When you fly into somewhere like San Diego or New York, you fly right over the city and are basically directly next to skyscrapers. But when you fly into somewhere like Austin or New Orleans, you’re flying over flatlands. How do pilots know clearance for certain areas, does ground control tell them how best to land or does that not matter?
In: Other
For aircraft flying under instrument flight rules there are minimum vectoring altitudes that Air Traffic Control is allowed to vector aircraft down to, and instrument approaches all have minimum altitudes and are built specifically to guarantee that as long as a pilot is correctly flying the procedure he will maintain the required separation from any and all obstacles. The same is true for departure procedures. Basically as long as a pilot follows the published instrument procedure, they can be sure they are well clear of any obstacles regardless of where they are.
For visual flight rules, there are charts that have the altitudes for big buildings and towers marked, but really its on the pilot to look outside and make sure they fly high enough or far enough away from any obstructions to stay legal and safe.
We have VFR charts that have almost everything that sticks out of the ground listed on them. For populated areas is 1000 ft above and 2000ft horizontally. For other areas is 500ft away from the tallest building or person.
If you wanna look at these charts, here’s a good website for it. https://skyvector.com/
As you move into IFR/Cloud flying, different clearances apply and there are ground based navigational aids as well as GPS to help. Even ATC has radar and minimum altitudes to vector planes around at to ensure no one hits anything.
Note that for commercial flights, *other* than landing and take-off, if they’re ever anywhere near the top of a building, something has gone horribly horribly wrong already.
For take-off and landing, commercial flights follow well-known approaches that have reasonable clearance. Planes are expected to follow certain *glide slopes*, typically around a 3° angle downwards towards the runway. There are several tools to help them, including [PAPI lights](https://global.discourse-cdn.com/infiniteflight/original/1X/4e5ee137d8fbd687cc38f0f76ec4e13f028c1440.gif) which show different colors depending whether you’re too high or too low, and ILS, or Instrument Landing Systems, which use overlapping radio signals to guide the autopilot down.
There are established “minimums” where the plane *must* be on a “stabilized approach” by a certain height above the ground, typically 1000ft but can be as high as 2000-3000 depending on the conditions and instructions from ATC. “Stabilized” means the plane is at a constant rate of descent, with a constant speed, so it stays on that 3° slope, and has “captured” the ILS – meaning, the system is tuned into the radio signal and knows where the plane is…if the pilot did NOTHING, the plane should go right where it’s supposed to go without any more input, other than very small corrections.
If the plane is not stabilized by that height, they must initiate a go-around. They abandon the attempt to land, they throttle back up, fly over the runway, and go around to try again. As long as the plane is even remotely within that glide slope, there shouldn’t be any buildings anywhere near them.
For private flights using Visual Flight Rules, or VFR, there’s a lot less equipment but the procedure for take-off and landing are similar. There is probably some kind of indicator like PAPI lights for the pilot to follow down, and they practice a *lot* so that even without an indicator, they know what kind of glide slope they need to capture and how to do it. VFR pilots often don’t have any help from ATC – there are plenty of non-towered airports and the pilots just have to pay attention and land according to their own discretion and training.
Every airport has [charts, diagrams, and additional information](https://skyvector.com/airport/ATL/Hartsfield-Jackson-Atlanta-International-Airport) which pilots have to know how to read. These charts will include the runway length, standard approach direction, and even notes about things like trees or buildings that are nearish the airport. None of them should be close enough to be a serious hazard for a normal landing or take-off, but the pilots may still want to know they’re there *just in case*, and can plan their maneuvers accordingly. Like, if you know you’re taking off at your max weight and there’s no wind to help you, you’d know that you’re going to climb pretty slowly so, hey, maybe let’s *not* take off on the runway with tall trees in that direction *just to be safe*.
There are even *more* charts that show the best, recommended, or required approaches. Like, if you’re coming into this airport, you *must* follow this line. This doesn’t just help avoid buildings, it helps keep planes organized and prevent them from hitting each other, almost like lanes on a highway.
For just flying around, like I said commercial flights should never be remotely close to anything on the ground. Private pilots flying VFR *usually* won’t be flying that low, but they might be. It’s up to the pilot to plan their route and look at the charts. The charts will have symbols showing tall landmarks, both to help the pilots avoid hitting them, but also to help them navigate because they are, well, *landmarks*. VFR pilots have a lot of tools to help them figure out where they are, but typically not GPS so having something really obvious to let you know where you are is useful. It’s also up to the VFR pilot to pay attention to what they’re doing and avoid running into stuff. VFR pilots are not allowed to fly without being able to see a good distance all around them. They can’t fly into or through clouds. They should be able to see everything in front of them, so avoiding stuff on the ground *should* be as easy as seeing it and not running into it. The only time they would be at risk is from doing something that *requires* them to be extremely close, like doing crop dusting. And yeah, they just need to be good pilots and really pay attention to avoid running into anything.
A private pilot flying IFR – instrument flight rules – are allowed to fly when they can’t see, since they’re trained to use their instruments to navigate. However, they should know better than to ever put themselves into a position where they’re at risk of hitting something close to the ground while they can’t see anything. They probably don’t have any kind of radar, so they need to just be aware that, based on what their altimeter says, they’re close to the ground and either they better know that there’s nothing tall around, or they need to get away from the ground.
Source: Currently taking online courses for private pilot ground school to hopefully get a private pilot certificate soon.
Check out Part 77 “imaginary surfaces” that require building/antenna tower/transmission line companies to notify the FAA when they are constructing a structure that exceeds certain criteria based on heights and distances from the runways of any airport.
Sometimes the FAA will deny a tall structure because it would have significant impact on the safety of aviation operations.
Sometimes the FAA will require the structure to have certain types of lights installed at the top or painted certain colors to make pilots more visually aware of it. The criteria for this is based on the Part 77 imaginary surfaces, as well as the Terminal Instrument Procedure (TERPS) that tell pilots how to make instrument-based approaches to a runway based on different criteria. It involves a lot of math and navigation calculations and can be found in FAA Orders 8260.3 and 8260.58.
The company building the structure is required to comply with these regulations and an FAA “Determination of No Hazard” is usually required to get the proper local and state permits to build it. After it’s constructed, the FAA will include it aeronautical charts available to all pilots.
Our maps (VFR) have big blue numbers in each area that tells us the proper attitude we need to be to avoid hitting things. For example, a map would have 25 or 2500 in huge text in one section that shows the highest object in that big ole area is 1,500 feet or less (they round up).
In IFR, we have routes like a road that we travel along. These routes use radio beacons (VOR) to provide established “lanes” or GPS. For example: a VOR airway may be a radial of 315 off Atlanta VOR, which means we intercept the VOR direction of 315 degrees based on that particular VOR. Such a route would be labeled V315 off Atlanta VOR.
These routes, like roads, require aircraft separation so we are issued an altitude to fly on by ATC (Center, departure control, approach control, whomever owns that airspace).
ATC can stack multiple aircraft on the same route and sequence us for landing in an orderly manner.
If there is a loss of communication, we are expected to maintain our issued flight clearance or whatever we filed for before takeoff. This means we stay at the last assigned altitude until we reach our destination initial approach fix.
Lost comms doesn’t happen very often but there is a procedure in place. It happened to me once with Boston Center during a handoff (moving from one ATC controller to another one). Boston Center was pissssssed at us once we landed but we did the paperwork n showed it was a malfunction in the avionics closet.
No matter what, it is the pilots responsibility to maintain proper clearance from not flying into stuff.
Real ELI5 without industry jargon:
You use a Map that has numbers to show how high you have to fly to avoid hitting the highest building.
In actual kid terms: the FAA puts out a list every day of obstacles over 500 feet tall. Obstacles on this list need to be identified when you make your flight plan. The list has everything from buildings to antennas to bridges to cranes.
Latest Answers