Md11 - Auto Tuning Of Vor/dme

[JRBarrett 3,048]

A quick question regarding the automatic tuning of VORs / DMEs in enroute operations. In most aircraft, the autotuning function will select two different navaids (whenever possible) to provide IRU position updating via a bearing/distance "cross-fix". This is the case with the PMDG 747, as well as other high-end add-ons that simulate this function.I have noted that the MD11 always, without exception, auto-tunes the both #1 and #2 Nav receivers to the same VOR/DME station. The selected navaid continuously changes as the aircraft proceeds along its route, but I have yet to see the auto-tune function tune the two receivers to two different stations at the same time.Is this normal operation for an MD11, or a possible bug?Other than that, I am extremely satisfied with the way this aircraft performs on my system. No errors, lock-ups, CTDs whatosever - even when flying online in high-traffic areas with SB4, along with ASX weather. I never thought you'd top your own 747 product, but the MD11 is one sweet aircraft.Jim Barrett

[Tabs 2,790]

Jim, I believe there is a reason for this and it is realistic - I'll let someone like Michael or Markus respond in detail though.

[Guest rellehenk]

Normal operation...The VOR's that are displayed on the EIS map dispay (ND) are tuned by the FMC's. FMC1 tunes VOR1 and FMC2 tunes VOR2. You can see the tuned navaids on the FMC NAV RAD page and the ND. The Navaids for display on the ND are automatically tuned according to a programmed priority.1. manually tuned VOR2. Navaid on flightplan leg3. Upcoming flightplan navaid4. preceding flightplan navaidetc...Navaids are also tuned in the background for position calculation. Normally the FMC position is calculated using GPS and IRS, but if GPS is not available (quite rare) the FMC uses IRS/Radio Nav for position calculation.Radio position is computed using the following priority:1. DME/DME2. DME/Bearing3. LocalizerFor position calculation, two independent DME's are used.Navaids displayed on the ND (FMS NAV RAD page) are mostly the same unless manually tuned.

[JRBarrett 3,048]

Navaids are also tuned in the background for position calculation. Normally the FMC position is calculated using GPS and IRS, but if GPS is not available (quite rare) the FMC uses IRS/Radio Nav for position calculation.Radio position is computed using the following priority:1. DME/DME2. DME/Bearing3. LocalizerFor position calculation, two independent DME's are used.Navaids displayed on the ND (FMS NAV RAD page) are mostly the same unless manually tuned.

Thanks for the information. It makes sense to have the system autotune enroute navaids, so that they would be immediately available for navigation should there be a failure in the FMS lateral NAV function.Jim Barrett