Mountain wave PIREP

[Flying_Nun]

Say what? Is 20 kts that critical in the flight levels?

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[FORANE]

Is a B738 type the same as a 737 max 8?

 

[PaulS]

Reading about mountain waves, or gravity waves in Scott's new book, interesting stuff.

 

[MooneyDriver78]

Say what? Is 20 kts that critical in the flight levels?

At 37000’ that’s pretty close to its ceiling limit I would think, so their IAS would be pretty low.


Tom

 

[3393RP]

Is a B738 type the same as a 737 max 8?

It's a 737-800 NG, part of the -700/-800/-900 Next Generation series.

 

[PaulS]

Say what? Is 20 kts that critical in the flight levels?

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Potential coffin corner issue??

 

[Todd82]

Is a B738 type the same as a 737 max 8?

737 Max 8 is "B38M" in that nomenclature.

 

[mwagg737]

Say what? Is 20 kts that critical in the flight levels?

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Depends on weight. Yes, could be a problem.


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[mtuomi]

Say what? Is 20 kts that critical in the flight levels?



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Yes it is. It really is. Especially when you're heavy.

 

[benyflyguy]

Yes it is. It really is. Especially when you're heavy.

So help me learn more about this. I read about it on Wikipedia but want to learn a bit more. Can you give an example perhaps?

 

[1RTK1]

...

 

[mtuomi]

So help me learn more about this. I read about it on Wikipedia but want to learn a bit more. Can you give an example perhaps?

The envelope between redline and stick shaker gets pretty narrow high up when you're heavy.
The plane I fly, for example, at 85'000lbs and FL410 has a speed envelope of 25kts between the redlines. You cannot even turn the plane without losing altitude at that point. 1.3g moderate turbulence would stall the plane.

A more realistic scenario would be something like 80'000lbs and FL390. It's 67kts there, you cruise probably roughly halfway in the envelope, so 20kts loss will get you uncomfortably close to the stick shaker.

 

[PaulS]

The envelope between redline and stick shaker gets pretty narrow high up when you're heavy.
The plane I fly, for example, at 85'000lbs and FL410 has a speed envelope of 25kts between the redlines. You cannot even turn the plane without losing altitude at that point. 1.3g moderate turbulence would stall the plane.

A more realistic scenario would be something like 80'000lbs and FL390. It's 67kts there, you cruise probably roughly halfway in the envelope, so 20kts loss will get you uncomfortably close to the stick shaker.

Stick shaker, which is uncomfortably close to stall. Let's say you do stall, what happens then?

 

[mtuomi]

Stick shaker, which is uncomfortably close to stall. Let's say you do stall, what happens then?

You push the nose down, you don't have any excess power. You will easily lose around 3000-4000ft of altitude on the recovery.

 

[benyflyguy]

so while airspeed is important.. is it more a function of loss of lift due to less dense air- hence needing more airspeed (IAS) to generate more “air” Over the wing.
Until This moment. The idea of a plane zipping along at 450kts in level flight stalling was something I never even dreamed possible.

 

[mtuomi]

so while airspeed is important.. is it more a function of loss of lift due to less dense air- hence needing more airspeed (IAS) to generate more “air” Over the wing.
Until This moment. The idea of a plane zipping along at 450kts in level flight stalling was something I never even dreamed possible.

Yes, you have to remember that the plane zipping at 450kts probably has his indicated airspeed in the mid 200's in very thin air.