mrniji
Topic Author
Posts: 5382
Joined: Sun Feb 29, 2004 11:51 am

### Altitude Of Landing Aircraft

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?
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PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

### RE: Altitude Of Landing Aircraft

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.
Fly fast, live slow

ZID
Posts: 292
Joined: Mon Jan 28, 2002 4:33 am

### RE: Altitude Of Landing Aircraft

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
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

### RE: Altitude Of Landing Aircraft

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
Posts: 6465
Joined: Wed Aug 29, 2001 8:47 pm

### RE: Altitude Of Landing Aircraft

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
Topic Author
Posts: 5382
Joined: Sun Feb 29, 2004 11:51 am

### RE: Altitude Of Landing Aircraft

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]
"The earth provides enough resources for everyone's need, but not for some people's greed." (Gandhi)

HAWK21M
Posts: 30007
Joined: Fri Jan 05, 2001 10:05 pm

### RE: Altitude Of Landing Aircraft

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
Posts: 4464
Joined: Fri Jul 16, 2004 5:59 am

### RE: Altitude Of Landing Aircraft

 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
Posts: 924
Joined: Sat Jan 01, 2000 11:45 am

### RE: Altitude Of Landing Aircraft

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
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation

chazzerguy
Posts: 271
Joined: Sat Jun 29, 2002 4:06 am

### RE: Altitude Of Landing Aircraft

 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
Posts: 2120
Joined: Fri Jan 30, 2004 3:01 pm

### RE: Altitude Of Landing Aircraft

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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