PIPER ARROW ACFT IN CRUISE; RPTR PLT FELT THUMP IN AIRFRAME AND SUSPECTS IT WAS THE NOSE GEAR RETRACTION EXTENSION SPRING BREAKING; BECAUSE ON LNDG THE NOSE GEAR COLLAPSED. RPTR PLT HAD PREPARED FOR THE EMER LNDG.

Narrative

DEPARTED EL MONTE; CA; FOR IFR PROFICIENCY FLT. WHILE ENRTE TO SMO FOR VOR RWY 21 APCH; FELT SLIGHT THUMP IN AIRFRAME. ALL GAUGES APPEARED NORMAL; FLT CHARACTERISTICS NORMAL; ENG OP NORMAL. ASSUMED POSSIBLE BIRD STRIKE. VECTORED ONTO APCH; AT FAF GEAR EXTENSION FAILED TO SHOW DOWN AND LOCKED NOSE GEAR. APCH TERMINATED IN VISUAL CONDITIONS. LOW PASS OVER SMO; GND OBSERVERS RPTED GEAR DOWN. STANDARD EMER GEAR CHKLIST EXECUTED INCLUDING: CHK INDICATOR BULBS; CHK CIRCUIT BREAKERS; CYCLE GEAR; EMER GEAR EXTENSION MANEUVERS (FISHTAILING; HIGH-G CLBS/DIVES; ETC). CONTINUED FAILURE TO GET POSITIVE INDICATION OF NOSE GEAR LOCKED IN PLACE. APCHED BUR IN VISUAL CONDITIONS. EXECUTED A SINGLE LOW PASS OVER BUR RWY 8. GND OBSERVERS AGAIN RPTED GEAR APPEARED DOWN. BRIEFED COPLT FOR LNDG: COCKPIT SECURED; EMER LNDG PROCS REVIEWED. EXECUTED SOFT-FIELD LNDGS; SHUT OFF ELECTRICAL EQUIP AND ATTEMPTED FUEL SHUTOFF ON SHORT FINAL. ENG STOPPED VERY SHORT FINAL (MIXTURE TO IDLE CUTOFF). COULDN'T LOCATE RELEASE MECHANISM ON FUEL SHUTOFF/TANK SELECT SWITCH; EVEN THOUGH I KNEW WHERE IT WAS; SO FUEL MAIN WAS NOT SHUT OFF. DOOR OPENED PRIOR TO TOUCHDOWN. NOSE HELD OFF AS LONG AS POSSIBLE. NOSE GEAR COLLAPSED WHEN IT FINALLY CAME DOWN; NOSE SETTLED TO RWY AND ACFT SLID TO A STOP. EXITED ACFT EXPEDITIOUSLY; NO FIRE DAMAGE. ACFT SUSTAINED DAMAGE TO LOWER COWLING NOSE GEAR MECHANISM AND 1 PROP BLADE (POSSIBLY DUE TO WINDMILLING; AS THE ENG WAS SHUT DOWN PRIOR TO TOUCH DOWN). BELIEVE THAT 'THUMP' WAS RETRACTION/EXTENSION SPRING FAILING INFLT. MECH ALSO RPTED NO HYD PRESSURE ON INSPECTION THE FOLLOWING DAY. THIS MAY HAVE BEEN DUE TO SOME STRUCTURAL FAILURE CAUSED BY THE BREAKING SPRING; OR MAY HAVE BEEN A SEPARATE FAILURE. APCH CTL AND BUR CTLRS PROVIDED SUPERB ASSISTANCE. BUR EMER/FIRE CREWS WERE EXTREMELY PROFESSIONAL. MUCH THANKS TO EVERYONE WHO PROVIDED ASSISTANCE.