Boeing 767 Hydraulic/Electrical Question
 

Hiya, I am looking for some clarification with the 767.

I understand that the ADP pump supplies hydraulic power to the center system as long as there is bleed air pressure available. This hydraulic pressure then in turn provides pressure to drive the HDG which provides electrical power to the system. The RAT only provides hydraulic pressure to the flight controls. My question is, suppose you are having a real lousy day and you lose both engines and have no apu. Since you no longer have bleed air, you now have no hydraulics and the only source of electrics other is your battery. You only have flight controls. Is this correct?


Alta

Yes it is, but its late and I may have forgotten something.

Just to add some discussion into the mix:
If you have an U/S APU and have a generator failure on takeoff during in low visibility procedures - you may well stop where in other situations you wouldn't.
The reason being that you wouldn't have two sources of electrical power (excluding the battery), so you couldn't autoland.

If the APU is U/S and a genny fails, then you have to land ASAP (only 1 source). If you have a genny failure and can use the APU as a second generator, you can continue.

It would have to be really bad day for both the gennys and the APU to be broken.

But has happened - Gimli Glider with Air Canada back in the 90's - 767 ran out of fuel so lost gennys and APU.

Just to theorize a little further (and stray into the never could happen zone)

With the loss of both engines and a failure of the Rat to extend and/ or function correctly would the windmilling engines provide any, or adequate pressure to operate the flight controls?

If u lose both engines, and now the RAT malfunctions, you are indeed having a bad day, if airspeed is high enough, you might have enough windmilling energy to power the eng-driven hyd pumps, but not too sure of that either

Thanks for the replies.

Alta

There is also a min speed for the RAT. It is 135kts. There was an aircraft that was hijacked and they ran it out of gas. It crashed into the ocean just off a beach. There was a video of it and as it slowed it lost control and entered the water with one wing low. They figured it was because they got below 135kts and could no longer control the ac.

The Gimli glider is a great story , well worth the read. :ok:




No Engines ,No APU, No RAT - what's next, No wings ? :}

I define the Gimli Glider as a "bad day"! Hence I stand by my previous comment.

A few RAT's have been tested and found to stick in the up position, so no RAT is not beyond belief.

Perhaps it is a sign that it is your time!:(