An interesting tidbit on the 300

 

APU to Pack Takeoff

 

Before engine start, selecting APU from the FMC scratch pad to the SEL-APU

field on the THRUST LIMIT PAGE arms

the system for APU to pack takeoff.

Approximately one minute after starting the second engine, the bleed air supply

system configures for APU to pack takeoff.

When APU is selected to the SEL-APU field after both engines are running but

before takeoff, the bleed air supply immediately configures for APU to pack

takeoff.

In APU to pack takeoff configuration:

• the left engine bleed valve is closed,

• the L ENG OFF light is illuminated and remains illuminated,

• the APU provides air to air demand pump C1 and the left pack,

• the center bleed isolation valve is closed,

• the right engine provides air to air demand pump C2,

• the right pack valve is closed, and

• the R PACK OFF light is illuminated and remains illuminated.

The system reconfigures from APU to pack takeoff to normal operation when:

• thrust is reduced to climb thrust, or

• approximately 10 minutes after takeoff, or

• the airplane is above 11,400 feet altitude, or

• APU to pack configuration cannot be continued because of failures in

other systems, or

• APU to pack mode is deleted manually.

Wow, cool feature.

 

Never seen that, might be an airline option.

Never seen that, might be an airline option.

Nope, it's on all of them.

And it is used for takeoff performance calculation with the OPT (Onboard Performance Tool by Boeing) software to increase the payload by increasing the maximum takeoff weight (OTOW). The APU to packs procedure gives the same performance as with Packs Off takeoff. The advantage is that the cabin has conditionning air during takeoff.

Stephane