I never tried a single unit operation as it doesn't allow this
http://img30.imageshack.us/img30/8171/updatedw.jpgwhile the two unit one (which seems to be a virtual three unit one) allows this mode and delivers a high accuracy.
The manual states
Quote:3 DME POSITION UPDATING The INS positions may be updated by a single or dual DME (Distance Measuring Equipment). Optimum single updating may be obtained selecting a DME station “off track”, at least 15 NM off the intended track, and within 200NM of range. Optimum dual DME updating is obtained tuning a second DME along track. |
Maybe you are using ontrack VORs then which don't allow the best single mode update.
Where there any single unit planes flying at any time? I can recall at least two visible units in the cockpits I saw so far, that's why I always go for the dual solution.
By the way,
it would be nice to see independent HSI units on the B-52 Driver. You can currently tune two Nav radios but you only get one showing up on the Captain's and FO's side.