A pilot of a B747-400 noted that the prescribed test duration for the emergency power system may be ...

Attributes
ACN	802581
Time
Date	200809
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	ground : parked
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 240 flight time total : 15000 flight time type : 2500
ASRS Report	802581
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

During preflight checks; I found that the standby emergency power system could not maintain the emergency electrical load. When I placed the standby power switch to bat; all upper EICAS's and the left CDU failed after about 10 seconds. I am in the habit of keeping the test going for at least 15 seconds. The failure we experienced did not manifest itself the first time for 10 seconds into the test. The system subsequently failed 10 of 12 tests and the problem was a faulty APU standby inverter; and the failures occurred between 1 and 70 seconds. My concern is that the test procedure that is published in the flight manual is inadequate. That procedure can be accomplished in less than 5 seconds; and would not have exhibited the failure. Had this failure gone unnoticed by performing only the minimally-required test as published in the flight manual; an in-flight loss of electrical power could have resulted in loss of the aircraft. The test procedure needs to be changed to require more than just a momentary (5 seconds or less) check of the system. Rather; the standby power switch should be placed into the bat position for at least 30 seconds to see that the system can sustain the load and normal parameters are observed.

Original NASA ASRS Text

Title: A PLT OF A B747-400 NOTED THAT THE PRESCRIBED TEST DURATION FOR THE EMER PWR SYSTEM MAY BE INADEDEQUATE LENGTH TO PROPERLY TEST THE APU STANDBY INVERTER.

Narrative: DURING PREFLIGHT CHECKS; I FOUND THAT THE STANDBY EMERGENCY POWER SYSTEM COULD NOT MAINTAIN THE EMERGENCY ELECTRICAL LOAD. WHEN I PLACED THE STANDBY POWER SWITCH TO BAT; ALL UPPER EICAS'S AND THE LEFT CDU FAILED AFTER ABOUT 10 SECONDS. I AM IN THE HABIT OF KEEPING THE TEST GOING FOR AT LEAST 15 SECONDS. THE FAILURE WE EXPERIENCED DID NOT MANIFEST ITSELF THE FIRST TIME FOR 10 SECONDS INTO THE TEST. THE SYSTEM SUBSEQUENTLY FAILED 10 OF 12 TESTS AND THE PROBLEM WAS A FAULTY APU STANDBY INVERTER; AND THE FAILURES OCCURRED BETWEEN 1 AND 70 SECONDS. MY CONCERN IS THAT THE TEST PROCEDURE THAT IS PUBLISHED IN THE FLIGHT MANUAL IS INADEQUATE. THAT PROCEDURE CAN BE ACCOMPLISHED IN LESS THAN 5 SECONDS; AND WOULD NOT HAVE EXHIBITED THE FAILURE. HAD THIS FAILURE GONE UNNOTICED BY PERFORMING ONLY THE MINIMALLY-REQUIRED TEST AS PUBLISHED IN THE FLIGHT MANUAL; AN INFLT LOSS OF ELECTRICAL POWER COULD HAVE RESULTED IN LOSS OF THE AIRCRAFT. THE TEST PROCEDURE NEEDS TO BE CHANGED TO REQUIRE MORE THAN JUST A MOMENTARY (5 SECONDS OR LESS) CHECK OF THE SYSTEM. RATHER; THE STANDBY POWER SWITCH SHOULD BE PLACED INTO THE BAT POSITION FOR AT LEAST 30 SECONDS TO SEE THAT THE SYSTEM CAN SUSTAIN THE LOAD AND NORMAL PARAMETERS ARE OBSERVED.

Data retrieved from NASA's ASRS site as of May 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 pilot of a B747-400 noted that the prescribed test duration for the emergency power system may be inadedequate length to properly test the APU standby inverter.