Narrative:

Approximately 5 mi final; landing gear was lowered. Both pilots verified that gear was down and locked '3 green.' landing was normal with a slight crosswind. After all 3 wheels were on the ground; the left side of the aircraft started bouncing. On the 4TH or 5TH bounce; the left main gear collapsed. The left engine was shut down during the collapse. The aircraft slid on the runway approximately 1000 ft; and remained on the runway. When the aircraft came to a stop; the right engine was secured; and both pilots evacuate/evacuationed the aircraft. There were no passenger on this flight and there were no injuries. It appears that the left main landing gear down lock mechanism failed after touchdown. This resulted in the bouncing of the left side and subsequent collapse of the left main gear. Cause of the failure is unknown at this time. This aircraft has no previous history of lng gear problems. Callback conversation with reporter revealed the following information: reporter stated that the over-center mechanism failed and as the gear departed the fully extended sensing switch; the electric gear down motor again drove it to the gear down limit (fully extended). As the motor moved the gear to the gear down limit; the gear pushed the aircraft left wing back up causing an apparent bounce. As the aircraft settled onto the wing; the reporter feathered the engine thereby reducing damage. The FAA was on the field that day and because the damage was set at $100;000 did not consider it an accident.

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Original NASA ASRS Text

Title: A C421 L MAIN LNDG GEAR OVER-CTR DOWN-LOCK FAILED. AS IT RETRACTED; THE L GEAR DOWN MOTOR EXTENDED THE GEAR AGAIN CAUSING THE ACFT TO BOUNCE. ULTIMATELY; A BOLT FAILED; ALLOWING THE L GEAR TO FULLY COLLAPSE.

Narrative: APPROX 5 MI FINAL; LNDG GEAR WAS LOWERED. BOTH PLTS VERIFIED THAT GEAR WAS DOWN AND LOCKED '3 GREEN.' LNDG WAS NORMAL WITH A SLIGHT XWIND. AFTER ALL 3 WHEELS WERE ON THE GND; THE L SIDE OF THE ACFT STARTED BOUNCING. ON THE 4TH OR 5TH BOUNCE; THE L MAIN GEAR COLLAPSED. THE L ENG WAS SHUT DOWN DURING THE COLLAPSE. THE ACFT SLID ON THE RWY APPROX 1000 FT; AND REMAINED ON THE RWY. WHEN THE ACFT CAME TO A STOP; THE R ENG WAS SECURED; AND BOTH PLTS EVACED THE ACFT. THERE WERE NO PAX ON THIS FLT AND THERE WERE NO INJURIES. IT APPEARS THAT THE L MAIN LNDG GEAR DOWN LOCK MECHANISM FAILED AFTER TOUCHDOWN. THIS RESULTED IN THE BOUNCING OF THE L SIDE AND SUBSEQUENT COLLAPSE OF THE L MAIN GEAR. CAUSE OF THE FAILURE IS UNKNOWN AT THIS TIME. THIS ACFT HAS NO PREVIOUS HISTORY OF LNG GEAR PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE OVER-CTR MECHANISM FAILED AND AS THE GEAR DEPARTED THE FULLY EXTENDED SENSING SWITCH; THE ELECTRIC GEAR DOWN MOTOR AGAIN DROVE IT TO THE GEAR DOWN LIMIT (FULLY EXTENDED). AS THE MOTOR MOVED THE GEAR TO THE GEAR DOWN LIMIT; THE GEAR PUSHED THE ACFT L WING BACK UP CAUSING AN APPARENT BOUNCE. AS THE ACFT SETTLED ONTO THE WING; THE RPTR FEATHERED THE ENG THEREBY REDUCING DAMAGE. THE FAA WAS ON THE FIELD THAT DAY AND BECAUSE THE DAMAGE WAS SET AT $100;000 DID NOT CONSIDER IT AN ACCIDENT.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.