Strong downdraft, Wave?

[jimhorner]

I had an interesting thing happen to me this past weekend while flying back home from Long Beach to San Jose, and I thought I would share the experience and perhaps get some ideas on what was happening.

I was cruising along in my Bellanca Super Viking at 8000 ft at about 160knots TAS. The Stec-60 autopilot was on in altitude hold mode and the GPSS mode was following the Garmin 430W's magenta line. All was right with the world.

Around Santa Maria, the plane started to pitch up quite noticeably with a corresponding speed decay. Even with the pitch-up the plane wasn't maintaining altitude. I turned off the autopilot and took control. In a level attitude, I was in about a 1000 fpm descent. The engine was running fine and producing good power. It was clear that the autopilot had implemented the pitch up in order to maintain altitude, and that was going to lead to a stall at some point because there was just no way either it or I was going to be able to maintain the 8000ft.

I called the controller and reported the situation, and he immediately gave me a block altitude clearance of 6000-8000ft. A couple of minutes later, the descent stopped and I was able to climb back to 8000 and continue on home. Having the block altitude helped, because I was able to keep the speed up, trade altitude for speed, and get out of the sink pretty quickly.

It seem pretty clear that I was in some sort of significant sinking air, and I'm wondering if maybe it was some sort of wave action over the San Rafael mountains? There was no turbulence to speak of, and my ground speed was close to my airspeed, so I'm not sure that there was much of a horizontal component of wind, but there sure was a significant down component! Maybe just a big area of sinking air? Not sure about the wave theory, since I don't think there was all that much wind.

Anyway, it was strange. Glad I was high enough to ride it out.

The picture below shows the ground track and speed and altitude graph from flightaware as well as a detailed picture showing the speed and altitude at various points during the incident. I went from a ground speed of ~200mph to around ~125mph in just a few minutes.

 

[dell30rb]

Yes, that happens. You can be in completely smooth air and experience a mountain wave downdraft/updraft. If that is not the proper definition, forgive me. But something I have experienced.

Instead of fighting the downdraft, assuming you have plenty of terrain clearance, the right thing to do is actually to maintain your airspeed until you are out of the downdraft. Don't fight it. This way you will spend less time in the downdraft. When you hit the updraft, climb as fast as you can.

Happened to me once, i was lightly loaded at 8000 feet in a warrior during the winter. going down 500 FPM while at full throttle and at Vy. Completely smooth air.


I was headed west over the appalachians. Terrain 20 miles ahead rose to 6000 feet. Winds were strong from the west (I had a ridiculous headwind). I went down as far as 7200 msl, then caught an updraft and rode up to 10,000 feet. I crossed at 10k with no more wave action.

 

[jimhorner]

Yes, that happens. You can be in completely smooth air and experience a mountain wave downdraft. If that is not the proper definition, forgive me. But something I have experienced.

Instead of fighting the downdraft, assuming you have plenty of terrain clearance, the right thing to do is actually to maintain your airspeed until you are out of the downdraft. Don't fight it.

Happened to me once, i was lightly loaded at 8000 feet in a warrior during the winter. going down 500 FPM while at full throttle and at Vy. Completely smooth air

Yeah, I'm thinking wave, but I guess I would have expected some wind for that, and I don't think there was much wind to speak of. Could be wrong though on that. However, the METAR for Santa Maria was showing calm...

I did get into the downside of a wave in New Mexico one time, with the same sort of issue about holding altitude. However, that time the air was ROUGH. I was definitely feeling shaken and not stirred then.

Definitely agree about maintaining the airspeed. There was a delay while I was diagnosing what was going on. Increasing pitch on the autopilot, autopilot off, level attitude and seeing the 1000fpm down, determining that the engine wasn't losing power, then the ah-ha "I'm in some sink here" moment. Once that happened I put the nose down a bit and scooted out of there.

 

[tonycondon]

Mountain wave by definition is smooth air. And yes speed up in the sink to minimize altitude lost and slow down in the lift to gain it back.

 

[dell30rb]

Yeah, I'm thinking wave, but I guess I would have expected some wind for that, and I don't think there was much wind to speak of. Could be wrong though on that. However, the METAR for Santa Maria was showing calm...

It does take wind. What was the wind aloft?

Were there any cumulus clouds around? You can get into sink while between rising cumulus clouds.

 

[Henning]

Had the plane pitched down and picked up speed prior? As soon as you get in a leeward mountain wave approaching from downwind, you will typically get into a lift before you get to the down. As soon as you note the lift, you want to cut the ALt Hold and climb with the lift, because you are about to run into the sink that you want to dive in to get out the backside as quick as possible. I try to take a pitch that takes me just over the ridge. If I am below ridge level in the sink, I turn to intersect the slope parallel and get behind a mountain and climb next to the slope to take advantage of the lift as I climb to go around it on the windward side. From this approach the air currents will help me climb.

It sounds like you got into it with reasonably mild winds and the up draft may have been very weak if the down was only 1000fpm. When the Santana's are blowing 70 kts though, the ride can be a wild one. Once on the way from LGB- Vegas I got hit by a lift that pegged my VSI as I approched Lake Arrowhead. I called ATC, "04Y is in an uncontrolled climb and don't know how high I'm going" and they issued me a clearance and a block to FL210. Luckily I was in my TN-Travelair with O2 if I needed, but I didn't

 

[Henning]

Yes, that happens. You can be in completely smooth air and experience a mountain wave downdraft/updraft. If that is not the proper definition, forgive me. But something I have experienced.

Instead of fighting the downdraft, assuming you have plenty of terrain clearance, the right thing to do is actually to maintain your airspeed until you are out of the downdraft. Don't fight it. This way you will spend less time in the downdraft. When you hit the updraft, climb as fast as you can.

Happened to me once, i was lightly loaded at 8000 feet in a warrior during the winter. going down 500 FPM while at full throttle and at Vy. Completely smooth air.


I was headed west over the appalachians. Terrain 20 miles ahead rose to 6000 feet. Winds were strong from the west (I had a ridiculous headwind). I went down as far as 7200 msl, then caught an updraft and rode up to 10,000 feet. I crossed at 10k with no more wave action.

Actually the correct response for the down draft is dive for airspeed to get out the backside ASAP.

 

[jimhorner]

It does take wind. What was the wind aloft?

Were there any cumulus clouds around? You can get into sink while between rising cumulus clouds.

That's the thing, since my GS was about equal to my AS, I don't think there was much wind aloft, at least at my altitude. No clouds in the sky at all.

Can a wave have regions of calm under the peaks? Meaning if the wind is strong higher up, can there be regions of not much wind before entering the region where the wave is causing the downdrafts?

 

[jimhorner]

Had the plane pitched down and picked up speed prior? As soon as you get in a leeward mountain wave approaching from downwind, you will typically get into a lift before you get to the down. As soon as you note the lift, you want to cut the ALt Hold and climb with the lift, because you are about to run into the sink that you want to dive in to get out the backside as quick as possible. I try to take a pitch that takes me just over the ridge. If I am below ridge level in the sink, I turn to intersect the slope parallel and get behind a mountain and climb next to the slope to take advantage of the lift as I climb to go around it on the windward side. From this approach the air currents will help me climb.

It sounds like you got into it with reasonably mild winds and the up draft may have been very weak if the down was only 1000fpm. When the Santana's are blowing 70 kts though, the ride can be a wild one. Once on the way from LGB- Vegas I got hit by a lift that pegged my VSI as I approved Lake Arrowhead. I called ATC, "04Y is in an uncontrolled climb and don't know how high I'm going" and they issued me a clearance and a block to FL210. Luckily I was in my TN-Travelair with O2 if I needed, but I didn't

No, no noticeable pitchdown or airspeed increases prior. Everything was going fine, straight and level until the autopilot started its pitchup effort to maintain the altitude.

 

[tonycondon]

my hypothesis is the wind was northeasterly and you went through the wave with mostly a crosswind, hence why your groundspeed and airspeed were close, and also why you spent so much time in the downdraft.

sometimes there is only a primary, no secondary and tertiary, etc.

turbulence is UNDER the wave not over it. The rotor is under the crest of the wave and that is the bumpy part. The wave itself is smooth.

Clouds are optional just depending on how moist the airmass is. Both of the times that I have wave soared in Oklahoma have been cloud-free.

Next time find the updraft side, pitch down and speed up to stay level and turn parallel to the ridge. zoom zoom.

 

[Bill Watson]

Definitely mountain wave effects there.

The autopilot in altitude hold mode will do exactly the wrong thing from the standpoint of efficiency but if you are on a clearance you might just let it go. Otherwise as others have said, dive and go faster through the sink -- slow down and let her climb in the lift. Turbulent rotor is not always present but if you see a ragged looking cumulus type cloud with no bottom, stay away from it.

 

[RalphInCA]

Several people here have recommended that if this happens you not try to maintain altitude "if you have plenty of clearance"

My question is how do you know if you have plenty of clearance?

How do you know how far you will sink before you are out of the downdraft?


Sent from my iPhone using Tapatalk

 

[tonycondon]

you don't so if you are approaching the ridge from the lee side, approach at a 45 degree angle and be ready to turn away if you're not sure you will clear it

 

[Henning]

Several people here have recommended that if this happens you not try to maintain altitude "if you have plenty of clearance"

My question is how do you know if you have plenty of clearance?

How do you know how far you will sink before you are out of the downdraft?


Sent from my iPhone using Tapatalk

The same way you know if you'll make the threshold. If it is moving down in your sight picture, you will clear it. If it is moving up in your sight picture, you will not.

 

[jimhorner]

my hypothesis is the wind was northeasterly and you went through the wave with mostly a crosswind, hence why your groundspeed and airspeed were close, and also why you spent so much time in the downdraft.

That actually makes a lot of sense.

 

[Henning]

That actually makes a lot of sense.

Yep, also may explain why you missed the up draft.

 

[denverpilot]

I had an interesting thing happen to me this past weekend ...

The guys in the UPS Airbus were whining to ZDV that their autopilot ran out of throttle and they fell off their assigned altitude by 400' in the flight levels, the night I was flying home from LNK to APA and the flight started for me showing a 98 knot ground speed at 8500 MSL.

You gotta love a multi-state westerly blow in the winter. Heh. Wind wind and more wind that night. I did my best salmon trying to spawn impression and eventually made it home.

 

[Richard]

I know that route very well. From KSBA to KSMX I have experienced the same when winds are from every point except 270. The OP didn't say the winds and the last week has had some different weather so Tony may be correct about winds out of the NE.

About half way between Avenal and Priest VORs (AVE and ROM) there is a mountain. It isn't really that high (although it sets the MEF for that grid) but it is massive. I forget it's name but I call it Mt. Turb. It can set up a flow to rattle your teeth even when flying V-25. If the winds were N - NE you were down wind of Mt Turb.

Whenever I have contacted mtn wave, it is best to try to slide up or down wind a bit to see if the ride stabilizes.

Story time: one time while heading north at 8,500 at just north of KIZA Santa Ynez I was ascending over 1,500 fpm. I could not keep from entering the assigned alt of a Lear at 11,000 opposite direction. Before ATC could say anything I began to descend faster than I had gone up. I heard the Lear say his AP couldn't keep up with the uncommanded alt change of his aircraft. We slipped past one another at about same alt but about one mile horizontal separation because we both turned to the right. Winds aloft were from the south and it was the hills north of SBA which were the culprit that time. The Santa Lucia Mtns usually don't cause any trouble except where they turn to run east/west in the Pt Conception/Santa Barbara region.