Narrative:

On okc-lo sector, frequency 128.4/290.2, if the transmitter is keyed continuously for more than 28-30 seconds, a chain of events is initiated which ultimately unkeys the transmitter even while the controller is still issuing control instructions. On jan/xx/97, XX18 pm local, I was giving an aircraft the ads WX, followed by dfw landing conditions. In the middle of the dfw conditions, my transmitter became inoperative. Had these been control instructions, the consequences would have been more than just the inconvenience of reading back the WX. This transmitter 'automatic-termination' problem has existed since vscs was installed. My supervisor says 'it's always been that way.' I consider it an unsafe situation. This 'automatic- termination' feature exists on at least 4 of our 6 sectors. Callback conversation with reporter revealed the following information: reporter stated that he was told by the facility manager that automatic terminate of the transmitter has always been that way in order to prevent overheating of the transmitter equipment. Reporter stated that prior to the vscs equipment, there was no indication that the transmitter had shutoff and indicated that there is an aural alarm as well as a screen printout showing a loss of the transmitter. Reporter stated that it occurs during lengthy xmissions such as WX or flight plan information and that once the transmitter is unkeyed it is automatically reset for operations.

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Original NASA ASRS Text

Title: RPTR CLAIMS XMITTER HAS AUTO TERMINATION PROB IF KEYED FOR MORE THAN 28-30 SECONDS. RPTR CONSIDERS IT AN UNSAFE SIT.

Narrative: ON OKC-LO SECTOR, FREQ 128.4/290.2, IF THE XMITTER IS KEYED CONTINUOUSLY FOR MORE THAN 28-30 SECONDS, A CHAIN OF EVENTS IS INITIATED WHICH ULTIMATELY UNKEYS THE XMITTER EVEN WHILE THE CTLR IS STILL ISSUING CTL INSTRUCTIONS. ON JAN/XX/97, XX18 PM LCL, I WAS GIVING AN ACFT THE ADS WX, FOLLOWED BY DFW LNDG CONDITIONS. IN THE MIDDLE OF THE DFW CONDITIONS, MY XMITTER BECAME INOP. HAD THESE BEEN CTL INSTRUCTIONS, THE CONSEQUENCES WOULD HAVE BEEN MORE THAN JUST THE INCONVENIENCE OF READING BACK THE WX. THIS XMITTER 'AUTO-TERMINATION' PROB HAS EXISTED SINCE VSCS WAS INSTALLED. MY SUPVR SAYS 'IT'S ALWAYS BEEN THAT WAY.' I CONSIDER IT AN UNSAFE SIT. THIS 'AUTO- TERMINATION' FEATURE EXISTS ON AT LEAST 4 OF OUR 6 SECTORS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE WAS TOLD BY THE FACILITY MGR THAT AUTO TERMINATE OF THE XMITTER HAS ALWAYS BEEN THAT WAY IN ORDER TO PREVENT OVERHEATING OF THE XMITTER EQUIP. RPTR STATED THAT PRIOR TO THE VSCS EQUIP, THERE WAS NO INDICATION THAT THE XMITTER HAD SHUTOFF AND INDICATED THAT THERE IS AN AURAL ALARM AS WELL AS A SCREEN PRINTOUT SHOWING A LOSS OF THE XMITTER. RPTR STATED THAT IT OCCURS DURING LENGTHY XMISSIONS SUCH AS WX OR FLT PLAN INFO AND THAT ONCE THE XMITTER IS UNKEYED IT IS AUTOMATICALLY RESET FOR OPS.

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.