SMA'S LNDG GEAR COLLAPSES UPON TOUCHDOWN ON RWY AFTER PRIMARY ELECTRICAL SUPPLY PROBLEM IN A NIGHT OP.

Narrative

FEB/XX/92 I AND 1 PAX DEPARTED DALLAS LOVE FIELD ON AN IFR FLT PLAN AT XY:00 PM LCL TIME FOR WACO REG ARPT. WE CLBED TO 6000 FT; OUR FLT PLANNED ALT. UPON DSCNT IN IMC CONDITIONS INTO WACO; THE TWR REPORTED THEY HAD LOST OUR TRANSPONDER. UPON XING THE OM I PLACED THE GEAR HANDLE DOWN AND HEARD THE PUMP ACTUATE. APPROX 3 MI INSIDE THE OM I NOTICED THE LIGHTS BEGAN TO PULSATE WEAKER; THEN STRONGER; THEN WEAKER IN RHYTHM. WE BROKE OUT OF THE 'SOUP' SLIGHTLY ABOVE MIN ON A 3/4 MI FINAL; AT THIS TIME WE LOST ALL ELECTRICAL PWR. I STARTED A 'GUMP' CHK WHEN I GOT TO UNDERCARRIAGE; I ASKED MY PAX WHO IS ALSO A PLT; TO MAKE A VISUAL CHK FOR THE GEAR. HE OPENED THE R WINDOW; USED A FLASHLIGHT AND CONFIRMED THE GEAR WAS DOWN. I PROCEEDED WITH LNDG; AND ON TOUCHDOWN THE MAIN GEAR COLLAPSED. THE NOSE GEAR REMAINED DOWN AND LOCKED. DAMAGE TO THE AIRPLANE WAS MINOR. THE R HORIZ STABILIZER WAS DAMAGED WHEN THE AIRPLANE CAME TO REST. OTHER THAN THIS THERE WAS NO DAMAGE TO THE BELLY OR ANY OTHER MECHANICAL STRUCTURE OF THE AIRPLANE. IT IS MY OPINION THAT THE MASTER/ALTIMETER SWITCH HAD A FAULTY CONNECTION WHICH ALLOWED THE BATTERY TO RUN THE ELECTRICAL SYS WITHOUT A LOW VOLTAGE LIGHT ILLUMINATING.