I was just wondering as I passed the airport this morning why, whilst we are flying, do I never see any other planes nearby? There must be millions of planes and millions of people flying each day, I appreciate the sky is massive but these planes must follow roughly the same routes so how is it that they never seem to pass by any other aircraft?
9$\begingroup$ It's more like thousands of planes, and they typically stay at least a few miles apart. With the distance and relative speed between them, they can be hard to spot. That's why ATC works to keep them separated. $\endgroup$– foootJun 22, 2016 at 14:25
42$\begingroup$ Not sure how often you fly but I see other airplanes every time I get in one, GA or commercial, and yes, while cruising. I guess being a pilot I've learned to look? $\endgroup$– Ron BeyerJun 22, 2016 at 14:25
4$\begingroup$ @fooot nope, 1000 feet is usually enough, as long as it's vertical. $\endgroup$– falstroJun 22, 2016 at 14:41
2$\begingroup$ @jean I've seen that as well. It's pretty startling when that happens, and it really gives you a sense of your speed. $\endgroup$– TristanJun 22, 2016 at 16:08
7$\begingroup$ I've often seen jets alongside the flight I'm on for long periods. Typically about a mile apart horizontally and a couple of flight levels above or below. One of my favourite "spotting" opportunities is in a stack at Heathrow looking up and down in the turns. $\endgroup$– SimonJun 22, 2016 at 16:54
If you're not seeing them, you're not looking.
I see planes all the time when flying commercial. Obviously, I see them a lot more when close to a major center, and a lot less when in the sparse parts of the Pacific Northwest (Montana, Idaho, Oregon, Washington).
I think spotting them may take some practice. Visually, a plane 10+ miles away is a very small dot, and easily missed. Try looking for contrails and be sure to look at altitudes above and below you. Scan the sky in narrow, 10° concentrated "fields of view" to scan from left-to-right all the way across the sky.
15$\begingroup$ "Scan the sky in roughly 10 degree segments making 18 different, concentrated "fields of view"" I want to fly as a passenger on an airplane that has 180° field of view! Usually only a pilot gets such a wonderful picture of the sky, at least in the air. $\endgroup$ Jun 22, 2016 at 15:07
$\begingroup$ I was taught 10-degree segments during my flight training. And from the cockpit, I can probably see a bit more than 180 degrees; As a commercial passenger, you will see a lot less admittedly. $\endgroup$– abelenkyJun 22, 2016 at 15:18
7$\begingroup$ I think I have seen another airplane on just about every flight I've ever taken. $\endgroup$– BillDOeJun 22, 2016 at 18:10
2$\begingroup$ I think "you're not looking" may be a bit harsh. Your 3rd paragraph perfectly addresses why - "I think spotting them may take some practice". $\endgroup$– FreeManJun 23, 2016 at 12:21
2$\begingroup$ It's also easier to see other planes at night, with the navigation lights. $\endgroup$ Jun 23, 2016 at 17:51
If you look at sites like Flightradar24.com, you'll see aircraft following the same route, and close enough to allow each other being seen by passengers. Screenshot (look at the scale):
From my personal experience, seeing other aircraft is really common, as already commented and answered, even far from busy airports. I took this picture over Germany, the other aircraft is just a bit higher:
I let who is interested compute the aircraft distance from the size of the static wick. Actually there was a third aircraft in the background, still a common occurrence:
Nearby aircraft can be missed when there is no condensation trail. In general it's easier to spot an aircraft flying at a lower altitude, because Sun's light is reflected by the airframe.
There must be millions of planes and millions of people flying each day
At the time of the question there were about 100,000 commercial aircraft and 9 million passengers flying at a given time in the world. That's not a large number if we consider the size of the planet, but as you said they choose the same routes (for economical reasons). Airways can be very crowded and the absolute separation required for safety purposes is not so large (can be 1,000 ft, 300 m).
7$\begingroup$ Nice photo, mins! Are those yours? How was that for a nice way of asking for attribution? :) $\endgroup$– FreeManJun 23, 2016 at 12:23
Aircraft are usually routed one in front of the other, often at different flight levels.
Situations where another aircraft would be flying alongside yours, where they would be easily visible, are fairly rare. They do happen though. I was flying from Chicago to Boston last Thanksgiving and there was another heavy alongside about 2000 feet below and 3000 feet to port.
If aircraft are on an intersecting airway, they will generally be several miles away, so they will be very small, and will usually be at different flight level.
That's not true, you DO see other planes in the sky. I fly very infrequently (on average probably 1 flight a year) but I've seen other planes in flight. I remember on one flight, my airplane entered a quite steep bank to the left, I was sitting by the right side window, and I saw another passenger jet fly past above me, it was rather close, probably a 1000ft altitude difference.