On descent a DC9-10 lost electrical power to the left bus. APU switched to power left bus.

Attributes
ACN	362705
Time
Date	199703
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : msp
State Reference	MN
Altitude	msl bound lower : 8000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : msp
Operator	common carrier : air carrier
Make Model Name	DC-9 10
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : atp pilot : flight engineer pilot : instrument pilot : cfi
Experience	flight time last 90 days : 150 flight time total : 12000 flight time type : 2800
ASRS Report	362705
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer oversight : pic
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa other other : unspecified cockpit
Resolutory Action	flight crew : overcame equipment problem other
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

In sum: on approach to msp the left air-conditioning electrical bus failed. Had off lights on xtie lockout, left generator, left air-conditioning bus, and pitot/stall warning heater. First officer was flying and we were on approach control descending to 8000 ft. We asked approach control for vectors so we could solve our electrical problem. The first officer flew the aircraft while I worked the cockpit operating manual procedures to restore power back to the left air-conditioning bus. APU power was switched to the left air-conditioning bus to restore power. Returned to msp for landing without further incident. Callback conversation with reporter revealed the following information: airplane was on descent about 8000 ft when pitot heat light came on with generator off light. Noticed generator voltage was below limits. The APU which was running was switched on to power the left bus. Went through cockpit operating procedures and proceeded to land. Maintenance replaced the left engine constant speed drive as corrective action.

Original NASA ASRS Text

Title: ON DSCNT A DC9-10 LOST ELECTRICAL PWR TO THE L BUS. APU SWITCHED TO PWR L BUS.

Narrative: IN SUM: ON APCH TO MSP THE L AIR-CONDITIONING ELECTRICAL BUS FAILED. HAD OFF LIGHTS ON XTIE LOCKOUT, L GENERATOR, LEFT AIR-CONDITIONING BUS, AND PITOT/STALL WARNING HEATER. FO WAS FLYING AND WE WERE ON APCH CTL DSNDING TO 8000 FT. WE ASKED APCH CTL FOR VECTORS SO WE COULD SOLVE OUR ELECTRICAL PROB. THE FO FLEW THE ACFT WHILE I WORKED THE COCKPIT OPERATING MANUAL PROCS TO RESTORE PWR BACK TO THE L AIR-CONDITIONING BUS. APU PWR WAS SWITCHED TO THE L AIR-CONDITIONING BUS TO RESTORE PWR. RETURNED TO MSP FOR LNDG WITHOUT FURTHER INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: AIRPLANE WAS ON DSCNT ABOUT 8000 FT WHEN PITOT HEAT LIGHT CAME ON WITH GENERATOR OFF LIGHT. NOTICED GENERATOR VOLTAGE WAS BELOW LIMITS. THE APU WHICH WAS RUNNING WAS SWITCHED ON TO PWR THE L BUS. WENT THROUGH COCKPIT OPERATING PROCS AND PROCEEDED TO LAND. MAINT REPLACED THE L ENG CONSTANT SPD DRIVE AS CORRECTIVE ACTION.

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.