PIPER AEROSTAR 601, N3645D, WAS ARRG AS BELL 412 (HELICOPTER), N78S, WAS DEPG. N3645D RPRTD THE ACFT'S NOSE GEAR INDCR LGT DID NOT ILLUMINATE TO VERIFY THE NOSE GEAR WAS DWN & LOCKED. CREW OF N78S HEARD THE COM & SAW N3645D AS THEY CROSSEDBENEATH N3645D'S APCH PATH. THEY RPRTD N3645D'S NOSE GEAR APPEARED TO BE EXTDD. N3645D FLEW PAST THE TWR & TWR PSNL ALSORPRTD THE NOSE GEAR APPEARED TO BE EXTDD. AS N3645D WAS CLRD TO TURN DWNWND, N78S OFFERED TO JOIN FOR A CLOSER LOOK. CAPT OF N3645D ACCEPTED THE OFFER. DRG JOINUP, N78S CONVERGED FM LEFT REAR, THEN RPRTD THEY WOULD PASS ARND THE RGT SIDE& LOOK AT EVERYTHING AS THEY WENT BY. THEY RPRTD THAT EVERYTHING LOOKED OK. MOMENTS LTR, THE 2 ACFT COLLIDED & CRASHED TO THE GND. NO MECH RSN WAS FND THAT WOULD HAVE RESULTED IN THE ACDNT. NONE OF THE PLTS HAD TRNG FOR FLT IN CLOSE PROX- IMITY TO ANOTHER ACFT. THERE WERE INDCNS THE CAPT OF N3645D LACKED TRNG IN ACFT SYSTEMS & THAT HIS EMPLOYER (THE OPER) LACKED SURVEILLANCE BY THE FAA. THE EMERG PROC SXN OF THE AEROSTAR FLT MANUAL LACKED INFO ON EMERG GEAR EXTN.