Single Pack Ground Operation on B767

[Gards]

Question for engineers around. In a hot and humid climate is running air-conditioning for the whole aircraft with cargo doors open, passenger doors open, and all window shades open ie. no attempt to keep the cabin cool an overburden on a single pack controller? I was told not long ago by a captain who had no answer to this question that we are saving fuel by turning off one pack controller on the ground. To me its not saving that much if the single pack has to put out that much more air to maintain temp in the cabin.

For the small cost in savings of operating on one pack where is the tradeoff before an expensive pack controller goes tits up?

Thanks in Advance!

Gards!

[Blacksheep]

It won't overload the pack controller but the the mechanical bits down below, like the ACM for instance, will be working their tits off and they're very expensive to repair. But then, so are APUs; why not rent an Air-Con cart for an hour or two? The problem is that bean-counters have short term perspectives and prefer to use direct operating costs. :rolleyes:

[mono]

Why on earth would a pack controller (a solid state electronic device) fail if used alone instead of as a pair? As Black sheep says it is possible you will reduce the MTBF of some of the pack componants (ACM for example) as they have to work harder.

However, your captain is incorrect. The most efficient way to operate the APU/packs (on the 75/76) is either with no packs AND the bleed turned off, or with BOTH pack operating.

The APU EGT is a fair measure of how efficiently it is operating. If the APU is running and the bleed is off the the APU EGT will be low (for a good APU below 300 degs C on a standard day). Switch the bleed on and the EGT will rise quite sharply (a 100 deg temp rise is fairly normal) then as each pack is switched on the EGT drops again. With both packs operating the EGT will be lower than with a single pack operating.

I believe Boeing recommended SOP is as per the above and it is the SOP in my company.

Hope this helps.

[punk666]

On the 737, During 1 pack ops the APU must supply higher bleed air pressure to assure proper control system operations. This higher pressure requires a greater Inlet Guide Vane (IGV) open position than that required for 2 pack operations. Since there is less airflow required to operate 1 pack than is needed, a significant amount of unused bleed air is exhausted through the surge control valve. Higher IGV open position and large quantity of unused air translates into higher APU fuel burn and higher turbine inlet temps during 1 pack operations.

[Gards]

I appreciate all your responses! Thanks! Happy New Year!

[lloyd_dsouza]

Hi Gards,

WRT ur question abt the 767. We handle an airline here in india tht operates a 767. The airline recommends to operate only 1 pack on ground and the reason same being TO SAVE FUEL.But if the airline wnts to save fuel why not shut of the APU itself and use the GPU and ground AIRCON. I did not see much diff in fuel consumption when only 1 pack was operating.

PSST: I am not a pro in maintenence,just started my career.