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An air carrier flight crew discovered that their stuck microphone had blocked center frequency for an extended period of time. The captain reported that the problem was insidious because the radios had operated normally until level off at cruise.
| Attributes | |
| ACN | 333275 |
| Time | |
| Date | 199604 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : abq |
| State Reference | NM |
| Altitude | msl bound lower : 33000 msl bound upper : 33000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zab |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 180 flight time total : 10000 flight time type : 4000 |
| ASRS Report | 333275 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 150 flight time total : 10000 flight time type : 4000 |
| ASRS Report | 332757 |
| Events | |
| Anomaly | aircraft equipment problem : less severe |
| Independent Detector | other flight crewa |
| Resolutory Action | other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | other |
Narrative:
Microphone stuck open. Blocked center frequency. This was an insidious problem because communications for flight had been normal all the way to level off at cruise. Detection of the problem was difficult because virtually no feedback or radio noise was heard over headsets (headsets -- no overhead speakers were in use). It was not until we realized an absence of radio chatter that we had any indication of a radio problem. Blocked or stuck mikes are not an uncommon problem. After the situation was remedied we discussed measures which could indicate when a microphone was open. The use of a light which would illuminate when xmissions were made or a tone which sounds after a microphone transmitter is open after a given time may be possible solutions. Supplemental information from acn 332757: during cruise we checked in with ZAB. Some time after that we lost communication because of our stuck microphone. I had removed my hand microphone from its holder clip and placed it on a flat surface.
Original NASA ASRS Text
Title: AN ACR FLC DISCOVERED THAT THEIR STUCK MIKE HAD BLOCKED CTR FREQ FOR AN EXTENDED PERIOD OF TIME. THE CAPT RPTED THAT THE PROB WAS INSIDIOUS BECAUSE THE RADIOS HAD OPERATED NORMALLY UNTIL LEVEL OFF AT CRUISE.
Narrative: MIKE STUCK OPEN. BLOCKED CTR FREQ. THIS WAS AN INSIDIOUS PROB BECAUSE COMS FOR FLT HAD BEEN NORMAL ALL THE WAY TO LEVEL OFF AT CRUISE. DETECTION OF THE PROB WAS DIFFICULT BECAUSE VIRTUALLY NO FEEDBACK OR RADIO NOISE WAS HEARD OVER HEADSETS (HEADSETS -- NO OVERHEAD SPEAKERS WERE IN USE). IT WAS NOT UNTIL WE REALIZED AN ABSENCE OF RADIO CHATTER THAT WE HAD ANY INDICATION OF A RADIO PROB. BLOCKED OR STUCK MIKES ARE NOT AN UNCOMMON PROB. AFTER THE SIT WAS REMEDIED WE DISCUSSED MEASURES WHICH COULD INDICATE WHEN A MIKE WAS OPEN. THE USE OF A LIGHT WHICH WOULD ILLUMINATE WHEN XMISSIONS WERE MADE OR A TONE WHICH SOUNDS AFTER A MIKE XMITTER IS OPEN AFTER A GIVEN TIME MAY BE POSSIBLE SOLUTIONS. SUPPLEMENTAL INFO FROM ACN 332757: DURING CRUISE WE CHKED IN WITH ZAB. SOME TIME AFTER THAT WE LOST COM BECAUSE OF OUR STUCK MIKE. I HAD REMOVED MY HAND MIKE FROM ITS HOLDER CLIP AND PLACED IT ON A FLAT SURFACE.
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.