Hydraulic Driven Generator
 

Reading the B767-300 ER manual it states that HDG needs bleed air to work from the center ADP. In case of all engines fail, the HDG won't work is that right?

I'm sure the Ram air turbine will be deployed.

By starting the APU you can power the ADP....

Fuel..... Litres/pounds??

By staring the APU, you will not have need for the HDG.

It does not answer the question....the Hydraulic driven generator needs the ADP to work that means that if you don't have the APU and experience an all engine failure, you Will only have battery power and hence only some instruments on the captain side.

Statement retracted for fact finding mission.

Had a quick look through the manuals and yes you require the ADP to provide enough power to drive the HDG. The RAT function is centre flying control pressure only.

The HDG is solely for AC bus failures and will produce 5 KVa. It is an electrical back up only.

The HDG can be driven by the electric pumps when testing on the ground so theoretically the rat could produce enough power to run it but Boeing installed a check valve so it can't.

Dual Engine failure you are on battery buses only, rat or windmilling for hydraulics.

Without looking in the MEL I presume with a u/s ADP it will drop you to non-ETOPS. Haven't got one to hand to check.

Thank you Beeline......

The HDG is intended to extend the range beyond the 30 minute (design) limit of the battery powered standby system. Given a dual engine failure, I don't think anything beyond 30 minutes is really going to help.

Back when I was at Boeing, the question of 30 minutes came up. According to authoritative sources, it was an FAA requirement. Given a dual engine loss at maximum cruising altitude and optimal gliding conditions, I'm not certain if a 767 (or anything else) can remain airborne longer. But that issue was never addressed. There was (is?) a dual battery standby option required by some customers which may have been made to address this issue.

The HDG is intended to give a non time limited critical systems electrical supply in order to allow for diversion to alternate sites beyond the 30 minute battery capacity. This allows for operation further from such sites. Of course, this assumes you have at least one engine operating.

Starting the APU might assist in restarting engines or providing hydraulics (if windmilling is insufficient), but the battery standby system is adequate to support all electrical loads critical at this time.

If you can start the APU, you'll get L/R AC back (unless you've had catastrophic L/R AC bus failures instead of L & R Generator failure) and the HDG will shut down.

The presence of the HMG allows dispatch with an INOP APU generator over longer range routes.

As noted, if you lose all engines, your max flight time is pretty limited. At cruise altitudes, you've got roughly 100 miles max range, and maybe 25 minutes max flight time available. Hence (assuming a healthy battery), 30 minutes on the battery is enough to keep basic instruments as long as you're going to be airborne.
The hydraulic motor generator is unrelated to the all engine-out event. It's back up electrical generation to cover the case of a failed engine generator but with the engine still operating.
Some aircraft (the 777 comes to mind) have the RAT drive both a hydraulic pump and an electrical generator. But the 767 is not so equipped.