I’m not a good flier. I’m particularly unnerved when the road is bumpy. Today, the pilot told us that he had reports that the flight would be choppy from San Diego to Chicago, and we’d be cruising at 29,000 feet. Enjoy the flight. As it was, we flew much of the time bumping and bouncing around. If they know the air is choppy, why don’t they fly someplace else, e.g. another altitude, a modified route, etc. My guesses: it might cost too much to change the flight path too much. (Maybe an acceptable reason.) The air might be choppy at all altitudes from here to there (seems unlikely). It might be too hard to keep track of all the air traffic moving up and down (seems unlikely). A combination of these? Maybe. Something else? Maybe. Any help here, Dopers?
I’m more then posative several of the flying dopers will chime in with the correct answer, but my guess is that even though it may be choppy and somewhat rough and/or unnerving, it’s still perfectly safe. As long as it’s safe and flyable it’s probably too much work to rearrange every plane’s path to go around rough weather.
It’s primarily an issue of too many other aircraft in the air to make re-routing easy.
29,000 is a little (but not by much) low for that length of flight, but there was probably LA - Chicago traffic at 31,000, and Phoenix - Minneapolis at 30,000, etc. The routes and elevations are hypothetical, but there truly are a lot of airplanes flying any any particular moment, and there are some large spacing requirements between them all.
Speaking of too many aircraft, just yesterday, I was a little surprised to see that two different airlines had flights leaving San Jose, CA for Denver not 15 minutes apart, from adjacent gates.
So, not only could they bump into each other in mid-air, if they flew at the same altitude, but they might even dent each other’s wings while taxiing from their gates to the runway. 
On United Airlines you can usually listen to the cockpit communications on channel 9 of the entertainment system. I’ve often overheard conversations in which the pilot is asking ATC for another altitude because of “light chop” at the level the airplane is currently flying. Sometimes the controller will say that other aircraft have reported the chop at all available altitudes, so the pilot just doesn’t have a good alternative.
Ed
Airline pilot here …
Most enroute turbulence, and particularly from the West Coast to abeam central Kansas (ie 2-1/2 timezones out of four) is driven by the jetstream. You’ve probably seen the graphics on the Weather channel.
When that snaky band of wind extends down from British Columbia to central AZ, then turns north again up towards South Dakota, then snakes south again towards Mississippi, then the entire USA is going to have a bumpy ride. The only practical way to avoid it is by altitude. Going from San Diego to Chicago by way of El Paso, New Orleans, Cincinnati then Chicago would take waay too long and probably require at least one stop for fuel. And you’d still have to penetrate it at least once, taking 30+minutes if you could cut straight across it, more if you’re cutting diagonally.
Normally, the region of turbulence is only maybe 4000-6000 feet thick. That sounds like it’d be easy to avoid. Not really. Despite all the talk of recession, they sky’s pretty full of jets these days. The altitudes available for eastbound operations are 25,000 feet, 27000, 29000, 33000, 37000, and 41000.
Many older jets can’t get to 41000 at all and maybe 1/4th of the newer ones can’t get to 37000 on that long a flight. They simply lack the power to climb that high So their choices are more limited. If the turbulence extends from say 28000 to 35000 (altitudes used for westbound traffic), then all the traffic that normally fits into 29000 & 33000 is trying to squeeze into 27000 or 37000 if they can make it up there.
Imagine a 3-lane freeway with 2 lanes closed. That’s what 27000 starts to look like. Some airplanes above the norm can fit down into the smoother strata, not all. So the pilot stuck at a bad altitude faces a choice: bump along as we are, while trying to get a minor routing change to get to a better altitude, or drive an hour out of the way (and be an hour late) hoping (since we can’t see this stuff) that we’ve guessed correctly on a direction that’ll actually avoid it.
The other choice is to drop below the jet altitudes to the low-mid 20’s, avoid the traffic, and watch your fuel consumption jump 20%. If yu planned for that and took extra gas, it just means your employer is losing even more money on this flight than usual. If you didn;'t plan for it, or couldn’t carry the extra gas due to weight or capacity contraints, then dropping down to a smooth altitude means stopping in Kansas City for gas. It’s not out of the way leterall, but just like pulling off the interstate for fuel, by the time you do the offramp, into the station, and back on to the onrap, you’ve blown at least an hour and your schedule is trashed.
When the turbulence is so bad that a route or altitude is impassible, such as when it’s casued by thunderstorms, not the jetstream, then the choice is easy. Safety is job #1 and we drive out of the way as required, stoip for gas as needed, and to heck with the schedule and customer’s connections and people waiting to meet them and …
But when the bumps are merely annoyance level, the need to keep most of the customers happy by arriving close to on-time precludes making a couple of people happy by spending an hour or more deviating around.
Rest assured we don’t enjoy bouncing along any more than you do. We’re not nervous about it, but it is a PITA, and we sit through it enough day in and day out that avoiding it is real high on our list of things to do, within reason.
p.s. Quit worrying. I know it’s hard not to, but the sort of turbulence that’d hurt the airplane is so far different from the stuff you were experiencing, it’s like the difference between a hurricane and a breeze. Every few months you hear of a passenger or flight attendant being hurt when they encounter a real severe jolt and they bounce off the ceiling. Guess what. It didn’t hurt the airplane, and therefore didn’t risk the other passengers. Seat belt on = no worries.
My point is not that we’re cavalier about trying to avoid turbulence, but just that if you’ve got your seat belt on, there’s nothing a sane pilot would ever fly into that could hurt the jet or you. Spill your soda in your lap, sure, but injury … no way.
I’ve seen three different airlines all leaving Heathrow for Dublin in a similar timescale - even ended up with all the luggage on the same carousel. And yes, my flight was 3/4 empty :dubious:
LSLguy is the expert here but I’ll echo one thing that he said that came to mind while reading the OP.
Most of the other passengers are willing to endure even a few solid hours of choppy stuff if it means getting to theur destination faster. I’m somewhat sensitive to motion myself (even a fast elevator leaves me a little quesy) and it would have to be extreme turbulance for me to want to fly a few thousand miles out of the way, especially with a fuel stop.
One more thing…
CC when you get on an airplane and hear us make a PA about turbulence, it means that we have looked at the route of flight and have run through all of the possibilities that LSLGuy mentioned, but we cannot avoid the turbulence that is out there.
The PA is to tell people that this flight will not be smooth.
It will be SAFE, of course. Flying in (up to moderate) turbulence is NOT unsafe. It may be unpleasant, but it is NOT unsafe. The light chop that self-stirs your drink is nothing more than expansion joints on a highway.
Have you ever driven off of a paved road onto a dirt road? When the dirt road got rough, did you slow down?
We do the same thing in the air: we try to find the paved road, but if everything is rough then we slow down and plow along the dirt road.
Now: when you were on the dirt road in your car, did you fear for your life? No. Were you safe? Yes. Was it unpleasant? Yes.
Use the same logic the next time you fly: smooth would be ideal, but bumpy (while unpleasant) is not unsafe.
An aside:
LSLGuy, have you noticed that these airline/airplane threads come and go in waves?
We can go three months with no question that I have answer for, and suddenly there are three within one day.
(And of course I’m late getting back that day and you’ve answered them all! 
)
Pilot 141: Yup. I suppose one thread triggers the thoughts in the backs of the other poster’s minds.
Damn crazy schedules. You’ll cover for me next week. No sweat.
(p.s. It always seems to me like I get to these threads long after you’ve been there 
)
Does it take more fuel to fly at lower altitudes than at higher altitudes?
Yes. The whole reason aircraft fly high is because it is faster and more efficient. I’ll let Pilot141 and LSLGuy explain in more detail.
The explanation is not too complicated. It is because the air is more dense at lower altitudes than higher altitudes.
I too am a “poor” air traveller. pilot141’s comment hit the nail on the head for me:
I get completely anxiety ridden during chop because I start to anticipate a really big “drop”. I’ve tried to work through this on the highways (since the bumping there can often be worse than typical turbulence), but it doesn’t work because on a road I know I’m on a flat surface and can extrapolate the worst vibration I’m likely to encounter (no 15 ft unexpected potholes).
The vibrations are “limited”.
On an airplane, during my anxiety-time, I can’t make that same adjustment; for all I know we’ll suddenly plunge 500 feet and just as suddenly rise.
If pilot141 could tell me that such plunges during turbulence are rare or physically impossible, then I (and maybe others) might be able to travel a little easier. Or better still, tell us what is happening during the worst of chop; are we falling or rising a vast amount of height? Does it just seem really bad?
Many thanks.
Plus, I would imagine, gravity (and therefore drag) is stronger. But if it takes more fuel to fly at lower altitudes, then couldn’t it sometimes be impractical if not impossible to change a high altitude to a lower one just to avoid turbulence?
Nice follow-up, Bob. I have similar questions. I’ve gotten to the point that I’ve imagined that the chop is the same thing (basically) as a bumpy road, and it helps somewhat, but I get stuck on the fact that I’ve never experienced a sudden hole in a road that caused me to drop, say, 30 feet, and then raised me up again like a too-fast elevator - which seems to be what these occasional “air pockets” must be like. I’m getting better at flying, but it’s not easy. Knowing more helps. Pilots who are friendly, open and sympathetic about the chop are much better than those who don’t ever say anything. I appreciate LSLguy and Pilot141 weighing in here. Knowledge and understanding trump fear any day.
A back-of-the-envelope calculation indicates that the difference would be negligible. Consider a 5000-foot difference in altitude. That would put the plane 1 mile closer to the center of the Earth’s mass. So, it would be 3999 miles from the center instead of 4000 miles (very roughly). That’s a difference of 1 mile out of 4000. Since the effect of gravity varies with the square of the distance, the force of gravity would change by one part in 16 million. (Have I got this right, or do I need more caffeine before attempting feats of crude mathematics?)
Sucks to be that flight attendent, though. :eek:
That’s something LSLGuy mentioned; that if you do drop down to a lower altitude, the fuel consumption rises accordingly. Impractical, and more expensive, but not impossible.
Oh, and LSLGuy and pilot141: Don’t worry, when you guys aren’t around, Broomstick and I pick up the slack!
Well, the reason I said it might be impossible is that tanks hold only so much fuel.