It suppresses a certain frq range but leaves the others relatively open. You can still hear what the engines are doing its just that you don't have to boost the RT to hear of the top of them. You can hear if the engine starts burping and farting or a mag has dropped out.
There are some old and bold out there that always bang on they don't like them for that reason. Commercially you get notices that you should turn it off for engine starts etc when CP's get a bee in there bonnet about it. But to be honest these old and bold hearing is that shagged after years of noise damage they will hear the same as the ANR headset pilots anyway.
You will get hearing damage what ever you use, ANR reduces it. Engine failures are very rare and if its going to fail having ANR on or not, aint going to stop it failing.
And to add the DC's arn't for everyone, I have lent a pair to a FO and after a couple of hours he had to take them off because his ears had got a burning sensation and his head felt as if it was in a clamp. I had mine on for 8 hours that day and suffered no discomfort.
Last edited by mad_jock; 23rd Feb 2011 at 11:34.