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Minimum Distance Between Commercial Planes
Why Do
Commercial Planes Need To Have Lateral And Vertical Separation?
Ashish
If the title seems confusing or doesn’t make sense to you, allow me to
elaborate.
You might already know that commercial planes need to maintain a
minimum distance from other commercial planes during flight. That’s why the ATC
(Air Traffic Control) exists.
One of the primary and most critical tasks of the ATC workers is to
ensure that every plane taking off, landing or even passing through their
airport doesn’t fly too close or get in the way of other planes flying in
the same airspace.
Because if that happens, it could potentially lead to a catastrophe of
epic proportions.
That’s why commercial airplanes maintain separation from other planes,
i.e., they keep a safe distance away from other planes in their vicinity.
However, military aircraft are nothing like that. They often fly very
close to each other in tight formations on purpose. They don’t maintain a
miles’ worth of clearance from other military aircraft in the formation. It
doesn’t seem to make sense.
Why do large, commercial airplanes require vertical and horizontal
separation, but military aircraft don’t?
Separation
In the field of flying and aeronautics, the term ‘separation’ is used
to refer to the concept of keeping a plane at least a minimum distance from
another aircraft.
The basic reason behind this is to keep planes from running into each
other and avoid accidents due to secondary factors (e.g., wake turbulence).
Two planes need to either maintain at least 1000 feet (305 meters) of
vertical separation or 3 miles of lateral separation. These values increase if
the planes in question are larger.
Interestingly enough, not all aircraft need to be separated by the
ATC.
Whether airplanes actually need such a separation depends on the class
of the airspace in which they’re flying, and the rules under which their pilots
are operating their aircraft.
These are the rules under which an aircraft can be flown: Visual
Flight Rules (VFR), Special Visual Flight Rules (SVFR) and Instrument Flight
Rules (IFR).
Commercial aircraft are almost always operated under IFR.
Why do commercial planes need separation?
The primary reason is to prevent collisions.
Commercial airliners carry hundreds of passengers (as opposed to
military jets, which carry only a few) and operate under civil air traffic
guidelines, which are followed by every commercial aircraft flying in that
airspace.
By maintaining an appropriate clearance, they make sure to
never get in the paths of other aircraft. This minimizes the risk of collisions
occurring between planes.
They also maintain a separation because of something called wake
turbulence.
When a big plane flies, its wings produce the lift it needs, which in
turn produces wake turbulence, i.e., turbulence left in the wake of the plane.
If two commercial planes fly too close to each other, they risk
getting mixed up in the disturbance in the wind created by the leading
plane, which could have nasty implications for the trailing plane.
Commercial airliners are also less maneuverable than military planes,
and their pilots are less likely to be trained in formation flight.
Lastly, there is simply not a good enough reason to make planes fly
closer than they already are.
Why can military aircraft fly so close to each other?
Of course, military aircraft also need a minimum separation from other
aircraft, but they easily manage to fly in close, tight formations composed of
quite a few planes. There are a few reasons behind this.
Fighter
aircraft are much more maneuverable than commercial planes. They can take sharp
turns and dip/climb in a split second at the very last moment.
As
mentioned earlier, separation between aircraft is for safety during sudden,
unexpected maneuvers, not just for avoiding wake turbulence.
Since
military pilots are talking directly to the other pilots in the formation on a
discrete radio frequency at all times, they know well in advance what maneuver
their fellow pilots will make and can prep themselves accordingly.
Long
before the actual flight, each pilot in the formation is briefed about the
general flight plan, how it will be carried out and what formations they
will be flying in.
Thus,
there are minimal chances of a pilot engaging in an unexpected maneuver to
begin with. That’s why military pilots manage to pull off such death-defying
stunts in the air, because it’s all planned and prepped in advance.
Last but not least, military pilots are trained to fly in tight formations. They spend
hours and hours learning about flying in such
formations, and then actually practice flying in them.
The majority of commercial pilots can be generally assumed to not have
that level of training or expertise to fly so close to other commercial planes.
That’s why commercial planes need to maintain a safe distance
from each other, whereas military aircraft often fly very close to each other.
Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.
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The guys sitting in the ATC have a huge
responsibility. In a way, the lives of thousands of people depend on how they
manage the airspace around their airport.
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In the US, normal aircraft separation guidelines
under IFR are defined in an FAA order.
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This picture from a NASA study on wingtip
vortices qualitatively illustrates the wake turbulence.
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This picture is clicked from within a passenger
airliner (Boeing 767) at cruising altitude. Notice the trail of another
airplane flying below it. See how there is a separation between both these
aircraft.
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