Hello Captain Lim,
I would like to seek your clarification regarding enroute diversions on the Boeing 777.
Firstly, as you might know, the Airbus FMS have 5 closest airports and ETP pages where pilots can refer to in the predictions of the enroute alternate airports.
1. On the Boeing 777, how do you find the ETP and related predictions using the FMC?
The only way I think is, use the FIX page where you can create two circles to intercept the mid point. For the two airports, you create a circle on each of them. The perpendicular line joining the two circle intercepts that cuts along the active flight plan route, gives the equal distance point. As long as the wind entry is correct, it can be used as an ETP.
In case of a diversion, how do you tactically decide which airport to divert to, taking into consideration the latest wind updates? I would also like to know the thought process that goes on when you plan a diversion on route.
2. On the ND (Navigation Display) - if you select the ARPT in the EFIS panel, you get the display of all the airports around the aircraft based on the range you have selected.
My question is: do you get the display of only those airports that can handle the Boeing 777s or do you get information of any airports nearby?
If the former is true, do the Navigation Aids database exist in the 777 systems? If the latter is true, what is the reason for displaying a small county airport if it cannot handle a Boeing 777?
Thanks a lot for your precious time.
1. The Airbus FMS (Flight Management System) seems to be better than the Boeing 777 where calculation of ETP (equi-time point) is concerned. On the Boeing 777, the calculation process is more tedious and your description of the mathematical interception is quite right when the wind effects are ignored.
Which airport to divert to would depend on whether you have passed the ETP. Before the ETP, you return to the departure airport or whichever one was used for the calculation of the ETP. If the emergency were to occur after the mid point, then you would divert to the next calculated airport.
I will not elaborate on the lengthy thought process that goes on in the pilot*s mind during an in-flight diversion, but things to consider are: the weather trend of the alternate airport, its support and backup facilities, hotel accommodation for passengers, the length of the diversion, etc.
2. You only get airports that can handle the Boeing 777s in the ARPT (Airport) page. If the airports are in the database, then the Navaids (Navigation aids) are there. Small airports with short runways that cannot support the Boeing 777 will not be in the ARPT page.