ASFKAP,
...this signal is resolved within the IRU and the result is called Inertial vertical speed and is displayed on the IVSI...
"I" in the IVSI stands for "Instantaneous" instead of "Inertial" in older versions of Operations Manual of Boeing. Regardless what it stands for, it implies an immediate indication will be displayed rather than a delay as in the conventional VSI.
In fact, intial querry was due to contradiction of my opinion with my other company collegues who claim that "IVSI works in the case of total static blockage since the V/S indication is derived from IRS input. That sounds illogical to me who has some basic knowledge of physics. That is : IRS can only be capable to measure or calculate "Geometric Height" change not Barometric Height" change. Therefore, to be in conformity with the altimeter which is the measurer of Barometric Altitude, IVSI should be definitely fed with static input. That is the reason I have come up with question "How IVSI works"; whether it works in conventional way without IRS input ? I am more or less sure that IVSI will not work without static input. However, as I mentioned in my previous posts, in SIM (neither EFIS i.e B 737 400 nor NG i.e B 737 800) among the failures which can be practiced, there is no such a failure as "complete static blockage" to confirm this conclusion.
Since my last post, I have directed this question to engineers. After they have gone through the schematics of system in maintenance manual, they have also come up with: "For both types of airplane, IVSI will be unservicable in the case of loss of either input from IRS or static".
Thanks.