You add 50 feet to your MDA gives you about 320 AGL.
Originally Posted by malabo
The 50' figure commonly thrown around relates to the height above the runway threshold intended by the constant descent angle, and is about where the flare should begin.
No, in other countries, the 50ft is added to the MDA to create a "derived decision altitude" at which the go-around must be commenced if not "Visual". It is designed to ensure that the aircraft does not go below the MDA (or if it does, not by very much) during the go-around manoeuvre. You won't catch me flaring at 50ft!