A C172 PLT RPTS AN ELECTRICAL FAILURE AND A SUBSEQUENT LNDG AT A CLASS D ARPT WITHOUT A CLRNC VIA THE TWR CTLR'S LIGHT SIGNALS.

Narrative

WHILE TAKING A LCL VFR FLT IN CLR SKIES IN THE DENVER METROPOLITAN AREA; MY ACFT SUFFERED A COMPLETE ELECTRICAL SYS FAILURE. ALL SYS WERE LOST INCLUDING BOTH RADIOS; ADF; AND XPONDER. I DETECTED THE ONSET OF THE FAILURE BY NOTICING THE GRADUAL DIMMING OF THE RADIO FREQ DISPLAY LIGHTS. SHORTLY THEREAFTER; (IE; MINS) ALL ELECTRICAL SYS WENT DARK. AFTER AN ESTIMATED 5-10 MINS OF TROUBLESHOOTING ON MY PART; I DETERMINED THAT I WAS NOT GOING TO RESTORE PWR. I WOULD HAVE TO RETURN TO CENTENNIAL RPT FOR LNDG WITHOUT OBTAINING THE CURRENT ATIS INFO OR BEING IN RADIO CONTACT THE CTL TWR. I DID NOT INTEND TO OPERATE ON BATTERY PWR ANY LONGER THAN NECESSARY. I ENTERED THE CLASS D AIRSPACE IN AN AREA AND AT AN ALT TYPICAL OF ARPT TFC AND PROCEEDED TO APCH THE ARPT AREA. WHEN APPROX 2-3 MI FROM THE ARPT; I SIGNALED THE CTL TWR BY WAVING (IE; ROLLING) MY WINGS IN A FASHION DESIGNED TO INDICATE THAT MY ACFT HAD A PROB. AT THAT TIME I HAD THE CTL TWR IN CLR VIEW. I STUDIED THE TWR CAREFULLY FOR LIGHT SIGNALS BUT RECEIVED NONE. AFTER HAVING DETERMINED THAT THERE APPEARED TO BE NO ACFT IN THE TFC PATTERN FOR RWY 17R; I ENTERED THE RWY 17R PATTERN DOWNWIND MIDFIELD AT PATTERN ALT. DURING THE DOWNWIND PHASE I CONSTANTLY MONITORED THE TWR FOR SIGNALS BUT RECEIVED NONE. I CONTINUED WITH THE APCH; TURNED BASE AND FINAL WITHOUT ANY INDICATION OF LIGHT SIGNALS FROM THE CTL TWR. AT THAT POINT I COMMITTED THE ACFT FOR LNDG AND PROCEEDED TO LAND WITHOUT RECEIVING AN AUTHORIZING LIGHT SIGNAL. AT ANY GIVEN TIME; CENTENNIAL ARPT IS QUITE BUSY AND IT IS ESPECIALLY BUSY AT THAT TIME OF THE MORNING. IN MY JUDGEMENT; ALTHOUGH I HAD RECEIVED NEITHER CLRNC NOR DENIAL TO LAND; IT WAS SAFER FOR ME TO COMPLETE THE LNDG THAN TO GO AROUND AND WAIT FOR AN AUTHORIZING SIGNAL (WHICH I WAS UNSURE AS TO WHETHER I WOULD RECEIVE OR NOT). CONDITIONS AT THAT MOMENT WERE EXTREMELY FAVORABLE AS THERE WERE NO OTHER ACFT (THAT I COULD SEE) IN THE PATTERN OR ON THE GND IN THE IMMEDIATE VICINITY OF MY INTENDED RWY. AFTER COMPLETION OF THE LNDG ROLLOUT I TAXIED TO AND STOPPED AT THE INTXN OF RWY 17L WHERE CLRNC TO TAXI IS REQUIRED TO CROSS THE RWY. I DID FINALLY RECEIVE A FLASHING GREEN LIGHT FOR TAXI CLRNC FROM THE TWR AT THAT TIME. I TAXIED BACK TO MY PARKING AREA WITHOUT FURTHER INCIDENT.