# How does a G1000 equipped with a GDC 74 calculate IAS from dynamic pressure?

How exactly does a G1000 system equipped with a GDC 74 air data computer calculate the indicated airspeed that is displayed on the PFD from difference between the total and static pressure (i.e. dynamic pressure) measured from the pitot-static system?

The reason I ask is because I want to reverse the calculation and convert KIAS back to dynamic pressure, i.e. $$q$$ as defined below:

$$q = \frac{\rho u^2}{2}$$

My objective is to calculate dynamic pressure from the KIAS value that is logged to the data logs written to the top SD card by the MFD. The problem is that there are multiple ways to perform this calculation -- i.e. does the G1000 display an indicated airspeed that is uncorrected for instrument and position error (IAS, in the traditional sense) or corrected for instrument and position error (CAS)?

• The ADC uses pressure transducers inside the unit to convert the pitot and static pressures to electrical voltages that are digitized and processed by software. How you would tap into the raw signal, dunno. There might be a ground maintenance function in the unit that allows the real time raw signal data to be displayed. – John K Mar 27 at 2:32
• I am trying to calculate dynamic pressure after the fact from the KIAS value that is logged once per second to the G1000 data logs. – Joe Crivello Mar 27 at 2:43