MD-11 Flight Crew Operations Manual
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FMS -
Controls and Displays
FMS.30.94
• FMC POSITION MISMATCH appears. The pilot should go to the POS
REF page 1/3 and compare FMC position on both FMCs. The message
appears when the two FMC positions differ by more than 5 NM or double
the RNP distance in nautical miles (NM). The message goes away if the
positions are less than 3 NM or double the RNP distance in nautical miles
(NM), respectively. After comparing, use the FMC considered to be the
most accurate. The above is generally a result of poor radio DME position
computation.
• VERIFY AIRCRAFT POSITION appears if a single FMC radio position
varies from the IRS's. Usually it shows on only one MCDU. Check the
IRS status page on that MCDU. If the condition persists it is advisable to
use the other FMC as primary for navigation. It is possible to have this
message on both MCDUs if a single IRS has drifted more than 12 NM.
Comparison of both IRS status pages should confirm this. Again, use the
FMC considered to be the most accurate.
October 02, 2006
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