Standard SID climb gradients are based on 3.3 pct (2.5 plus 0.8). If due to obstacles (such as the Burj Khalifa) you need more it will be stated on the chart as a min clb gradient up to a certain altitude. The obstacle(s) might be close to the DER or further away or both. If obstacles penetrate the standard OIS the required gradient will be changed. I believe you can not penetrate the given surface as you might hit an obstacle. Especially where you have a high distant obstacle requiring say 5 pct up to 4000 and a low near obstacle requiring a climb gradient of say 4.9 pct up to 2000. By going lower you cannot guarantee obstacle clearance unless you designed the plate yourself. You can therefore climb more than 5 pct and then less as long as you don't penetrate the surface. You can do so by passing 3 nm > 1000ft 6 nm > 2000ft or any other way you want. But you cannot fly level and then climb crazy fast to reach 4000 by the 12nm from the DER (about 5% average). The reference is doc 8168 Part I — Section 3, Chapter 1 paragraph 1.5.5 (It also refers to a nice profile drawing). If the 5 % gradient was due to noise it would be a noise abatement procedure and not a given rate on the plate. So on a normal departure you will climb way steeper until you retract the flaps (and perhaps have a momentary lower gradient) but in my opinion that's totally ok as long as you don't bust the non-standard surface.
Last edited by president; 7th Feb 2017 at 23:23.