"TO-B" Setting on 744 FMC Thrust Limit Page

[QAVION]

G'day, fellow PPRuNers...

Would anyone be familiar with the FMC "TO-B" or "Takeoff Bump" thrust setting?

It appears below the TO, TO-1 and TO-2 selections on the THRUST LIM page on some aircraft.

I noticed that, when pushed, the EPR Thrust Ref limits(cursor and digital display) and amber EPR limits completely disappear from the EICAS engine displays.
Does a SEL Temp need to be entered on this page for this selection to work properly?...or is it a fly by the seat of your pants selection???

Ta.
Q.

[Cornish Jack]

QAVION
Don't know anything about it in operational terms, but my tome of FMS info says that it is perf code dependent. In other words the code has to be selected on the perf maintenance page LSK1. It is effective, if the appropriate code is operative, until the first power reduction.

"LSK1 (The Perf code) displays the binary state of Perf Option Code program pins. Program pins aredisplayed in left to right order of MP15F, MP15E, MP15D and MP15K. Program pin status is only updated after a long term power interrupt while on the ground.".........What did Horace say, Winnie? http://www.pprune.org/ubb/NonCGI/confused.gif http://www.pprune.org/ubb/NonCGI/redface.gif :)

[mutt]

Qavion,

It is possible that you airline didnt "buy" the thrust bump option, therefore although you see the selection on the FMS, the actual data isnt there!

I guessing this because it wouldnt make sense for you to enter a temperature, the "bump" is designed to give you extra power which should be at actual temperature!

Mutt

[ACARS]

Gday

Take your question to the forum www.aerowinx.com (http://www.aerowinx.com)
I am sure someone there can answer your question.

[QAVION]

Thanks for the responses, chaps...

Re:
"my tome of FMS info says that it is perf code dependent."

and...

"It is possible that your airline didn't "buy" the thrust bump option, therefore although you see the selection on the FMS, the actual data isnt there!"

I did notice that the Perf Code was the ubiquitous "1111". Seems odd that it should be the same as those without the Bump feature. If they bought it, then they only bought half of it :-)

"It is effective, if the appropriate code is operative, until the first power reduction. LSK1 (The Perf code) displays the binary state of Perf Option Code program pins. Program pins are displayed in left to right order of MP15F, MP15E, MP15D and MP15K. Program pin status is only updated after a long term power interrupt while on the ground.".........What did Horace say, Winnie?"

LOL... I don't know what they're saying either... If the "1111" is only changeable through pin programming (i.e. by modifying the aircraft wiring), then I don't see the status changing at all through pilot use.

"I'm guessing this is because it wouldnt make sense for you to enter a temperature, the "bump" is designed to give you extra power which should be at actual temperature!"

I was thinking you could enter a lower temperature.... instead of the usual higher temperature for derates. I didn't get around to trying this though.

"Take your question to the forum www.aerowinx.com (http://www.aerowinx.com) I am sure someone there can answer your question."

Thanks, but I already did... with no success. Even "PS1" doesn't model this feature (ref page 158 of the Aerowinx manual)

Anyway, thanks for trying, chaps.
Cheers.
Q.

[Cornish Jack]

QAVION
Just a little add-on, the LSK1 entry codes were, like the other entries on the Perf Maint page, able to be entered by the engineers or the flight crew. Don't wish to 'educate granny in egg-sucking' but the method of entry is to enter ARM on the dotted line at LSK6R to allow editing of the other line values.

[This message has been edited by Cornish Jack (edited 21 February 2001).]

[QAVION]

"....the method of entry is to enter ARM on the dotted line at LSK6R to allow editing of the other line values."

Ooops... Sorry for the late response, Cornish... I'm having trouble acessing this site (I had to disable my Java to get the page to load).

I've been told that the "1111" at LSK L1 can't be modified even with the ARM command. I have since learnt, however, that the BUMP function is not activated by messing with this line.

Anyway, dribs and drabs of data coming in, so I should have this problem sorted soon...

Cheers.
Q.