"Whoop Whoop, Pull Up" vs. Stall Recovery?

[Center_Mid]

Does a GPWS usually emit a "whoop whoop, pull up" warning when the aircraft starts descending in an aerodynamic stall? Wouldn't a "pull up" command contradict stall recovery procedure? This question arose after reading about the NTSB report in the Empire ATR 42 crash in Lubbock:

"The captain continued the unstabilised approach, even though he received additional stick-shaker activations and an aural 'pull up' warning from the terrain awareness and warning system [...]"

I don't fly anything close to an ATR and never have. But it seems like the stick shaker is telling the pilot to push the nose over while the GPWS is screaming pull up. Maybe those two cues aren't contradictory if you can power an ATR out of a stall in a nose-up attitude, but is that realistic on a low approach?

 

[jynxyjoe]

Does a GPWS usually emit a "whoop whoop, pull up" warning when the aircraft starts descending in an aerodynamic stall? Wouldn't a "pull up" command contradict stall recovery procedure? This question arose after reading about the NTSB report in the Empire ATR 42 crash in Lubbock:

"The captain continued the unstabilised approach, even though he received additional stick-shaker activations and an aural 'pull up' warning from the terrain awareness and warning system [...]"

I don't fly anything close to an ATR and never have. But it seems like the stick shaker is telling the pilot to push the nose over while the GPWS is screaming pull up. Maybe those two cues aren't contradictory if you can power an ATR out of a stall in a nose-up attitude, but is that realistic on a low approach?

I was pretty sure the "pull up" was warning of imminent crash due to low altitude or soon to be low altitude (peak of mountain coming up).

Tough on I don't really know :/ I would guess it is irrelevant because if you are getting the shaker while getting the pull up it's all over with anyhow.

 

[Center_Mid]

I would guess it is irrelevant because if you are getting the shaker while getting the pull up it's all over with anyhow.

That's what I was thinking. The NTSB used the words "additional stick-shaker activations" meaning the earliest cues would be to push the nose over. By the time you get a GPWS aural warning, maybe it's too late anyway.

 

[dasleben]

Does a GPWS usually emit a "whoop whoop, pull up" warning when the aircraft starts descending in an aerodynamic stall? Wouldn't a "pull up" command contradict stall recovery procedure? This question arose after reading about the NTSB report in the Empire ATR 42 crash in Lubbock:

"The captain continued the unstabilised approach, even though he received additional stick-shaker activations and an aural 'pull up' warning from the terrain awareness and warning system [...]"

I don't fly anything close to an ATR and never have. But it seems like the stick shaker is telling the pilot to push the nose over while the GPWS is screaming pull up. Maybe those two cues aren't contradictory if you can power an ATR out of a stall in a nose-up attitude, but is that realistic on a low approach?

Well, realistically the shaker is a warning of an impending stall, not the stall itself. Proper recovery for that isn't necessarily to push over (you're not in the stall yet), but of course, it isn't to pull back either. Unless you're low to the ground, you won't get both the GPWS and shaker activating at the same time.

 

[TUCKnTRUCK]

Well, realistically the shaker is a warning of an impending stall, not the stall itself. Proper recovery for that isn't necessarily to push over (you're not in the stall yet), but of course, it isn't to pull back either. Unless you're low to the ground, you won't get both the GPWS and shaker activating at the same time.

You will get both in an airplane that has older, non integrated systems. Older atr's may lack a warning tone prioritization system

 

[BobDDuck]

You will get both in an airplane that has older, non integrated systems. Older atr's may lack a warning tone prioritization system

I've gotten both in the sim in a CRJ. If you run a landing stall scenario where you follow the glideslope down, fully configured and at 1000 AGL pull the power to idle you will get a shaker by about 600 feet and if you pull it back (which is a bad, bad, VERY bad thing to do) until you get a pusher before adding any power in, you will generally recover at about 50 feet with both the stall warbler and the GPWS alert going off.

At least that is my recollection. I also vaguely remember seeing the trees on the riverbank just short of 27R in PHL going out the top of the visuals on the sim.

 

[Center_Mid]

If you run a landing stall scenario where you follow the glideslope down, fully configured and at 1000 AGL pull the power to idle you will get a shaker by about 600 feet and if you pull it back (which is a bad, bad, VERY bad thing to do) until you get a pusher before adding any power in, you will generally recover at about 50 feet with both the stall warbler and the GPWS alert going off.

If you push the nose over at around 600 feet in response to the shaker, do you get a GWPS alert? How hard (or how many degrees) would you have to push the nose down?

 

[BobDDuck]

If you push the nose over at around 600 feet in response to the shaker, do you get a GWPS alert? How hard (or how many degrees) would you have to push the nose down?

No idea, but if you wait for the pusher to knock the nose over you get about 1600 fpm down before you can add power and start (sort of) climbing.

 

[dasleben]

If you push the nose over at around 600 feet in response to the shaker, do you get a GWPS alert? How hard (or how many degrees) would you have to push the nose down?

Like I said above, you won't push in response to a shaker. A shaker is simply a warning of impending stall. There won't be altitude loss associated with a shaker unless you allow it to develop into an actual stall. Generally you'll fly the aircraft out of a shaker with thrust. If you get the stick nudger (actual stall), well, it's probably aircraft dependent like TUCKnTRUCK mentioned. I go back to the schoolhouse in a couple weeks for my fun and exciting 6 month sim event, so I guess I'll have to give it a shot.

 

[Hacker15e]

Isn't the "Pull Up" command generated by the GPWS? In that case, until the RALT and DTED data start showing that a collision with the ground is immimnent (based on flightpath, closure rate, and proximity to the dirt), I don't see how it relates to a stall or stick shaker (which is generated by AOA, I'm assuming).

 

[dasleben]

Isn't the "Pull Up" command generated by the GPWS? In that case, until the RALT and DTED data start showing that a collision with the ground is immimnent (based on flightpath, closure rate, and proximity to the dirt), I don't see how it relates to a stall or stick shaker (which is generated by AOA, I'm assuming).

I think the question is about whether the GPWS or shaker gets priority if both occur at the same time. That's at least how I read it.

 

[SpiraMirabilis]

It's been a while since I've flown anything above 12,500 but on the mighty Dash-8 as far as I remember there was no stall warning tone, just the stick shaker and that isn't generated by the GPWS and the GPWS doesn't know what your AoA is either -- so there is nothing that would stop both the stick shaker and the GPWS low terrain warning from going off. The first terrain warning won't be the Whoop Whoop Pull Up though, unless you're in a bad way.

By the way, the "Pull Up" is not a command that you have to follow. It says "Pull Up" because "Increase Rate of Climb" is too long to say when you're about to hit a mountain.

 

[Center_Mid]

By the way, the "Pull Up" is not a command that you have to follow. It says "Pull Up" because "Increase Rate of Climb" is too long to say when you're about to hit a mountain.

I figured as much, but I thought that for some pilots hearing "pull up" might instinctually prompt a pull up reaction. Like Hacker15e wrote above, I assumed GWPS basically calculates that the flight path leads to a collision with terrain. I then wondered whether, in certain circumstances, the GPWS could be saying "pull up" when the correct response is to do the opposite. Or, is it always going to be too late if you're in a stall and hearing the GPWS go off?

As far as the shaker goes, I understand that it's triggered pre-stall, but if the aircraft is porpoising through successive stalls, won't the shaker de-activate and re-activate? As more and more forward energy continues to bleed off and the aircraft descends after each oscillation, I would think you could get a condition where the GPWS is going off while the shaker is activating.

 

[jynxyjoe]

I figured as much, but I thought that for some pilots hearing "pull up" might instinctually prompt a pull up reaction. Like Hacker15e wrote above, I assumed GWPS basically calculates that the flight path leads to a collision with terrain. I then wondered whether, in certain circumstances, the GPWS could be saying "pull up" when the correct response is to do the opposite. Or, is it always going to be too late if you're in a stall and hearing the GPWS go off?

As far as the shaker goes, I understand that it's triggered pre-stall, but if the aircraft is porpoising through successive stalls, won't the shaker de-activate and re-activate? As more and more forward energy continues to bleed off and the aircraft descends after each oscillation, I would think you could get a condition where the GPWS is going off while the shaker is activating.

I would assume this. Keep in mind though, I've been taught the GPWS is a "oh no!" moment where you pull up with full power unless you've got VFR day conditions.

I've been given situations in the sim where you can actually fly within close proximity (can't see the peak of the mountain) of a mountain and not get a warning until you so far past any logical response time. It's a situation where you have day VFR conditions, the mountain is filling the entire picture, and the GPWS just carries along its merry way with red across your Nav screen. Then you get this, "Oh hey, you're dead in 10...9...8..." you get the picture.

 

[fish314]

Isn't the "Pull Up" command generated by the GPWS? In that case, until the RALT and DTED data start showing that a collision with the ground is immimnent (based on flightpath, closure rate, and proximity to the dirt), I don't see how it relates to a stall or stick shaker (which is generated by AOA, I'm assuming).

I imagine it would be possible to link the two in certain airplanes, but I don't know of any that are. The tanker has E-GPWS (enhanced GPWS, whatever that means), and it talks to the TCAS. So you can't get a "Descend, Descend" for traffic and a "Pull-UP, pull-Up" from the GPWS at the same time. In fact, I have to check the books, but I think the TCAS just turns off below a certain altitude. So, I would imagine that it's probably a similar process to link a stick shaker to GPWS... but again, don't know if anyone has actually done that. We've got "natural" stall warning, so no shakers, horns, etc.

 

[BobDDuck]

TCAS II normally goes to TA only (no RA) mode below a preset altitude. I think ours is 1000 feet.

The CRJ has a stall warbler that activates after the aircraft stalls. The chronology, which occurs at various speeds in relation to the actually stall speed depending on the alpha margin is: continuous ignition, stick shaker and warbler and then a stick pusher.

I've only ever seen a pusher in the sim (thankfully) but there are scenarios (windshear is one I can think of) where we will get an intermittent shaker/warbler and pusher as you try to get your best pitch rate and not stall the aircraft. Some people call it humping the moose.

 

[jynxyjoe]

TCAS II normally goes to TA only (no RA) mode below a preset altitude. I think ours is 1000 feet.

The CRJ has a stall warbler that activates after the aircraft stalls. The chronology, which occurs at various speeds in relation to the actually stall speed depending on the alpha margin is: continuous ignition, stick shaker and warbler and then a stick pusher.

I've only ever seen a pusher in the sim (thankfully) but there are scenarios (windshear is one I can think of) where we will get an intermittent shaker/warbler and pusher as you try to get your best pitch rate and not stall the aircraft. Some people call it humping the moose.

In the windshear demo's we've been taught to look for the red caterpillar and shoot for ten knots under. Meanwhile keep an eye on the yellow eyebrows and try to follow and anticipate.

For a dumb Tprop guy like me, seeing that red thingy move and being able to anticipate the yellow eyesbrows sure helps.

You ever been presented with that technique? Any thoughts?

 

[SpiraMirabilis]

I figured as much, but I thought that for some pilots hearing "pull up" might instinctually prompt a pull up reaction. Like Hacker15e wrote above, I assumed GWPS basically calculates that the flight path leads to a collision with terrain. I then wondered whether, in certain circumstances, the GPWS could be saying "pull up" when the correct response is to do the opposite. Or, is it always going to be too late if you're in a stall and hearing the GPWS go off?

As far as the shaker goes, I understand that it's triggered pre-stall, but if the aircraft is porpoising through successive stalls, won't the shaker de-activate and re-activate? As more and more forward energy continues to bleed off and the aircraft descends after each oscillation, I would think you could get a condition where the GPWS is going off while the shaker is activating.

It might confuse a student pilot, but by the time you're flying an airliner you should be more experienced and recognize the conditions each GPWS alert comes at.

The GPWS has a few of different modes:

Mode 1 alerts when you have an excessive rate of descent when in proximity with the ground. You will hear the "soft" warning "SINKRATE" first, then "SINKRATE, PULL UP PULL UP".

Mode 2 gives an alert if your flight path will bring you into proximity with terrain. It is divided into 2 submodes, Mode 2a and Mode 2b -- the difference is if you have landing flaps set 2b will be checked for, otherwise 2a will be checked for. First the caution of "TERRAIN, TERRAIN" -- this warning can be inhibited by a switch and you have to do that in a couple of airports. The hard warning is TERRAIN TERRAIN, PULL UP PULL UP.

Mode 3 covers just after take off (or go-around) If you lose a certain percentage of altitude gained then it will trigger and the first soft warning is I believe DON'T SINK, followed by TOO LOW TERRAIN.

Mode 4 will check if your too low and the gear and flaps not extended -- TOO LOW FLAPS, TOO LOW GEAR

Mode 5 goes off if you're deviating too far off the glideslope and are in close proximity to terrain. It will yell GLIDESLOPE.

Mode 6 is the WINDSHEAR, WINDSHEAR alert. I don't think we had Mode 6 on the Dash-8-200.

Here is a list of alerts and their priority within the GPWS system, since someone was talking about the priority before:

1 WINDSHEAR WINDSHEAR WINDSHEAR
2 PULL-UP (SINK RATE)
3 PULL-UP (TERRAIN CLOSURE)
4 PULL-UP (TERRAIN CLOSURE)
5 V1 CALLOUT
6 TERRAIN TERRAIN PULL-UP
7 WINDSHEAR AHEAD
8 TERRAIN TERRAIN
9 MINIMUMS
10 CAUTION TERRAIN
11 TOO LOW TERRAIN
12 TOO LOW TERRAIN
13 ALTITUDE CALLOUTS
14 TOO LOW GEAR
15 TOO LOW FLAPS
16 SINK RATE
17 DONT SINK
18 GLIDESLOPE
19 MONITOR RADAR DISPLAY
20 APPROACHING MINIMUMS
21 BANK ANGLE
22 RA (CLIMB, DESCEND, ETC.)
23 TA (TRAFFIC, TRAFFIC)

 

[BobDDuck]

In the windshear demo's we've been taught to look for the red caterpillar and shoot for ten knots under. Meanwhile keep an eye on the yellow eyebrows and try to follow and anticipate.

For a dumb Tprop guy like me, seeing that red thingy move and being able to anticipate the yellow eyesbrows sure helps.

You ever been presented with that technique? Any thoughts?

I have not. What is the "red caterpiller"? I'm assuming it's on the airspeed tape? Our recovery involves simply flying the flight director (which often times is pitching up and down like crazy). We are specifically taught to ignore the eyebrows as far as pitch guidance goes.

In the sim I've always felt that a severe windshear recovery was pretty uncontrolled. I had a 35 knot loss at 50 feet going into DCA on 33 a few months ago, and while it was pretty intense, it was very controllable powering out of on the go around, which leads me to believe that the sim's reproduction of windshear escapes (much like it's reproduction of single engine handling characteristics) is pretty much a WAG by the engineers and not a duplication of reality.

 

[jynxyjoe]

I have not. What is the "red caterpiller"? I'm assuming it's on the airspeed tape? Our recovery involves simply flying the flight director (which often times is pitching up and down like crazy). We are specifically taught to ignore the eyebrows as far as pitch guidance goes.

In the sim I've always felt that a severe windshear recovery was pretty uncontrolled. I had a 35 knot loss at 50 feet going into DCA on 33 a few months ago, and while it was pretty intense, it was very controllable powering out of on the go around, which leads me to believe that the sim's reproduction of windshear escapes (much like it's reproduction of single engine handling characteristics) is pretty much a WAG by the engineers and not a duplication of reality.

What type are you in? The CRJ-900 is my first glass cockpit (unless you count the EFIS on the tprop) so maybe you have another type with a different cues from the magic box. The red caterpillar is the cue for stall. On the earlier post I said 10 knots under I should have said "over".

Back in 'Nam I didn't have any of this crap.