Thanks for the info, but I'm still a little confused regarding the attenuation. Isn't 744 flight deck wind noise mostly high pitched hissing? What's the point if these headsets are blocking mostly low frequency sound?
I didn't realise the attenuation was based on constant external sound levels. I was thinking they were more advanced than that.
Notwithstanding, our first 744's noise-cancelling headsets blocked TCAS aurals to the point where flight crew couldn't wear them below a certain altitude (above this altitude, the danger was considered less serious!).
Other side-effects:
As previously stated, some headsets are so good, they pick up aircraft "faults". e.g. humming in the audio system on Classic 747's, which has been on the aircraft since they left the factory. With loud background noise, you couldn't hear it. It was so annoying, the flight crew simply couldn't wear the headsets.
The headsets also caused vergito in some people if you only wore one earpad.
As MBlackey says, there are (so-called approved) models which might possibly block sound (passively), so all headsets still need some kind of trial. I still don't see how the company will let you select your own. Not all headsets are compatible with the aircraft electronics.
Rgds.
NSEU