Irs Info B737
 

Will FMC give ground speed , TAS with IRS in ATT
during flight, :confused:

737 Tech. Manual :

If allignement is lost in flight, the nav. mode (inc. present position and GS outputs) is inop for the remainder of the flight. However, ATT allows the system to provide ADI attitiude, and can also provide HDG information, but must be synchronised with the compass, and will drift at 15 degrees per hour.

I'm not familiar with the 737, but wouldn't TAS come from the ADC's?

BTW, where is TAS normally displayed on your aircraft? (EHSI?)

Rgds.
Q.

Qavion - I think you're right that TAS comes from the ADCs (CAS corrected for altitude (pressure) and temperature (density) errors). TAS is only displayed in the FMS, on progress page 3, not on the flight instruments (its not really much use on its own except for flight planning maybe). However, to get the wind vector on the EHSI, the IRSs compare TAS with GS, and HDG with Track. Hope this helps.

GS is displayed on the EADI in the bottom LH corner next to Mach Number. Also can be displayed on the IRS overhead display.

737ng
Both TAS and GS are displayed on the EFIS, with TAS appearing only if greater than 100 kts. TAS is also on the FMC progress page 3.