Trent 800-B777 cruise altitude

[r304ndy]

To all Trent 800-B777 drivers: Can any of you enlighten me on what the recommended Vs normal (if different) cruising altitude for the Trent 800-B777? What are the reasons behind the difference if any?

Thanks folks!

[Shaka Zulu]

Normally RCMND Crz Alt is pretty close to the Flight Levels planned for the route.

however sometimes winds can be different than forecast requiring an early climb/descent.
or entering NON RVSM airspace can require you to be significantly off your recommended crz alt as calculated by the FMC

[r304ndy]

Thanks Shaka Zulu. What I really would like to know is if the there are some Trent-specifically operating instructions which do not allow you cruise at or near recommended cruise altitude? Any TO derate restrictions perhaps?

Cheers!

[Old Smokey]

There are no "Trent Specific" limitations upon cruising at or near recommended cruise altitude. The aerodynamic limitations regarding buffet margins apply as in all other aircraft. For the moment, Trent engines must have a Climb Thrust application within the last 2 hours of flight, due to the fuel iceing problems associated with the BA accident.

TO derate restrictions, or to be more specific, Takeoff Reduced Thrust restrictions, applied only to the GE 115 versions prior to modification. In our company (SIA) all GE engines are now modified, and no restrictions apply.

Regards,

Old Smokey

[SuperRanger]

reoandy,

The reason for the difference between the OPT ALT & RECMD ALT is the WIND (to a smaller extend, TEMP)! In NIL wind, OPT ALT & RECMD ALT will be the same. The difference maybe obtained from the WIND-ALTITUDE TRADE table in PI section of FCOM 1 (i still think Boeing should have left it in the QRH!).

Barring any ATC restriction, all flights shown be flown as close to the RECMD ALT as possible as it should be most economical (GIGO discounted!)

I know not of any restriction saying otherwise.

SR

[hotcurry]

SR I don't quite agree.

OPT alt, is the altitude that minimizes trip cost when ECON speed is selected.In other words, OPT displays the most economical altitude to fly, based on gross weight.When LRC or SEL SPD is selected, OPT alt displays the altitude that minimizes trip fuel.

RECMD alt is the recommended cruise flight level to fly at for the next 500 NM. This calculation is based on the following:

Specified route
Selected cruise speed schedule
Estimated aircraft drag and fuel flow information
Wind and temp forcastThe recommended flght level can be any flight level in the present step altitude schedule up to the maximum altitude ( MAX ALT) and down to 9000 ft below the current FMS cruise alt.

The big visual difference on the FMS is that OPT alt increases in 100 ft increments for obvious reasons.
RECMD alt is always a flight level based on selected step climb of either 4000 ft (ICAO) or 2000 ft (RVSM)

Laters