Not_Delta 191

[Evan]

But oddly enough, my objection is your blindness to some extremely plausible additional alternatives.

Sorry to be such an absolutist. They may have been diving to avoid a meteor, I suppose. I hadn't considered that 'plausibility'.

Although... the report does say:

Unaware that they had penetrated the first part of the microburst, the captain commanded the first officer to execute a standard missed approach instead of a windshear escape procedure.

Again, give me one plausible alternative for 1016, where the crew were aware of the microburst and decided that pushing down was a good idea.

It has to fit this:

18:42:16 - (CPT) USAir 1016's on the go. [decision to go-around]
18:42:17.7 - (CPT) Max power [we would prefer 'TOGA' here].
18:42:18.5 - (F/O) Yeah, max power? [He does not advance power to TOGA however. EPR rises to 1.82]
18:42:19.4 - (F/O) Flaps to 15.

Thus far, the crew is executing a go-around. There is no stall warning yet.

18:42:22 - (CPT) Down, push it down.

This is where I believe the crew is focused on go-around and not onset of windshear recovery. This looks nothing like windshear recovery.
They are climbing through 1000ft. Pitch is 15deg up. Pitch is reduced for the next critical 10 seconds to -5deg down. At that point upward pitch is briefly commanded, but then reduced again to neutral before the GPWS warning and the final desperate full aft pull up.

18:42:25.5 (F/O RADIO) Up to three we're taking a right turn by captain here. [The F/O does not appear to be aware of the developing situation either]
18:42:28.4 Whoop whoop whoop
18:42:32.7 Stickshaker [first stall warning]
18:42:35.6 Crunch

Which is sad considering that the report also concluded that they would have successfully recovered if they had maintained the 15 ANU pitch and had applied maximum power.

[Gabriel]

A little perspective...

[3WE]

Evan: Think. Look beyond the book. Recognize shades of gray.

They know there is a wind shear risk.

They know that you basically go around at full power.

They also know there’s a stall risk (ask Gabriel to explain why there’s a stall risk, and if there’s a few unfavorable aspects to stalls)

Is “We’re getting slow, into stall territory and in a buch of turbulence and a downburst where we may lose more speed and stall, so maybe we need a little speed” a reasonably plausible explanation?

At least as plausible as “I’m a highly trained military and airline pilot, so in spite of the mantra to “trust the instruments”, I’m just going to do what the feelings in my ass and inner ear are telling me, and push over.”?

And all the words matter, Evan. I said extremely plausible. Meteors not_extremely plausible.

Shear and go around procedures are the same- no one in the cockpit DECIDED they would consciously not pull up aggressively nor DECIDED to consciously use a low power settining. The called full power and maintained climb speeds, but it was a real-time, 130 knot, bouncing bicycle, 300 feet in the sky…and you lack the context of 10 knots bouncing on the ground.

Footnote: They suggest bicycle helmets, because there is risk and cowboy improvisation and imperfect, slower-than-computer human perceptions and responses are required to stay upright.

[Evan]

Evan: Think. Look beyond the book. Recognize shades of gray.

They know there is a wind shear risk.

They know that you basically go around at full power.

They also know there’s a stall risk (ask Gabriel to explain why there’s a stall risk, and if there’s a few unfavorable aspects to stalls)

Is “We’re getting slow, into stall territory and in a buch of turbulence and a downburst where we may lose more speed and stall, so maybe we need a little speed” a reasonably plausible explanation?

At least as plausible as “I’m a highly trained military and airline pilot, so in spite of the mantra to “trust the instruments”, I’m just going to do what the feelings in my ass and inner ear are telling me, and push over.”?

And all the words matter, Evan. I said very plausible. Meteors not_very plausible.

Shear and go around procedures are the same- no one in the cockpit DECIDED they would consciously not pull up aggressively nor DECIDED to consciously use a low power settining. The called full power and maintained climb speeds, but it was a real-time, 130 knot, bouncing bicycle, 300 feet in the sky…and you lack the context of 10 knots bouncing on the ground.

Footnote: They suggest bicycle helmets, because there is risk and cowboy improvisation and imperfect, slower-than-computer human perceptions and responses are required to stay upright.

3WE: Look at the book. Brush up on windshear escape procedure. Read the conclusions of the official report. Read about human factors, especially the part about sensory illusions and tunneling and how these things affect very experienced pilots who cannot later recall or explain their actions. Then read about how formal standardized and rehearsed instant-recall procedures defend pilots against this phenomena.

And then re-read the windshear procedure: maintain maximum allowable pitch until exiting the threat. That means you avoid stall by reducing pitch when the stickshaker tells you to. Is it ideal? No, there is no ideal situation in microburst. That’s why we now avoid it like a piano lesson.

[3WE]

I HAVE read the book, I understand it well.

You have NOT_riddren a bicycle.

Therefore you are blind that they are following wind shear procedures AS WELL AS don’t stall the GD airplane procedures and deal with turbulence procedures.

Guess what: My bicycling procedures are not_perfect.

Delta 191 and these guys procedures weren’t perfect.

We can cite shortcomings, but it’s easy to do from the easy chair and if you tried a bike, you might get beyond the black and white mindset that the experienced military pilot chose the wrong procedure and mis interpreted the negative AOA stall warning.

Gabriel: what are your thoughts regarding the grossly overdone nose down inputs shown in the graph?

[Gabriel]

Gabriel: what are your thoughts regarding the grossly overdone nose down inputs shown in the graph?

Despite the "push it down" instruction from the PIC, the push down inputs by the FO (PF) were brief in duration and small in deflection.
It looks to me that most of the pitch down motion was not commanded, but the result of a wind that went from 30+ head to 20+ tail with the subsequent loss of 30 kts of airspeed (despite the plane having positive longitudinal acceleration), and of encountering a ~2000 fpm downdraft.

[Evan]

Despite the "push it down" instruction from the PIC, the push down inputs by the FO (PF) were brief in duration and small in deflection.
It looks to me that most of the pitch down motion was not commanded, but the result of a wind that went from 30+ head to 20+ tail with the subsequent loss of 30 kts of airspeed (despite the plane having positive longitudinal acceleration), and of encountering a ~2000 fpm downdraft.

Of course, but that's downdraft for you. And that's the reason why you never make even brief and small pitch down inputs when you are in it. And, I will repeat, the findings of the official report concluded that if they had maintained the healthy 15deg pitch they had in the go-around and applied full power they would have escaped it. The cause was pilot error (which is not necessarily, as 3WE thinks, 'blaming the pilots') for the following actions:

- failure to execute a timely missed approach when the danger presented itself
- failure to fully advance the power setting
- failure to maintain an optimum nose-up attitude

Beyond all the improvements in windshear detection, the most important thing to understand is why the pilots failed in these three respects. On the last two errors, I strongly believe it was lack of situational awareness where the crew were executing a missed approach procedure and unaware of the microburst situation until it was too late to recover. And that confusion is to be expected, thus the focus has been on avoiding downbursts and severe weather cells that bring them on.

And that has worked ever since. I'd be interested, however in seeing reports from subsequent encounters where the crew successfully recovered.

[Gabriel]

You definitely do not apply sustained airplane-nose-down pitch as the captain called for here.

If the stall warning is brought on by downburst and a negative AoA

What accident report are you looking at, Evan?

I do agree with Evan a couple of things:

- Despite some similarities, a go around and a windshear escape maneuver are fundamentally different maneuvers. The windshear escape is more similar to a CTIF escape than to a go around.
- The main goal in a windshear escape maneuver is "don't sink", and the best way to achieve it is "don't think".Just execute it. Don't change config, firewall the throttles, pitch up to either 20 degrees or to the stickshaker onset (whatever is reached first). In airplanes equipped with PLI just pitch to PLI. Don't watch the airspeed. Don't watch the altitude. Don't watch the vertical speed. Let the PM monitor all that until out of the mess.

There were several problems here:
- ATC knew about low level windshear but transmitted that info to the pilots in a frequency different than the one being used by the pilots that needed it most.
- The windshear warning in the plane (which it was equipped with) did not trigger.
- The pilots executed a go-around instead of a windshear escape, and they never "officially" changed it a windshear escape (they never verbalized it) although in the last seconds they did firewall the throttles and pulled up to the onset of the stickshaker. While it was too late to prevent the crash, that last-second actions most likely saved the lives of all those that survived.

The nose down inputs look perfectly reasonable to me in a context of an until-then-normal go-around with the plane established in a climb with 15 degrees pitch and more than 2000 fpm up and the plane accelerating, when the PIC noted a quick decay in airspeed (again, despite the plane actually accelerating i.e. speeding up, which they could feel). That's what happens when your inertial speed increases but the headwind reduces / the tailwind increases even faster than that.

As I said, it looks to me that most of the pitch down was not the result of the pitch down inputs.

[Evan]

The captain called "push it down" not "reduce your pitch" or "don't pull". I interpret that as an imperative to command a nose-down attitude.

Ok, not "negative AoA" but a negative effect on AoA. The AoA is reducing due to the downdraft (I don't know enough about the effects of a 4000fpm downdraft to know if that can reduce the AoA to a negative value. I also realize that, as the plane subsequently descends, this will raise the AoA. But I'm only referring to the moment the captain commands "push it down". Doing so will cause the airplane to sink, and mantra here must be 'don't sink' as well as 'don't stall'.

What accident report are you looking at, Evan?

The link is in the original post.

I do agree with Evan a couple of things:

- Despite some similarities, a go around and a windshear escape maneuver are fundamentally different maneuvers. The windshear escape is more similar to a CTIF escape than to a go around.
- The main goal in a windshear escape maneuver is "don't sink", and the best way to achieve it is "don't think".Just execute it. Don't change config, firewall the throttles, pitch up to either 20 degrees or to the stickshaker onset (whatever is reached first). In airplanes equipped with PLI just pitch to PLI. Don't watch the airspeed. Don't watch the altitude. Don't watch the vertical speed. Let the PM monitor all that until out of the mess.

There were several problems here:
- ATC knew about low level windshear but transmitted that info to the pilots in a frequency different than the one being used by the pilots that needed it most.
- The windshear warning in the plane (which it was equipped with) did not trigger.
- The pilots executed a go-around instead of a windshear escape, and they never "officially" changed it a windshear escape (they never verbalized it) although in the last seconds they did firewall the throttles and pulled up to the onset of the stickshaker. While it was too late to prevent the crash, that last-second actions most likely saved the lives of all those that survived.

The nose down inputs look perfectly reasonable to me in a context of an until-then-normal go-around with the plane established in a climb with 15 degrees pitch and more than 2000 fpm up and the plane accelerating, when the PIC noted a quick decay in airspeed (again, despite the plane actually accelerating i.e. speeding up, which they could feel). That's what happens when your inertial speed increases but the headwind reduces / the tailwind increases even faster than that.

As I said, it looks to me that most of the pitch down was not the result of the pitch down inputs.

That is my point exactly.

I had considered the possibility the the initial headwind increase had caused the vertical path to increase and that might have caused the captain to command a reduction in pitch, but it doesn't fit in a go-around scenario.

I've also read a report outlining the results of studies using a constant pitch target vs a variable pitch method. While the variable pitch method led to better control and airspeed, it did so at the expense of altitude. In a low altitude situation, altitude must take primary concern, thus the constant pitch procedure was recommended.

https://commons.erau.edu/cgi/viewcontent.cgi?article=1032&context=db-theses

[Evan]

Microbursts degrade airplane performance through a decrease in both lift and stability. The combination of horizontal and vertical wind shear reduces lift through a reduction in relative airflow and angle of attack for the aircraft.

[Gabriel]

You definitely do not apply sustained airplane-nose-down pitch as the captain called for here.

There was no call for sustained airplane-nose-down pitch and no sustained airplane-nose-down pitch was applied. There was some nose down pitch and not enough pull up pitch for a windshear escape maneuver.

If the stall warning is brought on by downburst and a negative AoA

Negative AoAs, or negative effect on AoA as it is reduced by a downdraft, do not bring on the stall warning. The stall warning is brought on ONLY* by an excessive positive angle of attack, like when they pulled up at the end and by doing so they exceeded the stickshaker AoA which is the real thing that brought on the stall warning.

Because of the 2 points above is that I, sarcastically, asked what you report are you reading. I omitted the blue font memory item.

* except spurious warnings due to a vane damage or system malfunction.

[Evan]

There was no call for sustained airplane-nose-down pitch and no sustained airplane-nose-down pitch was applied. There was some nose down pitch and not enough pull up pitch for a windshear escape maneuver.

Which is all that matters here. Not only not enough pitch up, but some actual forward-of-neutral pitch down, a fatal error. And not an accidental error. An intentional, commanded error. What we are discussing here is why that command came into his mind (for the record, he has no idea). While executing a go around with a proper 15deg of pitch and 140kts indicated airspeed, and no stall warning or barberpole, what might have led him to call out "Down. Push it down"?

[BoeingBobby]

Not like it isn't done in the simulator every PC!

[Gabriel]

In this video there are several windshear-related go-arounds.

It called my attention that the pilots always call "go around" and follow go around procedures not only for the predictive windshear warning but also for the actual reactive windshear warning (or at least I think that some of them are reactive).

So what is the trigger to execute a windshear escape maneuver?

https://www.youtube.com/watch?v=3RTE5pS0akY

[Evan]

In this video there are several windshear-related go-arounds.

It called my attention that the pilots always call "go around" and follow go around procedures not only for the predictive windshear warning but also for the actual reactive windshear warning (or at least I think that some of them are reactive).

So what is the trigger to execute a windshear escape maneuver?

https://www.youtube.com/watch?v=3RTE5pS0akY

Well, obviously it is when the aural WINDSHEAR warning occurs and/or the PFD WINDSHEAR warning appears. TOGA + 15-20deg pitch until it is removed or you are clearly in positive climb above a safe altitude and out of danger. I mean, it is a lot like a go-around in terms of pitch and power because there isn't much else you can do, but with important differences, such as no configuration changes and no pitch reductions for any reason except stickshaker. In the desperate scenario of microburst it is pitch up to stickshaker. Do not sink!