19981021044259A

Accident · Substantial damage

FAA accident report · Mooney M20C · Denver, CO · October 21, 1998

Date: October 21, 1998 · 08:28 local
Place: Denver, CO
Airport: Centennial Airport
Phase of flight: Forced/Precautionary Landing
Operating rules: General operating rules (Part 91)
Damage: Substantial damage
Aircraft: N6405U
NTSB investigation: NTSBDEN99LA015
Reported as: Mooney M20C
Reported engine: Lycoming O360A1D
Fatal injuries: 0
Pilot’s flight hours: 1,018 total834 in this make and model43 in the last 90 days

From the FAA’s Accident/Incident Data System (AIDS), through its Aviation Safety Information Portal, as reported. The NTSB investigates accidents separately, and its record of an accident is the fuller one. The aircraft is matched to the registry by N-number and event date, checked against the reported make and model; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.

What happened

The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.

(.4) During climb following departure, the engine lost power. The pilot reported the emergency to the tower and attempted to return to the airport. Determining that he would be unable to make it back, he made an emergency landing in a field one and a half miles southeast of the airport. Postaccident examination of the engine revealed that the camshaft gear retaining bolts connecting the camshaft gear to the camshaft had lost torque. As a result, the lobes failed to open their respective valves, creating discontinuity to the gear train. The tread on each of the four camshaft gear bolts exhibited shiny, worn patterns. According to a Textron Lycoming engineer, loss of camshaft retaining bolt torque is indicative of the bolts being improperly torqued during the engine overhaul. According to aircraft maintenance records, the engine was overhauled on March 15, 1985, and had accumulated 833 hours since overhaul.

As the FAA filed it

(.4) DURING CLIMB FOLLOWING DEPARTURE, THE ENGINE LOST POWER. THE PILOT REPORTED THE EMERGENCY TO THE TOWER AND ATTEMPTED TO RETURN TO THE AIRPORT. DETERMINING THAT HE WOULD BE UNABLE TO MAKE IT BACK, HE MADE AN EMERGENCY LANDING IN A FIELD ONE AND A HALF MILES SOUTHEAST OF THE AIRPORT. POSTACCIDENT EXAMINATION OF THE ENGINE REVEALED THAT THE CAMSHAFT GEAR RETAINING BOLTS CONNECTING THE CAMSHAFT GEAR TO THE CAMSHAFT HAD LOST TORQUE. AS A RESULT, THE LOBES FAILED TO OPEN THEIR RESPECTIVE VALVES, CREATING DISCONTINUITY TO THE GEAR TRAIN. THE TREAD ON EACH OF THE FOUR CAMSHAFT GEAR BOLTS EXHIBITED SHINY, WORN PATTERNS. ACCORDING TO A TEXTRON LYCOMING ENGINEER, LOSS OF CAMSHAFT RETAINING BOLT TORQUE IS INDICATIVE OF THE BOLTS BEING IMPROPERLY TORQUED DURING THE ENGINE OVERHAUL. ACCORDING TO AIRCRAFT MAINTENANCE RECORDS, THE ENGINE WAS OVERHAULED ON MARCH 15, 1985, AND HAD ACCUMULATED 833 HOURS SINCE OVERHAUL.

NTSB investigation

The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.

NTSB DEN99LA015Accident · Serious injuriesLimited investigationFinal reportEnglewood, COThe undertorquing of the camshaft gear retaining bolts during engine overhaul by maintenance personnel. A factor was the unsuitable terrain for a forced landing.Oct 21, 1998 · Substantial damage