As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NUMBER ONE NP GAUGE FLUCTUATED FROM 85 PERCENT NP TO 35 PERCENT NP IN CRUISE FLIGHT (BOTH DIGITAL AND ANALOG INDICATIONS). NO OTHER ENGINE INSTRUMENTS WERE ABNORMAL. RETURNED TO LAX. REPLACED LEFT ENGINE NP PROBE AND NP INDICATOR. OPS CHECKS GOOD. RAN AT CRUISE POWER SETTING AND OPS CHECKS GOOD.