Mrniji From , joined Dec 1969, posts, RR: Posted (9 years 9 months 4 weeks 10 hours ago) and read 6145 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
PhilSquares From , joined Dec 1969, posts, RR:
Reply 1, posted (9 years 9 months 4 weeks 8 hours ago) and read 6108 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 (9 years 9 months 4 weeks 8 hours ago) and read 6090 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.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 3, posted (9 years 9 months 4 weeks 7 hours ago) and read 6061 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.
HAWK21M From India, joined Jan 2001, 31713 posts, RR: 55
Reply 6, posted (9 years 9 months 3 weeks 6 days 11 hours ago) and read 5833 times:
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.
Meister808 From United States of America, joined Jan 2000, 973 posts, RR: 1
Reply 8, posted (9 years 9 months 3 weeks 6 days 2 hours ago) and read 5772 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.
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
Chazzerguy From United States of America, joined Jun 2002, 277 posts, RR: 2
Reply 9, posted (9 years 9 months 3 weeks 6 days 1 hour ago) and read 5754 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.