A B737-800 on climb at 9000 ft declared an emergency and returned to ZZZ due to left wing body overh...

Attributes
ACN	628688
Time
Date	200408
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	climbout : initial climbout : intermediate altitude
Route In Use	departure sid : n/a
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	628688
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	628687
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : body overheat system warning other flight crewa other flight crewb
Resolutory Action	flight crew : declared emergency
Consequence	other other
Supplementary
Problem Areas	Maintenance Human Performance Aircraft Chart Or Publication
Primary Problem	Aircraft

Narrative:

Right wing body overheat illuminated on taxi out, light was extinguished as per checklist re-illuminated and we confirmed with maintenance. Light was extinguished again as per checklist procedure, initiated flight with APU off, right engine bleed off, right pack off, and isolation valve closed. At 9000 ft on climb out, the left wing body overheat came on. We powered back on left engine, declared an emergency, and returned to ZZZ. Got to go, new aircraft at gate, and into min rest at ZZZ1. Supplemental information from acn 628687: during taxi out, right wing body overheat light illuminated. We followed checklist and in 2 mins the light went out. The aircraft was extremely warm, we reset the iso-valve, bleed valve and tuned on right pack to help cool aircraft. Our departure was delayed due to departures, 10 mins later the same right wing body overheat light illuminated again. We re-did the checklist, notified maintenance of our problem and dispatch ok'd the flight to continue on 1 bleed/1 pack 25000 ft restriction an no icing en route. We departed and climbing out of 9000 ft, the left wing body overheat illuminated and I immediately declared an emergency. We headed to ZZZ and first officer told the flight attendant's via interphone we were returning and to prepare for immediate return. As first officer worked the checklists, I called for fire trucks to be there, feeling this was a very high potential of a 'real bleed leak.' on a 9 mile final, I made a PA to state to the crew to prepare for an emergency landing. We landed with a tailwind, and got the ok to taxi to a gate. Callback conversation with reporter acn 628688 revealed the following information: the reporter stated it appeared odd that two separate sensing loops would fail and give a false warning. The reporter said on the ground, maintenance made a bite check of the system and found the control unit had failed. The reporter stated the control unit was replaced and both sensing loops checked ok. The reporter said the airplane was a B737-800.

Original NASA ASRS Text

Title: A B737-800 ON CLB AT 9000 FT DECLARED AN EMER AND RETURNED TO ZZZ DUE TO L WING BODY OVERHEAT WARNING ON. R WING BODY OVERHEAT PREVIOUSLY DEFERRED AS INOP.

Narrative: RIGHT WING BODY OVERHEAT ILLUMINATED ON TAXI OUT, LIGHT WAS EXTINGUISHED AS PER CHECKLIST RE-ILLUMINATED AND WE CONFIRMED WITH MAINT. LIGHT WAS EXTINGUISHED AGAIN AS PER CHECKLIST PROC, INITIATED FLIGHT WITH APU OFF, R ENG BLEED OFF, R PACK OFF, AND ISOLATION VALVE CLOSED. AT 9000 FT ON CLB OUT, THE L WING BODY OVERHEAT CAME ON. WE POWERED BACK ON L ENG, DECLARED AN EMER, AND RETURNED TO ZZZ. GOT TO GO, NEW ACFT AT GATE, AND INTO MIN REST AT ZZZ1. SUPPLEMENTAL INFO FROM ACN 628687: DURING TAXI OUT, R WING BODY OVERHEAT LIGHT ILLUMINATED. WE FOLLOWED CHECKLIST AND IN 2 MINS THE LIGHT WENT OUT. THE ACFT WAS EXTREMELY WARM, WE RESET THE ISO-VALVE, BLEED VALVE AND TUNED ON R PACK TO HELP COOL ACFT. OUR DEP WAS DELAYED DUE TO DEPS, 10 MINS LATER THE SAME R WING BODY OVERHEAT LIGHT ILLUMINATED AGAIN. WE RE-DID THE CHECKLIST, NOTIFIED MAINT OF OUR PROB AND DISPATCH OK'D THE FLT TO CONTINUE ON 1 BLEED/1 PACK 25000 FT RESTRICTION AN NO ICING ENRTE. WE DEPARTED AND CLBING OUT OF 9000 FT, THE L WING BODY OVERHEAT ILLUMINATED AND I IMMEDIATELY DECLARED AN EMER. WE HEADED TO ZZZ AND FO TOLD THE FA'S VIA INTERPHONE WE WERE RETURNING AND TO PREPARE FOR IMMEDIATE RETURN. AS FO WORKED THE CHECKLISTS, I CALLED FOR FIRE TRUCKS TO BE THERE, FEELING THIS WAS A VERY HIGH POTENTIAL OF A 'REAL BLEED LEAK.' ON A 9 MILE FINAL, I MADE A PA TO STATE TO THE CREW TO PREPARE FOR AN EMER LNDG. WE LANDED WITH A TAILWIND, AND GOT THE OK TO TAXI TO A GATE. CALLBACK CONVERSATION WITH RPTR ACN 628688 REVEALED THE FOLLOWING INFO: THE RPTR STATED IT APPEARED ODD THAT TWO SEPARATE SENSING LOOPS WOULD FAIL AND GIVE A FALSE WARNING. THE RPTR SAID ON THE GND, MAINT MADE A BITE CHECK OF THE SYSTEM AND FOUND THE CTL UNIT HAD FAILED. THE RPTR STATED THE CTL UNIT WAS REPLACED AND BOTH SENSING LOOPS CHECKED OK. THE RPTR SAID THE AIRPLANE WAS A B737-800.

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.

A B737-800 on climb at 9000 ft declared an emergency and returned to ZZZ due to left wing body overheat warning on. Right wing body overheat previously deferred as inoperative.