Flaps 30 Go-Around in Severe Windshear — Is Flaps 15 a Valid Option?
 

I am a captain flying the B737NG and MAX.
Recently, I encountered severe windshear during an ILS approach, which led me to initiate a go-around. I did not change the aircraft configuration from the Flaps 30 landing configuration (gear down, flaps 30). However, because of the severe windshear, the airspeed fluctuated by more than ±15 knots.

I tried to keep the airspeed within limits using pitch control, but the airspeed briefly exceeded the Flaps 30 placard speed of 175 knots for a few seconds.

After this experience, I started wondering whether the Boeing Windshear Escape Maneuver must be followed strictly in every situation. In a scenario like mine—where the aircraft was already above 500 ft AGL, with a strong positive climb rate (more than +2000 fpm and stable)—would it make sense to select Flaps 15 to prevent exceeding the flap placard speed?

I’m questioning whether my thought process is flawed, and I’d like to hear how other 737 pilots think about this.

A proud member of overthinkers anonymous, I love it.

1. What is the problem you are trying to solve? What's the downside here? Absolute worst case scenario, you have damaged the flaps and the aircraft will need maintenance. No injuries, no undesirable aircraft state, no huhu. Actual scenario ... nothing. A few knots for a few seconds in an abnormal situation is not an issue.
2. If the airspeed is fluctuating that much, is that a safe time to retract flaps? If it jumps up so much that you exceed the barber pole, what happens when you retract the flaps and it drops an equal amount?
3. As you have discovered, a severe windshear is a very busy time. Dynamic. Not a good time to be calling for weird things and grabbing levers. A "wait for staging" kind of situation. Once you are out of the windshear and the airspeed stabilizes, then you can calm down and think about retracting flaps.

It's left up to you to decide when you're out of windshear and can transition away from the windshear escape maneuver. In the Simulator for Windshear/GPWS etc the procedure itself is usually flown well and the recovery screwed up.

I have a 73 type but can’t remember anything specific about it.
When these weather conditions are expected (ATIS LLWS advisory, TWR report or preceding aircraft) it may be prudent to either abandon the approach earlier or select a different flap setting for landing if performance allows it.
Besides don’t you have flap load relief from 30 to 25?
Same as above, momentary flap overspeed is not going to damage anything.
Its harder to explain why you deviated from a procedure than why you stuck to it also.

I have two questions:

1. Did the aircraft generate a windshear warning?
2. If yes, skip this next question, but if not, since when is +/-15kts "severe" windshear?

Thank you in advance.

The OP is Korean. Have you ever worked at an Asian airline? If so you’d be familiar with the rigid enforcement of SOP’s, which don’t leave any room for ‘common sense’, but when their rigid application leads to a bad outcome the pilot is blamed.
Reading between the lines here I suspect this captain is being hounded by his company for a flap overspeed which you laugh off.
Caught between a rock and a hard place - that’s flying inAsia.

Killaroo wish I could give you multiple up ticks. You are so right. Someone has to be blamed, normally the bottom rung…

This depends on the situation and the type of wind shear. You would have to be absolutely certain at that altitude to go back to initiating a normal go-around procedure. Think of it this way:

The procedure is designed to give you maximum angle of climb by putting you close to the maximum AoA. If you change the configuration you're changing the centre of pressure, the coefficient of lift and the centre of gravity. If the wind shear returns as you reconfigure you could stall the wing. Personally, I would leave it to a higher altitude, but I wasn't there to see what the was shear was like. Safest option usually works out though, even with a minor flap overspeed.

* Predictive windshear: the call is yours ("Windshear ahead") with a preference for the windshear escape maneuver (QRH quote "or at pilot's discretion, perform a normal go-around").

* Windshear encountered ("Windshear, Windshear, Windshear" warning or unacceptable flight path deviations). It is a FD guided maneuver (activated by TOGA), I don't understand why you would try to control airspeed with pitch control when the FD should be guiding you.

Personal thoughts: above 500ft AGL I wouldn't really call it a safe altitude to end a windshear maneuver, that's really low. If things turn around suddenly to 2000fpm ROD, you hit the ground in 15secs. Also, you would consider setting the flaps in movement in gusty conditions at placard speeds (hence g-forces and wingload present)? I would prefer to keep them where they are until conditions settle down a little.

No. I would not retract the flaps that low in that situation.

I agree with the above. I would not consider 500' AGL, even with a significant positive uptrend, to be out of the windshear. That's just too close to the ground for something to suddenly start trending the other way. You wouldn't change the configuration that low during a normal take-off or go around, so why do it so soon in windshear? You're more likely to throw off your FO who is not expecting it, setting your flight deck up for confusion in a dangerous moment. That's not to say that sometimes we have to think outside of the box, but I don't think this is one of those moments to throw surprises at your winger. I do understand your thinking - Flaps 30 to 15 is less drag, so that surely should improve performance. But, it's also less lift. Less lift at a time when maximizing lift production is the key to a successful outcome. That's why Mr. Boeing says not to change the configuration. It would not be a very nice day to lose that lift right at the moment that your trend goes the other way.

I vaguely remember being told by our engineering staff during a ground school a few years ago that for a flap overspeed excursion of up to 15 knots, it's just a visual inspection. I remember that this instructor was prone to exaggeration at times, so I do take the number with a grain of salt, but I don't think an overspeed of a few knots warrants much from an engineer. I stand ready to be corrected by much more knowledgeable people on the matter, but even if it's 10 knots, a flap can be fixed if it's in a million pieces. I can't.

I would also question if Flap Load Relief triggered. It should have if you exceeded 176 knots in either an NG or Max, so even if you did exceed the Flap 30 limit for a few seconds, FLR should have taken care of it for you.

Windshear; "once in two lifetimes", but not knowing which life you are experiencing.
 

It is good professional practice to question our thoughts, our recollections, but don't forget that the safety objective must be to learn from 'experiences', not change many years of operations which could be included in manufacturers procedures.
If change is required - your justified opinion, then inform the regulator/manufacturer; who like us should note that the world is in constant change and not always for the better.
Change may be warranted, but who judges …?

A single event is limited to just one context, as might be the recollection of other people.
Procedures - rarely perfect, have to consider a wide range of situations; it is best to followed them at the time, don't outthink the situation because you may not have a complete understanding of the event - atmosphere or aircraft.
"once in two lifetimes", but not knowing which life you are experiencing.

Fig 1 in the event described below shows the range of airspeeds which might be encountered in a microburst, 110-150, and note that aircraft have a "robust construction", with certification margins.

https://www.dropbox.com/scl/fi/oz9jq...=f1a3gohe&dl=0

Going back to the OP, if you are doing the WEM because you had a reactive WS warning or you decided enough was enough given the conditions, then if the initial actions were performed correctly you should be at max thrust following the FDs in TOGA and keeping the config; if the speed gets a bit frisky then so be it. The PM should be monitoring the aircraft performance as they know you are executing a WS GA because you said so.

At some point following this, you need to assess whether or not the conditions that caused you to discontinue the approach in this manner are still present and affecting you negatively. If not, then it is SOP in most outfits to call a GA which should trigger config changes in the normal way and start the process of rebuilding the flight path into something less frantic. The trap as I see it is to mix up the two stages which leads to confusion - either continue the WEM or change to a standard GA, don’t do half and half as the poor PM will have some big question marks over their head at that point.

There’s also the consideration about the environment. Is it just gusty and turbulent or is there microburst activity? (Which the WEM is ultimately there to counter). If it’s strong winds and/or mechanically induced turbulence then I would be quicker to revert to normal flight as opposed to the powerful vertical and horizontal shears associated with convective activity/downdraughts.

If you look at his posting history...well, let's just say I have doubts he is being "hounded" by anyone for anything.

The aircraft generated a predictive windshear warning: ‘Go around, windshear ahead.’ However, we were already experiencing windshear after passing 2000 ft AGL.

Luckily, I’m not under any pressure from my company. What I keep wondering is when I run into a similar situation next time, how far I can step away from Boeing’s WEM procedure without getting into trouble.

Referring to Post No. 9 in which the writer states: It is a FD guided maneuver (activated by TOGA), I don't understand why you would try to control airspeed with pitch control when the FD should be guiding you.

My comment: Be wary of blindly following the FD indications during the windshear avoidance or GPWS escape maneuver. . Use for guidance by all means but be aware of the actual body angle while at the same time cross referencing the other flight instruments e.g altimeter. ASI, VSI and even a quick glance at the standby ADI which gives you raw data. Study of past accidents involving loss of control revealed the PF was blindly following the FD to the detriment of scanning the other flight instruments.

Centaurus, noting the general caution; a critical issue in any abnormal situation is to know what the FD/AP is capable off, and how that should be used as specified by the manufacturer. Similarly for flight instruments which may be erratic or suffer display lag which auto systems can bypass or smooth out.

Some quite modest systems have approved (certificated) wind-shear guidance and control which are designed to manage the conditions - some trading transit speed for climb performance based on excess energy.

With surprise and its effects on human performance, the technology will out perform the human, particularly in these rare and highly dynamic situations.

As much as it important to understand the situation, its vital that crews understand the design, operational assumptions and capabilities of their aircraft, systems, and technology; via education not rote training.

I don’t know your SOPs but for us there is a choice when in receipt of a PWS warning between a normal GA and the WEM. Most importantly, you can attempt to laterally avoid the detected WS area but if you go straight to the WEM that goes away (wings level). Given that not flying in WS is the primary goal, leaving options open in terms of avoidance would appear to be a good strategy? At any point you can revert to the WEM, if needed.

As I said in my last post, mixing procedures often leads to confusion, especially in a scenario that requires crew coordination. I don’t think that this situation is that difficult to resolve: are we in WS? If so do the WEM, otherwise try to avoid flying into it - there’s not a lot of grey to interpret here or any need to invent procedures? TCEs like WS, RTO, GPWS, etc. need consistent rote responses because there is little to no time for cogitation, just action.

Why do we leave the gear and flap as they are in the WEM? The gear is in case the WS is severe enough to cause ground contact, which gets a better result than using the engines and/or fuselage for this purpose and the flap is so you don’t lose lift at a point where you might need every last bit of it. People with bigger brains than ours have spent quite a while thinking these things through on the ground in peace and quiet so we don’t have to in the air. There is a time for ideas and deviation from SOPs, in fact that’s one of the main reasons we are there, but not really with basic QRH drills, unless by executing them the aircraft would be left in a more dangerous state. If you had a hard GPWS going into Tokyo, then popped out of cloud to see Mt Fuji directly in front of you, a turn in either direction would seem to be prudent, despite what the recall items said...

I was going to write something similar. The raw data could be all over the place and as a pilot what are you going to prioritise - speed, altitude, pitch, terrain clearance? They might all be in a bad way and following mathematically derived guidance would likely achieve a better overall result than just winging it. In a severe encounter it might be a matter of life and death. If you’re not going to follow the FD in TOGA/WS, how do you decide whether to pitch up or down and by how much? Whatever you do differently has a good chance of being suboptimal.

I think you are using bad examples here... Did those accidents involve windshear?

FD is a primary guidance. The QRH is clear that an initial pitch up to 15° is required. When the speedbrakes are confirmed retracted, the FD becomes primary _guidance_. If you don't focus on correct pitch, "the nose is everywhere and nowhere" because people chase other instruments. You better make people follow the FD as is expected by Boeing "within a certain pitch range", and not chase other instruments. That is also explained in these words in the procedure: "Intermittent stick shacker or initial buffet is the upper pitch attitude limit" (or pitch limit indication). The PF does not need to do anything else.

The _PM_ has to monitor vertical speed and altitude, callout trends towards terrain or _significant_ airspeed changes. But the ACT of flying is done through pitch. The standby ADI should NOT be glanced at, for no single reason other than IRS failures. The ASI should not be taken "literally" but used for tendencies as the speed in a violent windshear can be all over the place. The word by Boeing for PM to make a callout is correctly "significant".

Secondly, GPWS warning recovery is NOT a FD guided maneuver.

I've been an airline pilot for almost 19 years now with three airlines. In those 19 years, I received a windshear warning exactly 3 (three) times, 2 (two) on approach, 1(1) on takeoff. Of the 2 approach ones, one was definitely false, one was probably false. The takeoff one was the only one that was legit.

My point is I doubt you have a pressing problem here. You may not see another warning for years, if at all.

It's the things that happen the least often that need the most thought and the most preparation for.

What we are talking about here are really two separate maneuvers, firstly a Windshear Escape Maneuver, during which the configuration should not be changed, and then once clear of the windshear transition into a go around with the resultant configuration changes.

A minor flap overspeed is really little cause for concern but trying to overthink the situation in the heat of the moment can lead you into trouble you don't need.

Regards,
BH.

I think it is unwise to go against manufacturer’s guidance underpinned by company sops reinforced in training. A flap over speed within limits is fairly innocuous in terms of post flight engineering inspection. Secondly the B737 has Flap Load Relief which should alleviate any over speed margins. With respect I think the OP is overthinking this. Company and blame culture is another matter which I’m not going to comment on!

I agree. Unlike, say, finishing a sentence with a dangling preposition, which seems to happen all the time.

There is no rule against doing so and the need to avoid doing so is rejected by modern language authorities as it is based on Latin grammar and not English.

But, like everything else, I'm sure you knew that.

I did not know that. English is my fourth language, I'm barely getting by over here.

​​​​​​​Thanks for sharing your experience. You’re right, windshear warnings don’t come up very often, and some of them do turn out to be false alarms. But the whole point of having SOPs and QRH maneuver instructions is that when real windshear does happen, we don’t waste time thinking. We just act.

Even if the odds are low, the consequences of getting caught in actual windshear are serious, so consistency in procedures matters more than frequency. I think that’s why the industry emphasizes rote responses for things like WS, RTO, and GPWS.

And in my case, it was an actual windshear. Also during the approach, I heard my preceding go around because of a windshear warning.

Thanks Brace Brace. I stand to be corrected. It has been many years since I flew a 737 and a bit out of touch with all the new avionics. The previous accidents I referred to were all loss of control although windshear was not a contributory factor.

Some good advice already, so to summarise :

“Windshear x 3” warning (reactive / immediate warning) : do the WS escape manoeuvre - do not change flap under any circumstances until clear of WS and then perform a normal G/A.

“Go-around, WS ahead” or “monitor radar display” : ideally a normal GA and turn to avoid (flap 15). However if you encounter actual wind shear then do WS escape.

If you ‘pilot detect’ actual WS (conditions listed in QRH) do the WS escape manoeuvre.

For me the grey area comes if you get positive shear first - that’s what happened to me once - the thrust levers were coming back and speed going up so I actually called “unstable go-around” and did a normal go-around. During that got the negative WS and reactive WS warning so converted into WS escape. The point is if you’re not sure and you’re not receiving a reactive warning then a normal go-around is a good option - pressing TOGA and getting the aircraft climbing away at 2000ft/min is a pretty good starting point. And if you’re doing that you’re not in negative WS!

main risk with reactive windshear is uncontrollable descent and terrain contact. Increasing speed and strong climb is not an issue. In a windshear a pilot should be too happy with +2000ft climb. To avoid overspeed all he has to do is to just pull up and bring the speed back. This high ROC may even take the aircraft out of windshear itself. Why bother about flap at this stage? On the other hand falling airspeed and descent is a serious issue and tricky to handle. You may have pull back to stop descent till stick shaker and fly with intermittent shaker on and hope gust changes direction to allows to resume climb at normal speed.