Lost communication procedure, code 7600, and priority handling initiated by the flight crew of a B73...

Attributes
ACN	558473
Time
Date	200208
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : zoa.artcc
State Reference	CA
Altitude	msl bound lower : 9000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc tracon : o90.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 220 flight time total : 9000 flight time type : 6000
ASRS Report	558473
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 186 flight time total : 9000 flight time type : 500
ASRS Report	558474
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

At FL310 we noticed we had not heard any radio chatter for several mins. Since we were approaching top of descent we attempted communication with ZOA. After several calls with no acknowledgement nor reception of other aircraft we suspected radio failure. Extensive troubleshooting of both radios, mikes, circuit breakers, and headsets was conducted with still no communications with outside world at all. We even suspected stuck microphone, but eventually ruled it out. Several mins later, communications were reestablished. Normal descent was initiated and equipment checks were conducted. All radios and equipment appeared to operate normal. We suspected cause was those nasty stray 'trons.' once established direct intersection gilro and level 9000 ft, ZOA gave us a vector 25 degrees right for traffic. That was the last radio communication we heard for the next 7-9 mins. Suspecting multiple radio failure again, we conducted troubleshooting with no satisfaction. Since we were well right of course and approximately 25 mi from field we elected to squawk 7600 and transmit in the blind our intention to turn direct to sjc field. A couple of mins later, communications were reestablished. ZOA switched us to bay approach control. We asked for clearance to land early should the radios fail again. Bay approach control cleared us for visual runway 30R and landing. They also asked if we were 'operations normal' in the cockpit. We affirmed that we were. Landing and taxi went normal. Dispatch and maintenance were called once parked. Tower asked us to call bay approach control when able. The bay approach manager did not understand why we 'strayed' off course rather than intercepting VOR inbound to sjc. After explaining our sequence of events, he then understood it was ZOA that gave us the vector 25 degrees right for traffic before we lost all communications. He had become very concerned of a possible hijacking. We ended conversation agreeing that all appropriate procedures had been followed on both his part and ours.

Original NASA ASRS Text

Title: LOST COM PROC, CODE 7600, AND PRIORITY HANDLING INITIATED BY THE FLC OF A B737-300 WHEN THEY HAVE INTERMITTENT LOSS OF COM FREQ WITH CTR CTLR AT ZOA, CA.

Narrative: AT FL310 WE NOTICED WE HAD NOT HEARD ANY RADIO CHATTER FOR SEVERAL MINS. SINCE WE WERE APCHING TOP OF DSCNT WE ATTEMPTED COM WITH ZOA. AFTER SEVERAL CALLS WITH NO ACKNOWLEDGEMENT NOR RECEPTION OF OTHER ACFT WE SUSPECTED RADIO FAILURE. EXTENSIVE TROUBLESHOOTING OF BOTH RADIOS, MIKES, CIRCUIT BREAKERS, AND HEADSETS WAS CONDUCTED WITH STILL NO COMS WITH OUTSIDE WORLD AT ALL. WE EVEN SUSPECTED STUCK MIKE, BUT EVENTUALLY RULED IT OUT. SEVERAL MINS LATER, COMS WERE REESTABLISHED. NORMAL DSCNT WAS INITIATED AND EQUIP CHKS WERE CONDUCTED. ALL RADIOS AND EQUIP APPEARED TO OPERATE NORMAL. WE SUSPECTED CAUSE WAS THOSE NASTY STRAY 'TRONS.' ONCE ESTABLISHED DIRECT INTXN GILRO AND LEVEL 9000 FT, ZOA GAVE US A VECTOR 25 DEGS R FOR TFC. THAT WAS THE LAST RADIO COM WE HEARD FOR THE NEXT 7-9 MINS. SUSPECTING MULTIPLE RADIO FAILURE AGAIN, WE CONDUCTED TROUBLESHOOTING WITH NO SATISFACTION. SINCE WE WERE WELL R OF COURSE AND APPROX 25 MI FROM FIELD WE ELECTED TO SQUAWK 7600 AND XMIT IN THE BLIND OUR INTENTION TO TURN DIRECT TO SJC FIELD. A COUPLE OF MINS LATER, COMS WERE REESTABLISHED. ZOA SWITCHED US TO BAY APCH CTL. WE ASKED FOR CLRNC TO LAND EARLY SHOULD THE RADIOS FAIL AGAIN. BAY APCH CTL CLRED US FOR VISUAL RWY 30R AND LNDG. THEY ALSO ASKED IF WE WERE 'OPS NORMAL' IN THE COCKPIT. WE AFFIRMED THAT WE WERE. LNDG AND TAXI WENT NORMAL. DISPATCH AND MAINT WERE CALLED ONCE PARKED. TWR ASKED US TO CALL BAY APCH CTL WHEN ABLE. THE BAY APCH MGR DID NOT UNDERSTAND WHY WE 'STRAYED' OFF COURSE RATHER THAN INTERCEPTING VOR INBOUND TO SJC. AFTER EXPLAINING OUR SEQUENCE OF EVENTS, HE THEN UNDERSTOOD IT WAS ZOA THAT GAVE US THE VECTOR 25 DEGS R FOR TFC BEFORE WE LOST ALL COMS. HE HAD BECOME VERY CONCERNED OF A POSSIBLE HIJACKING. WE ENDED CONVERSATION AGREEING THAT ALL APPROPRIATE PROCS HAD BEEN FOLLOWED ON BOTH HIS PART AND OURS.

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.

Lost communication procedure, code 7600, and priority handling initiated by the flight crew of a B737-300 when they have intermittent loss of communication frequency with center controller at ZOA, ca.