WING-BODY OVERHEAT can we go?

[Driver170 42]

Sitting on the ground just before push and i got a wing body overheat! Carried out the QRH and this didn't solve it? Is it a electrical fault or what? Can we dispatch?

[Gwhaarmann 3]

No. It means that you may have duct leak in the wing or air conditioning bay. Must be repaired before flight. I used to work on airliners.

[Korber 4]

If warning light does not extinguish by closing the isolation valve and the engines/apu bleed valves (engines/APU operating), that means it is an indication and not a real air leak problem.

Real or indicating you can dispatch, but with serious operating limitations:

-Airplane is not operated in known or forecast icing conditions

-Limit altitude to FL 250

 

26.2 Fire Protection-MMEL

 

26-12 Wing-Body Overheat Detector System (Left)

Except for ER operations, may be inoperative provided:

a. Right pack and engine bleed is used for pressurization only.

b. Use of APU is prohibited except for engine start.

c. Isolation valve and left engine bleed valve remain closed for all operations

except engine start.

d. Airplane is not operated in known or forecast icing conditions.

MAINTENANCE NOTE

Refer to DDG item 21-01-01 (M) procedure, as applicable, for information when

the left pack is not used.

OPERATIONS (O)*

1. Refer to DDG Item 21-01-01 (O) procedure for information when the left

pack is not used.

2. Except for engine start, do not use the APU for pneumatic air supply and/or

electrical power.

3. After engine start, make sure that:

A. ISOLATION VALVE switch is set to CLOSE

B. APU switch is set to OFF

C. L PACK switch is set to OFF

D. R PACK set as desired.

4. Do not dispatch into known icing or forecast icing conditions.

 

26-13 Wing-Body Overheat Detector System (Right)

Except for ER operations, may be inoperative provided:

a. Left pack and left engine or APU bleed air is used for pressurization only.

b. Isolation valve and right engine bleed valve remain closed for all operations

except engine start.

c. Airplane is not operated in known or forecast icing conditions.

MAINTENANCE NOTE

Refer to DDG item 21-01-01 (M) procedure, as applicable, for information when

the right pack is not used.

OPERATIONS (O)*

1. Refer to DDG Item 21-01-01 (O) procedure for information when the right

pack is not used.

2. After engine start, make sure that:

A. ISOLATION VALVE is set to CLOSE.

B. R PACK switch is set to OFF

C. L PACK as desired.

3. Do not dispatch into known icing or forecast icing conditions.

For -300/-400/-500/-600/-700/-800/-900:

4. Increased air flow will occur when flaps are extended (takeoff and landing)

if the APU is used instead of engine bleed to supply bleed air to the left

pack.

5. With the L PACK switch in AUTO, the pack operates in the high flow mode.

6. Do not set the L PACK to HIGH for takeoff and landing with the engine

bleed on.

7. Do not use APU bleed air at altitudes above 17,000 feet.

 

*OPERATIONS (O)

1. When dispatching with one operating pack supplied by engine bleed air on

takeoff:

A. Determine V1(MCG) based on engine bleed for packs OFF.

B. Determine takeoff performance based on packs AUTO.

2. Limit altitude to FL 250.

3. ER operations are not allowed.

4. For galley 4B food cart chiller installed, use only one chiller inflight.

5. Set R RECIRC FAN switch to OFF.

6. Set the PACK switch for the inoperative pack to HIGH.

7. Position the ISOLATION VALVE switch to CLOSE.

8. For increased air flow when the flaps are extended (takeoff and landing),

use the APU to supply bleed air to the operating pack.

 

A. Right pack inoperative

1) Do the Supplementary Procedure - Air Systems “No Engine

Bleed Takeoff and Landing” (Refer to the Flight Crew

Operations Manual).

NOTE: Keep the ISOLATION VALVE switch in the CLOSE

position.

 

B. Left pack inoperative - PRIOR to takeoff or landing

1) Engine No. 1 BLEED air switch to OFF

2) R PACK switch to AUTO

3) L PACK switch to OFF

4) ISOLATION VALVE switch to OPEN

5) Engine No. 2 BLEED air switch to OFF

6) APU BLEED air switch to ON.

 

C. Left pack inoperative - AFTER takeoff or landing

1) APU BLEED air switch to OFF

2) Engine No. 2 BLEED air switch to ON

3) ISOLATION VALVE switch to CLOSE

4) Engine No. 1 BLEED air switch to ON.

21-01

 

[Driver170 42]

Yeh i ran through all QRH checks and it still wouldn't extinguish! Thanks for helping out.

 

Where did you get that list from?

[ExNusquam 11]

Its from the Master Minimum Equipment List (MMEL). It is the Regulatory-Body approved list put together by the manufacturer for all equipment that can be broken on an airplane, and how to placard the broken equipment and how to operate the airplane with that equipment inop. Airlines have their own (approved) MEL, which is always more restrictive than the MMEL; basically airlines pick and chose what they want from the MMEL.

 

You can view all MMELs here: http://fsims.faa.gov/PICResults.aspx?mode=Publication&doctype=MMEL

[JoeDiamond 67]

I had that exact MEL last trip, left side wing-body overheat detection.  It's a real pain, can't use the APU except for engine start, cant use the left pack or bleed, can't go above FL250, can't fly in icing conditions.

 

That one is pretty rare though.

[Driver170 42]

I had both on left and right

[Stearmandriver 2,205]

Just for discussion sake (cause I'm THAT bored), why are we thinking that MEL applies to this situation? I mean, assuming this was a real duct leak. The MEL looks like it allows you to fly with a detector inop, as long as you isolate that side from bleed air. But I'm not thinking you could actually dispatch under it with a known duct leak. I mean, if the write up was for a genuine overheat, they couldn't sign it off by MELing the detector. Once mx determined it was a false indication, THEN they'd MEL the detector. But if it was real there'd need to be an inspection for thermal damage etc before the plane could fly. Point is, in this situation in the real world you wouldn't be MELing this, you'd be pulling back into the gate, shutting down and calling mx. Or am I misreading it? I don't mean to be "that guy" lol...

[Copper. 78]

The operating crew would make a decision whether to return to the blocks based on company guidance in the manuals and/or communications with maintenance on VHF/SATCOM/HF.

 

If crew return to blocks, we'd endeavour to meet them there, get a brief from you guys, run some tests, find the problem, then develop a solution. At this point, depending on the situation, we'd either apply MEL relief, carry out immediate corrective actions, or ground the airplane.

 

If it's just a detection issue, then I'm sure we'd apply MEL relief if it's available, not too restrictive, and agreeable to relevant stakeholders (I don't have the DDG on hand). If a physical pneumatic leak is identified, then corrective action should/must follow - that could come in many forms - replacement of faulty parts, an approval to do a temporary repair if you can etc. these decisions are made on an adhoc basis.

[JoeDiamond 67]

In our case we inherited the airplane with the MEL already in place. Based on the entries in the AML it was found to be a detector issue, not an actual pneumatic leak.

 

This particular item cannot be placarded by the flight crew so a return to gate would be required in any case.