Healthy avacado tree, every year, 100's of avacados form... but when they get to approx. the size of an egg, ALL turn black and fall off... why?

Question

I have a lush, green, and otherwise healthy Avocado tree, approximately 25 feet tall, and approximately 10 years old... looks to have sprouted from a seed… Every year for at least the last 5 years, the tree looks to be loaded with small baby avocados, but when they get to be about the size of an egg (maybe a little larger), ALL the fruit begins to exhibit small discolorations on the skin, which eventually turn the entire avocado black (on ALL the Avocados), and the fruit falls off the tree… WHAT is happening? I have a number of other avocado trees that have been around for years, and they produce normal fruit… Is this a disease? Is it the location of the tree? Is there a resolution or cure ?