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 Altitude Of Landing Aircraft
 Mrniji From , joined Dec 1969, posts, RR: Posted Mon May 9 2005 12:12:33 UTC (9 years 10 months 4 weeks 13 hours ago) and read 6241 times:

 While spotting, I often realized that smaller aircraft, landing at an airport, take a different approach. OK, let's take a point X, which, measured from the soil, has the distance Y to an airport (numbers are fictional). While landing, a 737 might be at an altitute of 1000 feet at X, a 747 might be at an altitute of 500 feet at X, while a small turboprop might be at 2000 feet.. why is this so? Do bigger planes have to commence their approach earlier, as they are not able to descend as fast as smaller planes? OK, confusing, so here the attempt to visualize in "two dimensions" 2000 ft Turboprop 1000 ft 737 0500 ft 747 ground X...................................................... Airport in distance Y Got my question?
 PhilSquares From , joined Dec 1969, posts, RR: Reply 1, posted Mon May 9 2005 13:26:11 UTC (9 years 10 months 4 weeks 12 hours ago) and read 6204 times:

 What you think you're seeing isn't really so. It's an optical illusion. They should all be at the same height AGL at the same point in space. If an ILS has a 3 degree glide slope at 5 miles all aircraft are at about 1500' AGL. (assuming on glide slope) What it looks like is a different story. It looks just as you described, and that's because of the relative size of the aircraft. If you look closely, the large plane appears to be going slower than the small one. Again, an optical illusion.
 ZID From United States of America, joined Jan 2002, 294 posts, RR: 4 Reply 2, posted Mon May 9 2005 13:58:20 UTC (9 years 10 months 4 weeks 11 hours ago) and read 6186 times:

 If it's a VFR day and therefore a glideslope doesn't come into play, a smaller aircraft is going to want to stay a little higher and land a little farther down the runway that any preceding larger aircraft in order to stay out of the larger aircraft's wake turbulence. That may have been what you were witnessing.
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 Air2gxs From , joined Dec 1969, posts, RR: Reply 3, posted Mon May 9 2005 14:33:26 UTC (9 years 10 months 4 weeks 11 hours ago) and read 6157 times:

 You may be seeing pilots in smaller aircraft compensating for the possibility of wake turbulance from a larger aircraft. When I was training for my PPL the instructor told me it was safer to land a little long (thus, be higher over the threshold) when following larger aircraft. By planning to land long, you assure yourself that the wake turbulance will be below and behind you during the approach and landing.
 Mandala499 From Indonesia, joined Aug 2001, 7078 posts, RR: 77 Reply 4, posted Mon May 9 2005 14:55:54 UTC (9 years 10 months 4 weeks 10 hours ago) and read 6144 times:

 And then U got props coming in on a dive bomber angle! but in most cases, it's only for tight and visual from 1500ft AGL or less... Otherwise U'll get puking pax... Mandala499
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 Mrniji From , joined Dec 1969, posts, RR: Reply 5, posted Tue May 10 2005 08:23:50 UTC (9 years 10 months 3 weeks 6 days 17 hours ago) and read 5954 times:

Thx guys!

 Quoting PhilSquares (Reply 1):looks just as you described, and that's because of the relative size of the aircraft.

Are you sure.. ? I thought so, too, but somehow the difference looked to significant?

Edit: silly question of mine "Are you sure"!   Just saw your profile and you being a pilot, you must be right, I suppose! Thanks man!

[Edited 2005-05-10 08:25:09]

 HAWK21M From India, joined Jan 2001, 31716 posts, RR: 55 Reply 6, posted Tue May 10 2005 10:35:25 UTC (9 years 10 months 3 weeks 6 days 15 hours ago) and read 5929 times:

 Subin. Likely to be just an Illusion. Speaking on Mumbai,I watch the Landings every night on Rnwy 27.Although mainly at nights.The Approaches looks similiar. What was your viewing Angle,that could be a reason. regds MEL
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 Logan22L From , joined Dec 1969, posts, RR: Reply 7, posted Tue May 10 2005 19:54:45 UTC (9 years 10 months 3 weeks 6 days 5 hours ago) and read 5873 times:

 Quoting PhilSquares (Reply 1):If you look closely, the large plane appears to be going slower than the small one.

I've noticed what appears to be a significant difference in speed based on aircraft size. What causes this illusion?

Logan

 Meister808 From United States of America, joined Jan 2000, 973 posts, RR: 1 Reply 8, posted Tue May 10 2005 20:00:01 UTC (9 years 10 months 3 weeks 6 days 5 hours ago) and read 5868 times:

 The illusion of a significant difference in speed comes from a significant difference in size. When you see something moving, you generally tend to judge it based on relative motion. Thus, a 737 looks like it is going twice as fast as the 747 just based on the fact that it covers its own length in a much shorter time. -Meister
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 Chazzerguy From United States of America, joined Jun 2002, 277 posts, RR: 2 Reply 9, posted Tue May 10 2005 20:44:45 UTC (9 years 10 months 3 weeks 6 days 5 hours ago) and read 5850 times:

 Quoting Meister808 (Reply 8):The illusion of a significant difference in speed comes from a significant difference in size. When you see something moving, you generally tend to judge it based on relative motion. Thus, a 737 looks like it is going twice as fast as the 747 just based on the fact that it covers its own length in a much shorter time.

They say this is why people often get killed at railroad crossings... Trains tend to look like they are going a lot slower than they really are due to their size.

 HaveBlue From United States of America, joined Jan 2004, 2150 posts, RR: 1 Reply 10, posted Tue May 10 2005 21:26:47 UTC (9 years 10 months 3 weeks 6 days 4 hours ago) and read 5846 times:

 About the size/speed comparisons and illusions. C-5 Galaxy length 247' F-16 Length 47' Pitts S-2 Biplane 17' So to cover 500', the C-5 is only moving one length ahead. To cover the same 500', the F-15 is covering 9 more lengths. To cover the same 500', the S-2 is covering 29 more lengths. Thus the illusion. And I agree with Phil, the same thing applies to height. At 1,500' the C-5 is only 6 of its lengths above ground. The F-16 is 30 of its lengths above ground. The S-2 is 88 of its lengths above ground.
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