Backcountry Pilot

The mountains make their own rough air. Wind pouring over a ridge, wave trailing off a peak, thermals coming up off a sun-baked valley, a pass that was calm in the morning and howling by noon—if you fly the backcountry, you fly turbulence. When it gets rough, you slow to maneuvering speed. But...when is it rough enough to pull the power? How slow is slow enough? And is the V_a in your flight manual even the right number once you've burned off half your fuel? Pilots flying central Idaho, the passes of the Alaska Range, and other backcountry areas have worked through this. Here's what they've figured out.

1 Know Your Own Threshold for Slowing Down

"I use two techniques. If things are 'trending' rough, I know the trim and power settings that will get me VA. If all hell is breaking loose, power back and pitch up to bleed speed quickly then fiddle with it later."
— flyingzebra
VA

Determine your threshold and your response to turbulence. On your next calm flight, note the exact power setting and trim that settle your airplane at V_a, and commit them to memory. Then when it's rough, you're able to act quickly. Have two responses ready: gradual settings for when it's slowly building, and a quick "power back, pitch up" for when it hits all at once.

"Typically if it's hard to adjust a heading bug, swap a freq, or write on my note pad it's slow down time, or try a different altitude or course, if I'm having to make notable corrections on my controls to maintain course it's VA time."
— Belloypilot
VA

When the routine tasks start getting difficult, the air is telling you something. Determine where you'll act. As it gets bumpier, there are less options. By the time you can't reach the throttle, the decision's been made for you.

"I pull the throttle when I get pissed. Usually, if the turbulence is enough to frustrate me, I slow it down. Or, when my two-year-old daughter yells 'Dad, the airplane is too tippy!'"
— CParker
VA

If you're getting rattled or your passengers are white-knuckling, that's a sign to take action. You’re not riding a mechanical bull although sometimes turbulence feels that way. Smooth it out, cowboy.

2 Know What "Severe" Actually Looks Like

"...not everyone perceives, or responds to turbulence the same. Part of that is related to your experience. Once you've ricocheted your noggin off the roof a few times, you tend to really, really cinch up those lap belts...I took my instrument checkride in the LA basin during a Santa Ana wind event...I was just completing the first steep turn when we hit one of those...the examiner, who was a pretty big guy, was slammed up against the ceiling, almost to his shoulders, with his head pushed way to the side. When he came down off the roof, he said 'That's good, let's land this thing.' I passed, but what a ride."
— mtv
My Lesson in Mountain Turbulence

Your tolerance for turbulence is personal and could change with experience or how you are feeling that day. What a bush veteran calls "a little bumpy" may be the edge of your envelope, and that's fine.

If you're uncomfortable with the conditions, turn around, wait it out, or not launch at all. If you do go, monitor whether the ride is getting better or worse.

Maule in Alaska. From the thread: Fly a Maule South From Alaska! (25 hours dual offered). Photo: asa

3 V_a Only Covers One Input, in Smooth Air

"Many pilots believe that as long as the airplane is at or below this maneuvering speed, they can make any control inputs they desire without any risk of harm to the airplane. This is not true...The design maneuvering speed (VA) is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only...in smooth air, without risk of damage to the airplane."
— PapernScissors, quoting FAA SAIB CE-11-17
Turbulence, How Much Is Too Much

In turbulence, you're getting hit on multiple axes at once by gusts, not making one clean input. Download SAIB CE-11-17 from the FAA, so you have it on hand. In practice, treat V_a as a "don't exceed" ceiling in rough air, not a floor you're safe beneath.

"...just slowing down 'a little bit' may bite us. We should slow down a lot and be VERY gentle with our control inputs. Some stuff I've read suggests the true Vturb (Turbulence penetration speed) is pretty close to Vy. That's a whole lot slower than Va."
— PapernScissors
Turbulence, How Much Is Too Much

Slow down more than you think you need to and be gentle on the controls. Some references put the turbulence-penetration speed down close to V_y, a good deal slower than V_a. A useful way to fly it: look up V_y for your airplane and treat the band between V_y and V_a as your rough-air working range. When it's genuinely bad—rotor on the lee side of a ridge, wave coming off a peak—fly toward the slow end of that band and stop chasing every bump with the yoke. Down in the canyons, that slower speed buys you a tighter turning radius, if you need to reverse course out of a pass that's going downhill.

4 When in Doubt, Land and Wait It Out

"...the primary and most effective way to deal with turbulence is to reduce speed. Sometimes you need to go a little slower, sometimes a lot slower (even more than just reducing speed back to maneuvering or turbulent air speed). Sometimes, you need to reduce your speed to zero and put on the tiedown ropes."
— EZFlap
Turbulence, How Much Is Too Much

Set down at a strip and wait a few hours for the wind to lie down. Plan for it before you go. Pick out a couple of fields along your route ahead of time, ideally ones you wouldn't mind being stuck at for a while. When the air gets rough, you already have a place to sit it out.

“More wave clouds: lenticulars and frayed rotor wisps” Mountains in Montana. From the thread: Five weeks of adventure with my Super 170. Photo: 140eagles

5 Find Your Own Airplane's "Mushy Waves" Speed

"In the Maule, I have found that slowing down to 90 or 100 mph air speed turns a lot of the jolts into mushy waves. Since your Bearhawk wing is a little longer, I suspect a little slower still would make a more comfortable experience."
— DeltaRomeo
My Lesson in Mountain Turbulence

There's a speed for every airframe where sharp jolts turn into softer, rolling swells, where the airplane stops slamming and starts wallowing through the bumps.

Wing design drives a lot of it. A longer, higher-lift wing generally wants a slower speed than a shorter one to settle into that "mushy" feel, which is why the number that works in a Maule isn't the number that works in a longer-winged Bearhawk. On a moderately bumpy day, experiment a little and note the speed where your airplane feels most settled, then write it down alongside your other rough-air numbers.

Panamint Springs Resort. From the thread: Backcountry Strips Near Las Vegas/ Boulder City? Photo: Fiddler

6 Plan the Route, and Read the Terrain, Before You Go

"When able to climb above, I try to clear mountainous terrain by 2,000 feet if the wind is blowing. When down in it, I try to make sure I am familiar with the realistic maneuvering speed for my weight configuration and fly that whenever it gets rough."
— Troy Hamon
My Lesson in Mountain Turbulence

Handling turbulence well is mostly about being prepared: knowing your airplane, your numbers, and your terrain. When winds aloft are up, build a 2,000-foot terrain buffer into your plan where you can, cross passes and ridgelines on the windward side, and leave the leeward canyon for a calm day. Windy lets you preview winds at altitude: drop a point on the map and step up through the levels with the altitude slider. One caution: those levels are modeled by pressure (hPa), not true MSL, so over high terrain the lower readings can be unreliable or even sit "below the ground". Check the wind at ridgetop level; if it's strong up where you'll be crossing, plan to stay low in the canyons instead.

"...Envisioning the wind as flowing like water over the mountains really helps to predict where the turbulence might be...I always check winds aloft, if the winds aloft at peak level are above 25knots, I fly low in the canyons and don't fly over any passes or not at all."
— CParker
My Lesson in Mountain Turbulence

The wind speeds up and smooths as it climbs the upwind face, then tumbles into rough, rolling air on the back side, the same way water churns just below a boulder. Reading terrain helps you estimate where the bad air will be before you fly into it: thin and fast over the crest, messy just past it.

This explains why lower is sometimes the smoother ride. Down in a pass you can be beneath the wave and rotor that build above and behind a ridge, so a line a thousand feet below the ridgetops can ride easier than one a couple thousand feet above them. This occurs at some passes and not others, so you need to have an understanding of the specific terrain. If the winds aloft at peak level are much above 25 knots, that's a sensible personal trigger to stay down in the canyons, or to not go at all.

7 Flying Technique for Rough Air

"Flying in NM on hot desert afternoons is not fun because of the thermal activity. The ground below you is at 6000' MSL which makes the cloud bases out of reach of your aircrafts ceiling, so over the top is not an option. Riding it out in the bumps below requires slowing down."
— DeltaRomeo
My Lesson in Mountain Turbulence

Desert and mountain-valley turbulence is largely thermal-driven, so it builds through the day. An early-morning departure gives you glassy air compared to bumpy air mid-afternoon. If you're stuck flying it midday, favor the shaded or windward side of the terrain and keep an escape route in mind—a valley or lower ground you can turn toward.

Next time you're in light chop with altitude to spare, try steadying the wings mostly with rudder and tolerating small bank excursions, and see if the ride smooths out. When you chase every dropped wing with aileron, the adverse yaw you create just feeds the wing-rock you're trying to stop. Using more rudder and less aileron settles the airplane noticeably in moderate turbulence.

"When you're in a strong downdraft increase airspeed...this will get you out of the down air quicker. The ride might be more miserable but you'll get to better air quicker. It's kind of like spin recovery."
— saddletramp
Turbulence, How Much Is Too Much

Another option besides adding airspeed, fly the windward side, stay off the lee, and cross ridges at a 45-degree angle so you can turn toward lower ground if it goes bad. And don't count on the air "flattening out" near the ground to save you, the airplane's own inertia can keep driving it down even after the wind turns horizontal. Don't be low over the lee side to begin with.

8 Adjust V_a for Weight—It Isn't a Fixed Number

"The heavier you fly, the faster maneuvering speed is, so operations at GW are substantially different than running light. And different airplanes have speeds in very different ranges in relation to their cruise operations, so you have to know what the specifics are."
— Troy Hamon
My Lesson in Mountain Turbulence

Maneuvering speed drops as the airplane gets lighter. The V_a you departed with at full gross is too fast once you've burned off fuel or dropped a passenger at a backcountry strip. On a mountain leg you're usually heaviest outbound and lightest coming home, so the number you fly to should change over the course of the trip rather than staying pinned to the gross-weight figure. And because different airplanes carry their speeds in very different ranges relative to cruise, you have to know your own specifics.

"A longtime pilot/check airman from Naknek 'GT' always said it's one of the most important speeds and to know how it varies with weight...I'm not as tolerant as I was before.....grey hairs."
— TVATIVAK71
My Lesson in Mountain Turbulence

Know your weight-adjusted maneuvering speed for each load by heart. Work out your V_a at a few representative weights—empty, typical load, and gross, so the right number is already in your head when the air gets rough.

"The formula to calculate our weight adjusted Va is: Vanew=((current weight/GTOW)^1/2)*(Va at GTOW)...I've found for my plane the reduction in Va (or Vy) works out to about 1 kt per 100 lbs under GTOW."
— PapernScissors
Turbulence, How Much Is Too Much

Your weight-adjusted V_a equals the gross-weight V_a times the square root of (current weight ÷ gross weight). Run it once for a few weights and you'll notice that there's roughly a knot slower for every hundred pounds under gross. See the reference below.