B777 Air Demand Pump Inop.

[Cropduster]

Dispatched with a center hydraulic air demand pump inop., MEL 29-11-03. The procedure required us to power the remaining ADP with the APU bleed for take-off by running the APU bleed and isolating the pump air supply with the L and R bleed isolate valves. After take off the APU was shut down and the bleed isolate valves are returned to their normal open positions.

This makes sense as it allows the remaining pump to provide hydraulic power for the gear retraction and flight controls (I believe primarily the TAC control of the rudder) in the event of an engine failure. What surprised us was that we were not required to re-configure the system for landing, What is different about a single engine go around than an engine out take off?

Any insight greatly appreciated.
Cropduster.

[TURIN]

A guess, less fuel on board so engine power not so critical.

[B2N2]

I’m thinking Maximum Landing Weight.
Significantly less then Maximum Take Off Weight.

[perantau]

Raising the gear with hydraulics, lowering it by gravity?

[Dave Therhino]

I'm pretty sure that configuration requirement is driven by critical takeoff rudder response requirements rather than climb performance (gear retraction time).

[BuzzBox]

Originally Posted by Cropduster

What is different about a single engine go around than an engine out take off?

As Dave Therhino said:

I'm pretty sure that configuration requirement is driven by critical takeoff rudder response requirements...

The immediate rudder response in the event of an engine failure during take-off is more critical than the go-around case. The remaining pumps provide sufficient response in the go-around case, without the need to use APU bleed for the operative C system ADP.

[Cropduster]

Dave, Buzz Box et all, thank you. There was a lot of head scratching about that on the flight.
Cheers Cropduster.