NTSB Identification: ATL91IA016.
The docket is stored on NTSB microfiche number 44899.
Scheduled 14 CFR operation of HELEASCO TWENTY FOUR, INC. (D.B.A. NORTHWEST AIRLINK )
Incident occurred Saturday, November 10, 1990 in MEMPHIS, TN
Probable Cause Approval Date: 12/30/1992
Aircraft: Saab-Scania AB (Saab) 340A, registration: N322PX
Injuries: 3 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.

NO PASSENGERS WERE ON THE AIRPLANE WHEN IT DEPARTED MEMPHIS. THE FLIGHT WAS UNEVENTFUL UNTIL THE CAPTAIN FELT A VIBRATION ON THE LEFT SIDE AND BELIEVED THAT THE PROPELLER WAS THE ORIGIN. HE ASKED THE FIRST OFFICER (FO) HAD HE EVER SEEN THE PROPELLER IN FEATHER; THE FO SAID NO. THE CAPTAIN INSTRUCTED THE FO TO GO INTO THE PASSENGER CABIN AND LOOK AT THE LEFT PROPELLER IN FEATHER. SECONDS LATER THE AIRPLANE STARTED A SERIES OF VIOLENT GYRATIONS, WHICH THREW HIM AND THE FLIGHT ATTENDANT AGAINST THE INTERIOR OF THE CABIN. AFTER LOSING SEVERAL THOUSAND FEET FROM 11,000 FEET, THE FLIGHT CREW MANAGED TO REGAIN CONTROL OF THE AIRPLANE AND LANDED WITHOUT FURTHER INCIDENT. A REVIEW OF THE EVENT AND THE REPORTED VIBRATION FELT ONLY BY THE CAPTAIN, FAILED TO REVEAL A MECHANICAL PROBLEM WHICH WOULD HAVE PRODUCED A VIBRATION. THE PROCEDURES EMPLOYED BY THE CAPTAIN WERE NOT IN ACCORDANCE WITH FAA OR COMPANY APPROVED DIRECTIVES.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

THE PILOT'S FAILURE TO FOLLOW APPROVED PROCEDURES FOR TROUBLESHOOTING INFLIGHT MAINTENANCE PROBLEMS AND IMPROPERLY USED THE FLIGHT AND ENGINE CONTROLS.

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