User avatar
SuseJ772
Topic Author
Posts: 871
Joined: Wed Aug 10, 2005 11:13 am

RAT Deployment and ETOPS

Thu Jul 11, 2019 4:05 am

How screwed is an ETOPS situation where a engine has to be shutdown and their is a failure of a RAT deployment. Assuming a modern wide body aircraft like the 787, A350, A380, etc...
Currently at PIE, requesting FWA >> >>
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Thu Jul 11, 2019 6:27 am

If an engine is shut down, you still have the other engine, and you can get redundant electrical power from the APU. So no need for the RAT at all
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
fr8mech
Posts: 7645
Joined: Mon Sep 26, 2005 9:00 am

Re: RAT Deployment and ETOPS

Thu Jul 11, 2019 7:21 am

I got my hands on a B787 GenFam Systems Manual. Looking at 29, the RAT is plumbed into the center system. The center system is powered only by electric pumps. So, loss of an engine would not affect operation of those pumps, unless there is some sort of load shed function. But, methinks, hydraulic pumps would be at the bottom of a list of things to shed in the event of an engine failure.

The book says the RAT comes out:
-dual engine failure
-total hydraulic failure (all 3 systems)
-essential buss loss
When seconds count...the police are minutes away.
Unless it's expressly prohibited, it's allowed.
You are not entitled to a public safe space.
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Thu Jul 11, 2019 12:37 pm

On the A350 the RAT generates electric power only. No hydraulic power. If you lose both engine you lose all four hydraulic pumps powering both systems. Emergency hydraulic power is provided by self-contained actuators. So even if you lose all (main) hydraulics you still have working control surfaces.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BoeingGuy
Posts: 6238
Joined: Fri Dec 10, 2010 6:01 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 4:16 am

Starlionblue wrote:
On the A350 the RAT generates electric power only. No hydraulic power. If you lose both engine you lose all four hydraulic pumps powering both systems. Emergency hydraulic power is provided by self-contained actuators. So even if you lose all (main) hydraulics you still have working control surfaces.


That’s true of the 787 also. RAT only powers electric.

777 RAT provides Electric and Hydraulic.

757/767 center Hydraulic only. Not sure about 747-8 but I expect Hydraulic only.

As long as your APU is functional, there is plenty of redundancy in the event of a single engine failure.
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 4:51 am

A330 is hydraulic only, powering the green hydraulic system. You get electric through the emergency generator, powered by the green system.

Either way, as BoeingGuy says, if you have the APU and one engine, you have plenty. Even with one engine and no APU, you will have most of the systems.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Lpbri
Posts: 164
Joined: Tue Sep 27, 2016 7:18 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 5:36 am

787 RAT has its own hydraulic pump. 5000 psi @ 10 gpm.
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 7:25 am

Lpbri wrote:
787 RAT has its own hydraulic pump. 5000 psi @ 10 gpm.


I'm confused. BoeingGuy says the 787 RAT only provides electric power. Is there a dedicated emergency hydraulic pump powered by the RAT electrical supply?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
fr8mech
Posts: 7645
Joined: Mon Sep 26, 2005 9:00 am

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 8:25 am

Starlionblue wrote:
I'm confused. BoeingGuy says the 787 RAT only provides electric power. Is there a dedicated emergency hydraulic pump powered by the RAT electrical supply?


According to the training manual I have:

The RAT system is powered by a
two-blade turbine, which drives an
electrical generator and a hydraulic
pump through a gear box.
When seconds count...the police are minutes away.
Unless it's expressly prohibited, it's allowed.
You are not entitled to a public safe space.
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
BoeingGuy
Posts: 6238
Joined: Fri Dec 10, 2010 6:01 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 6:51 pm

fr8mech wrote:
Starlionblue wrote:
I'm confused. BoeingGuy says the 787 RAT only provides electric power. Is there a dedicated emergency hydraulic pump powered by the RAT electrical supply?


According to the training manual I have:

The RAT system is powered by a
two-blade turbine, which drives an
electrical generator and a hydraulic
pump through a gear box.


Not to my understanding. Let me check.

EDIT: Hmmm. According to the 787 FCOM, the RAT does also provide Hydraulic Power. That’s different than what I’ve been told. Let me dig into that more and find out why I understood differently.
 
EasternSon
Posts: 658
Joined: Fri Jun 02, 2006 10:07 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 8:32 pm

It's been since late 2014 that I worked for a RAT and ADG manufacturer, so it's all a bit hazy, but I do seem to remember that the B787 would have a stacked hydraulic/electric capability. I never got to see one in person, but if I remember correctly from the CMM, the generator and pump were in-line on the leg of the RAT, and shared a drive shaft.

Also, I'm pretty sure that the B757/B767 RAT worked in tandem with the Constant Speed Motor Generator (CSM/G) to convert the hydraulic pressure from the pump into an electrical current for some of the emergency systems. But I could be wrong.
"The only people for me are the mad ones...." Jack Kerouac
 
User avatar
7BOEING7
Posts: 3016
Joined: Fri Oct 12, 2012 5:28 pm

Re: RAT Deployment and ETOPS

Fri Jul 12, 2019 9:35 pm

EasternSon wrote:
It's been since late 2014 that I worked for a RAT and ADG manufacturer, so it's all a bit hazy, but I do seem to remember that the B787 would have a stacked hydraulic/electric capability. I never got to see one in person, but if I remember correctly from the CMM, the generator and pump were in-line on the leg of the RAT, and shared a drive shaft.

Also, I'm pretty sure that the B757/B767 RAT worked in tandem with the Constant Speed Motor Generator (CSM/G) to convert the hydraulic pressure from the pump into an electrical current for some of the emergency systems. But I could be wrong.


The RAT on the 757/767 deploys when both engines fail, to provide hydraulic power to the flight controls. The HMG (Hydraulic Motor Generator) or HDG (Hydraulic Driver Generator) provides electrical power with loss of both AC buses. They do not work at the same time. With loss of both engines you have the RAT for hydraulics and battery for electrics -- the RAT doesn't provide hydraulic power to run the HMG. HMG is optional -- 0, 1, 2 (767 only). Qantas had 2 on some of their 767's.
 
OldAeroGuy
Posts: 3857
Joined: Sun Dec 05, 2004 6:50 am

Re: RAT Deployment and ETOPS

Sat Jul 13, 2019 3:08 pm

7BOEING7 wrote:
The RAT on the 757/767 deploys when both engines fail, to provide hydraulic power to the flight controls. The HMG (Hydraulic Motor Generator) or HDG (Hydraulic Driver Generator) provides electrical power with loss of both AC buses. They do not work at the same time. With loss of both engines you have the RAT for hydraulics and battery for electrics -- the RAT doesn't provide hydraulic power to run the HMG. HMG is optional -- 0, 1, 2 (767 only). Qantas had 2 on some of their 767's.


:checkmark: Yep for the 757/767.

If both engines fail or you run out of fuel, there is no need for the HMG to operate. The RAT will provide hydraulic power for essential flight controls and batteries will provide essential electrical power during the glide down to the surface, either land or water.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
mxaxai
Posts: 1033
Joined: Sat Jun 18, 2016 7:29 am

Re: RAT Deployment and ETOPS

Sat Jul 13, 2019 6:15 pm

Starlionblue wrote:
If an engine is shut down, you still have the other engine, and you can get redundant electrical power from the APU. So no need for the RAT at all

Although there have been RAT deployments even if both engines were operational, e. g. http://avherald.com/h?article=4b3d825b&opt=0 or http://avherald.com/h?article=4c1cc3f6&opt=0. Is the drag from a potential RAT deployment considered when calculating ETOPS flight time and fuel consumption?
 
thepinkmachine
Posts: 353
Joined: Tue Apr 28, 2015 4:43 pm

Re: RAT Deployment and ETOPS

Sat Jul 13, 2019 7:30 pm

mxaxai wrote:
Is the drag from a potential RAT deployment considered when calculating ETOPS flight time and fuel consumption?


I doubt it. ETOPS scenarios ale clearly specified and account for the most critical case out of: engine failure, decompression, or engine failure+decompression. Nonhe of these conditions require RAT deployment. APU use is taken into account IIRC, but not RAT.
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Sun Jul 14, 2019 4:24 am

mxaxai wrote:
Starlionblue wrote:
If an engine is shut down, you still have the other engine, and you can get redundant electrical power from the APU. So no need for the RAT at all

Although there have been RAT deployments even if both engines were operational, e. g. http://avherald.com/h?article=4b3d825b&opt=0 or http://avherald.com/h?article=4c1cc3f6&opt=0. Is the drag from a potential RAT deployment considered when calculating ETOPS flight time and fuel consumption?


As the pinkmachine says, it is most likely not considered. The drag from the RAT is pretty big.

Minimum fuel consumption from the most critical point is planned as the sum of :
- Fuel to the closest nominated alternate after an engine failure, decompression, or both.
- 5% contingency.
- 15 minutes final reserve.

With the following conditions:
- APU on.
- Severe icing.

(Your results may vary due national regulation variations.)
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
OldAeroGuy
Posts: 3857
Joined: Sun Dec 05, 2004 6:50 am

Re: RAT Deployment and ETOPS

Sun Jul 14, 2019 4:13 pm

Plus, if the RAT is deployed and not needed, the RAT blades will reduce pitch to control RPM. RAT drag under this condition will be considerably less than if hydraulic or electrical power was being produced.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
Posts: 3857
Joined: Sun Dec 05, 2004 6:50 am

Re: RAT Deployment and ETOPS

Sun Jul 14, 2019 4:14 pm

Double post
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
JayinKitsap
Posts: 1328
Joined: Sat Nov 26, 2005 9:55 am

Re: RAT Deployment and ETOPS

Sun Jul 14, 2019 8:44 pm

Isn't the RAT the last choice when both engines are out as well as the APU. A chance to land the glider?
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 3:31 am

JayinKitsap wrote:
Isn't the RAT the last choice when both engines are out as well as the APU. A chance to land the glider?


It is, but it is used in more situations. And even if you have the APU, you need the RAT for hydraulic power.

Example: In the A330 if you get low level in both green and yellow, or both and blue, hydraulic systems, the RAT deploys automatically. That way you'll have one system left (yellow or blue) and the green system. Way better than just the blue or yellow.

You could also, very much in theory, lose all generators without losing the engines and have dispatched with the APU inop. So you still have thrust but no electrics. The RAT will provide electrical power, either directly or indirectly.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
7BOEING7
Posts: 3016
Joined: Fri Oct 12, 2012 5:28 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 4:49 am

On the Boeing side, with the 757/767 it takes failure of both engines (or pulling of the appropriate circuit breakers -- to confirm proper operation) to get the RAT to drop. You have flight controls available for a smooth descent and the battery for instruments.

RAT switch also available but is only used during a DUAL ENGINE FAILURE checklist to back up the "auto drop" function.
 
GalaxyFlyer
Posts: 3119
Joined: Fri Jan 01, 2016 4:44 am

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 2:29 pm

Do any of the A or B planes RATs have a retract function? We did on the C-5 but didn’t on any of the BBD planes. Retract on the Lockheed was at a maximum of 180:KIAS, but it worked.
 
Armadillo1
Posts: 255
Joined: Thu Apr 20, 2017 5:14 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 2:57 pm

Starlionblue wrote:

Example: In the A330 if you get low level in both green and yellow, or both and blue, hydraulic systems, the RAT deploys automatically. That way you'll have one system left (yellow or blue) and the green system. Way better than just the blue or yellow.



what happens in case of leak in green system?
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 3:11 pm

Armadillo1 wrote:
Starlionblue wrote:

Example: In the A330 if you get low level in both green and yellow, or both and blue, hydraulic systems, the RAT deploys automatically. That way you'll have one system left (yellow or blue) and the green system. Way better than just the blue or yellow.



what happens in case of leak in green system?


You'd still have either blue or yellow, so you'd be sweating bullets but able to make it to the nearest suitable. The aircraft can fly on one hydraulic system only, but it is a high workload scenario.

Expansion: On the A330, each engine has two hydraulic pumps. Engine one powers Blue + Green. Engine two powers Green + Yellow. And the RAT powers Green only.

Dual hydraulic failure on the A330 is trained for, and it can happen. But it is highly unlikely. The A350 changes the game with the self-contained hydraulic actuators. Even if you lose both systems (the A350 has two hydraulic systems), you still have autopilot and the aircraft is way more responsive to control inputs than the A330 on one system.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
Starlionblue
Posts: 19263
Joined: Fri Feb 27, 2004 9:54 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 3:17 pm

GalaxyFlyer wrote:
Do any of the A or B planes RATs have a retract function? We did on the C-5 but didn’t on any of the BBD planes. Retract on the Lockheed was at a maximum of 180:KIAS, but it worked.


Not AFAIK. It's like disengaging an IDG. Red guard on the pushbutton and requires maintenance action.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
EasternSon
Posts: 658
Joined: Fri Jun 02, 2006 10:07 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 7:37 pm

7BOEING7 wrote:
EasternSon wrote:
It's been since late 2014 that I worked for a RAT and ADG manufacturer, so it's all a bit hazy, but I do seem to remember that the B787 would have a stacked hydraulic/electric capability. I never got to see one in person, but if I remember correctly from the CMM, the generator and pump were in-line on the leg of the RAT, and shared a drive shaft.

Also, I'm pretty sure that the B757/B767 RAT worked in tandem with the Constant Speed Motor Generator (CSM/G) to convert the hydraulic pressure from the pump into an electrical current for some of the emergency systems. But I could be wrong.


The RAT on the 757/767 deploys when both engines fail, to provide hydraulic power to the flight controls. The HMG (Hydraulic Motor Generator) or HDG (Hydraulic Driver Generator) provides electrical power with loss of both AC buses. They do not work at the same time. With loss of both engines you have the RAT for hydraulics and battery for electrics -- the RAT doesn't provide hydraulic power to run the HMG. HMG is optional -- 0, 1, 2 (767 only). Qantas had 2 on some of their 767's.


Thanks for clearing that up. My knowledge of the RAT really ended at the connection of the component to the aircraft. My knowledge of the hydraulic systems is very limited, admittedly.
"The only people for me are the mad ones...." Jack Kerouac
 
EasternSon
Posts: 658
Joined: Fri Jun 02, 2006 10:07 pm

Re: RAT Deployment and ETOPS

Mon Jul 15, 2019 7:40 pm

OldAeroGuy wrote:
Plus, if the RAT is deployed and not needed, the RAT blades will reduce pitch to control RPM. RAT drag under this condition will be considerably less than if hydraulic or electrical power was being produced.


The pitch of the blades for the RAT is regulated by the airstream. It's either a hydraulic governor (old tech) or spring, weight and counterbalance system.

True that the blades will feather, but only to a point. There will still be significant drag even at the lowest pitch.

And there will still be a HELL of a lot of noise.
"The only people for me are the mad ones...." Jack Kerouac
 
BoeingGuy
Posts: 6238
Joined: Fri Dec 10, 2010 6:01 pm

Re: RAT Deployment and ETOPS

Tue Jul 16, 2019 4:48 am

GalaxyFlyer wrote:
Do any of the A or B planes RATs have a retract function? We did on the C-5 but didn’t on any of the BBD planes. Retract on the Lockheed was at a maximum of 180:KIAS, but it worked.


Boeing airplane RATs do not auto-retract. Can only be stowed in the ground.
 
GalaxyFlyer
Posts: 3119
Joined: Fri Jan 01, 2016 4:44 am

Re: RAT Deployment and ETOPS

Tue Jul 16, 2019 1:02 pm

The three-position switch said, RETRACT-AUTO-DEPLOY. Parked on the ground it was in retract before shutdown and put in auto during pre-take-off checklist. New left seaters would sometimes drop with clunk. I’d just say, wait a moment, go to RETRACT, then try again to AUTO. It was nice being able to retract it after the annual in-flight test. The BBD planes didn’t retract either and it was loud, so the test tried to be done by about 5 mile final.

GF
 
OldAeroGuy
Posts: 3857
Joined: Sun Dec 05, 2004 6:50 am

Re: RAT Deployment and ETOPS

Tue Jul 16, 2019 2:42 pm

EasternSon wrote:
OldAeroGuy wrote:
Plus, if the RAT is deployed and not needed, the RAT blades will reduce pitch to control RPM. RAT drag under this condition will be considerably less than if hydraulic or electrical power was being produced.


True that the blades will feather, but only to a point. There will still be significant drag even at the lowest pitch.


But much less drag than if designed RAT power were being produced. And much, much less drag than an inoperative engine which must be considered when calculating the critical fuel scenario.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

Who is online

Users browsing this forum: No registered users and 26 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos