Marenostrum

airspeed managing

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Posted (edited)

Imagine this scenario:

I am cruising at FL370

The weather radar is showing some cumulonibus along my route.
They are on the right and on the left.
With a small deviation I am able to fly in the middle without crossing neither of them but the separation is about 10 mils so I expect turbulengce also in the clear sky in the middle of the two.
I fly and suddendly I enter in a not to heavy turbulence but the airpeed starts  to fluctuate and to enter in the overspeed zone.
What to do?
How to properly manage the airpeed in these conditions?
Can I allow the aircraft to violate the overspeed zone for some seconds whilst the autothrottle is slowing down to recover the situation?
Or have I to anticipate slowing down before entering in the supposed critical zone?
If I have to slow down...at what speed?

Thank you to all real pilot in advance!!!

 

Edited by Marenostrum

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1 hour ago, Marenostrum said:

What to do?

Look on the cruise page. There will be a value called TURB N1. Kick the autopilot off and set that manually with your throttles. Leave it there until the conditions subside.

1 hour ago, Marenostrum said:

How to properly manage the airpeed in these conditions?
Can I allow the aircraft to violate the overspeed zone for some seconds whilst the autothrottle is slowing down to recover the situation?
 Or have I to anticipate slowing down before entering in the supposed critical zone?
If I have to slow down...at what speed?

See above.

Also, check the turbulence slider in your weather program. It might be too high.

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Thank you...I will check it.

The AS16 turbulence factor has been moved many times (back) , expecially for the extreme sensitivity with the Majestic Q400 aircraft but The PMDG737 seems to behave better...anyway, have you any suggested sliders setting for AS16 on P3D 3.4?

Thank you

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3 hours ago, Marenostrum said:

Thank you...I will check it.

The AS16 turbulence factor has been moved many times (back) , expecially for the extreme sensitivity with the Majestic Q400 aircraft but The PMDG737 seems to behave better...anyway, have you any suggested sliders setting for AS16 on P3D 3.4?

Thank you

My sliders in ASP4 for turbulence effects are generally 25-30%.  Minor technical point concerning your WXR painting "cumulonimbus" is that WXR doesn't paint clouds but the precipitation, primarily ice, from within the cloud.  The cloud type is not a factor as far as the radar is concerned.  Second issue is that I have a friend that flew his Cessna Citation between two cells as you described and ended up flying into an undetected third cell that almost killed him.  He lost both the radome and leading edges, lost left PFD.  He was following his failed attitude indicator into a death spiral when his copilot hit him and pointed to the FO instruments, it was so loud they couldn't hear each other on the intercom, and he was able to recover after a loss of almost 20,000 feet. He still had engines,  but if he had lost engines  he wouldn't have recovered.  A 10 nm gap between cells is not wide enough, I'd keep at least 20 nm from an active cell and even there some turbulence in the real world could be expected.  Flying with him today one can see the stress on his face when we fly through even the lightest of precipitation.

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It doesn't take anywhere near severe turb to cause enough of an airspeed fluctuation to result in an overspeed, so there's not really a need to reference turb N1 in the box.  

A few techniques:

1.  Slow a bit before penetrating an expected area of turbulence. .76 - .77 mach is usually the middle of the safe speed window.  If you're in vnav you can do this by changing cruise speed in the box or using speed intervention.

2. If a fluctuation heads towards an overspeed, disconnect the autothrottles and retard the throttles to no lower than about midrange.  I'm not sure how the sim behaves, but if the real engines are pulled to idle at altitude, the spool-up time is significant.  Crews have put themselves into a stick shaker situation doing that. 

3.  If you need more decel, smoothly deploy the speed brake. 

4. Remember, an overspeed is not an emergency. If, despite your efforts, one occurs, just try to note the parameters for the subsequent mx write up.  ("overspeed, approx .84 mach for several seconds, FL360, weight 153.0").  No need for anything heroic; crews have gotten themselves into trouble, hurt FAs/pax and even caused a departure while trying to prevent or correct a minor overspeed.

5.  Last thing, tangentially related: in reality, it's common practice to not fly a 737 more than, say, 500 feet above optimum altitude. If you claw your way up to what the box reports is max altitude, not only are you burning a lot more gas up there (yes, even though you're higher), but your airspeed window is tiny. 

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Regarding distance between cells... It depends on the cells.  I don't have AS16 so maybe it does a better job, but my ASN does a lousy job depicting thunderstorms, visually and on radar.  Even a solid line is rendered by ASN into oversmoothed blobs.  I haven't used the NGX radar much but I remember thinking its picture was just like the radar display within ASN, so I'm sure it's an ASN issue.  Without a semi accurate radar and visual depiction of storms, it's pretty impossible to apply any realistic judgement to weather avoidance; about the best you can do is stay out of the red. 

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Posted (edited)

To downscc

Thank you for your reply (I will check my sliders). I am sorry that I did not take a picture of the radar image ( I will do next time) but I can say that:

- what it was visible in the air was what I expected to see in the radar image: two clear cumulonimbus that from their base arrived at an altitude higher than my FL370. In this sense it seems that AS16 depicts the sky quite well (compared to the radar image in this and other situations)
- both similar, with the radar image showing them thick and round with a clear strong precipitation in the middle. The highest level of precipitation in the core was very wide and large like almost all the perturbation, so I expected a very strong gradient that was telling me...STAY AWAY
- the shape was almost round and not depicting an irregular  shape with the risk of a shadow situation (neither the radar image showed this risk).

From what you say it seems that your friend falled in a shadowed cell (scary!!) bt I do not know if the weather radar of the Citation has the same features of the NGX, neither I know if the NGX radar is in reality so clever to find potential shadowed cells! I know it is the same (with some modifications) of the Airbus A320.

To Stearmandriver

all you say makes sense to me: to summarize
stage 1: try to slow down (I assume slowing down with the autotrhottle intervention) to a speed .76 - .77 BEFORE THE POTENTIALLY DANGEROUS ZONE
stage 2: if not enough....disconnect autotrh. and  retard the throttles to no lower than about midrange
stage 3: third stage....deploy the speed brake

What I worry (at FL370) is exactly the small speed window between overspeed and the stick shaker intervention speed.

In this sense, if I have "clear sky space" to reduce my FL due to the "verticality" of the two perturbations, could it be a solution also to reduce my FL, should we say from FL370 to FL340?

Is there a specific SOP addicted by each airline or are they general rules valid for all?

Really thank you to satisfy my immense curiosity!

Edited by Marenostrum

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55 minutes ago, Marenostrum said:

neither I know if the NGX radar is in reality so clever to find potential shadowed cells!

There is no magic involved, just more power.  The small nose of the Citation does not permit as large an antenna and I'm sure the high end stuff installed by air carriers also have much more powerful radar transmitters.

As for the simulated radar image and visual clouds, in my opinion, these are very rudimentary and barely represent what those monsters look like either visually or on an airborne radar.  Most ground pounders are used to the weather service provided doppler radar pictures.... these are very different from airborne radar.  so while you will get away with brushing aside a towering CB in the simulator, you would not chose to do that real world.  That was the only point I was making with my hangar story.

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Posted (edited)
11 minutes ago, downscc said:

so while you will get away with brushing aside a towering CB in the simulator, you would not chose to do that real world.  That was the only point I was making with my hangar story.

Sorry for my lack in understanding (english is not my mother language) ..when you say the in the real world you would fly differently you mean that you would stay far away from such a situation without flying in the middle of the two CB?

Edited by Marenostrum

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1 hour ago, Marenostrum said:

when you say the in the real world you would fly differently you mean that you would stay far away from such a situation without flying in the middle of the two CB?

Yes.  I would fly between two small cumulus, maybe with tops 16000, but I would never fly into a 10 nm gap between two CB that are 30,000 or higher.  In the US midwest, we see CB that top 50,000 and it's wise to stay 50 nm away from these beasts.

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4 hours ago, downscc said:

Yes.  I would fly between two small cumulus, maybe with tops 16000, but I would never fly into a 10 nm gap between two CB that are 30,000 or higher.  In the US midwest, we see CB that top 50,000 and it's wise to stay 50 nm away from these beasts.

Agreed.  Most air carrier SOP is to avoid strong echoes by at least 20nm.  As Downscc no doubt knows, that doesn't always happen but it's a good starting point. Also, from a real - world standpoint, you're always better going around a strong cell on the upwind side.  Anvil blowoff, with accompanying turbulence and hail/icing, blow much farther from the cell downwind.  That's not to say there aren't backsheared anvils with mammatus, hail, and rear flank downdraft that'll kill you, just that they don't extend as far upwind from the cell. 

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6 minutes ago, Stearmandriver said:

Agreed.  Most air carrier SOP is to avoid strong echoes by at least 20nm.  As Downscc no doubt knows, that doesn't always happen but it's a good starting point. Also, from a real - world standpoint, you're always better going around a strong cell on the upwind side.  Anvil blowoff, with accompanying turbulence and hail/icing, blow much farther from the cell downwind.  That's not to say there aren't backsheared anvils with mammatus, hail, and rear flank downdraft that'll kill you, just that they don't extend as far upwind from the cell. 

Great guidance. 

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Very interesting topic here,

thank you for your explanations: this is an area where the simulation is unable to be like the reals world.

Only few days ago I was flying on a real 737 NGX of Ryanair from the north of Italy to Sicily....the sky was an amazing picture...with a lot of CB. They where far from us and similar to what the simulator with AS16 and REX soft clouds depicts ...but what the simulator cannot simulate is how they are dangerous.

4 hours ago, Stearmandriver said:

 Most air carrier SOP is to avoid strong echoes by at least 20nm

I did some calculation...in the situation that I described it meant do deviate the course toward the upwind side of the right cell, then to fly around it staying at least 20NM away then to reconnect the original flight path.....in other words to extend the flight path of about 100 NM or more !!!!

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4 hours ago, Marenostrum said:

I did some calculation...in the situation that I described it meant do deviate the course toward the upwind side of the right cell, then to fly around it staying at least 20NM away then to reconnect the original flight path.....in other words to extend the flight path of about 100 NM or more !!!!

Yup... Depends on the situation, but when it's necessary, it's necessary. I've gone much farther out of my way than that before. 

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8 hours ago, Marenostrum said:

I did some calculation...in the situation that I described it meant do deviate the course toward the upwind side of the right cell, then to fly around it staying at least 20NM away then to reconnect the original flight path.....in other words to extend the flight path of about 100 NM or more !!!!

This is routine during the spring/summer storm season in the US.  For example, I'm just down the coast 200 nm from Houston and there have been days when I went North of College Station to get there, adding at least 100 nm to a 200 nm trip. 

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9 hours ago, Marenostrum said:

I did some calculation...in the situation that I described it meant do deviate the course toward the upwind side of the right cell, then to fly around it staying at least 20NM away then to reconnect the original flight path.....in other words to extend the flight path of about 100 NM or more !!!!

Yup... and that's why you checked the SigWx and other weather charts for your route beforehand and added some extra fuel, right? 😋

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15 hours ago, downscc said:

This is routine during the spring/summer storm season in the US.  For example, I'm just down the coast 200 nm from Houston and there have been days when I went North of College Station to get there, adding at least 100 nm to a 200 nm trip.

I see you are used to fly in a zone that is also hit by twisters..is it?

How are those cells seen by the cruising altitude?

What SigWx says and what to do?

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14 hours ago, skelsey said:

Yup... and that's why you checked the SigWx and other weather charts for your route beforehand and added some extra fuel, right? 😋

Sure 🙂

 

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8 hours ago, Marenostrum said:

How are those cells seen by the cruising altitude?

You cannot tell if a storm has or will spawn a tornado by looking at it in the air from an airplane.  Tornadoes do seem to come from a storm system that has multiple embedded CB but it's not true that such a system is required for or will always spawn tornadoes.

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You can often visually tell if a storm is rotating by horizontal banding, called striations, that appear on the main updraft.  Some extreme examples on this image search :

https://www.google.com/search?hl=en-US&biw=360&bih=255&tbm=isch&sa=1&ei=hlQ2W-ivEdLB0PEPzviSkA8&q=supercell+striations+aerial&oq=supercell+striations+aerial&gs_l=mobile-gws-wiz-img.3...0.0..6461...0....0.0.......0.1OQiLagx4wQ%3D

I have some more "typical" weak supercell (rotating thunderstorm) photos on my ipad from just last week, I think.  I'll see what I can find.

Most supercells do not produce tornados, but they're all severe enough to rip a jet into little pieces and spit them out the top, if you happen to wander into the main updraft. 

There are some visual indications of tornadogenesis, but you have to know what you're looking for.  Things like rear flank downdraft coupled with a rapidly forming clear slot, a collapsing then recycling overshooting top etc... Not stuff the average pilot would know about.  I only know this because atmospheric science is my background and I spotted/chased for the National Weather Service in the Midwest USA for years... In other words, I'm a weather nerd ;-). 

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19 minutes ago, Stearmandriver said:

Some extreme examples on this image search :

 

The pictures attached are very scary!!!! I For sure it is not necessary to browse the SOP to stay away from them more than 50nm. 

Some of them in the pictures are also very wide, tall and, if it is not enough, twisted ...to fly around such a large beast it could be a long way.

I suppose that inside them you find a mix of all the scary situations: high speed wind variation with rapid variation in direction, ascending and descending currents, hail, heavy rain...
I have read that they can build inside also vertical windshear  at high altitude rotating updraft!! (I knew about the descending windshear at low altitude dangerous in the approach phase, not vertical windshear dangerous at a cruising FL).

If I were a pilot facing a beast like that...I would like to be in a sim!

 

 

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1 hour ago, downscc said:

You cannot tell if a storm has or will spawn a tornado by looking at it in the air from an airplane.  Tornadoes do seem to come from a storm system that has multiple embedded CB but it's not true that such a system is required for or will always spawn tornadoes.

Interesting...

In any case from the pilot point of view, the key point is if these types of cells can be flown over their top or if they are the kind of monster that climb up to over FL350 ... so you can just stay away and fly around.

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2 hours ago, Stearmandriver said:

There are some visual indications of tornadogenesis, but you have to know what you're looking for.  Things like rear flank downdraft coupled with a rapidly forming clear slot, a collapsing then recycling overshooting top etc... Not stuff the average pilot would know about.  I only know this because atmospheric science is my background and I spotted/chased for the National Weather Service in the Midwest USA for years... In other words, I'm a weather nerd ;-). 

Fascinating. I flew by the storm that visited a tornado on Ft Worth ripping out windows from skyscrapers and didn't know it until I saw the news.  I was departing Dallas Redbird to the South so my route gave me a nice long view of it and I was glad I was heading away.  I lived in Norman OK for about four years and knew a few that worked at the National Storm Center... very sharp people, very dedicated.  As far as I'm concerned NOAA is one of the best branches of the unarmed government.

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1 hour ago, Marenostrum said:

In any case from the pilot point of view, the key point is if these types of cells can be flown over their top or if they are the kind of monster that climb up to over FL350 ... so you can just stay away and fly around.

If you're talking about the big tornadic supercells, you aren't going over unless you're in a U2 ;-). These types of cells can top FL600; that's well into the stratosphere where weather isn't supposed to be able to reach, but these updrafts are powerful enough to bust through the cap of the tropopause. 

Over still might not be a great idea in something like a U2; these storms also produce two rare types of lightning called sprites and jets that extend upwards from the storm basically to space.  They seem to be the electrical field of the storm interacting with the ionosphere.  Probably no one knows if it's possible to be struck by them but I wouldn't be the one to test it lol. 

OK, sorry, I'll reign in the weather geekery. 

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