# SDR 99ZZZX957

- Type: Service difficulty report (as reported; unverified)
- Difficulty date: January 18, 1998
- Submitted: March 26, 2000
- Operation: Air carrier
- Aircraft: N29MM
- Make and model: Cessna 402B
- Registry model: [Cessna 402B](https://openairdocs.org/model/cessna-402b) (OpenAirDocs)
- Aircraft serial: 402B0863
- Engine: Cont TSIO520E
- System (JASC): [8520 · Reciprocating Engine Power Section](https://openairdocs.org/jasc/8520)
- Part: Crankcase
- Part number: 643202
- Condition: Cracked
- Location: Engine
- Stage of operation: IN
- Nature of condition: O
- Precautionary procedure: K
- FAA source: FAA Service Difficulty Reporting System (https://sdrs.faa.gov/)
- Page: https://openairdocs.org/sdr/99ZZZX957

## Discrepancy

WHILE REPAIRING AN UNRELATED ITEM, THE MECHANIC NOTICED A CRACK APPROXIMATELY ONE INCH LONG (RUNNING TOP TO BOTTOM) ASSOCIATED WITH THE MOST FORWARD UPPER THROUGH-STUD ON THE NR 4 CYLINDER.  THE CASE WAS INSPECTED IAW TCM SB M90-17 AND DETERMINED TO BE UNAIRWORTHY BY THE LOCATION OF THE CRACK.  THE CASE HAD BEEN REPAIRED AT SOME TIME IN THE PAST IN LOCATION OF THE CRACK.  SUBMITTER SUGGESTED A POSSIBLE CAUSE FOR THE CRACK COULD BE FROM STRESS CAUSED BY THE REPAIR OR POSSIBLY IMPROPER HEAT TREATING TO THE SURROUNDING AREA OF REPAIR.

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