A lot of Six Flags and a few CF parks have height restrictions on how tall they can build their rides. One that comes to mind is SF Discovery Kingdom. If it was due to traffic control, shouldn't they just be able to put lights on top?

Lights are required by the FAA on EVERY structure taller than a certain height. (Side note: Please correct me if I'm wrong, but I believe Cinderella Castle at the Magic Kingdom was deliberately tweaked and reduced from its originally planned height to avoid being forced to put a flashing red light on top of the structure.)

The issue with height restrictions, or at least one issue (I don't know if there are others), is that structures too tall can potentially interfere with the ability of airplanes to take off and land safely at nearby airports. An extreme example of this is Kentucky Kingdom, which is not only directly across the highway from the Louisville International Airport, but also directly on the flight line of a major runway at said airport. KK cannot build above a certain height in order to ensure that the ability for planes to land and take off at the airport safely is not jeopardized.

(Insert "I am not a lawyer" statement and disclaimer here)

Lights are required by the FAA on EVERY structure taller than a certain height. (Side note: Please correct me if I'm wrong, but I believe Cinderella Castle at the Magic Kingdom was deliberately tweaked and reduced from its originally planned height to avoid being forced to put a flashing red light on top of the structure.)

 

I knew about that for the most part, the one I heard was that Tower of Terror was built 199 ft 6 in so it did not have to have a light. But why does it need that, is it state law for then and not Ohio? cuz TTD is way taller but doesn't have a beacon

Sometimes there's zoning laws at play as well.  Probably not often, but it depends where you've put your park.  You can't just build a massively tall structure wherever you want...no matter how you light it up for air traffic.

Top Thrill Dragster does have a light beacon atop the tower. It is clearly visible flashing in this video:

https://youtu.be/_hRp3RzvHZU

Sorry, I feel stupid, Its just not sticking out in normal pictures

Could be worse.  Alton Towers has a restriction where they can't build above the tree line because it's in a conservation area.  They've managed to get around that little hiccup pretty well.  

An extreme example of this is Kentucky Kingdom, which is not only directly across the highway from the Louisville International Airport, but also directly on the flight line of a major runway at said airport. KK cannot build above a certain height in order to ensure that the ability for planes to land and take off at the airport safely is not jeopardized.

(Insert "I am not a lawyer" statement and disclaimer here)

I saw that firsthand on Saturday. A plane was coming in for landing while I was riding Thunder Run, and WOW was it close! It was actually a little bit scary.

The height restrictions in regards to flight paths and such are almost certainly federal restrictions, just like the flashing beacons. Beyond that, it's largely up to local governments what goes. As far as KI is concerned, I'd imagine they only have to deal with the Warren County and Butler County airports. Warren County's is 7 miles away in Lebanon and Butler County's is 14 miles away in Fairfield Township (east of Hamilton), given that both of the closest international airports are 30+ miles away.

How about Catowinds? There where so many planes flying really low in perspective when I was on the lift hill for Fury and The Intimidator

Charlotte-Douglas Airport is only 10-15 miles from the park. One of the videos from Media Day showed an airplane passing above the lift hill on Fury 325.

Cool and eerie at the same time.

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Indeed, Cinderella Castle and Tower of Terror are both about 1 foot give or take a couple of millimeters (ground settling) below the threshold required by the State of Florida for a flashing light beacon.  In ancient times (early 70s), during the early years of WDW, there was an airfield located relatively nearby to the MK. It was built for early guests to easily fly into/out of Disney. Of course, within a few years, the sheer number of guests made the tiny airport expendable.  I have heard rumors that the land may be used during the upcoming reconfiguration of the Northern entrance to WDW.

Cinderella Castle was, if I recall correctly, the first use of forced perspective in theme park design, which is also employed on KI's International Street. It takes advantage of an optical illusion to cause it to look taller than it is. 

 

Also, in regards to height restrictions - some municipalities also have local ordinances against building above certain heights. For instance, Pigeon Forge had a restriction of no more than 100 ft, which is why if you look up and down the Parkway, you won't see huge structures except for the Wheel. The Wheel was granted a special exclusion to the restriction, at 186 ft tall. The go kart tracks which offer things like Skyscrapers and Skycoasters all use models that when "parked" are under 100 ft tall. Dollywood actually sits outside of Pigeon Forge city limits, and therefore is not restricted. 

Charlotte-Douglas Airport is only 10-15 miles from the park. One of the videos from Media Day showed an airplane passing above the lift hill on Fury 325.

Cool and eerie at the same time.

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If you want eerie, try riding Thunder Run at Kentucky Kingdom while a plane is coming in for a landing. I could practically see faces in the windows of the plane!

Indeed, Cinderella Castle and Tower of Terror are both about 1 foot give or take a couple of millimeters (ground settling) below the threshold required by the State of Florida for a flashing light beacon.  In ancient times (early 70s), during the early years of WDW, there was an airfield located relatively nearby to the MK. It was built for early guests to easily fly into/out of Disney. Of course, within a few years, the sheer number of guests made the tiny airport expendable.  I have heard rumors that the land may be used during the upcoming reconfiguration of the Northern entrance to WDW.

 

http://www.airfields-freeman.com/FL/Airfields_FL_OrlandoSW.htm#disney

 

A link to some information about the Walt Disney World Primary Airport.  Also some interesting information about other airports in the area as well. 

Whats interesting is to read that as of the last 15 years the airport was not really open but was still used by corporate jets and a president. 

Charlotte-Douglas Airport is only 10-15 miles from the park. One of the videos from Media Day showed an airplane passing above the lift hill on Fury 325.

Cool and eerie at the same time.

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If you want eerie, try riding Thunder Run at Kentucky Kingdom while a plane is coming in for a landing. I could practically see faces in the windows of the plane!

I'd would be up for a trip down to Kentucky Kingdom to see this first hand!

That is, if they let me in!

YOU SHALL NOT PASS.

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I think that rule only applies to me.

Terpy, not Toady.

Want to get a good look at a major airport? Climb the stairs to the top of Deep Water Dive's tower at Kentucky Kingdom. You will literally be as close to the airport as you can get inside the Hartland while standing on the open-air top of a 120-foot-tall tower. And with prevailing winds, airplanes will come over the park and right past you to land on the runway across the highway. The day I was there, I didn't stay at the top of the tower long enough for a plane to come through (plus I think a different runway was being used that day due to calm winds), so I can only imagine how low the plane would be. And I can imagine it practically at eye level.