NTSB Identification: FTW94FA141.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Accident occurred Sunday, May 01, 1994 in BROOMFIELD, CO
Probable Cause Approval Date: 07/31/1995
Aircraft: MOONEY M20E, registration: N1905Y
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

SHORTLY AFTER TAKEOFF, THE PILOT REQUESTED CLEARANCE TO RETURN FOR AN IMMEDIATE LANDING. A WITNESS SAID THAT HE HEARD A METALLIC NOISE FROM THE PLANE AS IT PASSED OVERHEAD. HE SAID THE PILOT MADE A STEEP RIGHT BANK TO LAND ON RUNWAY 29L; HOWEVER, THE PLANE IMPACTED BETWEEN THE PARALLEL RUNWAYS. AN EXAM OF THE ENGINE REVEALED 2 FINGER-TIGHT CYLINDER BASE NUTS & UNDERTORQUED BASE NUTS & CRANKCASE THROUGH-NUTS. A TEARDOWN REVEALED THE CRANKSHAFT HAD FAILED FROM FATIGUE BETWEEN THE #3 & #4 CONNECTING ROD JOURNALS. A METALLURGICAL EXAM OF THE CRANKSHAFT REVEALED HIGH LOCALIZED STRESS-INDUCED FATIGUE CRACKS. THE ENGINE HAD ACCUMULATED 266 HRS OF FLIGHT TIME SINCE MAJOR OVERHAUL ON 1/11/91. THE PLANE HAD BEEN MODIFIED WITH 2 STC'S, 1 FOR INSTALLATION OF A RAYJAY TURBOCHARGER, ANOTHER FOR INSTALLATION OF A 'BLACKMAC' PROPELLER. THE HOLDER OF THE PROPELLER STC REPORTED THE COMPANY WOULD NOT HAVE INSTALLED THE PROPELLER ON A TURBOCHARGED ENGINE, SINCE CERTIFICATION VIBRATORY TESTS WERE ONLY MADE ON NORMALLY ASPIRATED ENGINES. AFTER INSTALLATION ON 1/17/91, THE PROPELLER WAS REMOVED ON 3/19/91 FOR STATIC BALANCE & 'RE-INDEX PROP #1 BLADE 180 DEGREES;' ON 3/28/91, IT WAS REMOVED FOR A BLADE ANGLE CHECK; AND ON 5/23/91, IT RECEIVED A DYNAMIC BALANCE.

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

FATIGUE FAILURE OF THE ENGINE CRANKSHAFT; AND FAILURE OF THE PILOT TO MAINTAIN ADEQUATE AIRSPEED, WHILE MANEUVERING TO LAND, WHICH RESULTED IN A STALL AND COLLISION WITH THE TERRAIN. FACTORS RELATED TO THE ACCIDENT WERE: THE UNDESIRABLE ENGINE/PROPELLER VIBRATION, AND THE LOOSE CRANKCASE AND CYLINDER BASE NUTS.

Full narrative available

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