SMA ON DOWNWIND TO VNY DESCRIBED APPARENT TWR PWR FAILURE RESULTING IN INTERMITTENT RADIO COM WITH ATC.

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I WAS ON A R DOWNWIND FOR VNY RWY 16R. THERE WAS A CITATION AHEAD; HIGHER; AND OUTSIDE OF ME; ON THE TURBINE ACFT R DOWNWIND FOR RWY 16R. THERE WERE OTHER ACFT IN BOTH THE R PATTERN FOR RWY 16R AND THE L PATTERN FOR RWY 16L. WHEN I WAS ABEAM THE CTL TWR; IT BECAME APPARENT THAT THE TWR WAS NO LONGER TALKING ON THE RADIO. I COULD HEAR THE XMISSIONS OF OTHER ACFT; BUT NO RESPONSE FROM THE TWR. ALSO; THERE WERE NO LIGHT SIGNALS FROM THE TWR. AS I CONTINUED DOWNWIND; THERE WAS A BRIEF RADIO XMISSION FROM THE TWR CLRING ME TO LAND. AFTER I LANDED; I WAS CLRED TO CROSS RWY 16L; AND TO CONTACT GND CTL. WHEN I CALLED GND; THERE WAS NO RESPONSE; AND NO LIGHT SIGNAL. AFTER WAITING OVER 5 MINS; I TAXIED TO PARKING. LATER I HEARD THAT THE TWR HAD SUFFERED A PWR FAILURE. TWRS MUST HAVE BACK-UP SYS THAT ARE IMMEDIATELY AVAILABLE; EVEN IF THEY ARE ONLY HAND-HELD RADIOS; WHILE RADIO PROBS; OR PWR PROBS THAT PRECLUDE LIGHT SIGNALS; ARE BEING DIAGNOSED AND CORRECTED. ALL OF THE ACFT APCHING VAN NUYS WERE IN LIMBO: WAS THE TWR OTS; SO THAT THE ARPT WAS NO LONGER CTLED; AND UNCTLED ARPT PROCS SHOULD BE EMPLOYED; OR WAS THE TWR'S INABILITY COMMUNICATE ONLY VERY TEMPORARY; AND IN A FEW SECONDS; WOULD BE CORRECTED. IF SOME OF THE ACFT HAD DECIDED TO USE UNCTLED ARPT PROCS TO COMPLETE THEIR LNDGS; WHILE OTHER ACFT HAD DECIDED TO AWAIT THE RESUMPTION OF TWR COMS AND TO CONTINUE DOWNWIND; THERE COULD HAVE BEEN COLLISIONS BTWN ACFT.