marshals is classified. former air marshals say any mishap is unacceptable, because their agents operate at 34,000 feet. >> there's no backup. you have got to take care of business. you gotta do it very quickly and efficiently. >> reporter: henry preston says he on servbserved a decline in s practice, inconsistencies that could contribute to mistakes. >> they need training. there's no doubt about it. >> reporter: three of the apparent mishaps occurred during firearms training. in one case, an instructor allegedly threw training bullets into an open flame. they exploded and one staff member was struck in the face by flying debris. problems are nothing new to the controversial air marshal service. cnn has previously reported agents have continually complained about low morale, low staffing, grueling hours. a 2012 sleep study obtained by cnn shows 75% of domestic air