767 Fuel Jettison Load Shed

[NSEU]

According to one informative 767 website....

"Electrical load shedding will occur during fuel jettison :

- Equipment cooling fans (equipment cooling system reverts to OVRD mode)
- Bulk cargo vent fan
- Selected lights (landing lights, wing illumination, logo lights, galley lights)
- Window heat 3L & 3R
- PAX entertainment equipment
- Water line heaters"

Discussing this with fellow engineers and pilots from various airlines, no-one has been able to confirm that Water Line Heaters and external lights are affected by fuel jettison.

Would someone be able to independently confirm this?

Our schematic diagrams show the landing lights and water heaters may share primary circuit breakers, but relays exclude them from being affected by Fuel Jettison Load Shed.

Thanks in advance.

Rgds.
NSEU.

[Flight Detent]

That seems a little strange, load shedding all those services during fuel jettison, the IDG outputs must be pretty 'close to the wind', as regards electrical capacity!

The B737NG doesn't load shed at all during fuel jettison!

(and B4 you mention it - Yes, there are some NGs with fuel jettison!)

Cheers

[NSEU]

That seems a little strange, load shedding all those services during fuel jettison, the IDG outputs must be pretty 'close to the wind', as regards electrical capacity!

The 767 was Boeing's first twin/ETOPS aircraft so there was a tendency to over-engineer it. The fuel jettison loadshed in the earlier aircraft was designed to operate only when the aircraft was running on a single engine. Having said that, later aircraft appear to have been modified to load shed running on both engines also. Perhaps loadshedding the entertainment system is one way of getting the pax to listen to the flight attendants go through their emergency evac instructions?

The B737NG doesn't load shed at all during fuel jettison!

er... Hooray for the NG! Nevertheless, it does have a generic loadshed system which covers Galley or Cab/Util systems.

Does the NG variant you speak of use additional pumps for fuel jettison? (i.e is there an additional requirement for the NG to have fuel jettison loadshed nayway?).

Rgds.
NSEU

[Flight Detent]

Hi again,

No, the 737 varient I speak of does not use any additional fuel pumps to fuel jettison.

FD