Take the Mystery out of the Minima

The latest Aviation Wingman lesson focusses on explaining the approach minima for IR(R) holders, both how to calculate it and also how to use it in practice.




The process is a straightforward one once you know how to do it, but it can often be a topic of controversy between IR(R) holders.


1. Compare the OCH to the system minima.


Find the OCH (obstacle clearance height) on the approach plate and compare it to the absolute system minima, found in the table below. Choose the higher of the two.


A table showing the approach minima for ICAO approaches
Table of ICAO Approach System Minima

The trick to remember the system minima is that, with each bit of guidance you lose, 50ft is added to the minima.


The ILS minima is 200ft, as you lose the glide path and it becomes localiser-only, the minima is 250ft.


As the SRA's RTR is increased from 0.5nm to 1nm, the minima goes up by 50ft, and 50ft again when it's increased from 1nm to 2nm.


2. Add the 200ft IR(R) Holder Margin


It is recommended, not mandatory, to add at least 200ft to the figure above as an IR(R) holder.


3. Add the 50ft PEC for a precision approach


If you're calculating the minima for a precision approach, one with both vertical and lateral guidance, then add a 50ft PEC (precision error correction) to allow for altimeter errors in the approach configuration. If the approach is non-precision then skip this step and add nothing.


4. Compare your Calculated Minima to the IR(R) Absolute Minima


Compare the figure you've calculated so far to the absolute minima for an IR(R) holder:

  • 500ft for a precision approach,

  • 600ft for a non-precision approach,

Choose the higher of the two, this figure is your Decision Height or Minimum Descent Height for the approach!


To learn how to convert this height to an altitude, and how to use the figure during the approach, watch the full lesson!

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