Question: I was recently on a flight into Phoenix when the plane tipped sharply to one side. A moment later, we experienced more side-to-side turbulence. The pilot made an announcement that our plane had been caught in the wake of another plane. He said this was an extremely unusual event. Obviously the flight landed fine, but I'm wondering if this was dangerous, and why air traffic control would have allowed the two planes to be close enough for this to occur.

-- submitted by reader Sarah, Mass.

Answer: Interacting with the wake of another airplane is not that unusual. Yes, it will cause a roll, and sometimes a yawing motion. Usually the wake vortices descend below the airplane and out of the way of the following airplane. However, on some days, the wake can descend more slowly or the trailing airplane can be lower. In these cases, interaction with a wake is to be expected.

Wake turbulence is normally not dangerous; there are exceptions to this. When a small airplane is following a large one and is close to the ground, an encounter can be very dangerous. The Air Traffic Control system has minimum separation standards to allow dissipation of the vortices (high-energy rotating cones of air from the wingtips). History has proven that these separation standards work well.

ASK THE CAPTAIN: Can turbulence crack an airplane in half?

In your example, it sound like the preceding airplane might have been a little higher than your flight, allowing you to interact with the wake. No, it was not dangerous and the air traffic controller did have the proper spacing.

Q: I see jet trails going in the same direction. Do the pilots of these aircraft talk to each other, and if so, could the crew of a following plane ask for a new flight level if it's been overtaken by a higher plane with a faster tailwind?

-- Geoff , ENGM, UK

A: Pilots frequently talk about wind and any turbulence with other pilots and the air traffic controllers. If a different altitude has a better ride or better winds, it is common to change altitude to take advantage of it.

FROM THE ARCHIVES: When turbulence comes in waves