737 Flap Asymmetry questions

[oicur12.again]

Greetings all,

I will soon be returning to the sim and will be seeing a flap failure for the first time since my initial training 2 years ago.

It seems rather straight forward and the Boeing QRH is easy to step through however I do have some questions I would like to throw at the experts.

1. With a TE Flap Assy it suggests that normal operation can be continued if the Assy indication is removed after setting the flap handle to the nearest detent (equal to or less than). Our manual states that in the case of Assy “hydraulic power is removed” so I am assuming that hydraulic power is restored simply by moving the flap handle again in response to the QRH?
2. What would cause an Assy condition that could be cleared by moving the flap handle?

And a bonus question:

3. Our manuals/QRH have no information about brake cooling times and I am intrigued that this would not become a factor following an RTO. Do Boeing not provide these?

Cheers and thanks for any guidance that can be provided

[Maisk Rotum]

The QRH does not suggest normal operation can be resumed if moving the flap lever resolves it. With a skew or asymmetry the flap bypass valve is closed so no more movement is possible. The purpose of moving the flap lever to the lowest indicated flap setting is to use that position to determine your Vref.

Brake cooling schedules are in the QRH Performance in Flight section.

[oicur12.again]

Originally Posted by Maisk Rotum

The QRH does not suggest normal operation can be resumed if moving the flap lever resolves it. With a skew or asymmetry the flap bypass valve is closed so no more movement is possible. The purpose of moving the flap lever to the lowest indicated flap setting is to use that position to determine your Vref.

Brake cooling schedules are in the QRH Performance in Flight section.

Maisk

Thanks for the info.

I assumed this to be the case which is why I posted the question.

However, our QRH reads thus:

Trailing Edge Flap Asymmetry

Note: If there is no longer any indication of the flap asymmetry indication after the flap lever is reset in step 1 below, normal flap operation has likely been restored. The crew may stop the NNC and return to normal procedures.

Step 1. Set the flap lever to the nearest detent that is equal to or less than the smallest indicated flap position.

The above info implies that a flap “reset” is underway by selecting a different setting but I cant see how this can restore flap operation?

I flew the bus for many operators and knew the manufacturers SOP etc however this is my only Boeing airline and I have no way of determining exactly what comes from the manufacturer and what comes from star fleet command!

As for brake cooling, we dont have a QRH Performance section at all.

[FlyingStone]

Originally Posted by oicur12.again

Note: If there is no longer any indication of the flap asymmetry indication after the flap lever is reset in step 1 below, normal flap operation has likely been restored. The crew may stop the NNC and return to normal procedures.

This goes completely against objective of the Boeing's "generic" TE Flap Asymmetry NNC, which is to configure the aircraft for a landing (and not to restore the system for normal operation). I hope your airline involved Boeing into the decision to modify the NNC.

Originally Posted by oicur12.again

As for brake cooling, we dont have a QRH Performance section at all.

There is a brake cooling chart in FPPM (Flight Planning and Performance Manual), and calculation may be available as part of OPT app, but something tells me your airline doesn't give you access to any of those.

Do you have any other source of performance data than QRH or FCOM?

[oicur12.again]

Flying Stone,

Thanks as always.

Regarding brake cooling, I did manage to find “advisory brake energy data” charts in the Performance Handbook tucked away in an obscure section of the iPad. They are not at all user friendly charts and I suspect are just a box ticking provided by performance engineers. However after some mental gymnastics I have managed to figure out what they are telling me.

We do not have any OPT app in my company.

As for the flaps, I downloaded the interactive QRH from Boeing onto the iPad and found that indeed, the flap asymmetry chart is different to ours and the Boeing version DOES NOT make note of a possible return to normal flap operation as Maisk noted.

It will be interesting to see how our instructor squares this particular hole next week.

Cheers

[flightleader]

Following the NNC, after you position the flap level to one lesser flap, call the cabin and ask for a coffee! Don’t expect the flap to move immediately. Order the coffee, hold the NNC, carry out the missed approach, pick up a holding pattern, wait 2-3 minutes then you should see the flap retract back a step up and eliminated the flap split problem. Then come back try again after the coffee.

The gist is give it time.

[BraceBrace]

Originally Posted by oicur12.again

However, our QRH reads thus:

Trailing Edge Flap Asymmetry

Note: If there is no longer any indication of the flap asymmetry indication after the flap lever is reset in step 1 below, normal flap operation has likely been restored. The crew may stop the NNC and return to normal procedures.

NG or classic?

This is a company specific note. On the NG flaps are protected through the FSEU system (includes skew protection), on the classic it is simply a comparator.

On the classic there are known cases in which one of the 2 needles gets stuck inside the indicator and this blocks the extension of the flaps. It looks like an assymetry but it’s not. Putting the handle up might deblock the needle and resolve the problem... or it might not. We used to tap the indicator, but you might have to wait for touchdown to ’kick’ the indicator out of friction zone and then prepare for a battle with maintenance about your eyes 😀. Ah yes, flaps and slats on the 737... always fun.

[oicur12.again]

Originally Posted by flightleader

Following the NNC, after you position the flap level to one lesser flap, call the cabin and ask for a coffee! Don’t expect the flap to move immediately. Order the coffee, hold the NNC, carry out the missed approach, pick up a holding pattern, wait 2-3 minutes then you should see the flap retract back a step up and eliminated the flap split problem. Then come back try again after the coffee.

The gist is give it time.

Interesting. I'm wondering what sort of failure would result in a return to normal operation after waiting several minutes particularly having established that the FSEU removes hydraulic power when asymmetry or skew is sensed.

For info, my airline operates NG and Max when not grounded and I have never flown older versions.

Further reading on this issue highlights more questions about how to handle this situation.

Our up coming sim profile calls for a diversion to our takeoff alternate following the flap asymmetry after takeoff.

The only QRH reference is to set the flap handle to the nearest detent that is equal to or less than the smallest indicated flap position. In our case that would be flap lever to 2 as the takeoff would have been flaps 10.

Does this imply the lever must remain at position 2 or is it permissable to place the lever at 0 for the diversion in order to retract all LE devices.
Cheers.

[greatbigsea]

Originally Posted by oicur12.again

Interesting. I'm wondering what sort of failure would result in a return to normal operation after waiting several minutes particularly having established that the FSEU removes hydraulic power when asymmetry or skew is sensed.

For info, my airline operates NG and Max when not grounded and I have never flown older versions.

Further reading on this issue highlights more questions about how to handle this situation.

Our up coming sim profile calls for a diversion to our takeoff alternate following the flap asymmetry after takeoff.

The only QRH reference is to set the flap handle to the nearest detent that is equal to or less than the smallest indicated flap position. In our case that would be flap lever to 2 as the takeoff would have been flaps 10.

Does this imply the lever must remain at position 2 or is it permissable to place the lever at 0 for the diversion in order to retract all LE devices.
Cheers.

I wouldn't retract them completely unless the QRH guides you to. And its possible you'll be setting Flaps 5 depending on when/how the assym presents itself (i.e. 10* and 7* indications)

It can be a confusing checklist, but my understanding (and my operator has that same note about returning to normal ops) is you can attempt one reset. So from flaps 10 to 5 you get an assym, reset flaps to 10 and see if normal ops returns. If it does, continue with normal ops and retract. If not, set it to the smallest detent and continue with the checklist/divert.

Take at look at your company's Trailing Edge Flap Disagree QRH procedure. It may actually provide some guidance if you have flap issues during retraction.

[Gin Jockey]

Originally Posted by oicur12.again

Interesting. I'm wondering what sort of failure would result in a return to normal operation after waiting several minutes particularly having established that the FSEU removes hydraulic power when asymmetry or skew is sensed.

….

Does this imply the lever must remain at position 2 or is it permissable to place the lever at 0 for the diversion in order to retract all LE devices.
Cheers.

There is NO “returning to normal operation after waiting several minutes” with a flap assymetry. When an assymetry is detected, the trailing edge bypass valve closes and normal trailing edge flap operation is NOT possible. The valve can only be re opened on the ground by maintenance.

There are 3 parts to this checklist.
1. position flap lever (drives speed tape to correct position).
2. DONT USE ALTERNATE FLAP EXTENSION/RETRACTION.
3.pick a speed to land at (or if lever up do flap up checklist).

In terms of moving the flap lever to try and retract leading edge devices - NO, do not overthink this. The instructions to place the flap lever in a particular position is so it drives the speed tape correctly. Boeing has thought long and hard about this. Just do what it says.

[Vessbot]

Originally Posted by Gin Jockey

Just do what it says.

Generally a good paradigm, but in this case it seems the original poster has a company-modified QRH with apparently fictional statements about restoring flap power...

[framer]

My thoughts on how your sim scenario could possibly go;
- Take off at flap 10, on retraction to flap 5 one TE flap stops between 10 and 5, the other goes to 5.
- Climb above MSA and run QRH
Step 1 will have you leave the flap lever in the flap 5 detent
Step 2 will have you choosing to set Vref 40+30 . ( remember when setting up for landing that this number over-writes the existing ref 40 and the wind additive is then added in the normal fashion). You are then directed to step 4
Step 4 just gets you to calculate landing distance. (My books tell me the best I can do at MLW is 1480m, and AB 2 would stop me in 2800m.)
That’s the checklist apart from deferred items. The only deferred item of note is selecting the Flap Inhibit switch to Flap inhibit.
So there you are, now it’s just normal decision making around where to go etc. Part of that decision will be fuel burn. If the current burn rate sets you landing at your departure alternate with a low fuel state then tough decisions might be needed but I doubt that’s likely. From memory you’ll use approximately 15% extra fuel but don’t quote me on that, If it happened to me tomorrow I’d make the call based on the burn I was looking at. Also, runway length could make for a tough decision if your departure alternate is fairly short.
When discussing the decision with your partner state what the options are before choosing one so that the examiner can see that you’ve weighed it all up.
Use your companies procedures for communicating with the cabin ( NITS brief etc)

Can anyone see any holes in that? Obviously the flaps could hang up between 5 and 1, or 1 and UP , but it would be a similar process.

[flightleader]

Originally Posted by oicur12.again

Interesting. I'm wondering what sort of failure would result in a return to normal operation after waiting several minutes particularly having established that the FSEU removes hydraulic power when asymmetry or skew is sensed.

For info, my airline operates NG and Max when not grounded and I have never flown older versions.

Further reading on this issue highlights more questions about how to handle this situation.

Our up coming sim profile calls for a diversion to our takeoff alternate following the flap asymmetry after takeoff.

The only QRH reference is to set the flap handle to the nearest detent that is equal to or less than the smallest indicated flap position. In our case that would be flap lever to 2 as the takeoff would have been flaps 10.

Does this imply the lever must remain at position 2 or is it permissable to place the lever at 0 for the diversion in order to retract all LE devices.
Cheers.

I should have mentioned that I only flew the B737 classic for 10 years but I had 8 split flaps. It seems that when selecting a lesser flap after the split would not retract the flap immediately. But it would move to the selected lesser flap setting without any split after 2-3 minutes. Maybe it won't work on NG.

According to the maintenance guys, improper greasing of the flap mechanism can cause flap splits.

[oicur12.again]

All very sound advice and I appreciate the input.

Several pennies have dropped for me as a result of this discussion.

It still leaves me with a little suspicion over our QRH though!!!!

[Matey]

Originally Posted by flightleader

I should have mentioned that I only flew the B737 classic for 10 years but I had 8 split flaps. It seems that when selecting a lesser flap after the split would not retract the flap immediately. But it would move to the selected lesser flap setting without any split after 2-3 minutes. Maybe it won't work on NG.

According to the maintenance guys, improper greasing of the flap mechanism can cause flap splits.

If I remember correctly on the Classic flap asymmetry protection is provided by the detection of needle split on the actual gauge and a “sticky” needle could cause an asymmetry indication which prevents further flap movement. As someone else has mentioned, tapping the gauge could free the sticky needle and restore normal flap operation and this is something many 737 Classic pilots will have experienced as the engineers first fix upon landing! “Percussion engineering” at its finest. From the NG onwards, asymmetry detection is provided by the Flap Slat Electronic Unit FSEU.

[Vessbot]

Originally Posted by oicur12.again

Greetings all,

I will soon be returning to the sim and will be seeing a flap failure for the first time since my initial training 2 years ago.

It seems rather straight forward and the Boeing QRH is easy to step through however I do have some questions I would like to throw at the experts.

1. With a TE Flap Assy it suggests that normal operation can be continued if the Assy indication is removed after setting the flap handle to the nearest detent (equal to or less than). Our manual states that in the case of Assy “hydraulic power is removed” so I am assuming that hydraulic power is restored simply by moving the flap handle again in response to the QRH?
2. What would cause an Assy condition that could be cleared by moving the flap handle?

And a bonus question:

3. Our manuals/QRH have no information about brake cooling times and I am intrigued that this would not become a factor following an RTO. Do Boeing not provide these?

Cheers and thanks for any guidance that can be provided

I had a thought, that might resolve the discrepancy. I looked in my (also company-modified) QRH, and maybe someone with access to a pure Boeing one can also follow me through this.

Which exact checklist are you looking at? Mine has separates ones for:
"Trailing Edge Flap Asymmetry," and "Trailing Edge Flap Disagree"

Do you have these, or are they combined into one?

My "Asymmetry" checklist (like yours) has the first step to set the lever to the nearest equal/less detent than what's indicated, and (like everyone else on the thread) has no statement about restoring function... which also matches the system description of asymmetry protection permanently disabling TE flap movement.

However, the "Disagree" checklist does have the possibility of restoring function. First it also directs you to set the lever to a lower detent, then "Choose one" with the first choice being "Flaps move as commanded." And this matches the system behavior of the Flap Load Relief Lockout function, which stops TE flap movement if selected at too fast of an airspeed, but then (unlike asymmetry protection) movement is restored by going to a lesser detent than current displayed position.

I see the possibility of these checklists being mixed together and creating confusion (either by the resulting checklist being simply wrong, or being right but creating easy error from too many "choose one" decisions being followed wrong), or... a language barrier and/or false memory, where you should have done the Asymmetry checklist but are remembering the Disagree checklist... which both words sound very similar, but are different. In Asymmetry, the flaps are different from each other (and movement can not be restored) while in Disagree, the flaps are the same as each other, but disagree with the detent (and motion can be restored).

[oicur12.again]

Originally Posted by Vessbot

I had a thought, that might resolve the discrepancy. I looked in my (also company-modified) QRH, and maybe someone with access to a pure Boeing one can also follow me through this.

Which exact checklist are you looking at? Mine has separates ones for:
"Trailing Edge Flap Asymmetry," and "Trailing Edge Flap Disagree"

Do you have these, or are they combined into one?

My "Asymmetry" checklist (like yours) has the first step to set the lever to the nearest equal/less detent than what's indicated, and (like everyone else on the thread) has no statement about restoring function... which also matches the system description of asymmetry protection permanently disabling TE flap movement.

However, the "Disagree" checklist does have the possibility of restoring function. First it also directs you to set the lever to a lower detent, then "Choose one" with the first choice being "Flaps move as commanded." And this matches the system behavior of the Flap Load Relief Lockout function, which stops TE flap movement if selected at too fast of an airspeed, but then (unlike asymmetry protection) movement is restored by going to a lesser detent than current displayed position.

I see the possibility of these checklists being mixed together and creating confusion (either by the resulting checklist being simply wrong, or being right but creating easy error from too many "choose one" decisions being followed wrong), or... a language barrier and/or false memory, where you should have done the Asymmetry checklist but are remembering the Disagree checklist... which both words sound very similar, but are different. In Asymmetry, the flaps are different from each other (and movement can not be restored) while in Disagree, the flaps are the same as each other, but disagree with the detent (and motion can be restored).

Vessbot,



Thanks for the reply and sorry for my late one.

Our QRH is the same as yours in that there are different checklists for Asymmetry and Disagree.

However, they both refer to the possibility of resolving the situation by moving the flap handle.

I posed the question to our check airman and he was unsure however he did mention that this step had been added only recently, just prior to me joining the fleet two years ago.

Interestingly the failure we had in the sim was an asymmetry at the first flap retraction that produced a roll to the right during a right turn on the departure. Very cunning as it masked the asymmetric condition.

[aeromech3]

I'm not a pilot, but on a similar sized commercial aircraft we were getting Tech Log reports of the plane needing aileron trim input to fly level, we did all that the MM allowed except for adding a fixed tab which, as it was a lease, was not allowed by the parent Co.
After receiving a set of wing boards we checked the T/E flaps up, they were set in limits, the MM allowed small adjustments for the condition of level flight; the adjustment was at the mountings not the drive shafts; we adjusted by 1/4" out; the report back was level flight improved, but when flaps lowered a dramatic difference the other way!
Not my place to warn but asymmetry has to be detected early and managed by the system quickly. My experience is that a drive shaft break is highly unusual, but contamination in the signal generators with water condensation was the most common problem on this model.