Mooneys over mountains - riding a mountain wave.

[cnoe]

I thought I’d share an interesting experience from my latest trip into southern Colorado from my home base near the Texas Gulf Coast. For anyone flying over mountainous terrain this will demonstrate the awesome effects of wind over a mountain ridge and the resulting mountain wave effect. The phenomenon may extend many thousand feet above ground and may affect those flying turbo’d planes as well as normally-aspirated. FYI, on this flight I was in my normally-aspirated M20-J.

Departing Durango, CO (KDRO) on an IFR flight plan I climbed to my requested altitude of 15,000’ to top an overcast sky containing light snow with temps just below 0C. Icing was a possibility but pireps were positive so I kept a vigilant watch for any accumulation as I climbed briskly through the clouds. I broke out around 14,000’ without any trace of ice and was given a clearance for Direct-to the Albuquerque VOR (ABQ) shortly after leveling off at 15K. The winds along this route of flight were quartering from my rear at around 50 knots and the ride was fairly smooth. I experienced a few noticeable airspeed changes as my autopilot (altitude hold) eased up or down to hold the assigned altitude. After several minutes on course I requested and received a clearance for Direct-to CNX (the Corona VOR) southeast of Albuquerque.

As I approached the Sandia Mountain ridge that borders Albuquerque on the east I recognized a modest updraft as my airspeed increased nearly 20 knots while maintaining altitude (see photo Wave1). At this point I was at ~9,800’ AGL and on course to pass a few miles north of the highest peak (10,678’ MSL). Less than two minutes later I was again in straight-and-level flight a bit above 15,100 MSL with a typical cruise airspeed of 150 knots TAS (see photo Wave2).

Then, over the next minute-and-a-half my airspeed slowly eroded as the autopilot gradually pitched up more and more in an attempt to maintain the assigned altitude (see photo Wave3). At 18:47:35 Zulu I was still at 15,032’ MSL but experiencing a descent rate of over 450 fpm. My plane was climbing through the air-mass between Vx and Vy airspeed yet starting to lose actual altitude. I was nearly 7,300’ AGL and was not in any imminent danger but at that point I disconnected the altitude-hold and contacted ATC requesting a “block” of altitude due to the mountain wave. After a very-brief “stand-by” ATC returned with a block clearance of 15,000’ down to 13,000’.

As my altitude crossed below 15,000’ four seconds later (see photo Wave4) my rate of descent was passing 500 fpm. It wasn’t turbulent and I simply pitched to maintain airspeed. With still more than 7,000’ between me and the ground it was nothing to get excited about but was instead an event of great interest to me. Had I crossed the ridge at only 1,000’-2,000’ AGL it would have certainly been a bit more hair-raising.

Twenty-one seconds later my altitude had decayed another 128’ while my rate of descent was passing 750 fpm; I was obviously just “along for the ride” (see photo Wave5).

Thirty-seven seconds later my rate of descent reached a maximum of 868 fpm, all while in a full-power climb at 85 knots IAS (see photo Wave6). Just over one minute later my flight path bottomed out as the descent stopped approximately 1,000’ below my original altitude.

The entire ride lasted approximately three minutes and 45 seconds. A few minutes later ATC requested a Pirep which I gladly provided and upon reaching 15,000’ again I cancelled the “altitude block” request. I experienced some less pervasive wave activity over the next half-hour, none of which exceeded the performance capabilities of the plane.

My lesson learned in this was that adequate ground clearance (altitude) over the mountain ridge made this essentially a non-event. But with winds aloft of nearly 50 knots at my cruising altitude I would not have wanted to cross the ridge at only 2,000’ AGL or lower. Even at 3,000’-5,000’ AGL I believe the ride would have been alarming.

 

[carusoam]

CNOE,

Nice use of cloudAhoy for a flight data recorder.

High winds and 3D terrain can make for some interesting altitude changes...

Nice use of ATC, as well.

I have only experienced the mountain wave activity once.  In a C172, during IFR training much closer to the ground...  fortunately my CFII had the local experience.  I became a bit uneasy as the descent rate exceeded the climb rate.  I can see how a pilot would inherently want to keep pulling back on the yoke....

Thanks for sharing your experience.

Best regards,

-a-

[Marauder]

That is a pretty interesting flight. I had something happen on the flight back from the Mooney fly-in that I never experienced before as well. The winds weren't particularly strong at the surface, but we showing a solid 35 knots at 3,000 feet. As I was crossing over a ridge (probably 1,500 below me), with the AP on, I noticed a good 30 KIAS increase with the tail of the plane feeling like it was lifted. Lasted only for 5 to 10 seconds, but it was the strongest I have felt on the low hills around here. The other two Mooneys who flew in a similar direction didn't notice anything.

[thinwing]

Glider guys love pilot reports like this 

[carusoam]

I watched Paul/Rocket's recommended Redbull hang glider video last night... 

Tis the season for some awesome long X-country glider exercises...

Dial back the MP and see how much glide time you can get...  a whole new meaning for free flight...

Best regards,

-a-

[Skates97]

Thanks for sharing. Living out here I have tried to read up as much as I can on the mountain wave effect. With some trips planned from Corona (KAJO) to St. George (KSGU) as well as the Salt Lake area I am trying to educate myself as much as possible to avoid any problems. I was actually on the phone last night with a friend who has flown his Mooney frequently between Corona, CA and Bear Lake, UT asking him about what he looks for in the forecasts.

[cnoe]

1 hour ago, Marauder said:

That is a pretty interesting flight. I had something happen on the flight back from the Mooney fly-in that I never experienced before as well. The winds weren't particularly strong at the surface, but we showing a solid 35 knots at 3,000 feet. As I was crossing over a ridge (probably 1,500 below me), with the AP on, I noticed a good 30 KIAS increase with the tail of the plane feeling like it was lifted. Lasted only for 5 to 10 seconds, but it was the strongest I have felt on the low hills around here. The other two Mooneys who flew in a similar direction didn't notice anything.

 

1 hour ago, thinwing said:

 

Glider guys love pilot reports like this 

 

 Yep, when you're making 168 knots true airspeed at 15,000' in a J showing ~0 fpm on the VSI (as I was doing on approach to the ridge) it's a pretty good sign that you're in "glider heaven" and are about to be in "single-engine hell" once you cross the ridge.

[KSMooniac]

I cancelled a flight into the Rockies from KS 3 weeks ago due to 50+ knot winds aloft. I wanted no part of that crossing the big rocks going into Eagle or Rifle, so we stopped in Denver and drove the rest of the way. Mtn wave is something to be respected!

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[cnoe]

10 minutes ago, KSMooniac said:

I cancelled a flight into the Rockies from KS 3 weeks ago due to 50+ knot winds aloft. I wanted no part of that crossing the big rocks going into Eagle or Rifle, so we stopped in Denver and drove the rest of the way. Mtn wave is something to be respected!

Sent from my LG-LS997 using Tapatalk
 

I'm with you brother!

I scrubbed my flight into the area on Thursday the 23rd as the winds were already 50 knots across the ridges and 70 knots at 12,000' near Albuquerque. At safe altitudes I'd have been bucking 100+ knot headwinds and it still would have been a VERY rough ride.

One day later on the 24th I only took about 25 knots on the nose for the duration of the 850 nm flight as I was able to stay lower. Sometimes the best move is to simply not fly.

[dfgreene61]

Skates97 - I've been flying UT and ID for a long time and have never encountered a wave like the one cnoe describes.  Not that we don't have waves, I just don't fly if wind at ridge level is over 35kts.  Up to 25kts I'll fly over ridges 2,000+ agl.  Over 25kts I'll stick to the valleys at lower alt.  Bear Lake is a wonderful flight, nothing else like it in the west.  

 

 

[SantosDumont]

On my 4th or 5th flight ever I ran into the down side of a mountain wave after shortly after taking off from KMHV in a Cherokee 140 at about 2000 AGL.  Scared the ever living shit out of me as I was climbing at 75 and my IAS suddenly dropped below stall speed, stall horn wailed, wing went 45 degree bank and I dropped out of the sky for a few hundred feet before I recovered.  I almost gave up flying that day until I discovered that whiskey is a great cure for the shakes.

Mountain wave is something you want to be well above and never below.

Edited March 6, 2017 by SantosDumont

[wishboneash]

I have experienced similar mountain wave conditions in the Lake Arrowhead - San Bernadino - Banning pass area on the way to Palm Springs from Palmdale. With the AP on, you don't notice it until your view out the window changes and ground speed goes up / drops significantly.

[Hank]

I've found mountain wave activity just once in my C, coming by Mt. Mitchell (~6800 msl, highest point east of the Mississippi). It was a little windy, so I was at 10,000, and was slowly wafted 300' up, then lowered 600', and repeated several times, slowly tapering off. Each cycle was > 30 seconds, nice and gentle but noticeable. I did not try to hold altitude, just let my little Brittain hold course and up and down we slowly went . . . I was maybe 30 nm west of the peak at the closest, with winds out of the west (lots of 5000-6000' peaks out that way).

Turbulence, on the other hand . . . Nearly had my fillings shaken outhe on a similar route at 11,000 msl, where I had climbed hoping to reduce the jolt . . . No such luck. Fortunately it only lasted a half hour, like riding on an old dirt road, cinched down tight, bouncing and bucking and wishing for it to end. 

Edited March 7, 2017 by Hank

[thinwing]

Still...15 meter racing class Ventus B on my birthday dec 1989...Minden Nv,1800 fpm thru 37000...I will never forget...my triple Lenny experience

[mike28w]

I will never forget listening to Salt Lake center help a rather frantic Mooney near Jackson Hole.   He reported that he had just flown through a large mountain wave  ( clear day)  and was now looking to land at the nearest airport that center could find for him , "any airport"........

  I was heading west at the time , into that area......I spent the night in Casper, Wy...  No regrets for me !

[thinwing]

5 hours ago, dfgreene61 said:

Skates97 - I've been flying UT and ID for a long time and have never encountered a wave like the one cnoe describes.  Not that we don't have waves, I just don't fly if wind at ridge level is over 35kts.  Up to 25kts I'll fly over ridges 2,000+ agl.  Over 25kts I'll stick to the valleys at lower alt.  Bear Lake is a wonderful flight, nothing else like it in the west.  

 

 

Once upon a time....

[Marauder]

Once upon a time....

Interesting history on him. Did the mountain wave get him? Never said what caused the crash.

http://www.soaringmuseum.org/files/4iv_Symons.pdf


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[thinwing]

Not mountain wave..I think he was test flying a new 15 meter design ,a BG -12 that was built from plans or kits...I tried to get more info to see if it was a structural or control failure...no more info As far as I know...I think he headed up Sierra Wave Project in the 50 s

[thinwing]

19 hours ago, SantosDumont said:

On my 4th or 5th flight ever I ran into the down side of a mountain wave after shortly after taking off from KMHV in a Cherokee 140 at about 2000 AGL.  Scared the ever living shit out of me as I was climbing at 75 and my IAS suddenly dropped below stall speed, stall horn wailed, wing went 45 degree bank and I dropped out of the sky for a few hundred feet before I recovered.  I almost gave up flying that day until I discovered that whiskey is a great cure for the shakes.

Mountain wave is something you want to be well above and never below.

Actually ,it sounds like you experienced the "roter"..actual mountain wave  is very smooth ,very high rate of climb that doesn't extend very far down range from the generating peak.There is a wave window that is only a few miles on a side directly east of Freel peak south of Lake Tahoe.lt is used by ATC during wave activity so a glider can legally climb above 18 k and not be on an IFR flight plan and not require a tspd.Its kinda funny looking down on airliners westbound and atc calling traffic alerts.I am describing primary mountain wave...secondary and tertiary MW can form downstream but with much reduced lift..look for cigar shaped clouds.

[FloridaMan]

Flying across New Mexico on my way to Las Vegas pushing 50kt headwinds, I experienced an "I'm done" moment myself. It's like a little kid grabbed my airplane and played with it for about 15 seconds. Absolutely terrifying. 

[Tommy]

Not to rain on your parade, Cnoe, but do you think you got lucky this time around?

Aviation is all about giving yourself plenty of "way outs" and margins. I just failed to identify any with your flight. 10000-ft terrain in a NA single engine battling mountain waves / rotor... 

If it carried you higher, your engine will cough, splutter, and die

If it carried you lower...

How much extra time would it take to fly around it? 10 minutes? 5 minutes? 

[rpcc]

I'm a flatlander from the east coast and have never experience this.  Does the sink rate decrease as you approach the surface?  I can see that you would lose lots of altitude when the airmass is descending beyond your airplane's ability to climb, but what happens when as you approach the ground - does the decent rait continue or does it slow down as get closer to the ground?  I would think the airmass would need to spread out as the ground stops its descent.  

[carusoam]

Great question RPCC....

Vertical columns of air have a few methods of changing direction at the bottom...

The mountain behind you is going to lock the wind from going that way.

A tail wind isn't going to be very helpful if you ride it towards the ground.

The FAA eprints some good books.  Look up mountain waves and rotor clouds...

There are some standard strategies of how to avoid and get out of these situations.

Kind of like swimming and getting caught in an undertow current...  know before you go... 

 

Anyone have an answer or best place to look it up for RPCC?

PP thoughts, only. Not a CFI...

Best regards,

-a-

[cnoe]

Not to rain on your parade, Cnoe, but do you think you got lucky this time around?

Aviation is all about giving yourself plenty of "way outs" and margins. I just failed to identify any with your flight. 10000-ft terrain in a NA single engine battling mountain waves / rotor... 

If it carried you higher, your engine will cough, splutter, and die

If it carried you lower...

How much extra time would it take to fly around it? 10 minutes? 5 minutes? 

 

I appreciate your comments and the lively discussion. I'm certainly no expert on the subject of mountain flying but am instead a perpetual student. This was my 4th trip into the area in the past 3 years but I still realize I'm not yet ready to venture somewhere like Leadville or the high ranges of central Colorado. I'm a firm believer in progressive experience.

 

With that being said I still believe that I was well prepared and prudent in my planning for this particular flight. The climb-out at Durango was much more concerning to me than the ridge crossing due to icing concerns.

 

I approached the ridge at a 45 degree angle making an escape turn quite feasible, and I crossed in an area where my AGL was at least 7,000' the entire time. Even traversing the highest peak I'd have had ~5,000' of ground clearance. If I'd been flying 3,000'-5,000' lower I would certainly have deviated around the area.

 

While mountain waves can provide great lift and sink rates they are often smooth when encountered at sufficient altitude. Rotors on the other hand can be a beast but typically reside at the ridge height or lower and rarely exceed 2,000'-3,000' above that height. With 7,000' of ridge clearance I didn't feel in danger of a rotor incursion. And at 15,000' I was well above the conservative recommendation of 50% higher than the ridge for wave activity.

 

You are correct that I could have been carried higher by wave action but the biggest danger is being too low. I was already on O2 and regularly checking my O2 saturation. Had I not been on an IFR altitude assignment I would have been better off riding the wave "up" on the windward side but the altitude-hold had no problem maintaining altitude on the windward side. I DID have to hand fly the first lee-side wave to avoid a low-airspeed issue and that was a lesson not just for me but for anyone else reading this thread.

 

As far as the "engine-out" scenario you suggested, that's a total non-issue in my opinion. If I venture high enough that my engine will no longer run I'll simply pitch for best-glide and take her back down to an altitude where she lights up again. I encourage everyone to get comfortable with managing an engine-out. Running a tank dry, or pulling the mixture to idle-cutoff at altitude is truly a non-issue in these planes.

 

So in answer to your question... no, I think I was well-prepared rather than lucky in this instance.

 

 

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[cnoe]

 Anyone have an answer or best place to look it up for RPCC?
PP thoughts, only. Not a CFI...
Best regards,
-a-

There's some fairly good information here: http://www.pilotfriend.com/safe/safety/mountain_wave.htm



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