A B737-300 during climb out at FL270 experienced loss of #1 electronics bus. Returned to departure a...

Attributes
ACN	725923
Time
Date	200701
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 27000
Environment
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	climbout : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 167
ASRS Report	725923
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : failed #1 air data cpu other flight crewa other flight crewb
Resolutory Action	other
Consequence	other
Supplementary
Problem Areas	Chart Or Publication Aircraft
Primary Problem	Aircraft
Situations
Publication	QRH

Narrative:

We had departed ZZZ and during the climb out; we experienced a failure of the #1 115 vac electronics bus; as indicated by a tripped circuit breaker and loss of the #1 air data computer; TCAS; and egpws. This failure is interesting because this bus constitutes part of the #1 xfer bus; but its failure yields no warning on the electrical panel. Since the WX in ZZZ1 was 3/4 mi with snow; we elected to return to ZZZ where it was VFR. The remainder of the flight was conducted without incident. Callback conversation with reporter revealed the following information: when the #1 instrumentation began failing the circuit breaker panel was checked and #1 electronics bus 3 phase breaker was found tripped. Waited 2 mins and reset the breaker and it did not reset. The QRH does not cover this failure. The electronics bus is powered by the xfer bus but the remainder of the xfer bus was powered so no xfer bus 'off' light was illuminated. WX at the destination airport was not good so the decision was made to return to the departure airport. The cause of the failed bus was not reported by maintenance.

Original NASA ASRS Text

Title: A B737-300 DURING CLBOUT AT FL270 EXPERIENCED LOSS OF #1 ELECTRONICS BUS. RETURNED TO DEP ARPT. CAUSE OF BUS FAILURE UNKNOWN.

Narrative: WE HAD DEPARTED ZZZ AND DURING THE CLBOUT; WE EXPERIENCED A FAILURE OF THE #1 115 VAC ELECTRONICS BUS; AS INDICATED BY A TRIPPED CIRCUIT BREAKER AND LOSS OF THE #1 ADC; TCAS; AND EGPWS. THIS FAILURE IS INTERESTING BECAUSE THIS BUS CONSTITUTES PART OF THE #1 XFER BUS; BUT ITS FAILURE YIELDS NO WARNING ON THE ELECTRICAL PANEL. SINCE THE WX IN ZZZ1 WAS 3/4 MI WITH SNOW; WE ELECTED TO RETURN TO ZZZ WHERE IT WAS VFR. THE REMAINDER OF THE FLT WAS CONDUCTED WITHOUT INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: WHEN THE #1 INSTRUMENTATION BEGAN FAILING THE CIRCUIT BREAKER PANEL WAS CHKED AND #1 ELECTRONICS BUS 3 PHASE BREAKER WAS FOUND TRIPPED. WAITED 2 MINS AND RESET THE BREAKER AND IT DID NOT RESET. THE QRH DOES NOT COVER THIS FAILURE. THE ELECTRONICS BUS IS POWERED BY THE XFER BUS BUT THE REMAINDER OF THE XFER BUS WAS POWERED SO NO XFER BUS 'OFF' LIGHT WAS ILLUMINATED. WX AT THE DEST ARPT WAS NOT GOOD SO THE DECISION WAS MADE TO RETURN TO THE DEP ARPT. THE CAUSE OF THE FAILED BUS WAS NOT RPTED BY MAINT.

Data retrieved from NASA's ASRS site as of January 2009 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.

A B737-300 during climb out at FL270 experienced loss of #1 electronics bus. Returned to departure airport. Cause of bus failure unknown.