AP - NASA is making strong progress in changing its safety culture after the breakdown that led to the Columbia tragedy, but many workers are still afraid to speak their minds, according to survey results released Friday.{br}{br}View the Entire Article (http://us.rd.yahoo.com/dailynews/rss/science/*http://story.news.yahoo.com/news?tmpl=story2&u=/ap/20050222/ap_on_sc/nasa_culture){br}