Sign in to follow this  
Guest alexhn

couple of 744 systems questions

Recommended Posts

to any of the technically coherant amongst us... :)1. why would a flight crew use the 4th system auxilliary hydraulic pump (on the ground) when demand pumps 1 and 4 can run under bleed air, and demand pumps 2 and 3 are electrically run... most confusing is the fact that the sys 4 aux pump is run by electricity, and so are demand pumps 2 and 3... also, demand pumps 1 and 4 can be run by bleed air, so why the aux pump over these?2. with the STEP SIZE and STEP TO functions on the cruise page... -are these for stepping in CLIMB, or are these for steps to higher altitudes while in climb for fuel preservation etc.. -when entering a STEP SIZE value, will this designate the next alt that the 744 will climb to -finally, what does it mean when STEP SIZE is in 'ICAO'thanks :(

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Ok, the air driven pumps are used for backup purposes when the engine driven pumps fail to work.The air driven pumps are to work along with the engine driven pumps during high demand for hydraulic fluid.Systems 2,3 do not provide hydraulic fluid for the normal brakes.The air driven pumps are very powerful and are not required for such small ground operations.-----The step size determines how many feet the cruise altitude will increase by.When it is in ICAO or RVSM, a pre-determined increasement is selected.

Share this post


Link to post
Share on other sites

>The step size determines how many feet the cruise altitude will increase by.So this is mid cruise, and is done to save fuel or increase efficiency or whatever?When it is in ICAO or RVSM, a pre-determined increasement is selected.>Where does the pre-determined increase come from?basically, is the STEP TO function is used MID CRUISE to ascend MID CRUISE and the purpose is to increase efficiency?

Share this post


Link to post
Share on other sites

I suppose pre-programmedYes to increase efficiency.

Share this post


Link to post
Share on other sites

>>The step size determines how many feet the cruise altitude>will increase by.>So this is mid cruise, and is done to save fuel or increase>efficiency or whatever?You do a step climb to save fuel. When the arcraft has burned enough fuel it can climb higher due to the lighter weight. The higher you fly the less fuel the arcraft burns due to lesser air density.>When it is in ICAO or RVSM, a pre-determined increasement is>selected.>>Where does the pre-determined increase come from?>>basically, is the STEP TO function is used MID CRUISE to>ascend MID CRUISE and the purpose is to increase efficiency?>Standard ICAO step size is 4000 ft.Hope this helps!Christian

Share this post


Link to post
Share on other sites

Don't know the 744's box but shouldn't it be 2000ft upto FL290 and then 4000 ft from then on? (at least in non-RVSM airspace)Does anyone know if there are upgrade available so you can type in RVSM? That would mean 2000ft up to FL410 and then 4000 ft.Regards,Adrian

Share this post


Link to post
Share on other sites

>Don't know the 744's box but shouldn't it be 2000ft upto>FL290 and then 4000 ft from then on? (at least in non-RVSM>airspace)>>Does anyone know if there are upgrade available so you can>type in RVSM? That would mean 2000ft up to FL410 and then 4000>ft.>>Regards,>>AdrianHi Adrian,The 744 FMC doesn't take RVSM into account. This is the crews responsibilty to prgram and monitor the FMC since RVSM isn't global.Directly from the 744 AOM;--------------------------------------------------------"STEP SIZEDisplays climb altitude increment used by FMC to calculate optimum step climb. Defaults to ICAO. Valid entries are 0 to 9000 feet in increments of 1000 feet.""STEP TO AltitudeDisplays calculated step climb altitude based on STEP SIZE. May be overwritten with manual entry above CRZ ALT.Valid entry is FLXXX or XXX (flight level), or XXXXX (feet).Displays STEP TO altitudes entered on LEGS page. These altitudes may be greater or less than CRZ ALT and cannot be overwritten on the CRZ page.Blank when no active flight plan or when within 200 miles of T/D.Note: Calculated STEP TO altitude is always higher than OPT altitude.When using ICAO STEP SIZE, the STEP TO altitude is the next higheraltitude above OPT altitude corresponding to the direction of flightdetermined by the CRZ ALT entered before takeoff. For example: with anICAO STEP SIZE, a CRZ ALT of FL280 entered before takeoff, and anOPT altitude of FL337; the STEP TO altitude will be FL350. In-flightchanges to CRZ ALT will not affect the calculation of STEP TO altitudes when using ICAO step size. However, if an alternate route (for example, Route 2) is activated in flight, the hemispheric altitude will be calculated based on the current CRZ ALT.When using an altitude increment STEP SIZE, the STEP TO altitude is the next higher altitude above OPT altitude calculated by adding the STEP SIZE increment to the current CRZ ALT."------------------------------------------------------Hope this helps!Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

Share this post


Link to post
Share on other sites

so basically, the STEP TO function is to keep the plane always at an optimum altitude, to save fuel etc?also, can i manually enter different STEP TO and STEP SIZE values preflight?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this