Kongulu --
Welcome back to Google Answers!
As you can imagine, there are many variables that determine how far
away an aircraft is visible. However, the FAA's exhibits in Advisory
Circular AC 90-48C imply that air-to-air visibility for another large
aircraft should be about 10 miles:
Avweb
"A Radar for All Seasons" (FAA AC 90-48C, March 18, 1983)
http://www.avweb.com/newspics/ac90-48c.gif
Advisory Circular AC 90-48C (Pilots' Role in Collision Avoidance)
http://www.avweb.com/news/news/183050-1.html
In all of my years of flying (over 35), I can tell you that it's hard
to see another aircraft, often even at 1 mile. I've spent lots of my
time flying in and out of Paine Field, where Boeing produces its
wide-body aircraft -- and in areas such as Moses Lake, WA where pilots
are trained on wide body aircraft.
I have seen other objects -- most notably a hot air balloon backlit by
the setting sun late in the day -- from 10-15 miles.
Your best chances of spotting another plane are:
• when it is above you
• at night, when lighting makes aircraft visible for dozens of miles
• when there's a contrasting background (such as an aircraft flying
across the snow field of Mt. Rainier)
• at high altitude where the air is clearer -- and in the mountain and
coastal ranges like the western U.S. where the air is free of dust and
humidity.
You may have seen aircraft flying at altitudes of 35,000' to 45,000'
above you. What you notice first is the vapor trail, typically only
visible at altitudes above 35,000'. Even with a plane at 35,000' or
almost 7 miles, it's difficult to detect the plane -- even from the
ground, where you're stationary.
There are many attributes that reduce the visibility of another
aircraft, including the structure of the eye itself. The Airman's
Information Manual (AIM) notes, in its recommendations on proper
scanning techniques, that "foveal" vision -- the smaller center in the
rear of the eye -- provides only about a 10 degree angle for sharpest
vision. In warning pilots to set up a series of narrow scan in
successive 10-degree arcs, the AIM "An aircraft at a distance of 7
miles which appears in sharp focus with the foveal center of vision
would have to be as close as 7/10 of a mile in order to be recognized
if it were outside of foveal vision."
Federal Aviation Administration
AIM
Section: 8-1-6 Vision in Flight
One of the best documents on best practices for collision avoidance is
this Aicraft Owners' & Pilots Association (AOPA) publication:
AOPA
"Collision Avoidance" (2002)
http://www.aopa.org/asf/publications/sa15.pdf
In order to help pilots overcome the weaknesses of vision, we tend to
rely on several things:
1. a route structure that separates eastbound and westbound aircraft
into odd (east) and even (west) altitudes
2. commercial aircraft carry TCAS (Traffic Alert and Control Systems)
that electronically track other aircraft nearby:
Mitre Corporation
Traffic Alert and Control Systems (May 21, 2003)
http://www.caasd.org/proj/tcas/
3. and we rely on Air Traffic Control alerts about nearby
traffic. When you're flying cross-country and see few of the
airplanes nearby, it makes you realize how tough it is to see other
aircraft.
Google search strategy:
"collision avoidance" + vision + aircraft
Best regards,
Omnivorous-GA |
