What is the primary factor affecting indicated airspeed during a descent in IMC if the static port is blocked?

Indicated airspeed during a descent in Instrument Meteorological Conditions (IMC) can be significantly impacted when the static port is blocked because the airspeed indicator relies on pressure measurements to provide accurate readings. The airspeed indicator works by comparing static pressure (which corresponds to the ambient atmospheric pressure) to the dynamic pressure (which corresponds to the pressure created by the aircraft's forward motion). When the static port is blocked, the instrument cannot correctly measure the surrounding static pressure, leading to erroneous airspeed indications.

In this scenario, air pressure differences become the primary factor affecting indicated airspeed. If the aircraft is descending and the static pressure is not vented to the outside atmosphere, the instrument will not account for the increasing air pressure that occurs with descent. This can result in a misleadingly low airspeed indication, potentially leading to a dangerous situation where the pilot might believe the aircraft is flying more slowly than it truly is, risking a stall if not managed properly.

The other options, while they can influence flight conditions or pilot workload, do not have the direct impact on indicated airspeed that a blocked static port does. Air pressure differences are the fundamental principle at work in determining the readings on the airspeed indicator.