NTSB Identification: MKC87IA043.
The docket is stored on NTSB microfiche number 34457.
Scheduled 14 CFR
Incident occurred Friday, January 23, 1987 in SPRINGFIELD, MO
Probable Cause Approval Date: 07/10/1989
Aircraft: EMBRAER EMB-120, registration: N120AM
Injuries: 10 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
THE PIC OF THIS AIR MIDWEST FLT 4408 SAID THAT, WHILE ON INITIAL CLIMB, POWER (NP) ON THE LEFT ENGINE DECAYED TO 60% AND WOULD NOT RECOVER. THE ENGINE WAS FEATHERED BY CONDITION LEVER BUT THE TORQUE ROSE TO 140% WHILE RETURNING FOR A LANDING, ACCORDING TO THE PIC. THE AIRCRAFT LANDED SAFELY. A POST-INCIDENT INVESTIGATION DISCLOSED THAT AN OIL LEAK HAD BEEN TRACED, THE DAY PRIOR TO THE INCIDENT, TO A FRACTURED PROPELLER CONTROL UNIT SOLENOID. THAT PART WAS REMOVED AND REPLACED AS A PRECAUTIONARY MEASURE. THE PLASTIC BLADE RETAINING RINGS INSIDE THE PROPELLER ASSY WERE DAMAGED DUE TO THE ENGINE OVERTORQUE AND SUBSEQUENT SHUTDOWN. A TEARDOWN OF THE PROPELLER CONTROL UNIT (PCU) SHOWED THAT THE BETA TUBE HAD NOT FAILED NOR WAS IT FREEWHEELING INSIDE THE PCU. A SPECTROGRAPHIC ANALYSIS OF OIL SAMPLES, DRAWN FROM FOUR SEPARATE SECTIONS OF THE ENGINE, TESTED SATIFACTORILY. AS SUCH, NO REASON COULD BE FOUND FOR THE DROP IN ENGINE POWER (NP) AND SUBSEQUENT OVERTORQUE.
The National Transportation Safety Board determines the probable cause(s) of this incident to be:TURBINE ASSEMBLY..UNDETERMINED
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