I don't have the manual in front of me but I think full reverse is not supposed to be selected above 90 kts, due to resonance problems I believe. Years back I was Dh'ing on a Metro2 and the PIC slammed the a/c on about 1/2 way down a 4000' strip. teh engine spinners jumped up/down at least 4 ". Scared the cr@p out of me