I have been in several models of commercial aircraft during certification testing where we had to perform a max effort emergency descent as a part of the flight

I have been in several models of commercial aircraft during certification testing where we had to perform a max effort emergency descent as a part of the flight test profile. We routinely would hit rates of descent in the of 9,000-10,000 FPM range. I normally experienced this while strapped into a flight test workstation in the back of the plane, but once or twice had the opportunity to sit in the flight deck jumpseat. Once the aircraft is established in the descent, there is a bit of additional buffeting (light turbulence) and wind noise, but there is no highly unusual attitude involved. Initially, depending on how aggressively the pilot transitions from level flight to the descent, there can be a brief second of reduced or even zero G, but a smooth transition does not increase the total descent time by too much. I have a colleague who was involved with the flight testing of the C-17 military cargo plane. That aircraft can safely deploy all four thrust reversers while in-flight to make a high angle tactical descent - it can hit in excess of 25,000 FPM. Supposedly everyone on the test flight was supposed to have been medically cleared for this flight, but one crew member had a lingering ear infection, and blew out both eardrums during the test.