737 Max flap cycling after deicing

[767-300ER]

I was wondering if other 737 Max or NG operators have the requirement to cycle the flaps from UP to 40 and back UP after deicing the aircraft. I have watched 737 NGs going through deicing and never seen them cycle the flaps.

The following is from a 737 Max Airframe deicing checklist

FLAPS. . . . . . . . . . . . . . . . . . . . . . . . . . . . CHECK
Move the flaps from Flaps up to Flaps 40 back to
Flaps up (i.e., full travel) to ensure freedom of
movement.

So if you are deicing to remove frost from the upper surface on the wing, why is this necessary? It seems over the top and is quite time consuming when de-icing facilities are trying to get aircraft through the facility as quickly as possible.

Anyone have any explanations/answers? Is this procedure unique to the Max?

[nicolai]

I don't know if it's unique to the 737 Max. De-icing fluid (especially types II and IV) can accumulate in flap mechanisms and jam them.
For example see section 9 of EASA Safety Information Notice No. 2008-29. So there is a reason to exercise the flaps.

[Denti]

Back when i was still flying NGs that was the procedure we had as well. So not new for the MAX.

[wiedehopf]

this might be a stupid question but why is it time-consuming for the deicing facility?

don't you just do it on the way to the runway?

[767-300ER]

Thanks for the EASA notice...however, the generic advice about fluid rehydration would apply to all aircraft types and not unique to the 737.

(ii) Re-hydrated fluid residues.
Repetitive application of thickened de-icing / anti-icing fluids may lead to the
subsequent formation / build up of a dried residue in aerodynamically quiet areas,
such as cavities and gaps. This residue may re-hydrate if exposed to high
humidity conditions, precipitation, washing, etc., and increase to many times its
original size / volume. This residue will freeze if exposed to conditions at or below
0° C. This may cause moving parts such as elevators, ailerons, and flap actuating
mechanisms to stiffen or jam in flight.


Other Boeing types (767,777,787) do not have this advice to cycle the flaps, and as far as I know, Airbus (319/320/321) do not require this step.

[767-300ER]

Yes you can accomplish the flap cycle on the way to the runway. Boeing doesn't address how to accomplish this flap cycle while taxiing on slush or snow covered taxiways. Boeing suggests delaying the final t/o flap selection on contaminated taxiways, so I would think that Boeing wouldn't recommend a cycle to Flap 40 on snow/slush/ice covered taxiways (which stands a much better chance of getting contaminants on the flaps than a normal t/o setting of Flaps 5).

Caution!
Flap selection should be delayed if extended taxi through slush or snow conditions is anticipated.

[172_driver]

We don’t cycle the flaps, however wait with flap extension until reaching the runway if snow is falling. That is to avoid precipitation on areas not treated as the flaps come out.

Scandinavian operator. We often do several de-ice procedures a day. Not heard of any problems with rehydrated fluids. We log it in the book, so perhaps maintenance has an inspection cycle for it?

[fab777]

B737 NG. SOP is: deicing, then cycle flaps, then select TO flaps or, if taxiways are contamined, select flaps UP, then taxi. We do it this way.

[SR-22]

At least in my outfit B737NG and B737MAX yes as per FCOM to cycle flaps to 40 and up again after de-icing. Scandinavian operator.

[vapilot2004]

De-icing operations, cold weather taxi on sloppy tarmac or in cold precip require flaps UP. Also for our group, cold weather flap cycling (0-40-0) is always done before taxi.

Slow throttle application is also SOP around slushy macadam and on or near the deice station, although if applied too slowly, I believe one ends up throwing more wash than if the levers are brought up smartly.

[president]

It’s a cold weather flap check that must be done, de-icing or not. It’s the supplementary procedure for cold weather operation.

You can delay it until de-icing is completed. But that’s not to say you don’t do it without de-icing.

[Skyjob]

As in cold weather operation there is a risk of movement being impaired due to the (re)freezing of contaminants, the freedom of movement check makes a lot of sense.

Considering the checklist is done regardless if the aircraft landed 30 minutes ago or 30 hours, it is very sensible to do this. Contaminants could have accumulated in many cavities, including the flap fairings, either due landing on a contaminated runway, taxiing in on a contaminated taxiway, or due (winter) precipitation/deposits being washed off by deicing fluids. Why not ensure these vital flight controls have the ability to move freely, same for ailerons, rudder and elevator.

[sonicbum]

Fully agree with the above and I also would like to add to make sure that during this check at least one pilot keeps his eyes on the trailing edge flap indicator for any sign of flaps getting stuck on their way to 40 and backwards and in case promptly move the flap lever to the indicated position or the closest setting.

[172_driver]

I am aware of the SP. Though, in the FCOM we use it says nothing about cycling the flaps. As far as I remember the SP was about cycling the flaps in freezing conditions, rather than post de-ice.

If we expect ice in the flap arrangements after landing we leave the flaps extended until inspected. If taxiing through slush or snow we may taxi out with flaps retracted. Also, if snow is falling we leave them retracted until holding point.

Not saying you should hurry or not check properly, but if we were to apply the same thorough procedure as in my previous airline we’d definitely be running behind schedule...

[767-300ER]

So what is unique about the 737 that requires this procedure?

Not done on 757, 767, 777, 787 or Airbus 318/319/320/321....As far as I know.

[tdracer]

There are some pretty fundamental differences between the wing/slats/flaps on the 737 relative to the other Boeing 7xx wings. No first hand knowledge here, but I'm guessing the "aerodynamic quiet" places can be more of an issue on the 737 wing.

[EIFFS]

Procedure is the same for NG & MAX per Boeing FCOM, yes it takes a few minutes between 5 - 0 is very slow, but you’ve already spent 6 minutes starting the engines on the max

[vapilot2004]

I've been told the flap PDU, torque tubes, and drive screws are more exposed to the elements on the 737 compared to its bigger brothers. The mechanisms are also much closer to the ground than any other Boeing aircraft flying today. There is, at minimum, about a meter in height difference here.

[Skyjob]

It may also have to do with the proximity of those areas to the ground when compared to other models, just guessing...

[galdian]

In previous company (NG"s) always surprised me an otherwise good to excellent Bad WX Ops pamphlet had this flap exercise after pushback because:

- having just de-iced and anti-iced the wings/slats and gaps etc will be as clean as they can get;
- exercising if precipitation/snowing means allowing ice into the flap gaps to be crunched after retraction and freeze further even more on taxi out.

My procedure was to not do the check after pushback and taxi out flaps up, just before take-off exercise to 40 degrees, back to 5 degree (only company setting) and if all OK take off; any problems taxi back for de-icing etc.

Discussed with a checkie type who only smiled and said "as long as it is done somewhere at PIC discretion is OK", management did not want to buy into any talk about (maybe IMHO) changing the location for the check - so some crews would be stuck with "the C/L says MUST be done after pushback" mentality which didn't appear the best/safest option.

Cheers.