737NG Wing-body overheat on ground

[Nestle737]

Hi Guys,
I was discussing with an instructor about Wing-body Overheat on ground 737NG.
After you do the Wing-body Overheat NNC you isolated the system(Left side) and the Wing-body Overheat light extinguishes.
But you are still on the ground. If we check MEL ATA 26-12 it talks about the Wing-body Overheat System INOP, I think this checklist is not applicable as the system is working fine and telling you about the overheat Condition.
So is this a go (the light already extinguished because you isolated the problem and we assume single bleed operation on the opposite side) or no-go item ( as there is a possible leak in the bleed duct and should be investigated first by maintenance for any damage caused)
Thanks for your thoughts...

[Mattia1997]

I would say that as the WING BODY OVHT indicates a leak, the safest course of action would be to seek maintenance assistance while still on the ground.

[Checkboard]

You've turned off the hot air, the light goes out to confirm that, you can continue as you have already dispatched for that flight (so the MEL doesn't apply, although its useful for decision making) ... although wing anti-ice isn't available as it would now be assymetric, so flight into icing conditions is a no - go.

This doesn't mean that continuing is a great idea, you understand, just that it's legal/possible.

[+TSRA]

I see two separate questions here from your post. But, in short, I'd call maintenance and follow their advice. If they say go, then go. If they say don't go, don't go.

1. Is MEL 26-12-01 applicable?

• While it is most likely that the light is illuminated for a leak, it is also possible to get the light because of faulty equipment (sensor, detector, etc) or because of direct sunlight on a hot day (I've heard of the first two, been told by an instructor about the third). For these reasons, you don't know whether the MEL is applicable or not, and only a chat with maintenance will let you know. Leave it to them to decide if it is applicable or not, that's what they're paid for.

2. Is this a Go or No-Go Decision?

• While the QRH doesn't say anything about altitude, the MEL has a series of restrictions you want to consider, should it be applied You'll be restricted to FL250 on your next flight, and you won't be able to enter known icing conditions (for this flight or the next flight), and you won't be able to use the APU at your next airport once the MEL is applied, so you better have ground power and ground air. This is now not only a talk with maintenance but with your controlling dispatcher about flight routings, altitudes, and contingencies, just in case. Depending on your jurisdiction, the flight dispatcher may still have co-authority over the flight on the ground (they do where I work until power is applied for takeoff), so they'll have input into your scenario too.

[BraceBrace]

Originally Posted by +TSRA

I see two separate questions here from your post. But, in short, I'd call maintenance and follow their advice. If they say go, then go. If they say don't go, don't go.

Your response sounds very theoretical. To be honest, in many companies the reply will be very easy: go. Asking the question like this is not going to help you a lot. In many companies you need to inform dispatch very clearly on issues that in this case are not very clear. They have no clue what a wing body overheat system is, and you have no MEL item to reference to.

On this sector in theory you legally can leave for the flight. However on the next flight you will be grounded as you don't know the cause of the problem. So you need maintenance.

My course of action would be easy: call maintenance and tell them you are AOG. It is their choice to be AOG at the airport of departure, or the airport of destination. Secondary failures is something to take into account, but in general the chances of having secondary failures is very remote. Pressurisation comes to mind in the far back of my head though.

[+TSRA]

Your response sounds very theoretical. To be honest, in many companies the reply will be very easy: go.

Well, given that it was a discussion between instructor and student, and I've been an instructor and check pilot, yeah. I suppose it does come off that way. But I always look at these situations as though we're training Captains and future Captains on how to think problems through. I never talked about subsequent failures, just that the warning light can illuminate for different things other than, in this case, a bleed leak. While the MEL may not apply for the light in one case, it may in another and we don't know that until we talk to maintenance. When reading the first post, it struck me that the OP may not yet have had the experience where a straightforward situation is not straightforward at all, hence I suppose I did put more theory into my response.

With that said, it's certainly not my experience that maintenance will just say go. Maybe I've been lucky, but at the four airlines I've worked for, it was the opposite of what you're suggesting. I'd think we would be OK, but they'd apply the MEL anyway (assuming it applies). Hence, if they say go, go. If they say don't go, don't go. I'm not naive enough to think this is how it is all around the world, but we can only ever answer based on our experiences, no?

Also, while a dispatcher may not know about the aircraft systems, they nevertheless have co-authority over the flight until takeoff. That co-authority means that I call the dispatcher first to tell them we've had a problem and that I need to talk to maintenance. In my outfit, this ends up being a conference call between me, the engineer, and the dispatcher. I tell the engineer what happened, they tell me whether or not to apply the MEL and, if needed, the dispatcher begins working on a new OFP. It ends up being far more collaborative than other spots may be and often avoids the need for me to say "I'm AOG, deal with it" - although, I do keep that in my back pocket if I feel I need it.

[BraceBrace]

Originally Posted by +TSRA

Well, given that it was a discussion between instructor and student, and I've been an instructor and check pilot, yeah. I suppose it does come off that way. But I always look at these situations as though we're training Captains and future Captains on how to think problems through. I never talked about subsequent failures, just that the warning light can illuminate for different things other than, in this case, a bleed leak. While the MEL may not apply for the light in one case, it may in another and we don't know that until we talk to maintenance. When reading the first post, it struck me that the OP may not yet have had the experience where a straightforward situation is not straightforward at all, hence I suppose I did put more theory into my response.

Well I replied as a training captain...

The reality behind your theory is that the PIC has final authority. There is one thing you always have to keep in mind: it’s not because they say ’go’ it is that clear cut because you are sitting in the tube and you are responsible for your passengers/freight. They have authority to stop you from going, a simple solution we usually accept as it is safe. The problems arises when they say ’go’ and in those instances your new PIC needs learn to protect himself, or even stand up and say ’no’. That’s what I mean with the difference between theory and reality.

[meleagertoo]

Surely IFR flight is assumed to include icing conditions - so this is clearly a no-go item then? Apart from which it strikes me as being one heck of an assumption that Wing-Body Overheat is the entire story - how do you know there is not a great deal more to the problem until the engineers have checked it? Plus - you're willing to launch on the cer taintythat there are no icing conditions en route or during any possible diversion (unless it's a very short VFR flight you simply cannot) you'll be able to 100% guarantee avoiding them? I think departing with such a significant defect would be highly questionable and probably not legal.

[Cough]

IFR is different from IMC. Just because you're IFR doesn't mean you'll see a cloud.

A long time ago, I once dispatched with the above defect on a 35C day in a rainy Europe and simply picked a level below the freezing level (Planners gave us FL180 which was 1C lowest enroute - we flew below that). Just because you can't enter icing conditions doesn't mean you can't fly through clouds.