# SDR YWYR201209158826

- Type: Service difficulty report (as reported; unverified)
- Difficulty date: November 8, 2011
- Submitted: September 15, 2012
- Operation: General aviation
- Filed by: [Aerohp Maintenance LLC, repair station YWYR832L](https://openairdocs.org/faa-repair-station/YWYR832L/aerohp-maintenance-llc.md) (OpenAirDocs)
- Aircraft: [N1946G](https://openairdocs.org/aircraft/N1946G), registered now
- Make and model: Cessna 421B
- Registry model: [Cessna 421B](https://openairdocs.org/model/cessna-421b) (OpenAirDocs)
- Aircraft serial: 421B0846
- Aircraft time: 7,926 hours
- Engine: Cont GTSIO520H
- Engine time: 1,059 hours
- System (JASC): [7421 · Spark Plug/Igniter](https://openairdocs.org/jasc/7421)
- Part: Spark Plug
- Part number: RHB32S
- Condition: Cracked
- Part time: 1,059 hours
- Stage of operation: IN
- How discovered: V
- Nature of condition: O
- Precautionary procedure: K
- FAA source: FAA Service Difficulty Reporting System (https://sdrs.faa.gov/)
- Page: https://openairdocs.org/sdr/YWYR201209158826

## Discrepancy

PILOT REPORTED HIGH RPM DROP DURING MAGNETO DROP OFF CHECK.  ISOLATED PROBLEM TO NR 5 CYLINDER BY USE OF GRAPHIC ENGINE MONITOR.  REMOVED ALL SPARK PLUGS AND FOUND 1 SPARK PLUG ON NR 5 CYLINDER HAD CRACKED INSULATOR TIP.  INSTALLED NEW SPARK PLUG.  GROUND RUN UP AND MAGNETO DROP OFF CHECK WAS NORMAL.

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