I was riding the jump-seat home a while back in one of our Airbus A300s. One of the plane's air conditioning units was down for maintenance, so they were limited to 25,000 feet. Since they couldn't top the weather, they were running along the leading edge of a cold front the entire way and my world was getting rocked back there! So much for my nap. I got home feeling like I'd spent an hour in the back of a cement mixer.
I've said it before, I don't like turbulence any more than you do. It's annoying at best and at worst it can be downright scary. Unfortunately it's part of flying and to this day we only have limited ability to predict it.
Hopefully knowing a little bit about it can make it less scary.
So what exactly is turbulence? Well, I know it when I feel it, but the layman's definition is "rough air". Note that there is no such thing as an "air pocket". That's an old term that has hopefully gone out of circulation.
In aviation there are several types of turbulence that can mess up our day.
Wake Turbulence
Wake turbulence is a byproduct of the process that creates lift and allows an airplane to fly. Imagine a horizontal tornado spiraling back from each wingtip. Generally speaking the larger and heavier the plane, the bigger and stronger its wake is.
Wake turbulence. This was part of a NASA study. I'd guess the cropduster was releasing colored smoke or powder so that they could get the picture.
Military flying often required us to fly large airplanes very close together. This created plenty of opportunities to run into somebody's wake. Hit a B-52s wake a mile back and it's like God's very own crowbar smacking you upside the head.
You're most likely to encounter wake turbulence while taking off or landing. The tower controllers will wait at least two minutes before letting a smaller aircraft take off behind a larger aircraft.
A few tricks the pilot of the smaller aircraft can use: try lift off before the takeoff point of the preceding aircraft and try to climb out more steeply than the preceding aircraft. That will keep you above its wake.
When in doubt wait it out. The wake from a heavy jet can take a light aircraft or even a small airliner and flip it on its back.
Clear Air Turbulence
So you're cruising along in a wide-body DC-10 or L1011, enjoying the fine cuisine and top notch service provided by the domestic airlines. Oh wait, this isn't 1975? OK, I'll start over.
So you're crammed into Seat 13C of a Canadair Regional Jet, next to an NFL lineman whose immense bulk is crushing you against the side of the plane. The insensitive jerk ahead of you has his seat reclined into your lap. As you reach for your tiny packet of pretzels and half a diet coke, the plane starts shaking. You spill your diet coke on the NFL player's leg, but fortunately he's asleep with his head on your shoulder so he doesn't notice.
You've just encountered Clear Air Turbulence. What causes it is a rapid change in wind speed or direction at altitude.
The FAA has four classifications of turbulence: Light, Moderate, Severe and Extreme.
What you are most likely to encounter is Light Turbulence or Light Chop. This is defined as
Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw). Report as Light Turbulence.
or
Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude. Report as Light Chop.
Occupants may feel a slight strain against seat belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be conducted and little or no difficulty is encountered in walking.
Light turbulence is just an annoyance. I seem to encounter it invariably after pouring a cup of coffee. Next up is
Moderate. Moderate is where it goes from annoying to downright uncomfortable.
Turbulence that is similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variation in indicated speed. Report as Moderate Turbulence;
or
Turbulence that is similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable change in aircraft or attitude. Report as Moderate Chop.
Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult.
Severe Turbulence sounds bad and it is. If you've never encountered it, pray that you don't.
Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control.
Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food service and walking are impossible.
"Aircraft may be momentarily out of control." Doesn't that sound fun? For those few seconds you have about as much control over the aircraft back there in 13C as the pilots do.
Fortunately it's rare, but there is such a thing as Extreme Turbulence. I generally don't want to hear the word "extreme" applied to anything involving aviation, although "extreme pay raise" wouldn't be too bad.
Turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may cause structural damage. Report as Extreme Turbulence.
Not much I can add to that. Yikes!
Unfortunately we have only limited ability to predict Clear Air Turbulence. If the wind speed or direction changes significantly from one altitude to the next we can probably expect to encounter turbulence.
Mostly we rely on Pilot Reports or PIREPs. You'll be glad to know that pilots of passenger airliners are constantly trying to find you smooth air. I hear them on the radio all the time looking for which altitudes have the best ride.
Since us box haulers are usually out ahead of even the red-eye flights in the early morning, they're often depending on us for PIREPs. You're welcome. Sometimes we'll joke that "the boxes aren't complaining", but I don't like taking a beating any more than you do.
Convective
Basically this is turbulence related to updrafts and downdrafts. Frequently associated with clouds or rain showers. You may run into this on a hot summer day with puffy clouds all around. Each one of those clouds is sitting on top of an updraft.
We actually have the ability to predict turbulence in rain showers. Since our doppler radar can see the movement of the raindrops, it can recognize turbulent areas. These show up as magenta on our radar screen.
The worst form of this is found inside thunderstorms. The best way to avoid it? Stay out of thunderstorms!
I was flying over Ohio one night and heard a certain Ypsilanti Michigan based cargo carrier penetrating a cell in their 747. I recall this part of the conversation:
"We were getting severe turbulence and altitude spikes plus or minus 300 feet in the cell."
Note to self. Never ever jump-seat with those guys.
Mountain Wave Turbulence
Mountain Wave ripped the vertical tail off this B-52. Amazingly they were able to land it.
Last but not least by any means is Mountain Wave Turbulence. This can be encountered any time you're on the downwind side of a mountain range. As the wind flows across the mountains it can form either a
lee wave or a
rotor. The rotor is the more dangerous of the two but either one can get your attention.
The "lee wave" over the top of a mountain range. Glider pilots love this. The rest of us not so much.
Mountain Wave "rotor". Very dangerous for light aircraft but no fun in a heavy either.
Be ready for it any time you're going in or out of an airport near the mountains.
We hit this in the 727 once going into Casper Wyoming. The plane was shaking so bad I couldn't read the instruments. Then one of our Cessna Caravan "feeders" landed right behind us. When the pilot came up on the radio she sounded like she wanted to get out and kiss the ground right then. I can only imagine what it must have been like in that little plane.
What to do
As a pilot we do our best to avoid anything worse than light turbulence. Since we can't always avoid it, there are some tricks we have for dealing with it.
Avoid the aptly named "coffin corner". At the very edge of the aircraft's performance envelope is a narrow airspeed window where going faster will overstress the airframe and going slower will stall the wing. Since precise airspeed control can be difficult in rough air, it's best to leave yourself some margin.
If you get into turbulence, slow down! This is very important. Every jet has a "turbulence penetration" speed that will keep the structure from being overstressed by a sudden gust loading.
Change altitude. If you're taking a beating at your current altitude start asking around for a smoother one.
Avoid wake turbulence. Usually not a problem since we know where to look for it. If you get into somebody's wake, offsetting slightly to one side may get you out of it.
What can you do as a passenger? The biggest thing, numero uno, is to wear your seatbelt! Wear it all the time, even if the "fasten seatbelt" light is off. Unless I have to get up to use the bathroom, I never take my seatbelt off. The same goes for your kid. Keep them belted in. Sorry if they don't like it but they'll like having their head smashed against the overhead even less.
You see, except in very extreme cases, turbulence doesn't hurt the airplane. Jet airliners are built to take it. As long as the pilots slow down and don't do anything stupid, the plane will probably be just fine.
What hurts people is getting bounced around the inside of the plane during turbulence.
Think about it for a second. You're dealing with forces capable of tossing 800,000 pounds of 747 around. Unless your initials are "Incredible Hulk" you won't be strong enough to hold onto little Junior in a severe turbulence encounter. Keep 'em belted in and yourself too. Trust me on this one. I went floor-ceiling-floor in the back of a B-52 once because I wasn't strapped in. It hurt. A lot.
If you have a choice of aircraft, the bigger the better. The same gust that will toss a CRJ 70 around will barely budge an Airbus 380. Jets tend to ride better than turboprops, because the same wing that lets a turboprop take off from a short runway also causes it to bounce around more in turbulence.
If you have a choice of seats, just ahead or over the wing is the best ride. An airplane is like a teeter-totter. It pivots around its center of gravity in turbulence. The closer you can sit to the center of gravity the better. The worst ride is back in the tail. I try to avoid those last rows if possible.
That's all I've got. Smooth sailing, er flying.