# SDR CALA2026102620574

- Type: Service difficulty report (as reported; unverified)
- Difficulty date: October 21, 2026
- Submitted: October 26, 2026
- Operation: Air carrier
- Aircraft: [N29977](https://openairdocs.org/aircraft/N29977), registered now
- Make and model: Boeing 787-9
- Registry model: [Boeing 787-9](https://openairdocs.org/model/boeing-787-9) (OpenAirDocs)
- Aircraft serial: 66136
- Aircraft time: 29,727 hours, 2,993 cycles
- Engine: Ge GENX1B76AP
- System (JASC): [2422 · AC Inverter](https://openairdocs.org/jasc/2422)
- Part: Transformer
- Part number: T374290
- Part serial: 1790
- Condition: Faulted
- Part time: 18 hours, 3 cycles
- Stage of operation: CL
- How discovered: O
- Nature of condition: Z
- Precautionary procedure: A, D
- FAA source: FAA Service Difficulty Reporting System (https://sdrs.faa.gov/)
- Page: https://openairdocs.org/sdr/CALA2026102620574

## Discrepancy

ELEC ATU L LEFT AUTOTRANSFORMER UNIT FAILURE.DB LEFT 1 GENERATOR CONTROL UNITREMOVED AND REPLACED ATUC-L CONTACTOR REF AMM DMC-B787-A-24-22-05-00A-520A/720A-A. OPS CHECK NORMAL.  PERFORMED WIRING CHECKS AS REFERENCED IN FIM TASK DMC-B787-A-24-20-F0-47A-421A-A. NO FAULTS NOTED. REPLACED CONTACTOR STATED IN PREVIOUS ENTRY CURRENTLY NO FAULTS SHOWING ON STATUS PAGE. BUT DUE TO HISTORY OF REPEAT FAULTS OF LEFT ATU TECH SUPPORT RECOMMENDS REPLACEMENT OF LEFT ATU ALSO.  R & R LT ATU REF DMC-B787-A-24-25-00-01A-520A-A / DMC-B787-A-24-25-00-01A-720A-A, OPS GOOD.

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