Narrative:

Situation: plane to be relocated to a nearby airport. Early in the morning after a calm; clear night; aircraft was found to be covered by frost. Weather was unlimited visibility; temperature m01 dewpoint m03. Full duats weather brief obtained for the short hop. Plan was to show up early (before dawn) and do 3 night takeoffs and landings and then land at the nearby airfield. Wary of aerodynamics effect of frost; used a dragon to preheat engine and melt frost with hot air (water removed to prevent refreezing). Delay prevented execution of initial plan; therefore; only relocation of plane to be performed. Also; since the plane had a 50 hour inspection performed and ignition timing adjusted; there had been some discussion between the owners concerning the proper timing. Timing had been rechecked a second time by an a&P engineer. What ticked us for the recheck was an abnormal RPM drop doing a magneto check. After the further timing; magneto drop was reported at 80 RPM with no differential. Event: after a longer than usual preflight due to frost removal; I taxied to holding point and there; to my surprise; I was getting 200/250 RPM drop on left and 150 on right magneto. Thought that the drop could be due to spark plug fouling due to engine test runs at low RPM. I did a high RPM lean mix run; but situation did not improve initially. After an extended run; I finally barely managed to get within the 150 drop with no differential. Also the carburetor heat check I performed was inadequate: just applied carburetor heat and checked for a drop; did not wait a few seconds if by any chance would get an increase afterward (like you would do inflight). When lined up; I did check for full RPM and I have got them and additionally with 8;000 ft of runway; I was safe for takeoff and reject. Monitored acceleration and takeoff run length and was within parameters. During the second flight of the day (other owners) the mag drop went back to 80 with no differential. Same happened to me during the last flight of the day. Finally one of us came up with the icing possibility. And yes checking dew point and temperature; I was in the serious icing at cruise power conditions. Spring means carburetor ice; well I encountered carburetor ice several times in flight never on the ground. Did not recognize it; did not act on it. Two actions can save the day: 1) while checking on the carburetor heat in pre-take off checks leave it on for a few seconds rougher running engine and then increase of RPM means the same thing both in the air and on the ground: this ice is melting (missed this one). 2) ensure you have max power RPM on takeoff (which I did). Also; do not discard discrepancies: other owner (with mechanical experience) said mag were dropping 80 RPM after timing adjust and I was getting 250 or after cleaning plugs (or probably reducing icing due to higher RPM) 150 RPM; the latter is within limits; both a far cry from the 80 the plane performed the day before. Finally; if like in this case; you have 8;000 ft or runway in front of you; taking off with carburetor heat on would have been the best bet. Losing the engine on takeoff was not that far in my view.

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Original NASA ASRS Text

Title: Instrument rated private pilot feels he may have taken off with carburetor ice.

Narrative: Situation: Plane to be relocated to a nearby airport. Early in the morning after a calm; clear night; aircraft was found to be covered by frost. Weather was unlimited visibility; temperature m01 dewpoint m03. Full DUATS Weather Brief obtained for the short hop. Plan was to show up early (before dawn) and do 3 night takeoffs and landings and then land at the nearby airfield. Wary of aerodynamics effect of frost; used a dragon to preheat engine and melt frost with hot air (water removed to prevent refreezing). Delay prevented execution of initial plan; therefore; only relocation of plane to be performed. Also; since the plane had a 50 hour inspection performed and ignition timing adjusted; there had been some discussion between the owners concerning the proper timing. Timing had been rechecked a second time by an A&P engineer. What ticked us for the recheck was an abnormal RPM drop doing a magneto check. After the further timing; magneto drop was reported at 80 RPM with no differential. Event: After a longer than usual preflight due to frost removal; I taxied to holding point and there; to my surprise; I was getting 200/250 RPM drop on left and 150 on right magneto. Thought that the drop could be due to spark plug fouling due to engine test runs at low RPM. I did a high RPM lean mix run; but situation did not improve initially. After an extended run; I finally barely managed to get within the 150 drop with no differential. Also the carburetor heat check I performed was inadequate: just applied carburetor heat and checked for a drop; did not wait a few seconds if by any chance would get an increase afterward (like you would do inflight). When lined up; I did check for full RPM and I have got them and additionally with 8;000 FT of runway; I was safe for takeoff and reject. Monitored acceleration and takeoff run length and was within parameters. During the second flight of the day (other owners) the mag drop went back to 80 with no differential. Same happened to me during the last flight of the day. Finally one of us came up with the icing possibility. And yes checking dew point and temperature; I was in the serious icing at cruise power conditions. Spring means carburetor ice; well I encountered carburetor ice several times in flight never on the ground. Did not recognize it; did not act on it. Two actions can save the day: 1) While checking on the carburetor heat in pre-take off checks leave it on for a few seconds rougher running engine and then increase of RPM means the same thing both in the air and on the ground: This ice is melting (missed this one). 2) Ensure you have max power RPM on takeoff (which I did). Also; do not discard discrepancies: other owner (with mechanical experience) said mag were dropping 80 RPM after timing adjust and I was getting 250 or after cleaning plugs (or probably reducing icing due to higher RPM) 150 RPM; the latter is within limits; both a far cry from the 80 the plane performed the day before. Finally; if like in this case; you have 8;000 FT or runway in front of you; taking off with carburetor heat on would have been the best bet. Losing the engine on takeoff was not that far in my view.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.