The Real Reason for Airspace Rules

Airspace questions on knowledge tests are missed often, and pilots frequently violate airspace boundaries — no wonder, the rules are very complicated. Airspace seems to be one of the toughest topics for pilots to master and have caused more than one pilot to wonder why we have airspace rules in the first place…

When I first started flying, I hated to study airspace because it just seemed to be a bunch of memorization. You had to remember so many dimensions, weather minimums, and equipment rules. It all seemed to overlap and run together and at the time I didn’t learn it very well. It wasn’t until later, when I understood the reason why airspace rules are necessary, that I started to get it.

The purpose of airspace rules is Collision Avoidance.

Even in today’s ‘high-tech‘ world, pilots still rely on a very ‘low-tech‘ principle: In order to avoid other aircraft, pilots must see and then avoid each other. There are no force fields to keep us apart. Controllers can’t do anything about it when two airplane targets on their screen — all they can do is hope that they separate. Sure, the controller could give a traffic warning before the targets got close … but only if the airplanes happen to be on their frequency. And most airplanes out in the practice area are not talking to a controller — so the controllers watch when the two airplane targets ‘collide‘ and (in most cases) continue on their way.

The simple fact is that pilots can depend on nobody but themselves to see and avoid.

In order to avoid, the pilot must first be able to see. That’s where the airspace rules come in. If a pilot follows the airspace rules, they will have a better chance of spotting other airplanes in flight and getting out of the way before it’s too late.

The basic distance from clouds in ‘controlled‘ airspace above 1,200 feet AGL and below 10,000 feet MSL is ‘500 feet below; 1,000 feet above; 2,000 feet horizontal‘ and three miles visibility. How do these numbers work in practice and, more important, how much safety do they provide?

In situation 1 (below), the two airplanes are on a collision course. The regulations say, ‘When aircraft are approaching head-on or nearly so, each pilot shall alter course to the right.’ This works great… if the pilots see each other in time.

Translation: Unless one of the pilots sees the other and takes evasive action a collision will occur in 47 seconds.Situation 1, Example 1:
Recall that three statute miles is the basic VFR visibility minimum in controlled airspace below 10,000 feet MSL, and assume that in situation 1 the distance between aircraft A and aircraft B of situation 1 is three statute miles. The rule makes the assumption that if two airplanes are within one and one half miles of a collision (three miles apart but converging on the same point at the same speed), that there is plenty of time to see and avoid. The closure rate of two Cessnas would be approximately 200 knots.

Situation 1, Example 2:
A Piper with a speed of 100 knots and a Lear jet with a speed of 250 knots would have a closure rate of 350 knots. If the pilots in this situation were flying with only three miles visibility, the time to recognize the problem and get out of the way would be 27 seconds.

Translation: Three miles sounds like a long distance — but 27 seconds to see, identify, understand and avoid can be no time at all.

In Situation 2 (below), the planes may or may not be head-on, but they are on a collision course with each other. Their actual distance apart is 2,000 feet. If at this distance the pilots first saw each other there would be virtually no time to miss each other. No pilot would ever purposely place themselves so close to another airplane that there would be no time to avoid a collision — right? Well pilots do place themselves in this dangerous situation — often times without even knowing it and while following the rules. See situation 3…


In the next second, airplane B will pop out of the side of the cloud. Less than 15 seconds after that there will be an impact. The closer that airplane A gets to the cloud, the less time there will be to get out of the way. A pilot who flies just clear of clouds will have absolutely no time to avoid traffic at all.In situation 3, all factors are the same as in situation 2 except one. One of the airplanes is on an IFR flight plan at an assigned altitude flying through the clouds. The other pilot flying VFR either with or without a flight plan. Airplane B is inside a cloud and following their clearance. Airplane A has ventured to 2,000 feet horizontally of the cloud. The airplanes are on a collision course — and they can’t see each other yet.

Forget about the dangers of disorientation when VFR pilots fly in the clouds. The real danger is what may be inside the cloud — another airplane!

Now you can see that three miles visibility and a 2,000-foot horizontal clearance from clouds does not, in fact, offer much protection. Flying close to clouds may be legal but that does not mean its safe.

It is possible, and legal, for one airplane to be just outside a cloud, while another airplane is just inside the cloud.

How: Uncontrolled airspace offers even less margin of safety. In uncontrolled airspace below 1,200 feet AGL (700 feet AGL in some places), you are allowed to reduce the VFR minimums. In these locations, just one-mile visibility is required and pilots can fly as close to clouds as they wish as long as they do not actually enter the clouds. There are loopholes in the rules that allow IFR airplanes to fly in uncontrolled airspace.

BOTTOM LINE: Airspace is not just a bunch of imaginary lines drawn in the sky to confuse pilots. Airspace rules are collision avoidance protection. Since the rules and protection levels are different in controlled airspace versus uncontrolled airspace, it pays to know where controlled airspace starts and uncontrolled airspace stops. Identifying the different types is essential to flight safety and will be covered next week.

Editor’s note: Since 1995, Paul A. Craig has conducted innovative seminars on the airspace system at colleges and universities, Pilot Proficiency programs, and Flight Instructor Refresher Clinics across the country.