Narrative:

Approach control services to aircraft arrival den. Landing runway 35L. Both aircraft on base leg at 13000 ft MSL. Aircraft X from west and aircraft Y from east. All radios lost (transmitters) without warning. Tried standby. Response from pilots was 'unreadable.' tried emergency jack, 'unreadable.' conflict alert activated. Aircraft Y changed to another sector frequency. That controller gave an immediate right turn and descent during the transmitter loss. Another controller at a different sector tried the frequencys and also received an 'unreadable' response. Therefore, it did not appear to be a headset or position failure. ZDV arrivals were subsequently changed to another frequency. 20 minutes after the incident, af maintenance returned the frequency to service. This type of radio failure scenario has been happening all too frequently. Last month, den made front page news after losing radios for over an hour. The supervisor's log reports that maintenance rebooted the rdvs (voice-switching) computer to fix the problem. Radio returned to service. New question: if rdvs was rebooted, wouldn't all the frequencies be affected momentarily? I did not observe this happen. Callback conversation with reporter revealed the following information: reporter advised that the rdvs (rapid deployment voice switching) system was installed at ATC facs with 12 or more control positions to provide needed rapid access radio transmitter/receiver changes which existing 'standard' voice switching systems could not accommodate. The reporter thought nct and dfw tracons had the same new system. The reporter alleges the rdvs has had 'numerous' failures during the last 18 mos. The reporter advised that maintenance started by changing antenna location, utilizing 2 antennas. Those activities did not resolve the problem. The reporter advised that recent troubleshooting had identified the problem in rdvs memory card(south). Each time an airspace/runway confign has been executed, the memory cards 'store' the changes. Eventually, the memory cards are 'memoried out,' or reach capacity and 'lock out,' or fail. The reporter stated that when a card 'fails,' maintenance installs a 'new memory card.' the reporter advised that activity can be as little as 5 mins. The reporter's concern, as in this event, is during the 'off hour' times, when qualified communication personnel are not available onsite to conduct the maintenance activity for frequency restoration. The reporter was unable to learn if, or when, a 'fix' is expected.

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Original NASA ASRS Text

Title: DEN APCH CTLR (D01) INCURRED TFC CONFLICT VECTORING ACFT TO DEN RWY 35 FINAL APCH COURSE DUE TO FREQ FAILURE. FREQ FAILURE ATTRIBUTED TO THE RAPID DEPLOYMENT VOICE SWITCHING (RDVS) SYSTEM.

Narrative: APCH CTL SVCS TO ACFT ARR DEN. LNDG RWY 35L. BOTH ACFT ON BASE LEG AT 13000 FT MSL. ACFT X FROM W AND ACFT Y FROM E. ALL RADIOS LOST (XMITTERS) WITHOUT WARNING. TRIED STANDBY. RESPONSE FROM PLTS WAS 'UNREADABLE.' TRIED EMER JACK, 'UNREADABLE.' CONFLICT ALERT ACTIVATED. ACFT Y CHANGED TO ANOTHER SECTOR FREQ. THAT CTLR GAVE AN IMMEDIATE R TURN AND DSCNT DURING THE XMITTER LOSS. ANOTHER CTLR AT A DIFFERENT SECTOR TRIED THE FREQS AND ALSO RECEIVED AN 'UNREADABLE' RESPONSE. THEREFORE, IT DID NOT APPEAR TO BE A HEADSET OR POSITION FAILURE. ZDV ARRIVALS WERE SUBSEQUENTLY CHANGED TO ANOTHER FREQ. 20 MINUTES AFTER THE INCIDENT, AF MAINT RETURNED THE FREQ TO SVC. THIS TYPE OF RADIO FAILURE SCENARIO HAS BEEN HAPPENING ALL TOO FREQUENTLY. LAST MONTH, DEN MADE FRONT PAGE NEWS AFTER LOSING RADIOS FOR OVER AN HOUR. THE SUPVR'S LOG RPTS THAT MAINT REBOOTED THE RDVS (VOICE-SWITCHING) COMPUTER TO FIX THE PROB. RADIO RETURNED TO SVC. NEW QUESTION: IF RDVS WAS REBOOTED, WOULDN'T ALL THE FREQUENCIES BE AFFECTED MOMENTARILY? I DID NOT OBSERVE THIS HAPPEN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT THE RDVS (RAPID DEPLOYMENT VOICE SWITCHING) SYSTEM WAS INSTALLED AT ATC FACS WITH 12 OR MORE CTL POSITIONS TO PROVIDE NEEDED RAPID ACCESS RADIO XMITTER/RECEIVER CHANGES WHICH EXISTING 'STANDARD' VOICE SWITCHING SYSTEMS COULD NOT ACCOMMODATE. THE RPTR THOUGHT NCT AND DFW TRACONS HAD THE SAME NEW SYSTEM. THE RPTR ALLEGES THE RDVS HAS HAD 'NUMEROUS' FAILURES DURING THE LAST 18 MOS. THE RPTR ADVISED THAT MAINT STARTED BY CHANGING ANTENNA LOCATION, UTILIZING 2 ANTENNAS. THOSE ACTIVITIES DID NOT RESOLVE THE PROB. THE RPTR ADVISED THAT RECENT TROUBLESHOOTING HAD IDENTIFIED THE PROB IN RDVS MEMORY CARD(S). EACH TIME AN AIRSPACE/RWY CONFIGN HAS BEEN EXECUTED, THE MEMORY CARDS 'STORE' THE CHANGES. EVENTUALLY, THE MEMORY CARDS ARE 'MEMORIED OUT,' OR REACH CAPACITY AND 'LOCK OUT,' OR FAIL. THE RPTR STATED THAT WHEN A CARD 'FAILS,' MAINT INSTALLS A 'NEW MEMORY CARD.' THE RPTR ADVISED THAT ACTIVITY CAN BE AS LITTLE AS 5 MINS. THE RPTR'S CONCERN, AS IN THIS EVENT, IS DURING THE 'OFF HOUR' TIMES, WHEN QUALIFIED COM PERSONNEL ARE NOT AVAILABLE ONSITE TO CONDUCT THE MAINT ACTIVITY FOR FREQ RESTORATION. THE RPTR WAS UNABLE TO LEARN IF, OR WHEN, A 'FIX' IS EXPECTED.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.