Question about B777
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Join Date: Sep 2007
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Question about B777
Hello guys,
flying the Triple Seven for 8 months now there are still some questions about that airplane and I cannot find any answers in the books.
If you place on the PROG PAGE 3 a Waypoint with an RTA, why at the same time on the VNAV CRZ Page the information about OPT, MAX and RECM Flight Level disappears? That field remains blank until you overfly that waypoint and I canīt find anything in the books
Would appreciate some feedback from experienced Triple seven pilots
Many thnaks in advance
flying the Triple Seven for 8 months now there are still some questions about that airplane and I cannot find any answers in the books.
If you place on the PROG PAGE 3 a Waypoint with an RTA, why at the same time on the VNAV CRZ Page the information about OPT, MAX and RECM Flight Level disappears? That field remains blank until you overfly that waypoint and I canīt find anything in the books
Would appreciate some feedback from experienced Triple seven pilots
Many thnaks in advance
Join Date: May 2008
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On the VNAV CRZ page the OPT, MAX and REC CRZ data is dependent on the data that you have loaded into the FMC, namely Cost Index and the Winds/Temp data for the various altitudes/waypoints. You can see the Wind/Temp Alt Data by going to the LEGS page then RTE DATA and selecting a waypoint. It should then open up into a separate page with the predicted Winds and Temperature for up to 4 Altitudes. associated with that waypoint. The NEXT/PREV will scroll forward and back through the listed waypoints.
The actual calculation on the VNAV CRZ page is made using the data supplied for the current altitude with a slight bias of the current Wind and Temp to give a data set that is used for the calculation.
Note that the calculation uses the CI data for your particular airline and as such the same number ie CI = 100 may generate a different speed between airline A and Airline B.
When you put in an RTA you are overwriting the performance parameters by telling the aircraft to fly at this altitude to achieve a Way Point Crossing time of xxxx. Note that it comes up with a Max Speed that it will do and to achieve RTA the big controllable item to achieve this is speed.
Speed increase or decrease affects the altitude capability at a set weight thus the calculations on the VNAV CRZ Page are removed until RTA is either removed manually or by crossing the Waypoint
The actual calculation on the VNAV CRZ page is made using the data supplied for the current altitude with a slight bias of the current Wind and Temp to give a data set that is used for the calculation.
Note that the calculation uses the CI data for your particular airline and as such the same number ie CI = 100 may generate a different speed between airline A and Airline B.
When you put in an RTA you are overwriting the performance parameters by telling the aircraft to fly at this altitude to achieve a Way Point Crossing time of xxxx. Note that it comes up with a Max Speed that it will do and to achieve RTA the big controllable item to achieve this is speed.
Speed increase or decrease affects the altitude capability at a set weight thus the calculations on the VNAV CRZ Page are removed until RTA is either removed manually or by crossing the Waypoint
Join Date: Jun 2004
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ghw78 said "When you put in an RTA you are overwriting the performance parameters by telling the aircraft to fly at this altitude to achieve a Way Point Crossing time of xxxx. Note that it comes up with a Max Speed that it will do and to achieve RTA the big controllable item to achieve this is speed.
Speed increase or decrease affects the altitude capability at a set weight thus the calculations on the VNAV CRZ Page are removed until RTA is either removed manually or by crossing the Waypoint".
He is absolutely correct, that is the logic written into the FMC programme. Proved it only today, a fiddle here, a fiddle there, but nothing short of cancelling the RTA would restore the other parameters.
Quite logical when you think about it.
Regards,
Old Smokey
Speed increase or decrease affects the altitude capability at a set weight thus the calculations on the VNAV CRZ Page are removed until RTA is either removed manually or by crossing the Waypoint".
He is absolutely correct, that is the logic written into the FMC programme. Proved it only today, a fiddle here, a fiddle there, but nothing short of cancelling the RTA would restore the other parameters.
Quite logical when you think about it.
Regards,
Old Smokey
