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Ram Air Turbine Failures  
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Posted (8 years 1 month 1 week 5 days 6 hours ago) and read 4674 times:

Good afternoon everyone,

I was wondering how often the Ram Air Turbines (RATs) are checked. Is it done on a heavy "C" or a "D" check?

Also, how often do they fail? For what reason do you see them failing?

Any info would be appreciated.

Regards,


"The only people for me are the mad ones...." Jack Kerouac
28 replies: All unread, showing first 25:
 
User currently offlineKELPkid From United States of America, joined Nov 2005, 6346 posts, RR: 3
Reply 1, posted (8 years 1 month 1 week 5 days 6 hours ago) and read 4666 times:

Boy, that'd be a crappy day, loose all the powerplants and then, to top it off, the RAT didn't work...  Sad

I suppose if there was any fuel remaining, you could try an air start of the APU? What would that get you besides electrical power and air for engine starts?



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17002 posts, RR: 67
Reply 2, posted (8 years 1 month 1 week 5 days 6 hours ago) and read 4663 times:

Quoting KELPkid (Reply 1):
Boy, that'd be a crappy day, loose all the powerplants and then, to top it off, the RAT didn't work... Sad

I suppose if there was any fuel remaining, you could try an air start of the APU? What would that get you besides electrical power and air for engine starts?

Above a certain speed, I'm pretty sure you can airstart the engines just from windmilling.

Still, EasternSon is probably assuming a scenario where the engines cannot be restarted for some reason (gremlins on the wings again...)



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 3, posted (8 years 1 month 1 week 5 days 3 hours ago) and read 4620 times:
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No offence meant to EasternSon, but what is this boards fascination with RAT's?

To answer the question on the 340 they are checked & tested every 18 months or 8000 FH


User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 4, posted (8 years 1 month 1 week 5 days 1 hour ago) and read 4596 times:

At UAL, on the 757/767, we would do a deployment test (checking only that it drops properly) on certain "A" checks, and then a deployment and backdrive test (make sure it drops and also spinning it up to speed) during "C" checks. This was also done on A320 "C" checks.

Chris



Don't blame me, I don't work here...
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Reply 5, posted (8 years 1 month 1 week 4 days 13 hours ago) and read 4535 times:

No offense taken, VC-10, but I think the "fascination" with RATs on this board is a result of the beautiful simplicity of the machine itself. For me, I find it interesting that a huge aircraft like a B767 or and A340 can be kept aloft and manueverable by something basically engineered on the simple concept of a child's pinwheel.

Yes HelpKid and Starlion, it would be a hugely crappy day. I'm asking these questions to find out what goes wrong with them. In turn, I'm hoping to prevent them from failing if they're ever dropped in a real emergency.

Thanks for the help N8076U, your info is great. With regards to UAL, I've heard that, in the event of a failed backdrive for the B757/767, just the turbine is removed? Or do you remove the entire RAT?



"The only people for me are the mad ones...." Jack Kerouac
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3477 posts, RR: 67
Reply 6, posted (8 years 1 month 1 week 4 days 13 hours ago) and read 4530 times:

Quoting EasternSon (Reply 5):
For me, I find it interesting that a huge aircraft like a B767 or and A340 can be kept aloft and manueverable by something basically engineered on the simple concept of a child's pinwheel.

What do you mean by kept aloft? If a RAT needs to be deployed, the best the airplane can do is a controlled descent.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Reply 7, posted (8 years 1 month 1 week 4 days 13 hours ago) and read 4528 times:

You're right, oldGuy, poor choice of words.

But, nonetheless, it is an very interesting piece of equipment.



"The only people for me are the mad ones...." Jack Kerouac
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 8, posted (8 years 1 month 1 week 4 days 8 hours ago) and read 4494 times:

Photobucket - Video and Image Hosting
B752 RAT


Isn't the Hydraulic Pump affected.
regds
MEL

[Edited 2006-06-21 21:02:25]


Think of the brighter side!
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Reply 9, posted (8 years 1 month 1 week 4 days 7 hours ago) and read 4473 times:

Mel, the RAT pump had an AD issued for it a couple of years ago for a hanger arm replacement. Most of modifications should have already been performed.

What I'm specifically asking about is the most common reason for removal from the aircraft. Do the pumps leak? Are the blades bent? Low pressure output from the pump? Internal leakage too high? Etc.

Any insight would be very helpful.

Regards,



"The only people for me are the mad ones...." Jack Kerouac
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 10, posted (8 years 1 month 1 week 4 days 7 hours ago) and read 4472 times:

Honestly, I don't remember what got changed if the backdrive test failed on the 757/767, as I don't recall one ever failing.  Wink If I still worked there, I could tell you, but alas...

The problem at UAL is you work under different rules depending if you are working "C" checks (heavy maintenance) or "A" checks (line maintenance). You could do things during a "C" check that you couldn't as a line mechanic, and visa-versa. So changing just the pump could have been possible in one scenario but not the other.

I do recall seeing just the pump being changed during a "C" check on more than one occasion, but I don't believe it was for a failed backdrive test. What it really came down to on the line is if you could get just the pump as an LRU (line-replaceable-unit) with its own servicable tag, or had to get the whole thing. During "C" check, you could change just the pump, and the inspector would "bless" it, making it servicable.

I do know there was a problem with the 767 rat concerning hydraulic fluid seepage. The whole assembly had to be changed for that, as I believe the housing was to blame, and not the pump itself. When we did the drop test, everyone would cringe until they saw the rat was dry.

Chris



Don't blame me, I don't work here...
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Reply 11, posted (8 years 1 month 1 week 4 days 7 hours ago) and read 4461 times:

Thanks Chris, precisely the info I was looking for.

Anyone else care to share their experiences with RAT failures/replacements during checks?

Many Thanks!



"The only people for me are the mad ones...." Jack Kerouac
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 12, posted (8 years 1 month 1 week 3 days 21 hours ago) and read 4416 times:

Quoting EasternSon (Reply 9):
What I'm specifically asking about is the most common reason for removal from the aircraft. Do the pumps leak? Are the blades bent? Low pressure output from the pump? Internal leakage too high

Not Experienced any such abnormalaties so far on the RATs of the B752.But then I've just started out on them So maybe more Experienced Guys would know better.
regds
MEL



Think of the brighter side!
User currently offlineSfomb67 From United States of America, joined Dec 2005, 417 posts, RR: 0
Reply 13, posted (8 years 1 month 1 week 3 days 19 hours ago) and read 4401 times:

During 767 C-Cks. I've seen several pumps rpld, but I don't remember any common reason. Quite a few years ago there was a SB to replace one of the tubes (pump to strut) with a flex hose, I think. I remember that if we did rpl a pump, getting the tubes from the pump to the strut aligned, was a job. They were rigid tubes, supply, press & case drain, 90 deg with banjo type seals at both ends, not b-nuts. Had to shim them for correct alignment, so they wouldn't leak. A real pain! I always figured BACO didn't use B-nuts because of the vibration when in use, but never knew for sure.


Not as easy as originally perceived
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Reply 14, posted (8 years 1 month 1 week 3 days 13 hours ago) and read 4368 times:

Yeah, the SB for the flex tube is a pain to incorporate.

Also, if you've ever fiddled with the compensator valve, I heard that can be a bear as well.

Thanks for the info. I guess UAL is one of the few operators who actually tries to deal with these items on wing. I'm hearing that most of the time, RATs are just removed and sent out for repair or overhaul.

Regards,



"The only people for me are the mad ones...." Jack Kerouac
User currently offlineMechEngineer From Germany, joined Jun 2006, 46 posts, RR: 0
Reply 15, posted (8 years 1 month 1 week 2 days 12 hours ago) and read 4288 times:

Quoting KELPkid (Reply 1):
Boy, that'd be a crappy day, loose all the powerplants and then, to top it off, the RAT didn't work...

Well, there would always be the backup battery to run the important systems.
The Fairchild Dornier 728 was to be equipped with a truck-type battery that would contain enough juice for at least a 30-minute flight, time enough to get down in one piece.



Heavier-than-air flying machines...
User currently offlineDc10hound From United States of America, joined Dec 2000, 463 posts, RR: 5
Reply 16, posted (8 years 1 month 1 week 2 days 2 hours ago) and read 4243 times:

Quoting MechEngineer (Reply 15):
Quoting KELPkid (Reply 1):
Boy, that'd be a crappy day, loose all the powerplants and then, to top it off, the RAT didn't work...

Well, there would always be the backup battery to run the important systems.
The Fairchild Dornier 728 was to be equipped with a truck-type battery that would contain enough juice for at least a 30-minute flight, time enough to get down in one piece.

But the RAT only gives you hydraulic power, not electrical.

The ADG on the DC-10 and MD-11 supplies electrical power, with the option of operating system 3 auxiliary hydraulic pump.

I don't know of an aircraft battery big enough to supply power for a hydraulic
pump.



"Eagles soar. But weasels never get sucked into jet intakes.."
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 17, posted (8 years 1 month 1 week 2 days 1 hour ago) and read 4229 times:

An airliner's battery will only last 30 or so minutes on a good day. A couple unsuccessful attempts to start the APU and you're done for.

Although the RAT is a hydraulic pump, I seem to remember that some 757s (767 as well???) have a hydraulic-motor generator to create electrical power from the hydraulic pressure. The 777 didn't need that though, as each engine has a normal and backup generator, whereas the 757/767 have only one normal generator per engine.

Chris



Don't blame me, I don't work here...
User currently offlineDc10hound From United States of America, joined Dec 2000, 463 posts, RR: 5
Reply 18, posted (8 years 1 month 1 week 2 days ago) and read 4221 times:

Quoting N8076U (Reply 17):
I seem to remember that some 757s (767 as well???) have a hydraulic-motor generator to create electrical power from the hydraulic pressure.

HMG = Hydraulic Motor Generator. It's part of the equipment required for ETOPS. It uses hydraulic pressure from the Left Hydraulic System to produce AC current.

The RAT supplies pressure to the Center Hydraulic System.

So the RAT can not run the HMG. The function of the RAT is to provide hydraulic power for the center system. The center system only powers primary flight controls.



"Eagles soar. But weasels never get sucked into jet intakes.."
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 19, posted (8 years 1 month 1 week 1 day 23 hours ago) and read 4218 times:

I didn't remember any details, so thanks for confirming the specifics, Dc10hound. But I figured the "HMG" was worth mentioning anyways, as some A.netters may not know some aircraft have something like that.

Chris



Don't blame me, I don't work here...
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 20, posted (8 years 1 month 1 week 1 day 18 hours ago) and read 4202 times:

Quoting Dc10hound (Reply 18):
HMG = Hydraulic Motor Generator. It's part of the equipment required for ETOPS. It uses hydraulic pressure from the Left Hydraulic System to produce AC current.

Hence unless ETOPS required..The HMG is optional on most B757s.
BTW the B757 uses RH Hyd to stow the RAT.
regds
MEL



Think of the brighter side!
User currently offlineEasternSon From United States of America, joined Jun 2006, 668 posts, RR: 1
Reply 21, posted (8 years 1 month 1 week 1 day 7 hours ago) and read 4181 times:

Guys, is the HMG the same thing as the AC Motor Pump, or ACMP? I've seen on a few before, a hydraulic pump with a rotor/stator set-up on the back? Is this sometimes called the HMG?

Is this used only in emergency situations as a back-up, or is it just run infrequently? I do know they don't come off the aircraft very often.

Thanks and Regards,



"The only people for me are the mad ones...." Jack Kerouac
User currently offlineSfomb67 From United States of America, joined Dec 2005, 417 posts, RR: 0
Reply 22, posted (8 years 1 month 1 week 1 day 3 hours ago) and read 4160 times:

Quoting EasternSon (Reply 21):
Guys, is the HMG the same thing as the AC Motor Pump, or ACMP

No. The HMG is a Hydraulic Motor Generator. It uses acft. hyd press to generate electrical power. Whereas, the ACMP uses acft AC electrical power to generate hyd pressure. As far as I know, HMG's were first used on ETOPS acft.



Not as easy as originally perceived
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 23, posted (8 years 1 month 1 week 22 hours ago) and read 4136 times:

Quoting EasternSon (Reply 21):
Is this used only in emergency situations as a back-up, or is it just run infrequently? I do know they don't come off the aircraft very often.

The HMG is not the ACMP.
The HMG is used in Emergency use as a Back up Electrical source.Produced by Hydraulic power.
regds
MEL



Think of the brighter side!
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 24, posted (8 years 1 month 1 week 19 hours ago) and read 4127 times:

Yet another device, just to add to the confusion, was found on the 727, and I believe also on early 737's (100/200 if I remember right) but I'm sure someone more familiar can correct me if I am wrong. There was a hydraulic interconnect, which was a hydraulic pump/motor hooked up to the A system, and coupled by shaft to another hydraulic pump/motor which was hooked up to the B system. The primary use was for ground operations, as one of the systems was powered by two electrically powered hydraulic pumps and the other system was powered by two engine driven hydraulic pumps. In order to power the engine-driven system with the engines off, you turned on the interconnect, and the one system would power the other. I believe in emergencies you could also use this in flight. FYI, on the 727, the right engine had no hydraulic pump at all.

Later 737s had one engine driven pump and one electrically driven pump for each system A and B, which eliminated the need for the interconnect. I think I read that the 707 had that interconnect setup as well?

The A319/A320/A321 have a PTU, or power transfer unit which does a similar thing, but I don't know enough about it to go into any details, except that it involves the center system in some way.

Chris



Don't blame me, I don't work here...
25 Post contains images N8076U : Then there's the ADP, which is an air-driven hydraulic pump, and runs off the pneumatic system pressure.
26 OldAeroGuy : True enough for the 757/767, but the 777 RAT provides hydraluic and electric power.
27 HAWK21M : The B757 has a PTU too. regds MEL
28 MechEngineer : On the FD 728 the RAT was an electric generator, the aircraft being fly-by-wire with electric actuators. Sorry if I caused any confusion.
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