Real stats on engine failures?

(Rich Stowell) wrote
Your experience vis-a-vis how NTSB accident numbers (reported) stack
up compared to the actual total number of accidents (reported +
unreported) is not at all unusual. I too know of numerous unreported
accidents. But this isn't peculiar to aviation -- it probably happens
in a lot of different settings and more often than we realize. That's
what makes estimating and/or extrapolating accident information so
difficult. Perhaps if we always stated a number plus-or-minus some
estimate of the error that'd be satisfactory?

Well, it would be satisfactory if you had a valid way of estimating
the error. However, this still requires data. It's really very
unfortunate that data collection in GA is a bad joke. It's a lot
better at the Part 135/121 levels. For example, in those operations
every engine failure is reported (at least for turbine engines). A
skydiver friend of mine once looked up engine failure rates on the
PT-6 engines that power Twin Otters. The numbers looked artificailly
low to him. He started making phone calls to friends. It's not easy
data to get, but his best estimate is that Twin Otters in Part 91
service have an engine failure rate about 300 times higher than in
Part 91 service. He admits that the real number could be as low as 50
and as high as 1000, because of uncertainties in how operating hours
are estimated as well as uncertainties in which inciddents were
unique.

It's very frustrating as an instructor not to be able to give your
student solid estimates on which risks are truly significant, but the
alternative (reaching firm conclusions from nonexistent numbers) is
far worse.

"Relatively few" is the 1 accident per 331 (or X) total hazardous
encounters.

Well, that's great - now define hazardous encounters. With engine
failure, it's easy. The engine stops making power (or stops making
sufficient power to maintain level flight) and you have an encounter.
With off-field landings it's easy - when you commit to an off-field
landing, you have an encounter. Stall-spins are harder. Does the
hazard encounter start when autorotation begins? When the stall
breaks? When the buffet starts? When the stall horn goes off? See
the problem?

As a flight instructor charged with the task of educating pilots and
(hopefully) offering them guidance in terms of how often to practice
certain procedures/maneuvers on their own, what frequency do you
recommend in this regard, and on what is that recommendation based?

Whatever is required to maintain proficiency. If during your
recurrent training cycle you handle the engine failure competently
(meaning accomplish the task smoothly and with the successful outcome
never seriously in doubt) then you are maintaining proficiency.
Otherwise you are not.

Specific numbers are very much a function of the airplane and pilot
proficiency, and one size does not fit all.

I think we'd agree that the number of such practice approaches is
somewhere between 0 percent of the time (airline-type flying) and 100
percent of the time (gliders). Also, and though it hasn't been stated
explicitly, I'm talking in terms of the "average," "typical," "normal"
pilot flying the typical light airplane on a typical flight. That
said, I do believe that an average pilot who performs 10 gliding
approaches out of the 20 approaches annually will be likely to react
appropriately to an engine failure.

I think so too, assuming that what you mean by react appropriately is
point the plane someplace reasonable and maintain proper flying speed
to the flare. I doubt he will select the optimal location or make a
great landing, but those things are probably not crucial to his
survival.

Now, because this pilot may lack
the breadth of experience of your atypical 300-landings-per-year pilot
who practices gliding 10 percent of the time, the less-experienced
pilot (but who is more representative of the norm) may not be as
precise overall, yet the fundamental skill set needed to cope should
be there nonetheless.

No argument.

In fact, typical pilots under duress will invariably only be able to
perform as well as their most basic skill set allows.

Define most basic skill set. Keep in mind that for some, this will
include night partial panel flying. For others, it may be
substantially more limited.

And those skills
that are the most practiced, the most familiar, the most "natural" to
the pilot are the ones that will largely determine the outcome. Again,
this is based on my anecdotal experience instructing 1,000's of pilots
while they are placed under duress during emergency maneuver training
-- typical pilots from across the country who are representative
"products" of our national flight training system.

I'm not convinced that's true. I suspect that the pilots who
voluntarily get emergency maneuvers training are the same pilots who
doubt their ability to handle emergencies. Such doubts are usually
justified.

I don't believe a stall-spin involves a typical pilot at all.

The numbers and the anecdotal experience of professional
spin/aerobatic flight instructors are totally at odds with your
belief.

So how many inadvertent stall-spins do they get to see under normal
conditions?

The typical pilot is trained by the typical flight instructor,
who himself/herself has a marginal understanding of, and marginal
practical experience with, anything related to stalls and spins and
therefore, is incapable of adequately providing stall/spin awareness
training to their students.

That's probably true, but on the other hand most modern airplanes have
to be pretty severely mishandled to cause an inadvertent spin. The
same is not true of gliders and aerobatic airplanes, but the people
flying those tend to be trained by a completely different sort of
instructor.

And pilots with fewer than either 500 hours total time, or 100
hours in type, are more likely to encounter an inadvertent stall/spin
than to have a genuine engine failure.

Why do you keep going back to the patently unprovable? All we know is
that they are more likely to have an accident caused by stall-spin
rather than engine failure. This tells us nothing about the
likelihood of encountering either hazard.

Now let's consider something else. A pilot who flies 200 hours a year
is 10 times more likely to have an engine failure than one who flies
20 hours a year, since engine failure is not under his control. Are
you seriously suggesting that a pilot who flies 200 hours a year is 10
times more likely to inadvertently spin than one who flies 20 hours a
year? I would argue that he is LESS likely to inadvertently spin,
since the higher level of proficiency that is a nearly inevitable
result of flying a lot and often will make him less likely to miss the
rather obvious clues.

Consider the following 1987 stats as well: the U.S. boasted 699,653
active pilots who collectively logged an estimated 47.9 million flight
hours. Amortized, pilots averaged 68 hours each that year
(unfortunately, this average had decreased to less than 50 hours per
pilot per year during the 1990's).

However, only half of those are private pilots. Tens of thousands are
professional pilots who fly hundreds of hours a year. Thus the
reality is that a large number (maybe the majority) of these 'active'
private pilots are actually flying less than 20 hours a year. IMO it
is not possible for such a pilot to be proficient at all. In fact,
I'm going to take back what I said - if the average pilot is indeed
flying 20 hours a year, then I will readily admit that inadvertent
stall-spin accidents are going to happen to the average pilot. I
guess my point is that they ought not to happen to the proficient
pilot. Instead of looking at total hours, we should really be looking
at hours flown a year, and even then there are other factors since not
all hours are created equal.

Somewhere, somehow the discussion shifted from "total accidents" to
"fatal accidents only." The 1:30:300 is all hazardous encounters
leading to all accidents, not total accidents vs. fatal accidents vs.
some-injury accidents vs. non-injury accidents. Regarding mid-airs,
the question would be, "for each mid-air, how many times are airplanes
coming close enough to each other to be considered a hazardous
encounter (especially when pilots in both airplanes have their heads
buried in the cockpit on a clear VFR day)?" Maybe 331 times as many as
the total number of mid-airs that resulted in accidents (whether those
on board were injured, killed, or not)???

Sure. I guarantee you that there is SOME definiton of "close enough
to each other to be considered a hazardous encounter" that will make
the numbers work. By the same token, there is SOME definiton of
"stall-spin hazard" that will make the numbers work. This is
meaningless.

Michael

(Michael) wrote in message . com...

It's very frustrating as an instructor not to be able to give your
student solid estimates on which risks are truly significant, but the
alternative (reaching firm conclusions from nonexistent numbers) is
far worse.

I agree about the frustration. I disagree that I was in any way trying
to reach firm conclusions; just trying to offer some sense of the
scope of the potential problem, be it engine failures or stall/spins.

And I do think it is fair in the case of the stall/spin, for example,
to say that the last maneuver performed by nearly one out of four
pilots who's aviation career has ended in death and who also ended up
in the NTSB database was a stall/spin. This does provide some context
about the stall/spin risk, especially in the accident process leading
to generation of an NTSB report.


As a flight instructor charged with the task of educating pilots and
(hopefully) offering them guidance in terms of how often to practice
certain procedures/maneuvers on their own, what frequency do you
recommend in this regard, and on what is that recommendation based?

Whatever is required to maintain proficiency. If during your
recurrent training cycle you handle the engine failure competently
(meaning accomplish the task smoothly and with the successful outcome
never seriously in doubt) then you are maintaining proficiency.
Otherwise you are not.


But what about in between the recurrent training cycle? Do you make
any recommendations to your students at all in this regard? What to
work on, how to work on it, what frequency to practice? And in terms
of "smoothly with the successful outcome never seriously in doubt" --
do you apply Practical Test Standards to the tasks -- which are
minimum acceptable standards, i.e.: training to the lowest common
denominator -- or do you challenge your students to be better than the
average, the minimum standard? And if you challenge them to take their
flying to the next level, I would assume that would be based on your
own experience, both personally and as an instructor dealing with the
problems, errors, and misunderstandings your students commonly have
when they fly with you, no?

And I would bet that sans any hard scientific data to support your
anecdotal experience, you could tell me with reasonable certainty
where the problem areas will be, specifically what the errors will be,
etc. that you will encounter with the majority of your students under
certain tasks.


Specific numbers are very much a function of the airplane and pilot
proficiency, and one size does not fit all.

For the majority of GA pilots flying GA airplanes, I have not found
that to be the case at all. The problems I deal with with my students
all fall within a pretty well-defined envelope across the board,
across light, single-engine, GA airplanes. In fact, I would say I've
found it much more difficult for higher time pilots to break their bad
habits simply because the habits have been ingrained for far too long.
The typical profile of the pilot I fly with is a pilot who is active
in general aviation, active in the ratings process, active in the
pursuit of knowledge, experience, safety, and who has 100 to 600 hours
total time. These pilots come from all over the U.S., from all kinds
of flight schools, flying all kinds of light, single-engine airplanes.
And I often fly with them in the equipment they are used to flying.
Anything from the Cirrus SR20/22, to the J-3 Cub, to the C-206 Amphib,
to the Pitts, Pipers, Cessnas, RV's, Zlins, even rarer airplanes like
the Aero Subaru and the FAA Bravo.

In that sense, the pilots I deal with are likely above the average in
terms of their approach to flying and flight safety -- that's why they
are training with me. That and the realization that the primary flight
training process often leaves a lot to be desired in terms of dealing
with many different safety issues, not to mention the pure art of
flying the airplane.



In fact, typical pilots under duress will invariably only be able to
perform as well as their most basic skill set allows.

Define most basic skill set. Keep in mind that for some, this will
include night partial panel flying. For others, it may be
substantially more limited.

And those skills
that are the most practiced, the most familiar, the most "natural" to
the pilot are the ones that will largely determine the outcome. Again,
this is based on my anecdotal experience instructing 1,000's of pilots
while they are placed under duress during emergency maneuver training
-- typical pilots from across the country who are representative
"products" of our national flight training system.

I'm not convinced that's true. I suspect that the pilots who
voluntarily get emergency maneuvers training are the same pilots who
doubt their ability to handle emergencies. Such doubts are usually
justified.

See above about the typical pilot profile of those I fly with -- they
are likely above average and at least recognize and deal with any
issues they may have. But for each one of the pilots who takes spin,
EMT, or aerobatic training for safety reasons, there may be scores of
others who have no clue, or who have simply given up and left aviation
altogether because of unaddresses issues/fears that could have been
dealt with.


I don't believe a stall-spin involves a typical pilot at all.

The numbers and the anecdotal experience of professional
spin/aerobatic flight instructors are totally at odds with your
belief.

So how many inadvertent stall-spins do they get to see under normal
conditions?

I'm not sure I understand the question...


The typical pilot is trained by the typical flight instructor,
who himself/herself has a marginal understanding of, and marginal
practical experience with, anything related to stalls and spins and
therefore, is incapable of adequately providing stall/spin awareness
training to their students.

That's probably true, but on the other hand most modern airplanes have
to be pretty severely mishandled to cause an inadvertent spin.


Not true -- I routinely demonstrate one variant of the classic skidded
turn base-to-final at altitude with students, and in every single
spins-approved airplane I've ever tried this in, I've been successful
entering a spin from a left turn, with 1200-1800 rpm, without any
aileron, with less than full rudder and elevator inputs, and with the
ball less than 1/2 ball width out of center. This has been true even
in spins-approved airplanes that either would not, or were very
reluctant to, perform a left spin entered normally.

See also "Rudder and Elevator Effects on the Incipient Spin
Characteristics of a Typical General Aviation Training Aircraft." AIAA
Paper 93-0016. Reno, NV: January, 1993, by Patrick Veillette.



And pilots with fewer than either 500 hours total time, or 100
hours in type, are more likely to encounter an inadvertent stall/spin
than to have a genuine engine failure.

Why do you keep going back to the patently unprovable? All we know is
that they are more likely to have an accident caused by stall-spin
rather than engine failure. This tells us nothing about the
likelihood of encountering either hazard.

Thos enumbers are from an NTSB study. I'm notmaking them up. Perhaps
you'd be happier if I prefaced with "Pilots who make it into the NTSB
database share these characteristics..."


Now let's consider something else. A pilot who flies 200 hours a year
is 10 times more likely to have an engine failure than one who flies
20 hours a year, since engine failure is not under his control. Are
you seriously suggesting that a pilot who flies 200 hours a year is 10
times more likely to inadvertently spin than one who flies 20 hours a
year? I would argue that he is LESS likely to inadvertently spin,
since the higher level of proficiency that is a nearly inevitable
result of flying a lot and often will make him less likely to miss the
rather obvious clues.


You admitted yourself, all flight time is not equal. In that regard, I
would say the pilot who flies 200 hours a year of white-knuckled
X-country, averaging one power-on landing every 2 hours, who is
deathly afraid of stalls to begin with and has never spun, and flies
by the adage "maintain lots of extra flying speed just in case" is far
more likely to encounter an inadvertent stall/spin in a stall/spin
critical situation than a pilot who flies 20 hours a year in his
Pitts, 30 minutes at a shot, performing advanced aerobatic maneuvers
and averaging 4 gliding landings per hour (my former Pitts partner did
just this last year). I'd bet on the survival of this Pitts pilot over
the other one in a similar stall/spin critical scenario.

Perhaps a better gage of a pilot's ability to deal with stall/spin
critical operations is not flight time, but rather the number of
landings per hour. After all, one trip around the pattern exercises
many, many critical piloting skills. It would be interesting perhaps
to do a study with this as the hypothesis -- would this interest
you???

Rich
http://www.richstowell.com

(Rich Stowell) wrote
And I do think it is fair in the case of the stall/spin, for example,
to say that the last maneuver performed by nearly one out of four
pilots who's aviation career has ended in death and who also ended up
in the NTSB database was a stall/spin. This does provide some context
about the stall/spin risk, especially in the accident process leading
to generation of an NTSB report.

Yes, this provides some context. Where I disagree is that it provides
any information as to the relative occurrences of stall/spins vs.
engine failures.

But what about in between the recurrent training cycle? Do you make
any recommendations to your students at all in this regard?

Yes - but they are specific to the individual. It can't be otherwise.
I've done recurrent training for a variety of people ranging from low
time private pilots on end of the scale to an airline captain with 5
digit time on the other.

What to
work on, how to work on it, what frequency to practice? And in terms
of "smoothly with the successful outcome never seriously in doubt" --
do you apply Practical Test Standards to the tasks -- which are
minimum acceptable standards, i.e.: training to the lowest common
denominator -- or do you challenge your students to be better than the
average, the minimum standard?

I apply the minimum standard to decide if the person gets a signature
in his logbook certifying that he has completed a BFR/ICC. Beyond
that, I tailor the training to the individual. The guy with less than
10 hours IMC time is challenged when I give him the hardest task of
the flight - I fail his vacuum gyros and autopilot and he has to hand
fly the GPS approach. The airline captain gets to do a single engine
hand flown ILS to CAT II minima as a warmup. The idea that one size
fits all is ridiculous.

Specific numbers are very much a function of the airplane and pilot
proficiency, and one size does not fit all.

For the majority of GA pilots flying GA airplanes, I have not found
that to be the case at all. The problems I deal with with my students
all fall within a pretty well-defined envelope across the board,
across light, single-engine, GA airplanes. In fact, I would say I've
found it much more difficult for higher time pilots to break their bad
habits simply because the habits have been ingrained for far too long.
The typical profile of the pilot I fly with is a pilot who is active
in general aviation, active in the ratings process, active in the
pursuit of knowledge, experience, safety, and who has 100 to 600 hours
total time.

In other words, you're mostly flying with low time pilots. I suppose
the lower the experience level, the more consistent the performance.
After all, at zero hours most people perform about the same

Seriously, because of the kind of instruction you do, your clientele
is self-selected. I think that tends to homogenize the sample.

In that sense, the pilots I deal with are likely above the average in
terms of their approach to flying and flight safety -- that's why they
are training with me.

One could just as easily say that they lack confidence and feel the
need for additional training in emergency procedures, and maybe the
lack of confidence is justified.

I don't believe a stall-spin involves a typical pilot at all.

The numbers and the anecdotal experience of professional
spin/aerobatic flight instructors are totally at odds with your
belief.

So how many inadvertent stall-spins do they get to see under normal
conditions?

I'm not sure I understand the question...

When doing aerobatic (or emergency maneuvering) training, the
probability of inadvertent stall is high. In fact, I have
inadvertently stalled several times, and once almost spun, but every
one of those instances was while learning or practicing aerobatic
maneuvers. These are not normal conditions, and in any case the risk
is low because everything is done at relatively high altitude, in an
appropriate airplane, with proper training, etc.

I've also seen one inadvertent stall-spin from the back seat of a
glider. The student was a very low time power pilot on his first
glider flight, and he was practicing thermaling flight. That's what I
mean by normal conditions - when a student is doing routine things and
botches them badly enough to stall and spin.

Not true -- I routinely demonstrate one variant of the classic skidded
turn base-to-final

I think skidding the base to final turn AND being slow is pretty
serious mishandling of the airplane. In a glider instructional
situation, it's certain to cause noise from the back seat. Of course
the profile of the average glider instructor is a lot different from
the average power instructor.

And pilots with fewer than either 500 hours total time, or 100
hours in type, are more likely to encounter an inadvertent stall/spin
than to have a genuine engine failure.

Why do you keep going back to the patently unprovable? All we know is
that they are more likely to have an accident caused by stall-spin
rather than engine failure. This tells us nothing about the
likelihood of encountering either hazard.

Thos enumbers are from an NTSB study. I'm notmaking them up. Perhaps
you'd be happier if I prefaced with "Pilots who make it into the NTSB
database share these characteristics..."

No, the proper preface is "Accidents that make it into the NTSB
database share these characteristics." You have absolutely no idea
what sort of hazard encounters these pilots had that did not end in an
accident. The concept I'm going for here is "The rate of accidents is
not an indicator of the rate of hazard encounters."

Now let's consider something else. A pilot who flies 200 hours a year
is 10 times more likely to have an engine failure than one who flies
20 hours a year, since engine failure is not under his control. Are
you seriously suggesting that a pilot who flies 200 hours a year is 10
times more likely to inadvertently spin than one who flies 20 hours a
year? I would argue that he is LESS likely to inadvertently spin,
since the higher level of proficiency that is a nearly inevitable
result of flying a lot and often will make him less likely to miss the
rather obvious clues.

You admitted yourself, all flight time is not equal.

Absolutely. It's simply the only reliable measure we have.

In that regard, I
would say the pilot who flies 200 hours a year of white-knuckled
X-country, averaging one power-on landing every 2 hours, who is
deathly afraid of stalls to begin with and has never spun, and flies
by the adage "maintain lots of extra flying speed just in case" is far
more likely to encounter an inadvertent stall/spin in a stall/spin
critical situation than a pilot who flies 20 hours a year in his
Pitts, 30 minutes at a shot, performing advanced aerobatic maneuvers
and averaging 4 gliding landings per hour (my former Pitts partner did
just this last year). I'd bet on the survival of this Pitts pilot over
the other one in a similar stall/spin critical scenario.

No argument at all. And unfortunately I've met the 200 hours of white
knuckled XC guy. He absolutely refured to turn off the autopilot in
IMC; I could tell he was extremely nervous when I hand flew his plane
for a few minutes. His landings are all power-on. If he encounters a
spin, I doubt he will survive it. But he's not the norm, either.
Typically when a pilot flies 200 hours a year, he's proficient.

Perhaps a better gage of a pilot's ability to deal with stall/spin
critical operations is not flight time, but rather the number of
landings per hour.

I would say landings per year, and rate power-on and power-off
differently. For that matter, different aircraft rate differently.
In a glider, you're never far from a stall. In fact, I have to wonder
if my experience with students is skewed because so many of them are
glider pilots as well... In a Cherokee, you have to work hard to
stall.

After all, one trip around the pattern exercises
many, many critical piloting skills. It would be interesting perhaps
to do a study with this as the hypothesis -- would this interest
you???

Sure. Where would you get the data?

Michael