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Initial Turn at or above 400ft under IFR

Asked by: 930 views Commercial Pilot, Flight Instructor, General Aviation, Instrument Rating, Private Pilot

I read the AIM on ODPs and I got curious with this number "400" where it states that aircraft is to make first turn at or above 400ft and shall maintain 200ft/nm.

How did FAA come up with this number 400ft?

 

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1 Answers

  1. Best Answer


    John D Collins on Aug 06, 2016

    TERPS evaluates the departure from each runway using an OCS (obstacle clearance surface) of 40 to 1. This is a surface that rises 152 feet/NM. The standard climb gradient is 200 feet per NM and provides a buffer above the OCS of 48 feet/NM. Runways are evaluated for the initial climb area (ICA) out to 2 NM for obstacles along the centerline of the runway with a width of +/- 500 feet at the DER (departure end of the runway) to +/- 3756 feet at the two mile point from the DER. From that point, the evaluation is in all directions, but continues at a OCS of 40 to 1. Climb performance in this area is also assumed to be at least 200 feet per NM. So in effect, until you get to 2 NM from the DER, obstacle clearance is only assured when flying straight out. Since the assumed rate of climb is at least 200 feet/NM and the first 2 NM are evaluated, you need to be at 400 feet above the ground before evaluations of turns is considered.

    So with the TERPS criteria in mind, guidance to pilots is to climb to 400 feet before making any turns. If the 40 to 1 OCS does not work at 400 feet, their will be an ODP developed and the instructions may specify a specific altitude and direction of flight to climb to before proceeding on course. The ODP may involve a variety of tools, including a climb in visual conditions to avoid obstacles, climb in a holding pattern or over an airport, or a specific route to follow. The point of the DP/ODP is to provide the pilot a safe way of flying in non visual conditions that will avoid obstacles. In cases where the standard climb gradient won’t work, a non standard climb requirement may be specified, such as 350 feet/NM. If your airplane can’t make the climb performance, you should either depart under visual conditions or not go at all.

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