Hi guys, just thought I would give you some gen from an engineering stand point. It really depends on what sensors are driving your EFIS, which is in its basic form simply a display. Gyros can, and still do fail on EFIS equipped airplanes, such as the 146-300 and this has no extra monitoring of gyro validity than the older analogue version. The ATR is fitted with an AHRS system which again is just an advanced gyro that can have the same failure modes, the CRJ has IRS as an option but many are fitted with AHRS, there has been an incident on this aircraft where the AHRS boxes were swapped from side to side for diagnosis without allowing time for a full power down, this resulted in the left box still 'thinking' it was in the right hand tray and vice versa, the result, on rotation and the subsequent very careful circuit the ADI indications and compass indications were all reversed!!!!!! Consider that in bad wx.. .I would say a quick scan of the instruments on the taxi out is a very worthwhile practice.