DME Updating on the 737NG
Hello folks, my company has been receiving some brand new 737s since a couple of months and I made a curious observation - on all of them (in contrast to the older ships in the fleet) the DME updating is turned off by default - I have a couple of theories, but no solid evidence as to why this is the case. Usually I would turn it back on again, but I would like to know the reason behind this... One captain claimed that this was because the 'spurious accuracy' would deteriorate the ANP (yet VOR and LOC updating are both still on) - since the FMC is 90% or so biased towards the GPS position anyway this shouldnt matter one bit - throwing in another position source (and according to my ATPL knowledge the most accurate after GPS) should improve the overall accuracy and redundancy of the system.
Any thoughts?