B737 -300 / 400,.. NON GPS, Just DME/DME is the equipment I am asking about. After initialize IRS on ground, then the "update at TOGA" and reaching line of sight, the auto tune starts picking up various DME's from in range stations and gives a valid navigable lateral path. What specifically is driving the map or needle? is the FMC processing this DME information and driving the nav solution? or are the DME stations constantly updating the IRS/IRU's, then the IRS feeds this to the FMC's for navigation? The crux of the question is this, is the IRS once initialized on the ground constantly updating it's position with DME or will it only navigate when all other sources are failed?
This picture taken 350 miles from nearest station.
