerate
a certain amount of such abuse, but a turbocharged engine can't.
Turbos need TLC.
So if your airplane is used for training or rental use and flown
by lots of pilots, you probably don't want a turbo. But if you're
the sole pilot and you make a real effort to treat your engine
with care, you'll probably have excellent luck with turbocharging,
just as I have.
Some engines use turbocharging to gain additional sea-level horsepower,
rather than simply to maintain sea-level performance at altitude.
Highly ground-boosted engines like the 325 hp TSIO-520 found
in late-model T210s and P210s and many RAM-converted twins have
a dismal record of making published TBO, much less going beyond
it. The same is true of the 225 hp TSIO-360 in the P337.
All other things being equal, the higher the MP redline, the poorer
the longevity of a turbocharged engine. The best candidates for
good engine longevity are "turbo-normalized" engines
like the 285 hp engines in my T310 (red-lined at a very conservative
32" of MP).
If you fly a highly ground-boosted turbo with a MP redline of
38" or more, one of the best things you can do for engine
longevity is simply to "derate" the engine. Fly it at
lower power settings and it'll last far longer.
Some lower-cost turbocharged airplanes like the Piper Turbo Arrow,
Mooney 231 and Piper Seneca II use the problem-prone Continental
IO-360-series engine coupled with a fixed-wastegate system that
makes the turbocharger work hard even when you don't need it.
These installations rarely make TBO and usually require a mid-term
turbo overhaul. Fixed-wastegate engines also demand high pilot
workload because the manifold pressure tends to be quite unstable.
Fortunately, Cessna never produced an airplane fixed-wastegate
system. However, the T337 and P337 do use the troublesome Continental
TSIO-360 but with an automatic wastegate.
Back in the '70s, it was all the rage to hang aftermarket turbochargers
on all sorts of normally-aspirated engines. Rayjay made STC'd
kits to turbocharge a wide variety of airplanes. Most of these
installations were a real disaster, and proved extremely unreliable
and maintenance-intensive. Avoid them like the plague.
I used to advise staying away from all aftermarket turbo conversions.
But nowadays, I make an exception for the turbo-normalizing conversions
to Bonanzas and Cardinals done by
FliteCraft Turbo in Pagosa Springs,
Colorado (phone 970-731-2127, FAX 970-731-2524, email
These conversions are every bit as good as any factory
turbo installation, and better than most.
There have also been serious problems with aftermarket intercoolers
that many turbo owners add to factory-turboed airplanes.
In general, intercooling is a good idea, because it allows a turbocharged
engine to breathe cooler air, thereby improving detonation margins,
lowering CHTs, and increasing efficiency. The problem usually
isn't with the intercoolers themselves, but with the fact that
the STCs often don't require a proper flight manual supplement
with revised performance charts.
Because the engine is breathing cooler, denser air, the MP must
be adjusted downward to compensate, often by several inches. But
many owners wind up installing an aftermarket intercooler and
then trying to fly using the original factory performance data.
Doing this, it's easy to believe that you're cruising at 70% power
but actually be cruising at 85% power instead. You can imagine
what this does for engine longevity.
If you're flying an airplane with an aftermarket intercooler,
you'll need to reduce the MP shown in the POH performance charts
by 1 to 3 inches, depending on altitude. The higher you fly, the
more adjustment you need to make.
In general, fuel flow is an excellent indicator of power output.
If you find your airplane is burning more fuel than the POH calls
for, it's very likely that you're pulling more horsepower than
you think you are.
Oxygen versus pressurization
To take maximum advantage of turbocharging for getting above the
ice and bumps (and for catching that occasional 100-knot tailwind),
we need to climb up to the high teens or low twenties. And that
means we must either breathe supplemental oxygen or we must have
a pressurized aircraft.
Until the early 1980s, flying high and unpressurized meant wearing
an oxygen mask. And frankly, oxygen masks are a real pain in the
Personally, I find masks seriously uncomfortable. When I wear
one, my glasses usually fog up and my mustache always becomes
drenched with perspiration.
Masks also interfere with communications. You can't use your normal
headset microphone, and those in-the-mask microphones sound about
as intelligible as using a speakerphone from across the room.
In other words, oxygen masks suck!
In the early 1980s, the FAA approved the use of cannulas for breathing
supplemental oxygen in-flight. This proved to be a tremendous
boon for turbocharged-but-unpressurized aircraft. Cannulas are
extremely comfortable, so much so that it's easy to forget you're
wearing one. Cannulas allow you to breathe normally, communicate
normally, even eat and drink in-flight. And so-called "conserving"
cannulas, coupled with calibrated vernier flowmeters, permit you
to stretch your oxygen supply by a factor of two or three compared
to a mask.
Cannulas solve many of the problems associated with breathing
supplemental oxygen, but not all of them. Cannulas are approved
for use only up to FL180; some of us have been known to push this
limit a bit, but I can personally testify that a cannula does
not provide adequate oxygen much above FL200.
Furthermore, some folks simply don't do well on 100% oxygen, period.
It tends to dry out the mucous membranes of the nose and throat,
and prolonged breathing gives some people middle-ear problems.
Others suffer from "altitude sickness" that is a mild
form of "the bends."
Supplemental oxygen can also be problem if you carry a lot of
passengers. That oxygen bottle can last a long time if only one
or two people are breathing from it, but four or six can empty
it pretty fast. Furthermore, some passengers simply don't care
to fool with oxygen paraphernalia (cannulas or masks), and other
passengers (particularly children and infants) can't easily be
persuaded to use oxygen.
So if you tend to carry passengers or if you're one of those folks
who have a problem breathing through a tube, you may want to give
serious thought to a pressurized aircraft.
What does pressurization cost?
The costs involved are significant, however. Pressurized aircraft
are more expensive to buy, more expensive to operate, and more
expensive to maintain.
Let's look at a specific example. According to the latest Blue
Book, a pressurized 1980 Cessna 340A sells for an average retail
price of $265,000. Its unpressurized counterpart, a 1980 Cessna
T310R, has an average retail price of $168,000. So the pressurized
airplane commands nearly a $100,000 premium.
At the same time, the 340A weighs about 500 pounds more than the
T310R (but has no more useful load), burns 3 gallons-per-hour
more, and cruises a few knots slower at most altitudes.
Maintenance of the pressurized bird is also more expensive, but
not for the reason you might think. The pressurization system
itself requires very little maintenance and seldom gives any trouble.
When it does, the fix is usually quite simple: repairing a bad
door seal or cleaning a sticky outflow valve.
But pressurization makes certain other maintenance tasks much
more difficult and time-consuming. Installing a GPS antenna, a
fuel totalizer, or a multi-probe EGT system, for example, is a
far more difficult job on a pressurized airplane because of the
need to bring wiring through the pressure vessel. Changing an
engine control cable or a fuel line are also far more labor-intensive
for exactly the same reason.
It's difficult to quantify the additional maintenance cost of
pressurization in terms of a dollars-per-hour figure. Most routine
maintenance operations are no more difficult on a pressurized
airplane. But certain functions that involve penetrating the pressure
vessel can be a great deal more difficult, and therefore expensive.
In addition, pressurized airplanes tend to have more engine problems
than non-pressurized ones. Again, this is not the fault of the
pressurization system. It's simply because pressurized airplanes
tend to spend a lot more of their life flying at high altitudes
than non-pressurized ones. A Cessna T310R pilot will think twice
before climbing up to the flight levels simply because doing so
requires him to use oxygen, while a Cessna 340A pilot will climb
up there without thinking twice about it.
At high altitudes, the turbo works harder and the engine runs
hotter. In the long run, this means that all other things being
equal, a pressurized airplane will generally experience worse
engine longevity than its unpressurized sibling.
Of course, all other things don't have to be equal. A pressurized
airplane in the hands of a pilot who pays meticulous attention
to proper powerplant management (warm-up, cool-down, power settings,
leaning, temperature control) can have very good luck with engines.
And a turbocharged-but-unpressurized airplane in the hands of
a ham-fisted pilot can prove to be a maintenance disaster.
If you use your airplane as a serious traveling machine—especially
if you fly long trips in instrument weather like I do—you should
seriously consider turbocharging.
If you pay careful attention to powerplant management, use conservative
power settings, avoid troublesome engines (e.g., highly-boosted,
fixed-wastegate, or most aftermarket add-ons), and be careful
with aftermarket intercoolers, I think you'll find—as I did—that
the benefits of turbocharging far outweigh its very modest costs.
If you don't do much flying to high-altitude airports, the greatest
benefits of turbocharging lie in avoiding icing, thunderstorms,
And sooner or later, you'll catch one of those 100-knot tailwinds
and put a big smiley-face in your logbook.