Engine failure

The reason I do not think it was carb ice is that the weather was below
freezing, which means that the air was probably relatively dry and it
may even have been too cold for carb ice to form (the air would have to
have liquid water precipitate out of it to cause carb ice, meaning that
the air would have to be warmed in the carburetor, not cooled, and
somehow also exceed 100% humidity in the process).

The textbooks will tell you that water can exist in liquid form
down to minus 20 degrees Celsius, or about minus 3 degrees F. We have
encountered carb icing at these temperatures here in Western Canada, in
clear air. Carb ice can also form from dissolved water in the gasolne,
and all gas has at least a small amount of water in it. It can't be
seen unless the temp gets really low, where it finally clumps up and
forms snowflakes in the fuel.

I put a carb temp guage in my 182..at low power settings the carb temp
is near ambient air temp. It's only when you start sucking a lot of air
through the carb that the temps drop.

The 172's Lycoming will ice up easily enough after startup, while
idling, as will many other engines. There is a massive pressure drop as
the air squeezes past the throttle plate at idle, therefore a large
temperature drop, and ice WILL form there. Seen it many times since I
began flying in 1973. Unless the ambient temperature is very high, very
low, or the air is very dry, or that carb is plenty warm, carb ice can
form. It can catch the unwary when they fly in climates different from
what they're used to.

Dan

I have had an engine quit multiple times in my twin on roll out after
pulling the power back to idle. It ended up being an idle mixture
adjustment, not carb ice (fuel injected). The other possibility was sloppy
linkage in the throttle, but this was tight, and testing the fuel pressure
showed it to be too low at idle.

Don't assume it has to be carb ice.

George Patterson wrote:

Longworth wrote:

It sounded like carb ice problem to me.


If it were carb ice, the engine would not have restarted easily.

George Patterson
Drink is the curse of the land. It makes you quarrel with your
neighbor.
It makes you shoot at your landlord. And it makes you miss him.

As I recall, the OP said the engine was restarted after landing. The
warmth of the engine could have easily melted the ice during the final
approach and landing allowing a restart on the ground.

Matt

Jose wrote:

I had a situation in the Shenandoah Valley where, during runup when I
checked smooth operation at idle, the engine quit. It started up easily
enough, but quit again at idle. Taxiied back, went to the shop and they
poked around with the plugs and a few other things, finding nothing.
Their theory was that it was carb ice.

Never had carb ice on the ground before.

The carburetor doesn't know whether it is on the ground or in the air. :-)

Matt

Dale wrote:

In article .com,
"nrp" wrote:


I agree it is probably carb ice & a remelt situation. My 150 hp 172M
will actually ice up to a limit quite quickly under the right
conditions. Note that OP probably had a very low power approach over
his obstacle in which case there would be little heat available for the
carb heat stove.

Those who say Lycomings won't ice up just haven't encountered the right
conditions - yet.



I've never gotten carb ice at a low power setting, it has always been at
cruise or even takeoff power.

I put a carb temp guage in my 182..at low power settings the carb temp
is near ambient air temp. It's only when you start sucking a lot of air
through the carb that the temps drop.

Which is because you are then also sucking a lot of fuel through the
carb! :-)

Matt

Jay Honeck wrote:

Very weird. In our plane, the carb heat is checked prior to take-off,
and never touched again. In fact, I've only activated carb heat once
in flight (in ten years and 1500 hours) in ANY flavored Cherokee -- and
that was just an experiment.

The only time I've experienced carb ice was in an Archer. Of course I
was at 11,000 ft in cool moist air, but I had never experienced it
before, so I was caught by surprise. I noticed that my IAS was slowly
dropping (like 3-4 kts in the last 15 minutes). The throttle was still
firewalled (which at 11K feet, is ~55%), but I looked at the tach, and
noticed that my RPMs had dropped too. (This was before I was instrument
rated, so I didn't pay as close attention to the gauges as I should
have.) Just as I started to consider panicking, I thought about trying
the carb heat. That resulted in an immediate revolt by the engine as it
swallowed the water from the carb. It actually sounded a lot like an
ice-crusher... After about a minute everything was running smooth again
and I turned off the carb heat. For the rest of the flight I paid
closer attention to tach and had to apply the carb heat several more
times (although less of an event than the first time). Eventually, I
just left the carb heat on for the remainder of the flight.

But I've never had a problem since, so it is not a common event at all.
Sometimes the conditions are just right.


-m
--
## Mark T. Dame
## VP, Product Development
## MFM Software, Inc. (http://www.mfm.com/)
"Madness takes its toll. Please have exact change."

Peter R. wrote:

My fuel-injected, turbo-normalized Bonanza had a newly rebuilt engine
installed last February. Upon completion of the work, I took the aircraft
up for the proper first flight break-in. When I landed, the engine quit
just as I touched down (low idle) on the runway.

I was able to restart and taxied back to talk to the mechanic. He adjusted
the low-idle mixture so I took the aircraft up for the second flight
break-in. Again, upon landing the engine quit.

Suspecting something else now, the mechanic ran the aircraft on the ground
and was able to duplicate the problem. He then suspected the fuel pump so
he took it off and sent it back to the company who supplied it to the
engine rebuilder for inspection. The fuel pump inspectors discovered metal
shavings inside the fuel pump that were cutting off fuel flow at low idle.
That opened up an entire finger pointing session. Nice...

The source of the shavings was never identified but it was concluded that
somehow they were introduced when the engine was on the test cell.

I had a similar situation with a carburetor on the club's Archer. It
had been at the maintenance shop for some carb work. After ground
testing and a short flight around the patch, everything seemed be
working fine. So I took off and flew home. On final my descent rate
was a little fast, so I went to tweak the throttle and nothing happened.
Since I was less than a half a mile from the threshold with plenty of
altitude, it was no big deal to dead stick it in. I actually had enough
speed left on landing that had I been going the other way I probably
could have made it off the runway. (The runway at our airport has a
slight grade and I was landing uphill.) Instead I rolled to a stop
almost exactly mid-way down the runway and had to call for a tow because
the engine wouldn't restart.

It was discovered afterward that the shop that had worked on the carb
had gotten a washer stuck between the top half and bottom half of the
carb that prevented the float from properly shutting off the fuel flow.
The result was a flooded engine on final.


-m
--
## Mark T. Dame
## VP, Product Development
## MFM Software, Inc. (http://www.mfm.com/)
"And so it was only with the advent of pocket computers that the
startling truth became finally apparent, and it was this:

Numbers written on restaurant checks within the confines of
restaurants do not follow the same mathematical laws as numbers
written on any other pieces of paper in any other parts of the
Universe."
-- Life, the Universe, and Everything, Douglas Adams

Here it is: a graph I was hoping to find on the 'net that shows the
temperature ranges and dewpoint/humidites at which icing can occur.
Note that the range extends from well below freezing to over 100
degrees F. This graph will apply to avgas; mogas has a higher
volatility (evaporation rate) and can cause icing outside these
parameters.

http://www.wsaa.net/icing.htm

Icing can also occur in very cold temps if carb heat IS used: ice
crystals in the air can melt as the incoming air is heated, collect on
the throttle plate and other parts, and freeze due to the pressure drop
and evaporative cooling.

Dan

I wondere how much of a temperature gradient might be present in the
fuel/air stream at the sense point of a carb air temp gage. A lot of
things are happening quickly as air comes thru the air intake (heat off
only) or heat system, and then on to the carb heat box valve system
before it goes into the carb venturi, where the air is expanded & the
fuel added.

I agree that it is better to have an air temp gage but maybe one should
be a little suspicious of it.

RST Engineering wrote:

The OP said this was a 172.

Some are. So I have to ask.

Anyhow, if so it may be linked to a problem in the fuel pump. Mine was
actually missing a connecting spring (from factory) that did not allow
it to maintain a fuel flow at idle settings. So for years I go around
with it a bit high on the idle and sometimes on rollout, just at the end
and starting to turn off, the engine would shake and I would hit the
electric pump to bring it back. I actually had it down to a fine art.
The problem was only found when the pump was pulled and sent out to have
a seal changed.

John