Complex sentence: Ten NYCT R44s were involved in accidents and fires that led to their premature retirements, so they were not rebuilt during the GOH program and were stored in the system until 2000, when they were scrapped.
Split into simpler sentences: Ten NYCT R44s were involved in accidents and fires that led to their premature retirements before the GOH program for the R44s, so they were not rebuilt during the GOH program. They were stored in the system until 2000, when they were scrapped.