MD-80 Quiz

[balaton]

Just curious:

-On some MD-80's there is switch on the ovhd pnl labeled: APU - NORM/ECON. Any hints of it's function?

- The MD-80 FMS PERF INIT page fuel qty input must contain a designator N (normal) or A (alternate), any explanations of their meaning?

Cheers,
b

[pichu17]

Is an automatic system ( sb 28-58 or production) to alter the baseline fuel schedule . When both center tank boost pumps are in AUTO position ,float sws cycle the center tanks pumps on and off to burn a portion of the main wing tank fuel prior to comlpete burn of the center tank. AFB reduce the probability of ice formation due to cold soaked fuel,by reducing the quantity of fuel remaining in the main tanks upon landing.

[balaton]

Yes, thanks it answers my question No 2. ( I forgot the two optional fuel sched: NORMAL and ALTERNATE)
Still seeking a reply for my APU ECON Swc question. Some additional info: It is located just below the APU DOOR switch, probaly a company specified option or mod. (ALITALIA planes has it!). Here is a link to a photo: http://www.airliners.net/photo/Alitalia/McDonnell-Douglas-MD-82/0295626/L/ (http://www.airliners.net/photo/Alitalia/McDonnell-Douglas-MD-82/0295626/L/)
b

[md-100]

weird switch

i ve never seen it before

[xkoote]

We have it on two of our MD-80's. With the switch in ECON, the APU load control valve restricts the maximum amount of bleed air extraction, thus reducing fuel burn and APU EGT. It is used at times when maximum APU bleed air for cooling is not required.

Xander

[stilton]

We did not have this switch on our -80's. It must have been in the E & E compartment hardwired to econ as the air outlow in hot weather was pitiful !

[AIRSEABISCUIT]

Agree with xkoote,

in the NORM position you provide maximum bleed air to the pneumatic system, therefore it's the required position for engine start (anyway a modification was planned to automatically shut-off the economy mode valve regardless of the position of the switch, in order to prevent an hot start).
In the ECON mode the bleed air available for the packs it's reduced, therefore you have lower EGT and lower fuel consumption, and it's supposed to be used when the reduced flow it's sufficient to maintain the cabin temperature requirements.