YAK 50 ACFT EQUIP PROB. L MAIN GEAR COLLAPSED DURING LNDG ROLL. QUESTIONABLE CERTIFICATE OF REGISTRATION.

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ON AUG/XX/96; PLT PICKED UP ACFT; A YAK50; AT XX58 FOR DELIVERY TO AGENT FOR PROSPECTIVE PURCHASE IN OREGON. PLT PICKED UP THE ACFT FROM AGENT FOR THE OWNER/SELLER. ON AUG/XX/96; ON LNDG APCH TO CID; PLT SELECTED GEAR 'DOWN' AND THE LNDG GEAR WAS FULLY EXTENDED AS SHOWN BY COCKPIT INDICATOR LAMPS (2 GREEN LIGHTS). LNDG GEAR EXTENSION APPEARED NORMAL; USING MAIN AIR SUPPLY FOR ACTUATION AT PRESSURE APPROX 60 ATM SHOWN ON MAIN AIR PRESSURE GAUGE IN COCKPIT. LCL CTL REQUESTED A CLOSE R-HAND PATTERN TO RWY 9 AND PLT ACKNOWLEDGED AND COMPLIED. LNDG TOUCHDOWN WAS NORMAL AND SMOOTH IN 3 POINT ATTITUDE. ACFT ROLLED OUT ON MAIN GEAR AND TAILWHEEL FOR A SUBSTANTIAL DISTANCE IN A STRAIGHT LINE; ON RWY CTRLINE; WITHOUT BRAKE APPLICATION. L MAIN GEAR THEN COLLAPSED TO THE RETRACTED POS AND ACFT CONTINUED DOWN THE RWY ON R MAIN WHEEL; TAILWHEEL; AND L WINGTIP. THERE WAS NO PROP STRIKE AND R MAIN GEAR REMAINED DOWN AND LOCKED. ACFT DEPARTED RWY TO THE L AND CAME TO REST IN THE GRASS ALONGSIDE. PLT NOTIFIED LCL CTL BY RADIO; THEN SHUT DOWN ENG; TURNED OFF ELECTRICAL SWITCHES; CLOSED MAIN AIR VALVE; NOTED THAT LNDG GEAR SELECTOR REMAINED IN 'DOWN POS;' NOTED THAT MAIN AIR GAUGE STILL INDICATED PRESSURE OF 50 ATM PLUS; AND MOVED LNDG GEAR SELECTOR SAFETY SLIDE INTO PLACE. ARPT PERSONNEL THEN ASSISTED IN LIFTING THE L WING BY HAND; WHEREUPON THE L MAIN GEAR MOVED TO THE EXTENDED POS. ACFT CONTAINED 'PINK' COPY OF REGISTRATION APPLICATION; FORM 8050-1; WHICH BORE NO DATE. THE ACFT'S CERTIFICATE OF ACFT REGISTRATION; FORM 8050-3; WAS NOT ABOARD. PLT HAD NO REASON TO BELIEVE THAT FORM 8050-3 HAD BEEN ISSUED OR THAT FORM 8050-1 HAD BEEN SUBMITTED TO THE FAA ACFT REGISTRY MORE THAN 90 DAYS EARLIER. PLT HAD INSPECTED SPECIAL AIRWORTHINESS CERTIFICATE; FORM 8130-7; AND ASSOCIATED OPERATING LIMITATIONS DATED MAY/XX/95; INDICATING THAT APPLICABLE PROGRAM LETTER WAS IDENTED AS THAT OF A NAME THAT DIFFERED FROM THAT ON FORM 8050-1; SUGGESTING THAT THE ACFT HAD BEEN REGISTERED TO THE CURRENT OWNER SUBSEQUENT TO THE ISSUANCE OF THE ACFT'S SPECIAL AIRWORTHINESS CERTIFICATE. PLT INQUIRED ABOUT THE PROGRAM LETTER AND WAS INFORMED THAT KENTUCKY FSDO #1 HAD APPROVED OP OF THE ACFT FOR PURPOSES OF DELIVERY TO PROSPECTIVE PURCHASER WITHOUT A NEW OR AMENDED PROGRAM LETTER. PLT ACCORDINGLY AGREED TO OPERATE THE ACFT FOR THE DELIVERY FLT. 2 POINTS MERIT CONSIDERATION. FIRST; IT APPEARS THAT IN THE YAK50 IT MAY BE POSSIBLE TO EXTEND THE LNDG GEAR IN NORMAL FASHION; OBTAIN 'GREEN' LIGHTS; AND YET ENCOUNTER A FAILURE OF THE GEAR TO LOCK IN THE DOWN POS. SECOND; PLT MAY INSPECT NECESSARY ACFT DOCUMENTS; IN THIS CASE; FORM 8050-1; WITHOUT ANY INDICATION THAT OTHER DOCUMENTS; IN THIS CASE FORM 8050- 3; EXIST AND SHOULD BE ABOARD THE ACFT.