B747 Back up Hydraulics
 

I have been asked the questions as to how a 747 can get hydraulics whilst all 4 engine are out in flight. I refer to the Jakarta incdent, I know Airbus aircraft have a RAT which provides a minimal pressure to power flight controls, but have no experience of Boeing aircraft. Can you help.

I suspect Rainboe forgot about a couple of AC powered electric pumps.

Anyway, the original B747 was certainly not fool-proof with regard to hydraulics.
Witness JAL with all fluid loss.
There was only one first generation wide-body jet airliner that had hydraulic fusing as part of the original design (not added on, later)....the Lockheed L1011.
And yes, it has, just like the B747, four separate hydraulic systems.
A superb design.:ok:

Thanks Guys, That resoves the question.

Electric vs air-driven pumps were/are options on the 747. All our Classics have 4 air-driven pumps. Our 744s have 2 air-driven and 2 electric pumps.

Classics, the #4 has an additional electric hydraulic pump used for Push/Tow operations, some versions had a #1 electric as well.

DBW

not sure there will be enough wiggly amps to power AC electric pumps with all engines windmilling.:eek:

In addition to the 4 Engine driven pumps there are ADP's on systems 1 and 4 as they are heaviest users, AC motor pumps on 2 and 3 plus additional auxiliary ACMP on system 4 for braking when under tow/maint operations and as an option on system 1 for steering (these are powered by the ground handling bus though so will not be available in flight) slight drift from the original post I think but hopefully informative!

And the 747-8 will have a RAT too

Just like the L1011, many years before.
Of course, one can then mention hydraulic power transfer units....:D

Each engine has an engine driven hydraulic pump, or EDP. Each hydraulic system has an Air Driven Pump, or ADP. Standard is one electric hydraulic pump, or ACP, on system 4, and many airplanes have a system 1 ACP, as well.

You're correct that the electric ACP pumps powered through the ground handling bus, and therefore not available in flight.

Systems 2 and 3 do not have standard electric hydraulic pumps.

160 KIAS is the minimum windmilling speed, and this is for hydraulics. It has nothing to do with electrical power. It also does not permit use of gear or flaps, hydraulically.

...........that the original 747 classic also had!
Now I'm showing my age:(

Trapped 3 sys. fluid in a closed loop through a PTU operated by no. 4 system return pressure to operate the stab. IIRC.

B747 Ptu???
 

GULP!!

have to say that I have forgotten about any sort of PTU on the classic 747. Then again I did do the engineering course back in 1994 which was not yesterday!!!

However regards to the B744, yes as Rainbow said the AC pumps on systems 2 and 3 are options. If you look at MAS B744's (basic configuration) they have 4 ADP's across the ship. Took me by surprise first time I saw it as I had done the BA differences course from the classic.

Hope that this helps.

Flying Spanner :ok: :ok:

Gas Path..correct.....you are probably the same age as me!! Look in D. P. Davis' book Handling the Big Jets the schematic is in there......though he even mentions the 'Load Evener' system originally fitted to the Wing Gears and not used in service to my knowledge...Agree a brilliant aircraft :ok: and a pleasure to work on....Unlike the torture endured by those of us who tried to keep in the air a certain 3 engined, 4 hyd system wide body previously mentioned!!! :}

I believe the 'Standard' 4 EDP/4ADP/1ACP pump distribution on the Classic became a 4 EDP/2ADP and 2 Electric Pump/1ACP system on the -400...progress, and 2 and 3 systems of course do not really need the 37 gallons a minute 'flow' of the EDP/ADP.

Flying SPanner ....it would have been removed around 1970 during development of the aircraft........

Ah, but the pilots loved it...and still do.:ok::}

If by MAS you mean Malaysia Airlines, their B744 have ACMP as demand pumps in sys 2 and 3. Just went out and tryed it. APU off, 2 and 3 pressurise the hyds, so the AMM must be right.

744's were delivered with the #2&3 back up hydraulic systems with either air driven pumps or AC powered electric pumps. Twas an operator option. So, you never really know what your gonna have untill you climb in one.

We had a saying, our fleet was standard until we got the second airplane.
Obviously, we are talking about the used market.

The newest plane I have flown was the Tristar and at the time it was 10 or 12 years old. and that was 8 years ago!

You should have flown 'em directly from the factory...what a joy.:ok:
Even today, a nice aeroplane, although getting old...just like yours truly.:}

RAT on748
 

I was told by on of our big men that the 747-800 will have a RAT. Boeing and the FAA obviosly just "forgot" to have a RAT installed on the previous 747s.

Everything gets better now...:}

May I ask a few questions regarding the pumps... :}

How and where does the ADP get it's source of air from? Directly from the engine bleed air?

Should all the 4 engines decide to quit would there still be a source of electrical power without having the batteries to come online since the AC motors are powered by EDPs (if I remember reading it this way!)?

Cheers... and as usual, thanks to all! :}