mrniji
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Altitude Of Landing Aircraft

Mon May 09, 2005 7:12 pm

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

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PhilSquares
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RE: Altitude Of Landing Aircraft

Mon May 09, 2005 8:26 pm

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.
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ZID
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RE: Altitude Of Landing Aircraft

Mon May 09, 2005 8:58 pm

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
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RE: Altitude Of Landing Aircraft

Mon May 09, 2005 9:33 pm

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
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RE: Altitude Of Landing Aircraft

Mon May 09, 2005 9:55 pm

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
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RE: Altitude Of Landing Aircraft

Tue May 10, 2005 3:23 pm

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"!  Wink Just saw your profile and you being a pilot, you must be right, I suppose! Thanks man!

[Edited 2005-05-10 08:25:09]
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HAWK21M
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RE: Altitude Of Landing Aircraft

Tue May 10, 2005 5:35 pm

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
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Logan22L
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RE: Altitude Of Landing Aircraft

Wed May 11, 2005 2:54 am

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
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meister808
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RE: Altitude Of Landing Aircraft

Wed May 11, 2005 3:00 am

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.

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chazzerguy
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RE: Altitude Of Landing Aircraft

Wed May 11, 2005 3:44 am

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
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RE: Altitude Of Landing Aircraft

Wed May 11, 2005 4:26 am

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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