Narrative:

While taxiing for takeoff on runway 19 at dca, I became suspicious that the push-to-talk switch on my joystick might be sticking in the transmit position. This was confirmed when the ECAM caution message appeared indicating that the #1 VHF radio had been transmitting more than 1 min, ie, stuck microphone switch. I cycled the switch and the caution message subsided. We also began hearing ground control again and the controller was advising all aircraft to check for a 'stuck microphone.' I then changed frequencys to tower and we were cleared into position and hold on runway 19, traffic landing (or taking off, I don't recall which) on a crossing runway. While holding in position, we again got the ECAM caution message indicating a stuck microphone. I cycled my push-to-talk switch and also changed the transmit button on my audio panel to intercom (to make certain that a stuck microphone would not interfere with any frequency). At that time, we heard the tower controller ordering a go around for an aircraft landing runway 19. We saw the aircraft go overhead. Tower then advised us that they believed we had a stuck microphone. We switched to hand microphone, departed and continued to dtw without further incident where, upon arrival, we made a maintenance entry into the aircraft logbook. This was a simple mechanical failure that led to a potentially dangerous situation. At the least, it caused 1 or more aircraft to have to go around, at an airport (dca) with unique ATC problems. This problem has been studied many times and few technology solutions exist to help eliminate it. I give credit to the engineers of airbus to include a warning system that simply issues a caution message after 1 min of continuous VHF transmission. Without that feature, this particular situation would have almost certainly been worse. The real problem with this particular mechanical failure is how insidious it is. Both times we experienced the failure, it was during the readback, therefore any period of silence after the transmission did not seem unusual. Absent the airbus monitoring and caution system, the only indication of a stuck microphone problem is a prolonged period of silence or non response to a transmission, neither of which are all that unusual. The real long-term solution to this problem is a better communication system. For many reasons, including this incident, I have felt that a more technologically advanced communication system should be in place for the airline industry. The obvious choice at this point is a data link system, possibly using the ACARS system.

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Original NASA ASRS Text

Title: A320 CREW HAD A STUCK MIKE XMIT SWITCH AT DCA.

Narrative: WHILE TAXIING FOR TKOF ON RWY 19 AT DCA, I BECAME SUSPICIOUS THAT THE PUSH-TO-TALK SWITCH ON MY JOYSTICK MIGHT BE STICKING IN THE XMIT POS. THIS WAS CONFIRMED WHEN THE ECAM CAUTION MESSAGE APPEARED INDICATING THAT THE #1 VHF RADIO HAD BEEN XMITTING MORE THAN 1 MIN, IE, STUCK MIKE SWITCH. I CYCLED THE SWITCH AND THE CAUTION MESSAGE SUBSIDED. WE ALSO BEGAN HEARING GND CTL AGAIN AND THE CTLR WAS ADVISING ALL ACFT TO CHK FOR A 'STUCK MIKE.' I THEN CHANGED FREQS TO TWR AND WE WERE CLRED INTO POS AND HOLD ON RWY 19, TFC LNDG (OR TAKING OFF, I DON'T RECALL WHICH) ON A XING RWY. WHILE HOLDING IN POS, WE AGAIN GOT THE ECAM CAUTION MESSAGE INDICATING A STUCK MIKE. I CYCLED MY PUSH-TO-TALK SWITCH AND ALSO CHANGED THE XMIT BUTTON ON MY AUDIO PANEL TO INTERCOM (TO MAKE CERTAIN THAT A STUCK MIKE WOULD NOT INTERFERE WITH ANY FREQ). AT THAT TIME, WE HEARD THE TWR CTLR ORDERING A GAR FOR AN ACFT LNDG RWY 19. WE SAW THE ACFT GO OVERHEAD. TWR THEN ADVISED US THAT THEY BELIEVED WE HAD A STUCK MIKE. WE SWITCHED TO HAND MIKE, DEPARTED AND CONTINUED TO DTW WITHOUT FURTHER INCIDENT WHERE, UPON ARR, WE MADE A MAINT ENTRY INTO THE ACFT LOGBOOK. THIS WAS A SIMPLE MECHANICAL FAILURE THAT LED TO A POTENTIALLY DANGEROUS SIT. AT THE LEAST, IT CAUSED 1 OR MORE ACFT TO HAVE TO GO AROUND, AT AN ARPT (DCA) WITH UNIQUE ATC PROBS. THIS PROB HAS BEEN STUDIED MANY TIMES AND FEW TECHNOLOGY SOLUTIONS EXIST TO HELP ELIMINATE IT. I GIVE CREDIT TO THE ENGINEERS OF AIRBUS TO INCLUDE A WARNING SYS THAT SIMPLY ISSUES A CAUTION MESSAGE AFTER 1 MIN OF CONTINUOUS VHF XMISSION. WITHOUT THAT FEATURE, THIS PARTICULAR SIT WOULD HAVE ALMOST CERTAINLY BEEN WORSE. THE REAL PROB WITH THIS PARTICULAR MECHANICAL FAILURE IS HOW INSIDIOUS IT IS. BOTH TIMES WE EXPERIENCED THE FAILURE, IT WAS DURING THE READBACK, THEREFORE ANY PERIOD OF SILENCE AFTER THE XMISSION DID NOT SEEM UNUSUAL. ABSENT THE AIRBUS MONITORING AND CAUTION SYS, THE ONLY INDICATION OF A STUCK MIKE PROB IS A PROLONGED PERIOD OF SILENCE OR NON RESPONSE TO A XMISSION, NEITHER OF WHICH ARE ALL THAT UNUSUAL. THE REAL LONG-TERM SOLUTION TO THIS PROB IS A BETTER COM SYS. FOR MANY REASONS, INCLUDING THIS INCIDENT, I HAVE FELT THAT A MORE TECHNOLOGICALLY ADVANCED COM SYS SHOULD BE IN PLACE FOR THE AIRLINE INDUSTRY. THE OBVIOUS CHOICE AT THIS POINT IS A DATA LINK SYS, POSSIBLY USING THE ACARS SYS.

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.