Plane Answers: Airliners passing closely (with video) and how are tailwinds figured inflight?

Welcome to Gadling’s feature, Plane Answers, where our resident airline pilot, Kent Wien, answers your questions about everything from takeoff to touchdown and beyond. Have a question of your own? Ask away!

Tim asks:


Recently we (my wife and I) were going from PVD to TPA and while gazing out the window on a bright sunny day, we were amazed to notice a large amount (8-10) planes passing by us heading north. These planes “seemed” very close to our plane as I could clearly make out all of the markings on each one. Is this normal practice for the airlines?

Hi Tim,

I had a similar experience recently. Since I normally fly internationally, we don’t see quite as much traffic as you can pass on a domestic flight.

While flying from Dallas to Boston the other day, I decided to take some video during cruise of the numerous aircraft that we flew over or under. It makes for some nice scenes. At one point, we even pass under a pair of B-52’s.

You’re right in noticing that this seems to be more common. Since January 20th, 2005, the FAA has allowed aircraft to be flown at altitudes in 1,000 foot increments. Prior to that, flights above 18,000 feet were separated by 2,000 feet.

You might think this wouldn’t be as safe, but in fact, the opposite is true. Since opening up twice the amount of flight levels available to airplanes, the airspace is effectively doubled, giving controllers more room to operate flights around weather and to provide more direct flights.
Callum asks:

First off, thank you so much for taking the time to answer all these questions. I only recently found the list and I enjoyed reading your answers immensely.

My question is how does the in flight system that displays speed, location, heading etc. know what the tailwind speed is?

I imagine it’s easy to calculate your forward velocity through the air with some kind of windmill like device on the front of the aircraft. If this velocity is comprised of forward motion created by engine thrust and wind speed (positive or negative) how do the plane’s systems calculate each component?

(I bet I’m over thinking it and you’ll have a really simple, obvious answer :) )


Hi Callum,

You’re close. Almost all airplanes have a pitot tube that senses the airplane’s airspeed. Airliners also have GPS and/or ‘laser ring’ gyros that spin fast enough to sense any movement of the airplane. When the airspeed and heading is compared to the GPS or gyros, the relative wind speed can be displayed. We can see this on our map display at a glance, which is handy in the last few hundred feet before landing to get a preview of the crosswind we’ll likely have at touchdown.

I managed to take a quick picture of the highest winds I’ve run across at altitude, which was during a smooth ride, despite the fuzzy picture:

Do you have a question about something related to the pointy end of an airplane? Ask Kent and he’ll try to use it for next Monday’s Plane Answers. Check out his other blog, Cockpit Chronicles and travel along with him at work.