Understanding Obstructions on Sectional Charts

Flying Higher Than 400′

Obstructions allow the remote pilot to operate a drone above the 400 foot AGL altitude limit. When there is a structure in the area of operation and your UAS is within a 400 foot radius of that structure, you may fly 400 feet above the top of the structure.

The FAA doesn’t give us a clear definition of what a structure is, but it is probably safe to assume that it is a man-made structure such as a building, bridge, radio tower, etc.

Be careful that you are not flying in controlled airspace above a structure.

Example 1: Flying Above a Short Tower

In the following example you are flying your drone above the structure with a high point of 324 feet MSL. The airspace above the tower is Class C with a floor at 1,300 feet MSL. Since you can fly 400 feet above the high point of the tower, your maximum altitude would be 724 feet MSL (324 + 400) which is well below the Class C airspace floor of 1,300 feet MSL. You are clear to fly to 724 feet MSL.

Example 2: Flying Above a Tall Tower Into Controlled Airspace

In the following example you are flying your drone above the structure with a high point of 1,041 feet MSL. The airspace above the tower is Class C with a floor at 1,300 feet MSL. The tower does not enter Class C airspace itself but there is less than 400 feet distance between the two. The maximum altitude you could fly a UAS without ATC authorization would be 1,299 feet MSL (up to, but not including, 1,300 feet MSL.)

The Confusions of Class E Airspace

Lafayette airport, used in the examples above, also has a Class E airspace surrounding it. The two structures are located in Class E at 1,200 feet AGL. Therefore, wouldn’t the UAS be limited to 1,199 feet AGL since Class E is controlled airspace? Actually, authorization is not required in this case.

The point of confusion with Class E airspace comes from the fact that there are different types of Class E airspace. Even though Class E is controlled airspace, for most drone operations ATC authorization is not required. Generally, authorization is only required for type E-2, which is in the proximity of an airport. 

The FAA did a very good webinar on this topic in June 2019, explaining Class E airspace for drone pilots. The following is an excerpt. What we see here is that when operating a drone above a structure you may move into Class E airspace with a floor at 700′ AGL or 1,200′ AGL without ATC authorization.

Obstructions

The following obstruction types are shown on sectional chart legends. Get to know these now because they will be covered on the Part 107 exam. Also, if you get stuck you can refer to the Sectional Aeronautical Chart in the Chart Supplement handed out during the exam.

1000′ and higher AGL		This symbol is used for man-made structures which are at least 1,000 feet in height.
Below 1000′ AGL		This symbol is used for man-made structures which are less than 1,000 feet in height.
Group obstruction		Multiple obstacles are in an area which cannot be identified individually and the highest point is 1,000 feet or greater in height.
Group obstruction		Multiple obstacles are in an area which cannot be identified individually and the highest point is less than 1,000 feet in height.
1000′ and higher AGLHigh-intensity lightsMay operate part-time		An obstacle with high-intensity or strobing lights that is at least 1,000 feet in height.
Below 1000′ AGLHigh-intensity lightsMay operate part-time		An obstacle with high-intensity or strobing lights that is less than 1,000 feet in height.