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other waypoints between them. This anomaly most frequently occurs if the second
duplicate waypoint has an “at or above” altitude constraint, and one (or more)
waypoint on the legs page prior to the first occurrence also has a descent altitude
constraint. When the downtrack duplicate waypoint is selected to the scratchpad
and then entered in the discontinuity boxes (or after the first occurrence of the
waypoint), the FMC flight planning function may not identify the second
occurrence of the waypoint and subsequently reset. The FMCs may reset
alternately until one or both fail, or the modification is rejected. The FMC alert
message RESYNCING OTHER FMC and/or the FMC advisory message TIME
OUT - RESELECT may be observed.
Laboratory and incident analyses show up to eight minutes may elapse after the
flight crew modifies the route and the effects of the anomaly become apparent.
During this time the FMCs function normally. Once the anomaly is apparent, for
example FMC messages appear or CDU pages disappear, it takes between 30 and
70 seconds for the resets to complete.
Page 2 of 4
Operations Manual Bulletin No. ILF2-47(R2), Dated April 1, 2001 (continued)
Note: While the FMCs are undergoing reset and resynchronization, any
modifications or selections on either CDU will prolong the reset and
resynchronization period. During one reported incident, reset/resynchronization
exceeded eight minutes due to repeated flight crew CDU keystroke selections.
While the FMCs are undergoing reset and resynchronization, the ND MAP
display blanks. The ND VOR and ND APP modes are still available. The
navigation radios will remain on the same frequencies as before the FMC reset
began.
Operating Instructions
This bulletin does not apply to airplanes modified by Boeing Service Bulletin 747-
34A2672 (FMC Software load 15).
1. A route discontinuity frequently results when adding or modifying the arrival
portion of the flight plan. Should the modified route contain a waypoint that
already exists in the active route, do not close a discontinuity by placing the
downtrack duplicate waypoint in the discontinuity boxes, or in the waypoint
sequence immediately after the first occurrence of the duplicate. Instead, close the
discontinuity by entering the downtrack duplicate on top of the first occurrence of
the waypoint.
Note: if the first occurrence of the waypoint is the active waypoint, the anomaly
will not occur.
2. If the anomaly is experienced (duplicate waypoint not discovered prior to
execution of the modification), the FMCs may reset several times. Three outcomes
are possible:
A. Both FMCs may reset several times and recover with an inactive route and
no performance data. Reenter performance data and the route. Begin by reentering
origin and destination. This sequence is very important -- do not activate and
execute the inactive route. If the inactive route is simply activated and executed,
the FMCs will again reset and may fail. When reentering the route, follow the
steps in paragraph one above for a route discontinuity.
B. Both FMCs may reset several times and recover with no flight plan data.
Reenter performance data and the route. When reentering the route, follow the
steps in paragraph one above for a route discontinuity.
C. Both FMCs may reset several times and fail. If the EICAS alert messages
FMC LEFT and/or FMC RIGHT display, accomplish the FMC LEFT, RIGHT
non-normal checklist.
Note:While the FMCs are undergoing reset and resynchronization, do not attempt
any modifications or selections on either CDU. This will prolong the
reset/resynchronization process.
Page 3 of 4
Operations Manual Bulletin No. ILF2-47(R2), Dated April 1, 2001 (continued)
Administrative Information
This bulletin replaces bulletin ILF2-47(R1) dated October 29, 1999. Discard
Bulletin ILF2-47(R1). Revise the Bulletin Record to show ILF2-47(R1)
CANCELLED (CANC).
Insert this bulletin behind the Operations Manual Bulletin Record page in Volume
1 of your Operations Manual. Amend the Operations Manual Bulletin Record to
show bulletin ILF2-47(R2) IN EFFECT (IE).
This Operations Manual Bulletin will be cancelled after Boeing has been notified
all affected airplanes in your fleet have been modified by SB 747-34A2672. If you
do not plan to modify all your airplanes and would like the contents of this bulletin
incorporated in your Operations Manual, please advise Boeing accordingly.
Please send all correspondence regarding Operations Manual Bulletin status to
one of the following addresses:
Mailing Address:Manager, Flight Technical Publications (747-400)
Boeing Commercial Airplane Group
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
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