I can't find anything in the discussion of carb ice in The Lycoming Flyer to
make me think that full throttle somehow obviates carb ice when conditions
are conducive to icing. If ice is forming on the interior of the venturi,
the position of the throttle plate won't make much difference. Lycoming does
say that ice is more likely at low power settings, but I think we all know
that.

Bob Gardner

"Dan Luke" wrote in message
...
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.

--
Dan
C172RG at BFM