B737-400 diverts when dual IRS dc fail lights illuminate due to dead battery.

Attributes
ACN	776337
Time
Date	200802
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 34000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 250 flight time type : 800
ASRS Report	776337
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : master caution light other flight crewa
Resolutory Action	flight crew : diverted to another airport
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

On the last leg of the day on a B737-400; cruising at FL340; we had a master caution light and IRS annunciator. The IRS showed both left and right dc fail lights on. We ran the QRH checklist for IRS dc fail (both lights on) which led us to discover our battery was depleted (approximately 8 volts) and the battery charger didn't seem to work (battery charger circuit breaker was 'in'). The checklist mentioned several inoperative system associated with loss of battery; mainly loss of fire detection capability. The checklist also mentioned to land as soon as practicable. With no battery and no fire detection; we diverted into ZZZ. Maintenance control; and dispatch concurred with the divert decision; and we debriefed with ZZZ maintenance and our flight attendants. Can't think of anything we would have done differently.

Original NASA ASRS Text

Title: B737-400 DIVERTS WHEN DUAL IRS DC FAIL LIGHTS ILLUMINATE DUE TO DEAD BATTERY.

Narrative: ON THE LAST LEG OF THE DAY ON A B737-400; CRUISING AT FL340; WE HAD A MASTER CAUTION LIGHT AND IRS ANNUNCIATOR. THE IRS SHOWED BOTH L AND R DC FAIL LIGHTS ON. WE RAN THE QRH CHKLIST FOR IRS DC FAIL (BOTH LIGHTS ON) WHICH LED US TO DISCOVER OUR BATTERY WAS DEPLETED (APPROX 8 VOLTS) AND THE BATTERY CHARGER DIDN'T SEEM TO WORK (BATTERY CHARGER CIRCUIT BREAKER WAS 'IN'). THE CHKLIST MENTIONED SEVERAL INOP SYS ASSOCIATED WITH LOSS OF BATTERY; MAINLY LOSS OF FIRE DETECTION CAPABILITY. THE CHKLIST ALSO MENTIONED TO LAND AS SOON AS PRACTICABLE. WITH NO BATTERY AND NO FIRE DETECTION; WE DIVERTED INTO ZZZ. MAINT CTL; AND DISPATCH CONCURRED WITH THE DIVERT DECISION; AND WE DEBRIEFED WITH ZZZ MAINT AND OUR FLT ATTENDANTS. CAN'T THINK OF ANYTHING WE WOULD HAVE DONE DIFFERENTLY.

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.