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I've started working to make airport files for an online ATC game, and my first airport is Newark Liberty (DP: https://flightaware.com/resources/airport/KEWR/DP/all/pdf). What I already understand is that there are various climbs valid for different runways, and that the SID directs each aircraft to its first fix. What I don't understand is how the climb is determined for each aircraft. I also want to know how often airplanes use the SIDs, as I sometimes see planes on Flightradar not following the climb paths.

Thanks, this has confused me for a week or two.

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  • $\begingroup$ If you ask how steep is the climb then it is according to airplane/aviation company guides. Often this is derived from minimum flight time. $\endgroup$ – Antti Rytsölä Jan 8 at 12:32
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The LIB4 and EWR4 SIDs, and others like them with just a bunch of VORs, are designed to give ATC maximum flexibility and assume radar vectors. Basically, you take off, make a turn or two to get clear of the airport (and any low obstacles), and then ATC will vector and climb you based on conflicts with other planes at that moment, so you'll probably never get the same instructions twice. There is no real plan; it's literally made up on the spot by each controller for each plane.

The PORTT4 (RNAV) SID is completely different: you have various specific routes to follow and detailed climb plans for each. Many such arrivals and departures in an area will be carefully designed to never conflict with each other (the top and bottom altitudes listed usually indicate there's another SID/STAR crossing 1000ft above/below at that point), so ATC just watches to make sure everyone follows the plan—and gives out shortcuts when possible. Unfortunately, that SID is only valid for two of the six runways, though presumably they're the ones used most often.

Note the latter's lost comms procedure is just to follow the charted plan you're expecting to follow anyway, though without any shortcuts, whereas the former has an entirely different (and uncharted) plan that you'd probably never follow otherwise.

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The various climbs are usually determined by noise abatement interests and other stakeholders. You will find that some departures can be quite complex.

I cannot say anything to aircraft, that don’t follow the SIDs, they are there for a reason. Maybe those are aircraft at cruising altitude passing over the aerodrome?

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  • $\begingroup$ I think that especially in the US it used to be common to receive radar vectors (ATC telling aircraft where to head) instead of following published procedures, but not sure how it works these days. Additionally, aircraft might request to turn off the standard routes to avoid weather (mostly thunderstorms). These all might account for aircraft climbing off the SIDs. $\endgroup$ – Cpt Reynolds Jan 8 at 8:26
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The climb on a SID is determined based on the minimum climb needed to clear obstacles in the departure as well as aircraft performance. Passenger comfort also comes into play. Typically a pilot will follow at least the minimum requirements published on a SID unless otherwise directed by ATC. If a pilot’s aircraft cannot match the performance requirements of the SID, they should notify ATC prior to departure that they are unable and request a different DP their aircraft can comply with.

SIDs are created by the FAA or the individual operators and used by aircraft departing from airports to streamline the flow of traffic departing that location to their transition into the enroute structure ie establishing on low or high altitude airways. For heavy transports departing busy airports, a SID or an OCD will almost always be used. Light aircraft ie GA reciprocating and non transport category turboprops may make use of a SID - though some SIDS are restricted to turbojet aircraft only - and, at a bare minimum, a OCD is recommended in the case of marginal weather. Pilots operating in IFR may opt out of flying a SID by placing a “no SID” comment in the remarks section of their IFR flight plan.

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