Mechanic report regarding follow-up of an in-flight write-up on an HF transmitter problem. After tro...

Narrative:

On flight from XXX to ZZZ, dc-10, an inbound write-up stated that #1 HF will not transmit. When tuning, tone yyyts 15 seconds. I ran a 30 day history on communications for the aircraft. No prior history noted. I checked for faults both on the #1 HF transmitter and receiver, and on the annunciator panel under the flight engineer's worktable. Again no faults were noted. I then re-racked and checked for damaged or loose connectors and pins. On the #1 HF transmitter and receiver no problems were found. I accomplished a ground check of the #1 HF per maintenance manual. All system checked good. After the flight crew did their operations checks, the aircraft was ready to go. After the aircraft left, I was told the next day that about 200 mi from YYY to VVV, the aircraft had to divert to ZZZ because it had lost both #1 and #2 HF transmitters. They were unable to transmit. This is very peculiar to me having lost both HF radios at that point. Everything was in working order leaving las. The fix in ZZZ was to change both #1 and #2 HF transmitters and couplers. The problem was apparently solved with no repeat as yet. Again I state that having both HF radios not to transmit is very odd. In this system, through a wiring diagram, there are 2 keying relays and, if one was to stick this could have caused the problem. At the time I released the aircraft, all system checks were good with a backup operations check by the flight crew. If this should occur again on this particular aircraft or another one, one should also troubleshoot or pay close attention to the keying relays for any further problems down the line. Callback conversation with reporter revealed the following information: reporter states that he did tell his company and the maintenance people about checking the 2 keying relays for sticking when troubleshooting HF radio problems. He is surprised that there has been no FAA follow up since the aircraft had to divert. Analyst also spoke with air carrier pilots who know about this problem. They routinely will pull a circuit breaker, then activate it again when such a problem occurs. This allows the relay to release and it will usually work again.

Original NASA ASRS Text

Title: MECH RPT REGARDING FOLLOW-UP OF AN INFLT WRITE-UP ON AN HF XMITTER PROB. AFTER TROUBLESHOOTING THE PROB AND ACFT RELEASE, BOTH HF RADIOS FAILED INFLT.

Narrative: ON FLT FROM XXX TO ZZZ, DC-10, AN INBOUND WRITE-UP STATED THAT #1 HF WILL NOT XMIT. WHEN TUNING, TONE YYYTS 15 SECONDS. I RAN A 30 DAY HISTORY ON COMS FOR THE ACFT. NO PRIOR HISTORY NOTED. I CHKED FOR FAULTS BOTH ON THE #1 HF XMITTER AND RECEIVER, AND ON THE ANNUNCIATOR PANEL UNDER THE FE'S WORKTABLE. AGAIN NO FAULTS WERE NOTED. I THEN RE-RACKED AND CHKED FOR DAMAGED OR LOOSE CONNECTORS AND PINS. ON THE #1 HF XMITTER AND RECEIVER NO PROBS WERE FOUND. I ACCOMPLISHED A GND CHK OF THE #1 HF PER MAINT MANUAL. ALL SYS CHKED GOOD. AFTER THE FLC DID THEIR OPS CHKS, THE ACFT WAS READY TO GO. AFTER THE ACFT LEFT, I WAS TOLD THE NEXT DAY THAT ABOUT 200 MI FROM YYY TO VVV, THE ACFT HAD TO DIVERT TO ZZZ BECAUSE IT HAD LOST BOTH #1 AND #2 HF XMITTERS. THEY WERE UNABLE TO XMIT. THIS IS VERY PECULIAR TO ME HAVING LOST BOTH HF RADIOS AT THAT POINT. EVERYTHING WAS IN WORKING ORDER LEAVING LAS. THE FIX IN ZZZ WAS TO CHANGE BOTH #1 AND #2 HF XMITTERS AND COUPLERS. THE PROB WAS APPARENTLY SOLVED WITH NO REPEAT AS YET. AGAIN I STATE THAT HAVING BOTH HF RADIOS NOT TO XMIT IS VERY ODD. IN THIS SYS, THROUGH A WIRING DIAGRAM, THERE ARE 2 KEYING RELAYS AND, IF ONE WAS TO STICK THIS COULD HAVE CAUSED THE PROB. AT THE TIME I RELEASED THE ACFT, ALL SYS CHKS WERE GOOD WITH A BACKUP OPS CHK BY THE FLC. IF THIS SHOULD OCCUR AGAIN ON THIS PARTICULAR ACFT OR ANOTHER ONE, ONE SHOULD ALSO TROUBLESHOOT OR PAY CLOSE ATTN TO THE KEYING RELAYS FOR ANY FURTHER PROBS DOWN THE LINE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE DID TELL HIS COMPANY AND THE MAINT PEOPLE ABOUT CHKING THE 2 KEYING RELAYS FOR STICKING WHEN TROUBLESHOOTING HF RADIO PROBS. HE IS SURPRISED THAT THERE HAS BEEN NO FAA FOLLOW UP SINCE THE ACFT HAD TO DIVERT. ANALYST ALSO SPOKE WITH ACR PLTS WHO KNOW ABOUT THIS PROB. THEY ROUTINELY WILL PULL A CIRCUIT BREAKER, THEN ACTIVATE IT AGAIN WHEN SUCH A PROB OCCURS. THIS ALLOWS THE RELAY TO RELEASE AND IT WILL USUALLY WORK AGAIN.

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.

Attributes
ACN	325936
Time
Date	199601
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zzz
State Reference	US
Aircraft 1
Controlling Facilities	artcc : zzz
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	other personnel other
Qualification	other other : other
ASRS Report	325936
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Mechanic report regarding follow-up of an in-flight write-up on an HF transmitter problem. After troubleshooting the problem and aircraft release, both HF radios failed in-flight.