B737 LEADING EDGE TRANSIT LIGHT

[LEM]

I'll start by putting this question in a very simple form:

After takeoff one slat physically remains extended: are we limited to 230kts or 300/.65?

If you'd like to discuss it, we'll see that the QRH and the DDPG do NOT agree, and things are quite confused...

[gonso]

Hi LEM.
No, once you have recycled the flaps to 1 and back with no effect, you are not limited to 230kts UNLESS you encounter roll or you have more than 1 lights
I never thought that this is a complicated checklist. (I've seen quite a few of those).
All you are doing is checking whether you can retract the stuck slat by recycling the flaps to 1 and back. If after recycling flaps, the (one) light is still there and there is no roll, probably is an erroneous indication or the slat is not 100% retracted but...99.2% and it does not cause any more roll than a bent airframe!

[metabolix]

LEM

Once airborne, the DDPG is no longer relevant. The QRH is the controlling document.

First, limit airspeed to 230kts. If you have roll, it'll be a Flaps 15 landing. End of story. However, if there is no roll, then you can recycle the flaps to see if it will stow. If it does, great - no further limitation. If it doesn't, you have to see how many have stayed out. If it's just one, then you are limited to 300kts (.65) and a Flaps 15 landing. But if it's more than one, then you are limited to 230kts and a Flaps 15 landing.

In your scenario, it depends if you had roll or not. When there is only one light that won't go out, with no roll, then you are limited to 300kts (.65) and must plan a Flaps 15 landing.

[LEM]

Hi all.
The cklist is not complicated, what I'm trying to figure out is why exactly it is built like that.

I've got a few doubts:
1) Why can't I recycle even if I've got roll?
If one slat is stuck extended, maybe because of ice accumulation, I'd try the full extended position, using F10, then back to up...

2) I know the MEL are not applicable after the airplane starts moving under it's own power - at least here - but we can indeed use them once we are dispatched (that means during taxi, for example) to continue our flight and, say, come back from Sharm, instead of getting stuck there.

In case of problems with a faulty indication, it's the same if you have this light deactivated by maintenance, of if you ignore it considering it u/s.

And legally, you can use this trick during taxy out, if the airplane can be dispatched with that particular light u/s.

Let's say we are actually dispatched by maintenance with one light on the annunciator panel inop: the DDPG say "Verify leading edge position for the inoperative indication before each takeoff and landing."

It doesn't say to make this check after takeoff.

Since you don't have any light for that particular slat, which might get stuck extended that day, and you are not supposed to make a visual check, you just have to limit the speed to 300/.65, with one slat physically extended!

And this doesn't agree with the QRH, for which if you have an actually stuck slat - and, of course, roll - you are limited to 230 knots.

See what I mean?

[gonso]

Originally Posted by LEM

Hi all.
The cklist is not complicated, what I'm trying to figure out is why exactly it is built like that.
I've got a few doubts:
1) Why can't I recycle even if I've got roll?
If one slat is stuck extended, maybe because of ice accumulation, I'd try the full extended position, using F10, then back to up...

Well, consider this. If you have a single LE Slat light and roll, thats not an erroneous indication. If during retraction from F1 to Fup, that single slat panel gets stuck half way and it does give you roll, if you try to recycle to F1 or more (ignoring the QRH instructions), maybe that single slat will extend further with you not being able to retract it, ending up with more roll. So a possibly manageable situation with a roll that could be compensated and followed by a safe landing, could be aggrevated, becoming an uncontrollable roll.
Sometimes high lift devices can become stuck only in one direction. (i.e. not able to retract but able to extend and vice versa) .
As far as the MEL scenario you mention, I think is a little bit farfetched to have a (really) inop LE slat light and get that particular slat stuck on the same day.

[Wizofoz]

I think the INTENT of the QRH is that if roll is encountered, the slat is actually extended and thus the 230 knot limit applies. If there is no roll, it is purely an indication problem, the slat is assumed to be retracted, and the .65/300 limit is applied to limit roll in case of un-commanded extension of the slat that now has no indication system.

[LEM]

If during retraction from F1 to Fup, that single slat panel gets stuck half way and it does give you roll, if you try to recycle to F1 or more (ignoring the QRH instructions), maybe that single slat will extend further with you not being able to retract it, ending up with more roll. So a possibly manageable situation with a roll that could be compensated and followed by a safe landing, could be aggrevated, becoming an uncontrollable roll.

gonso, in no way there's a risk of an uncontrollable roll.
You've forgotten the Flaps 15 takeoff...

As far as the MEL scenario you mention, I think is a little bit farfetched to have a (really) inop LE slat light and get that particular slat stuck on the same day.

Not at all.
That's exactly what they want to protect you from, limiting the speed to 300/.65, since you can't see it.

Wizofoz
[QUOTE]I think the INTENT of the QRH is that if roll is encountered, the slat is actually extended and thus the 230 knot limit applies. If there is no roll, it is purely an indication problem, the slat is assumed to be retracted, and the .65/300 limit is applied to limit roll in case of un-commanded extension of the slat that now has no indication system. [QUOTE]

Do you realize the contradiction?
In the first part of your sentence, the limit is 230 kts because the slat is actually extended.
In the second part of your sentence, the limit is 300/.65 because the slat has actually extended by itself...

I told you it's not that simple subject, if we dig deep...

[gonso]

Huh???

I give up. I think it's straightforward. Good luck!

[LEM]

Ok, thanks for joining.

LEM

[I-2021]

Originally Posted by LEM

After takeoff one slat physically remains extended: are we limited to 230kts or 300/.65?

First of all : is the aircraft dispatched with the LE FLAP TRANSIT LIGHT INOP and/or one of the overhead indication light INOP ?

Leading Edge Flap Transit NN CKLIST.

-> If the trailing edge flaps are UP : Airspeed 230 MAX

Then the checklist asks about roll. The point here (I think) is understanding if you have roll or not Easy in smooth air, maybe not so in moderate turbulence. In the example you gave, you mention one slat extended. Therefore if you have roll, you must fly 230 kts , set Vref 15 +5, etc..
No roll, and the light is still on (LE FLAP TRANSIT) with one LE device extended, you may fly 300/.65.

If the aircraft is dispatched with some faulty light indications, you simply follow on ground the operational DDPG procedure according to that.

Ciao

[GearDown&Locked]

Do you realize the contradiction?
In the first part of your sentence, the limit is 230 kts because the slat is actually extended.
In the second part of your sentence, the limit is 300/.65 because the slat has actually extended by itself...

Allow me.
The 300/.65 limit is there for a "just in case it extends uncommanded at some point" situation, as you may not have any indication at all due to u/s indication light. Precaution, just that.

GD&L

[cwatters]

Originally Posted by LEM

Hi all.
The cklist is not complicated, what I'm trying to figure out is why exactly it is built like that.
I've got a few doubts:
1) Why can't I recycle even if I've got roll?

The Alaska Flight 261 accident might be worth a look.

[Wizofoz]

has actually extended by itself...

Not HAS, but MIGHT extend uncomanded and now has no indication because the sensor has failed.

(OK, Edited now I've read Down and Locked's reply to say "What he said"!!!!)

[metabolix]

LEM old son, you are tying yourself in knots.

Why can't I recycle even if I've got roll?
If one slat is stuck extended, maybe because of ice accumulation, I'd try the full extended position, using F10, then back to up...

In case you exacerbate the problem. What happens if it wasn't ice accumulation and the slat then stays at the full extended position?

but we can indeed use them once we are dispatched (that means during taxi, for example)

Quite so. The point being that you are not going to get airborne with a flying control problem (even if it is just a light - how do you know at that stage? Going back to have look from the cabin does not really count as a qualified check), particularly one which requires a full maintenance check of the system before you go to ensure that it is just an indication problem. If it was decided to not bother getting it checked out and get airborne anyway, then I respectfully suggest that there are bigger issues other than a perceived discrepency between documents.


Okay so let's suppose you get to the aircraft and you check the ADDs and see that the engineers have carried out a full operating check of the system (as per the DDPG) and, having established that it is a faulty indication, removed the bulbs from the affected leading edge flap. (You cannot go with a leading edge flap u/s. The DDPG is to check that it is only an indication problem).

Being aware that the bulbs have been removed when you get airborne, should you encounter any roll when the flaps are retracted (which you will get if any part of the leading edge stays out. The 300kts/.65 is there so that should a flap extend uncommanded, the roll doesn't become uncontrollable and having controlled it, you can then carry out the QRH which says to limit speed to 230kts) and all other systems indicate 'normal', then using one's undoubted powers of deduction, it would suggest that horror of horrors, not only did you have an indication problem with a particular leading edge device, but also that it happens to be that very same device that has now stayed out. Enter QRH and limit to 230kts. Simple.

[LEM]

Hi metalibox, appreciate your input, and agree with that.

Btw, see what I've just found
http://www.airliners.net/open.file?i...ext_id=0496922


Also, consider this: F5 takeoff.
The slat remains extended.
Roll is of course encountered.
According to the cklist, I limit the speed to 230. End of the story.

What harm can a recycle do?
If I extend to the FULL extended position, like in the picture above, and cannot solve the problem, nothing has changed.
I fly at the same 230 kts speed.
But if the recycle is successful, and we all know recycles are often successful, I avoid loads of trouble on a long flight.

Hi I-2021, following the cklist is easy. What I'm trying to do with this discussion is understanding if it really makes sense at 100%, or what is the exact sense...
Quite a few times I've seen cklist deeply revised over the years, that means Boeing also is after THE TRUTH, as we all are and keep learning.

[metabolix]

Ooooo nasty! Not something you see everyday. I would imagine they were back at max 230kts As it failed to retract, they would have been at a slow speed anyway as they would not be much above flaps up manoeuvring when they noticed it, so any roll would have been kept to a minimum. Had it happened at 300kts/.65, then it might have been a different situation!

What harm can a recycle do?
If I extend to the FULL extended position, like in the picture above, and cannot solve the problem, nothing has changed.
I fly at the same 230 kts speed.

Very true, but carrying out an airtest on flight controls (when you have a certain amount of roll already) with a plane full of passengers is not something that Boeing can be seen to recommend. What happens if you recycle and now 2 leading edges on the same side stay out? Your problems are now a bit more serious and the roll that much worse. Okay, it's still controllable, but why make your life potentially more difficult? The QRH is written to get you on the ground safely without the potential for making problems worse. They don't want too much messing about up there!

[LEM]

If you read the description, you'll see they recycled many times, and they continued to destination safely.

[metabolix]

Indeed it does. And should they have created a bigger problem then the subsequent board of enquiry would have crucified them for not following the QRH checklist properly.

As I said, Boeing cannot be seen to have a checklist that could potentially make the problem worse. If you as the skipper decide to do something off your own back, then so be it. But, as far as Boeing is concerned, you're on your own

Edited to add: I have no idea if the QRH is any different for aircraft with blended winglets. It may be that recycling the flaps is an acceptable procedure.... but I doubt it.

[I-2021]

Originally Posted by LEM

Hi I-2021, following the cklist is easy.

I agree But sometimes applying the correct one is not so

What I'm trying to do with this discussion is understanding if it really makes sense at 100%, or what is the exact sense...
Quite a few times I've seen cklist deeply revised over the years, that means Boeing also is after THE TRUTH, as we all are and keep learning.

For the purpose of some brainstorming, your discussion is very interesting, and I thank you again for having thrown the subject out, so I can take a chance to read the sticky pages of my personal QRH

Originally Posted by metabolix

Very true, but carrying out an airtest on flight controls (when you have a certain amount of roll already) with a plane full of passengers is not something that Boeing can be seen to recommend.

That's the point

[LEM]

A little step back, metalibox,

Going back to have look from the cabin does not really count as a qualified check

A visual check of the slats is not only acceptable, but required from the flight deck before takeoff and landing.
That's why on the 400 you cannot be dispatched if slats 3 and 4 are giving the indication problem, because you can't see them.

(well, if you just open your cockpit windows you can indeed, but not before landing... )