Emergency

"Ron Lee" wrote in message
...
If you are flying who cares? Unless you are in a sandstorm or
volcanic ash downfall area my ASSUMPTION is that unfiltered air in
flight is not a hazard for the engine.

Most of the time, that's true. However, I wouldn't limit the conditions to
rare events like "sandstorm or volcanic ash". I have flown through
significant dust plumes, cause by nothing other than winds aloft carrying
dirt from terrain. One time, I could see the plume stretch all the way from
Mt St Helens out to the coast, some 100 miles away.

Clearly this sort of condition isn't nearly as harmful as the more dense
events, like a sandstorm or volcanic ash. But still, I was happy to have my
engine breathing filtered air when I went through it, and this sort of thing
is quite a bit more common than the more dense events.

Pete

"Peter Duniho" wrote:

Of course, carb heat also reduces performance, since it lowers the density
of the air coming into the engine. Better to wait for signs of carb ice
and use the carb heat as needed, rather than as a general prophylactic.

In future I will be using carb heat as a matter of course when ambient
conditions are in the "severe" area of the chart. I definitely will not be
waiting for symptoms in such cases.

--
Dan
C-172RG at BFM

Dan, I wouldn't be so hard on yourself. Sounds like you did a great
job with the situation. Found the problem. Fixed it. Got the plane
down. Kept your cool. I'd say you were successful. Thanks for the
report. Helps all of us who never have been in this position, yet.

My only input. Carb heat is the #2 item on my emergency checklist.


Alan Bloom
Dogs can fly.
www.flyingmutts.com




On Mon, 27 Mar 2006 18:21:40 -0600, "Dan Luke"
wrote:

It was the 3rd leg of an Angel Flight and I wasn't even supposed to be
flying it. I'd already flown the second leg from Natchez, MS to
Monroeville, AL, but the 3rd leg pilot had mysteriously failed to show--no
call, no nothin'. It was late, I was tired and I was mad. I had two pax
aboard.

We were in the clouds and in the dark in a Cutlass RG approaching Macon, GA
(MCN). The outside temperature was 13 C and moisture was streaming back on
the windshield. The throttle was fully open, the RPM was set for 2500 and
the mixture was leaned to 10.5 gph. The autopilot was holding course and
altitude. I was studying the ILS approach plate when I noticed the AP's
"up" trim warning light illuminate.

A quick scan of the instruments showed the IAS at 100 and falling; normally
it would indicate 125 at that altitude. I had detected no change in the
engine sound. I immediately hit the AP disable switch to prevent its
stalling the airplane. This was right and wrong, as I now had to do all the
flying while troubleshooting the problem. What I should have done was
disable the altitude hold and allow the AP to continue keeping us on course
and wings level.

Any attempt to lift the nose resulted in a sickening drop in airspeed. The
situation was now officially scary: we were going down on a dark, rainy
night over central Georgia.

I shoved the prop and mixture full forward, confirmed the throttle was wide
open and the primer was in. No improvement. There was no unusual
vibration. The engine still sounded good and was still making 2500 rpm, but
the prop was probably in flat pitch to do it. I tried the electric fuel
pump: no joy. I glanced at the JPI engine analyzer and saw that all four
cylinders showed roughly even EGTs. All this took much less than a minute;
maybe only 30 seconds.

Finally, I pulled the carb heat. Within a few seconds I felt a surge of
power and we began to climb. I don't know for sure what a death row inmate
feels like when the governor calls at the last minute, but I'm guessing it
feels something like that.

My heart was pounding in my chest and I was so stoked on adrenalin my hands
were shaking. The front seat passenger was looking at me wide-eyed--he
didn't know what was happening, but he had figured out *something* wasn't
right. I had wandered 40 deg. off course and Atlanta Approach was repeating
a frequency change instruction. In a few moments I had us back on course
and altitude but I was still somewhat rattled and blew the readback on
Atlanta's initial approach instructions. Got that sorted out and made an
uneventful ILS approach to runway 5 at MCN.

Not a totally satisfying performance. I ended up doing the right thing and
we lived; that's the good news. The bad news is that allowed myself to rush
things. A moment's thought would have prevented the autopilot mistake. A
calmer, more orderly flow through the engine controls would have led me to
the carb heat sooner and saved a few unnecessary extra seconds of high
anxiety. Next time I have an emergency (please: NO next time!) I'll try to
take it a little slower.

I'm still surprised that the carb iced up at full throttle. Conditions were
in the bad area of the carb ice chart, but my engine has never seemed prone
to the problem. In 650+ hours I've only detected carb ice once before, and
that was after a long taxi on a cool, rainy day.

Alan wrote:

Helps all of us who never have been in this position, yet.

Perhaps "a subset of us" would be a more accurate than "all of us." I fly
an aircraft with a fuel-injected engine. No carb heat.


--
Peter

On Tue, 28 Mar 2006 17:00:58 -0500, T o d d P a t t i s t
wrote:


I've never quite figured out why carb heat is designed this
way. I've always got carb heat on during landing,

I'm curious as to why you keep your carb heat on during landing. I
usually pull it on during my GUMP check approaching an airport but
then shut it off. If you have to do a go around, you're not going to
get full power with it on.

Alan Bloom
Dogs can fly.
www.flyingmutts.com

I'm still surprised that the carb iced up at full throttle. Conditions were
in the bad area of the carb ice chart, but my engine has never seemed prone
to the problem. In 650+ hours I've only detected carb ice once before, and
that was after a long taxi on a cool, rainy day.

I had carb ice in the =runup= in a Dakota that had never had any kind of
carb ice problems before. It was warm and humid, ideal conditions, but
the engine hadn't been running for ten minutes yet. I applied runup
power and checked mags and such, no issue. Then I pulled the power all
the way back and the engine died. Tried it a few times, then took it
back to have it looked at. Nothing amiss. Final conclusion is that it
was probably carb ice.

Never happened before, or since.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

I'm curious as to why you keep your carb heat on during landing.

Some aircraft (certain Cessna singles for example) specify carb heat
below 2000 RPM. Others (certain Pipers) specify no carb heat for landing.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

"Jose" wrote:

I'm still surprised that the carb iced up at full throttle. Conditions
were in the bad area of the carb ice chart, but my engine has never seemed
prone to the problem. In 650+ hours I've only detected carb ice once
before, and that was after a long taxi on a cool, rainy day.

I had carb ice in the =runup= in a Dakota that had never had any kind of
carb ice problems before. It was warm and humid, ideal conditions, but the
engine hadn't been running for ten minutes yet. I applied runup power and
checked mags and such, no issue. Then I pulled the power all the way back
and the engine died.

In my case a couple of years ago I could not get the engine to rev past 1,000
rpm for the runup. That time I immediately suspected carb ice because of the
long taxi in the rain. I applied carb heat and finished the runup ok.


Never happened before, or since.

Not to me, either--until that flight to Macon last week.

--
Dan
C-172RG at BFM

Dan, this is one of those "for what it's worth" stories.

About 30 years ago I flew a Mooney ranger that was pulled around by a
normally carberated engine that loved to develop carb ice. The first
clue it was happening was that the EGT began falling really fast. Carb
ice drives the engine towards a richer mixture.

The same thing may happen in your airplane. If it does, include the EGT
in your instrument scan when you're at cruise. I was amazed when I
started doing that how often a 50 degree drop in EGT happened, and how
often it was recovered by yanking on the carb heat knob.

I'm glad it turned out OK -- angel flights should get lots of second
chances.

"T o d d P a t t i s t" wrote in message
...
"Peter Duniho" wrote:

I can't speak for all airplanes -- maybe there's one out there that uses a
filter with carb heat -- but yes, generally speaking carb heat means the
air
is not filtered.

I've never quite figured out why carb heat is designed this
way.

I suspect it's a matter of keeping the design simple. FAR 23.1091(b)
requires an alternate air source. FAR 23.1093(a) requires an induction air
heating source. It makes some sense to ensure that the alternate air source
would not be compromised by the same thing that required its use (such as
icing of the air filter), and it also makes sense to combine the two systems
into a single system.

I've always got carb heat on during landing, and as
soon as I land, I've got to start worrying about pulling
dust and debris into my expensive engine. I mean really!

I suspect that at the usual power settings used for landing (ie idle) that
sucking dirty air into the engine is less of a worry. Of more concern to me
is during the runup, when you are standing still (not getting a fresh supply
of air) and have the engine power set higher than idle.

[...]
I recognize that there are rare circumstances when one would
want to bypass the filter (impact iced over). Nonetheless,
it seems to me that accidents due to fiddling with the carb
heat after landing are at least as much of a concern.

How so? Induction icing can cause a forced landing, if not a crash.
Assuming the pilot has their priorities straight, fiddling with the carb
heat after landing should pose no risk at all.

Yes, there seems to be a window of opportunity for unfiltered air to get
into the engine, but that should not cause the pilot to forget about
controlling the airplane (and I think most airplanes have the carb heat
control in a more practical place anyway...I wouldn't denigrate the basic
idea of combining the carb heat and alternate air source on the sole basis
of one single aircraft type).

Is there some risk with the design as is? No doubt. But I have seen no
evidence that suggests that using the carb heat as the alternate, unfiltered
air source leads to any significant reduction in engine life, never mind any
traumatic failure of the engine.

Oddly enough, in reviewing the certification requirements, I found two
paragraphs that my own airplane doesn't appear to meet. My automatic
alternate air source (not carb heat, since I have no carb) does not provide
for a manual override by the pilot, nor is there any indication in the
cockpit to show that the alternate air source has been activated. Now I'm
curious how the airplane got certified. The type is new enough to be under
Part 23, but perhaps elements of the TC got grandfathered in via the
previous type on which this airplane was based. Or maybe there's a waiver
of some sort? I don't know. A new mystery...fun.

Pete