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Subject: Re: course, heading, track
From: Paul Hirose (paulhirose@XXX.XXX)
Date: Thu Feb 07 2002 - 15:40:22 EST
Trevor Kenchington wrote:
>
> So, if I understand that correctly, U.S. aviation terminology does not
> distinguish between what we surface-bound types call "heading" and
> "course". Are aircraft so stable in yaw that the distinction is not needed?
American fliers use "course" for intended path over ground, and
"heading" for the direction to point the aircraft nose to make good
that path. If both directions are measured from the same reference
(e.g., true), their difference is the "wind correction angle".
It's assumed aircraft movement through the air is identical to the
direction its nose is pointing. Airplanes have an advantage over
sailing vessels in this respect. They have a yaw indicator and a
control surface (rudder) dedicated to yaw. Since an airplane turns by
banking, the rudder's job is simply to control yaw, usually to
minimize it, but sometimes (as when making a crosswind landing) to
intentionally yaw the plane.
Actually, in aviation all three terms are commonly used with two
different meanings. The line from Point A to Point B is called a
course, but the word is also used for the direction of that line in
degrees.
Similarly, we speak of accident investigators reconstructing the
track of an airplane, but when an inertial navigation system
displays TRK 340, it's understood to be the instantaneous direction of
movement over the ground.
Heading is the predicted direction needed to make good the course,
and is also the direction the plane is pointed at a given instant.
I've never found these double meanings confusing, since the intended
one is obvious from context. Maybe it's the mother duck syndrome, but
I think the aviation terms are easier to keep straight.
--paulhirose@XXX.XXX (Paul Hirose)
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