A CORPORATE LTT LANDED WHEELS UP AFTER AN AIR DATA COMPUTER FAILURE.

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ON AUG/THU/92 AT PM15 LCL TIME; I WAS COPLT ON A CORPORATE JET WHICH LANDED GEAR-UP. EARLIER IN THE FLT; THERE WAS A FAILURE OF THE #2 AIR DATA COMPUTER. DUE TO THIS FAILURE; THE OVERSPD WARNING HORN WENT OFF EVEN THOUGH THERE WAS NO OVERSPD CONDITION. TO SILENCE THE HORN; THE CAPT PULLED OUT THE AURAL WARNING CIRCUIT BREAKER. UPON FINAL DSCNT FOR LNDG; THE CAPT DID NOT CALL FOR THE GEAR TO BE PUT DOWN OR FOR THE BEFORE LNDG CHKLIST. HOWEVER; THE CAPT DID CALL FOR FLAPS TO 10 DEGS; AND FULL FLAPS. ON SHORT FINAL I LOOKED AT THE BEFORE LNDG CHKLIST AND SINCE THERE WAS NO GEAR WARNING HORN AND FLAPS WERE ALREADY FULL; I ASSUMED THE GEAR WAS DOWN AND I PROCEEDED WITH THE LAST ITEMS ON THE CHKLIST. THE AIRPLANE WAS LANDED WITH THE GEAR IN THE UP POS. CONTRIBUTING FACTORS: CREW FATIGUE -- LAST LEG AFTER LONG DAY. MALFUNCTION OF AIR DATA COMPUTER. HIGH TECH AIRPLANE WITH FULL EFIS IN WHICH MINIMAL TRAINING WAS RECEIVED ON NEW AVIONICS. CREW TOTAL TIME IN EFIS AIRPLANE WAS ABOUT 200 HRS. LACK OF RECURRENT TRAINING IN LAST 13 MONTHS. DUSK CONDITIONS MADE COCKPIT LIGHTING POOR. CORRECTIVE ACTIONS: A FULL CHALLENGE AND RESPONSE CHKLIST WILL BE ADOPTED AS COMPANY PROC. RECURRENT TRAINING WILL BE SCHEDULED MORE REGULARLY; WITH ATTN TO AVIONICS MALFUNCTIONS. MORE ATTN FOCUSED ON CREW RESOURCE MGMNT.