Narrative:

A VFR flight was being conducted from cys to ida. The flight plan specified a route as follows: cys-rwl-ocs-mld-pih-ida. It was expected to terminate the flight early at ocs as the winds were 40 KTS off the nose resulting in a flight longer than comfortable for the passenger. Some difficulties with proper gear retraction was noted on the first takeoff of the day. Basically, the gear doors would not shut normally, however, the wheels raised and lowered properly. Proper gear up and gear down indication was obtained but was intermittent with a gear up warning horn occasionally being received. The flight was terminated and return to cys was completed. 2 flts were conducted after consulting with the hometown a&P to verify that the doors would operate properly. At the end of the test flts the gear doors were properly aligned, however, with the gear in the down position. I decided to return home with the gear extended and accept the lower airspeed. The flight proceeded normally from cys to a point 8 mi east of ckw VORTAC on the 240 degree radial. The ceiling in the area was lower than forecast and 8500 ft MSL was being maintained. This altitude was approximately 1500 ft AGL. An abrupt change in engine noise and vibration was noted approximately 1 1/2 hours into the flight. The closest downwind airport was rawlins and an immediate turn toward rawlins was conducted (approximately 1 min required). After conducting a 180 degree turn an indicated airspeed of 90-100 mph was established. A descent rate of 500 FPM was observed. Full rich, high speed propeller, switched fuel tanks and full power were verified. I noted that the engine seemed to operate better at high RPM and full rich although manifold pressure was indicating only 17 inches. Full power at 8500 ft would be 21 inches of manifold pressure. I attempted to open the alternate air damper. The engine immediately quit (this would not normally be expected). Restoring normal air eventually returned engine power but 500 FPM descent was still observed. I determined that a precautionary landing was the best course of action. I performed another 180 degree turn to land into the wind (2 1/2 mins total time). A break in the traffic on I-80 was available and a landing was conducted. No injuries or damage to the aircraft or vehicles occurred. The aircraft was pushed to the side of I-80 to re-establish normal traffic flow. The wy highway patrol and the FSS was notified via cellular phone. The initiating event was determined to be the loss of the right magneto. Several teeth on the nylon gear in the bendix magneto had failed. There was no obvious reason why the aircraft was unable to maintain level flight on the remaining magneto. The a&P called by the FAA idented that this failure could cause all the impulses for each of the six cylinders to be directed to 1 cylinder. This would result in combustion occurring in the intake manifold during the intake stroke. This would reduce the amount of fuel for other cylinders and combust the air intended for the other cylinders. This power loss was significant. During this incident, the magnetos were not individually selected as landing was imminent and power was needed to reach the traffic window. It is possible that had the individual magnetos been selected that power could have been restored and a landing at rawlins been completed. However, during testing on the ground with the a&P present, the engine was run at 2200 RPM (runup is normally conducted at 17000 RPM) with no difference in RPM or engine roughness noted with the left magneto selected or both selected. It was not immediately clear why such a significant power loss was observed on the loss of the right magneto, however, the scenario described by the a&P may be the reason. It is believed that operation with the gear extended might add sufficient drag so as to accentuate the effects of the power loss. The magneto was repaired and reinstalled. Each cylinder was checked to determine that uniform compression existed. The engine was started with runup at various rpms conducted. A significant drop in RPM was noted on each magneto. Continued high power operation for approximately 10 mins eventually returned the magneto drop to the normal range. The aircraft was flown from I-80 to ocs where a compression check was performed to complete verification that no other engine damage existed. Actions to prevent recurrence: 1) no procedure exists in the owner's manual for a partial power loss. Include in the immediate action steps for a power loss or a partial loss, a step to test operation with each magneto. This may restore power sufficient for level flight for some types of magneto failures. 2) extended operation with the landing gear extended may have too large a penalty to operate with 1 magneto. Consider, not conducting operation under this mode of operation at high altitudes where normal power is lower.

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Original NASA ASRS Text

Title: EMER OFF ARPT LNDG.

Narrative: A VFR FLT WAS BEING CONDUCTED FROM CYS TO IDA. THE FLT PLAN SPECIFIED A RTE AS FOLLOWS: CYS-RWL-OCS-MLD-PIH-IDA. IT WAS EXPECTED TO TERMINATE THE FLT EARLY AT OCS AS THE WINDS WERE 40 KTS OFF THE NOSE RESULTING IN A FLT LONGER THAN COMFORTABLE FOR THE PAX. SOME DIFFICULTIES WITH PROPER GEAR RETRACTION WAS NOTED ON THE FIRST TKOF OF THE DAY. BASICALLY, THE GEAR DOORS WOULD NOT SHUT NORMALLY, HOWEVER, THE WHEELS RAISED AND LOWERED PROPERLY. PROPER GEAR UP AND GEAR DOWN INDICATION WAS OBTAINED BUT WAS INTERMITTENT WITH A GEAR UP WARNING HORN OCCASIONALLY BEING RECEIVED. THE FLT WAS TERMINATED AND RETURN TO CYS WAS COMPLETED. 2 FLTS WERE CONDUCTED AFTER CONSULTING WITH THE HOMETOWN A&P TO VERIFY THAT THE DOORS WOULD OPERATE PROPERLY. AT THE END OF THE TEST FLTS THE GEAR DOORS WERE PROPERLY ALIGNED, HOWEVER, WITH THE GEAR IN THE DOWN POS. I DECIDED TO RETURN HOME WITH THE GEAR EXTENDED AND ACCEPT THE LOWER AIRSPD. THE FLT PROCEEDED NORMALLY FROM CYS TO A POINT 8 MI E OF CKW VORTAC ON THE 240 DEG RADIAL. THE CEILING IN THE AREA WAS LOWER THAN FORECAST AND 8500 FT MSL WAS BEING MAINTAINED. THIS ALT WAS APPROX 1500 FT AGL. AN ABRUPT CHANGE IN ENG NOISE AND VIBRATION WAS NOTED APPROX 1 1/2 HRS INTO THE FLT. THE CLOSEST DOWNWIND ARPT WAS RAWLINS AND AN IMMEDIATE TURN TOWARD RAWLINS WAS CONDUCTED (APPROX 1 MIN REQUIRED). AFTER CONDUCTING A 180 DEG TURN AN INDICATED AIRSPD OF 90-100 MPH WAS ESTABLISHED. A DSCNT RATE OF 500 FPM WAS OBSERVED. FULL RICH, HIGH SPD PROP, SWITCHED FUEL TANKS AND FULL PWR WERE VERIFIED. I NOTED THAT THE ENG SEEMED TO OPERATE BETTER AT HIGH RPM AND FULL RICH ALTHOUGH MANIFOLD PRESSURE WAS INDICATING ONLY 17 INCHES. FULL PWR AT 8500 FT WOULD BE 21 INCHES OF MANIFOLD PRESSURE. I ATTEMPTED TO OPEN THE ALTERNATE AIR DAMPER. THE ENG IMMEDIATELY QUIT (THIS WOULD NOT NORMALLY BE EXPECTED). RESTORING NORMAL AIR EVENTUALLY RETURNED ENG PWR BUT 500 FPM DSCNT WAS STILL OBSERVED. I DETERMINED THAT A PRECAUTIONARY LNDG WAS THE BEST COURSE OF ACTION. I PERFORMED ANOTHER 180 DEG TURN TO LAND INTO THE WIND (2 1/2 MINS TOTAL TIME). A BREAK IN THE TFC ON I-80 WAS AVAILABLE AND A LNDG WAS CONDUCTED. NO INJURIES OR DAMAGE TO THE ACFT OR VEHICLES OCCURRED. THE ACFT WAS PUSHED TO THE SIDE OF I-80 TO RE-ESTABLISH NORMAL TFC FLOW. THE WY HWY PATROL AND THE FSS WAS NOTIFIED VIA CELLULAR PHONE. THE INITIATING EVENT WAS DETERMINED TO BE THE LOSS OF THE R MAGNETO. SEVERAL TEETH ON THE NYLON GEAR IN THE BENDIX MAGNETO HAD FAILED. THERE WAS NO OBVIOUS REASON WHY THE ACFT WAS UNABLE TO MAINTAIN LEVEL FLT ON THE REMAINING MAGNETO. THE A&P CALLED BY THE FAA IDENTED THAT THIS FAILURE COULD CAUSE ALL THE IMPULSES FOR EACH OF THE SIX CYLINDERS TO BE DIRECTED TO 1 CYLINDER. THIS WOULD RESULT IN COMBUSTION OCCURRING IN THE INTAKE MANIFOLD DURING THE INTAKE STROKE. THIS WOULD REDUCE THE AMOUNT OF FUEL FOR OTHER CYLINDERS AND COMBUST THE AIR INTENDED FOR THE OTHER CYLINDERS. THIS PWR LOSS WAS SIGNIFICANT. DURING THIS INCIDENT, THE MAGNETOS WERE NOT INDIVIDUALLY SELECTED AS LNDG WAS IMMINENT AND PWR WAS NEEDED TO REACH THE TFC WINDOW. IT IS POSSIBLE THAT HAD THE INDIVIDUAL MAGNETOS BEEN SELECTED THAT PWR COULD HAVE BEEN RESTORED AND A LNDG AT RAWLINS BEEN COMPLETED. HOWEVER, DURING TESTING ON THE GND WITH THE A&P PRESENT, THE ENG WAS RUN AT 2200 RPM (RUNUP IS NORMALLY CONDUCTED AT 17000 RPM) WITH NO DIFFERENCE IN RPM OR ENG ROUGHNESS NOTED WITH THE L MAGNETO SELECTED OR BOTH SELECTED. IT WAS NOT IMMEDIATELY CLR WHY SUCH A SIGNIFICANT PWR LOSS WAS OBSERVED ON THE LOSS OF THE R MAGNETO, HOWEVER, THE SCENARIO DESCRIBED BY THE A&P MAY BE THE REASON. IT IS BELIEVED THAT OP WITH THE GEAR EXTENDED MIGHT ADD SUFFICIENT DRAG SO AS TO ACCENTUATE THE EFFECTS OF THE PWR LOSS. THE MAGNETO WAS REPAIRED AND REINSTALLED. EACH CYLINDER WAS CHECKED TO DETERMINE THAT UNIFORM COMPRESSION EXISTED. THE ENG WAS STARTED WITH RUNUP AT VARIOUS RPMS CONDUCTED. A SIGNIFICANT DROP IN RPM WAS NOTED ON EACH MAGNETO. CONTINUED HIGH PWR OP FOR APPROX 10 MINS EVENTUALLY RETURNED THE MAGNETO DROP TO THE NORMAL RANGE. THE ACFT WAS FLOWN FROM I-80 TO OCS WHERE A COMPRESSION CHK WAS PERFORMED TO COMPLETE VERIFICATION THAT NO OTHER ENG DAMAGE EXISTED. ACTIONS TO PREVENT RECURRENCE: 1) NO PROC EXISTS IN THE OWNER'S MANUAL FOR A PARTIAL PWR LOSS. INCLUDE IN THE IMMEDIATE ACTION STEPS FOR A PWR LOSS OR A PARTIAL LOSS, A STEP TO TEST OP WITH EACH MAGNETO. THIS MAY RESTORE PWR SUFFICIENT FOR LEVEL FLT FOR SOME TYPES OF MAGNETO FAILURES. 2) EXTENDED OP WITH THE LNDG GEAR EXTENDED MAY HAVE TOO LARGE A PENALTY TO OPERATE WITH 1 MAGNETO. CONSIDER, NOT CONDUCTING OP UNDER THIS MODE OF OP AT HIGH ALTS WHERE NORMAL PWR IS LOWER.

Data retrieved from NASA's ASRS site as of July 2007 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.