SMA PILOT REPORTS NOSE GEAR COLLAPSE AT FIRST ATTEMPT TO TAXI AFTER ENGINE START. ACFT HAD BEEN TOWED BY FBO PERSONNEL THE DAY PRIOR.

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ACFT WAS TOWED BY LINE PERSONNEL THE DAY PRIOR TO THE INCIDENT. ACFT WAS STARTED FOR FIRST TIME APPROX 10 MINS BEFORE INCIDENT. ACFT WAS IDLING AT APPROX 1000 RPM WITH PARKING BRAKE ACTIVATED WHILE PIC RETRIEVED IFR CLRNC TO ZZZ AND COMPLETED PRE-TAXI CHKLIST. PIC CALLED PHX GND FOR TAXI CLRNC AND IMMEDIATELY PRIOR TO INCIDENT. UPON RECEIPT OF CLRNC; PIC HAND-SIGNALED LINE PERSONNEL OF INTENTION TO TAXI; AT WHICH TIME PERSONNEL WALKED TO THE CONNECTOR TO TXWY H AND SIGNALED PIC TO ADVANCE. PIC RELEASED PARKING BRAKES AND ADVANCED THROTTLE TO APPROX 1300 RPM. ACFT MOVED NO MORE THAN A FEW INCHES BEFORE NOSE GEAR COLLAPSED; WITH ENSUING PROP STRIKE. PIC SHUT DOWN ELECTRICAL PWR AND FUEL SUPPLY; THEN EXITED ACFT. FOLLOWING THE INCIDENT; PIC TOOK EXTENSIVE PHOTOGRAPHS OF THE NOSE GEAR TRUSS THAT HAD FAILED; AND CONSULTED WITH SEVERAL REPAIR SHOPS WITH NATIONAL REPUTATIONS. THE UNANIMOUS OPINION AMONG THEM IS THAT THE MOST LIKELY CAUSE IS A HARD IMPULSE FORCE BEING APPLIED TO THE NOSE GEAR IMMEDIATELY PRIOR TO THE INCIDENT. THEY BASE THIS JUDGEMENT ON THE FRESHNESS OF THE BREAK THROUGH SOLID STEEL TUBES (WITH NO SIGNS OF AN OLD DEVELOPING CRACK); THE LOCATION OF THE BREAK; AND THE LACK OF EVIDENCE OF CORROSION. AN ALTERNATIVE EXPLANATION WOULD BE A HARD LNDG AND/OR PORPOISE IMMEDIATELY PRIOR TO THE INCIDENT. THE PIC TESTIFIES THAT NO SUCH HARD LNDG HAS OCCURRED IMMEDIATELY PRIOR TO THE INCIDENT OR; FOR THAT MATTER; IN THE 2 YRS THAT HE HAS OWNED THE ACFT.