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What is the difference between TCH and RDH ?

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Commercial Pilot, FAA Regulations, Flight Instructor, General Aviation, Instrument Rating

Hello Friends,

 

I realized that there are some approach charts that show us TCH ( Threshold Crossing Height) and in some approach charts we will see RDH ( Reference Datum Height), But I don’t know what is the difference between them. Does anyone can help?

1 Answers



  1. KDS on Jun 16, 2018

    I’m sure that John will come along and give you a better answer, but for now, this is what comes from FAA Order 8200.1C. That is the FAA’s instructions to the Flight Standards Inspection group:

    Threshold Crossing Height (TCH)/Reference Datum Height (RDH).

    CAT I. FAA Order 8260.3, TERPS Instrument Procedures, limits the CAT I procedural TCH to a maximum of 60 ft. Minimum TCH varies per the wheel crossing height of the user aircraft. TCH is normally determined by procedures personnel and is not evaluated by flight inspection. If FAA Order 8240.47, Determination of ILS Glidepath Angle, RDH, and Ground Point of Intercept (GPI), is applied to a CAT I facility, the flight check derived RDH replaces procedural TCH.

    I’ll take a stab at putting this into plain English. If the determination is made by flight inspection, then they calculate the RDH and it replaces the TCH.

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