B767 aircraft in cruise had a differential fault on the left AC system. Temporary loss of left side electrical until the APU was started and up to speed at which time it took the electrical load off the failed system. Flight crew requested priority handling but did not declare and emergency.

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Attributes
ACN	358159
Time
Date	199701
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : clt
State Reference	SC
Altitude	msl bound lower : 34000 msl bound upper : 34000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	B767 Undifferentiated or Other Model
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 : 25000
ASRS Report	358159
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Master caution light came on with icas messages (numerous) lft-btb-lft AC bus lft generator continued and several associated. Started APU but with run light on it did not pick up lft AC bus for 1 1/2 - 2 mins. During this period we started to divert to clt. (Also had a small whiff of smoke.) then APU picked up lft AC bus (because of smoke and generator operations). Lft btb closed leaving only lft generator control, lft engine bleed and lft pack off/pack inoperative lights on decision on then made it go to atl since operations were normal. Request priority handling just in case of a recurrence. Did not declare an emergency nor request emergency equipment to stand by. On landing, emergency equipment was standing by. Normal landing and taxi in. I was supposed to keep the airplane for the next leg to lax. The mechanic found differential fault message in east&east compartment. With that and the fact the APU would not pick up AC bus quickly I would not take aircraft. Equipment change was made.

Original NASA ASRS Text

Title: B767 ACFT IN CRUISE HAD A DIFFERENTIAL FAULT ON THE L AC SYS. TEMPORARY LOSS OF L SIDE ELECTRICAL UNTIL THE APU WAS STARTED AND UP TO SPD AT WHICH TIME IT TOOK THE ELECTRICAL LOAD OFF THE FAILED SYS. FLC REQUESTED PRIORITY HANDLING BUT DID NOT DECLARE AND EMER.

Narrative: MASTER CAUTION LIGHT CAME ON WITH ICAS MESSAGES (NUMEROUS) LFT-BTB-LFT AC BUS LFT GENERATOR CONTINUED AND SEVERAL ASSOCIATED. STARTED APU BUT WITH RUN LIGHT ON IT DID NOT PICK UP LFT AC BUS FOR 1 1/2 - 2 MINS. DURING THIS PERIOD WE STARTED TO DIVERT TO CLT. (ALSO HAD A SMALL WHIFF OF SMOKE.) THEN APU PICKED UP LFT AC BUS (BECAUSE OF SMOKE AND GENERATOR OPS). LFT BTB CLOSED LEAVING ONLY LFT GENERATOR CTL, LFT ENG BLEED AND LFT PACK OFF/PACK INOP LIGHTS ON DECISION ON THEN MADE IT GO TO ATL SINCE OPS WERE NORMAL. REQUEST PRIORITY HANDLING JUST IN CASE OF A RECURRENCE. DID NOT DECLARE AN EMER NOR REQUEST EMER EQUIP TO STAND BY. ON LNDG, EMER EQUIP WAS STANDING BY. NORMAL LNDG AND TAXI IN. I WAS SUPPOSED TO KEEP THE AIRPLANE FOR THE NEXT LEG TO LAX. THE MECH FOUND DIFFERENTIAL FAULT MESSAGE IN E&E COMPARTMENT. WITH THAT AND THE FACT THE APU WOULD NOT PICK UP AC BUS QUICKLY I WOULD NOT TAKE ACFT. EQUIP CHANGE WAS MADE.

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.