ignorantAndroid
2025-06-21T18:02:00
permalink Post: 11907949

Quote:

Originally Posted by jdaley

Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.

Boeing specifications say that the RAT will provide hydraulic power within 6 seconds and electrical power within 10 seconds. That would be the worst-case scenario, so it should usually be a bit less than that. Almost everything that gets electrical power from the RAT can also be powered by the main battery. So you don't have to wait for the RAT to spin up before you have instruments.

The engine-driven hydraulic pumps should still work for at least a few seconds after flameout. There's also a small amount of stored energy in the hydraulic systems even after the pumps stop. So even with that 6-second delay for the RAT, there shouldn't be any significant interruption in hydraulic power for the primary flight controls.

6 users liked this post.

TURIN
2025-07-01T08:49:00
permalink Post: 11914118

Quote:

Originally Posted by ignorantAndroid

They stay off until engine start because of load shedding. Once both engines are running, the pumps should be running too.

May I ask where this information of load shedding comes from please
In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc

Sailvi767
2025-07-01T12:39:00
permalink Post: 11914246

Quote:

Originally Posted by TURIN

May I ask where this information of load shedding comes from please
In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc

On the 767, 757 and A330 anytime you are in single generator operations the aircraft is load shedding. The 787 with a totally different electrical system might function differently.

ignorantAndroid 2025-06-21T18:02:00 permalink Post: 11907949	Quote: Originally Posted by jdaley Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that. Boeing specifications say that the RAT will provide hydraulic power within 6 seconds and electrical power within 10 seconds. That would be the worst-case scenario, so it should usually be a bit less than that. Almost everything that gets electrical power from the RAT can also be powered by the main battery. So you don't have to wait for the RAT to spin up before you have instruments. The engine-driven hydraulic pumps should still work for at least a few seconds after flameout. There's also a small amount of stored energy in the hydraulic systems even after the pumps stop. So even with that 6-second delay for the RAT, there shouldn't be any significant interruption in hydraulic power for the primary flight controls. 6 users liked this post.
TURIN 2025-07-01T08:49:00 permalink Post: 11914118	Quote: Originally Posted by ignorantAndroid They stay off until engine start because of load shedding. Once both engines are running, the pumps should be running too. May I ask where this information of load shedding comes from please In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc
Sailvi767 2025-07-01T12:39:00 permalink Post: 11914246	Quote: Originally Posted by TURIN May I ask where this information of load shedding comes from please In my experience the APU supplies enough power to run all systems. Hydraulic pumps, fuel pumps etc On the 767, 757 and A330 anytime you are in single generator operations the aircraft is load shedding. The 787 with a totally different electrical system might function differently.

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