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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:
Kent,
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 :) )
Thanks!
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.
Filed under: Plane Answers
Reader Comments (Page 1 of 1)
Marius Heersink Apr 20th 2009 4:44PM
Is that 239 Kts?
Bill Apr 20th 2009 5:05PM
Now that I've seen the video, with its close aircraft proximities, I'm even happier for contrails (and radar!).
Kent -- great work, once again.
J Apr 20th 2009 6:51PM
Fantastic video.
nzm Apr 21st 2009 9:10AM
Great video, Kent! Taken with the 5D MkII or your little Flip Mino?
I have a question on the contrails.
Over recent years I've done a LOT of air travel and spent many hours staring out of aircraft windows to spot other aircraft - I love to do so! I can only remember seeing black contrails from military aircraft in the past - mainly propeller-driven aircraft.
However, in recent months while flying routes between Iceland, Zürich, Berlin and Barcelona, I've noticed a lot of black contrails like some of the ones in your video - and emanating from commercial jet aircraft. I've never seen them before in such numbers.
What causes the black trails? Is it dirty fuel or badly maintained engines?
(BTW - my Google searches have led me to all sorts of websites claiming that contrails are chemicals being deliberately sprayed to control humans or weather-controlling experiments!)
Would love to know what causes the black trails!
cheers
Michele
http://mandjadventures.blogspot.com/
Kent Wien Apr 21st 2009 11:35PM
Thanks Michele,
It was the Canon 5D Mark II. I'm loving that camera.
The dirtier contrails come mostly from older 727s and even MD-80s to some extent. Certainly the B-52 would qualify. The brighter contrails happen whenever there's enough moisture in the air to produce the "condensation trails." You must have been flying on one of those days, as I was on the day this video was shot.
I checked out the conspiracy theories on the chemtrails. Thanks for the entertainment!
nzm Apr 22nd 2009 9:30AM
Thanks for your reply, Kent. You've been most diplomatic! At about 43s into your video, you also have a dirty-trail 747 - I guess that it's also probably an older model!
I'm also loving my 5D MkII. I've been in photography-related industries for over 25 years, and it is the first DSLR that I have deemed to be worthy of buying - save for the 1Ds which are out of my price range!
I was amused by the "chemtrail" conspiracies too! There's one voice in the darkness attempting to explain the theory of contrails and he does a damn good job: http://contrailscience.com/ but the other side don't/refuse to/won't get it!
Kent Wien Apr 22nd 2009 9:42AM
Love your blog, Michelle. Looks like we both picked up the 5D at the same time. I'm still learning...
The 747 has rather 'modern' turbofans, so they just put out a larger condensation trail. I'm sure there's a fair amount of exhaust mixed in there as well.
It's interesting to see the contrails fan out over time and turn into something that looks like a cirrus cloud, hardly recognizable as a contrail. It seems www.contrailscience.com has done a great job countering the other sites. Thanks for that.
Arrey Apr 21st 2009 12:56AM
Jeez, a 239kt headwind?! You must've been CRAWLING in those winds!
Kent Wien Apr 21st 2009 11:37PM
It was a bit of a crosswind, really. I wished it had been on our tail. That would have been a nice record since 239 knots is 275 m.p.h.
propellerdream Apr 21st 2009 7:11AM
ARREY, as far as I know, 239 is the wind direction, not the wind speed :) The wind is "heading" 239 true degrees.
Great video Kent! You do a great job with this project.
Best regards,
Mihai, Bucharest, Romania
nzm Apr 22nd 2009 11:08AM
Yes - During 9/11, I was in LA staying about half a mile away from the ocean end of the 2 LAX runways. It was interesting to see the "marine layer" totally disappear when the planes stopped flying for 3 days.
I've seen blue skies get covered over by the contrail cirrus - especially in Berlin where we lived for some time. There's no doubt in my mind that contrails do cause changes in climate - particularly temperature - but not as a conspiracy!
Thanks for the comment re our blog!
I really enjoy your posts on Gadling too.
James Apr 23rd 2009 7:53PM
I live on the shore line just North of Los Angeles. The Westerly winds keep LAX pretty clear. The marine layer burns off at different times come Fall. During September it's hit or miss, some days there is no layers and clear skys, other days it doesn't burn off and it's IMC or MVFR all day long. You should see the "Marine Layer" in City of Industry and more inland, makes LAX look like Alaska.
Thanks Kent for the postings.....ya gotta do one on when a 172 gets into wake turbulance!!!Good times!