2025-06-13T13:57:00
permalink Post: 11900543
Retired engineer here.
I have looked at the electrical systems on the B787 and this is my source. Book 1 Introduction to B787 Avionic/Electrical. Tried to post the URL but was unable to do so as I haven't made many posts.
I wonder if there may have been some kind of complex fault in the electrical system that day. The incoming flight passengers reported faults with the air conditioning and IFE. The electrical power system block diagram is on p. 84 mentioning engine generated power and the RAT which, if deployed, feeds a backup power bus. There is a power limit on the RAT system of 10kVA which probably isn't enough to retract the undercarriage (correct me if I am wrong). The main electrical system is 235V ac from the engines which is converted to DC using ATRU units (Auto Transformer Rectifier Unit) - see p. 95. These systems get very hot so there is a liquid cooling system called PECS. If there were malfunctions in ATRU units that may explain the air conditioning issues on the incoming leg. So, what exactly triggered the deployment of the RAT?. I'd be looking at the whole electrical network and not just the engine generation systems. The emergency lighting system (p. 146) is called WELS (Wireless Emergency Lighting System). The survivor mentioned that was flickering. Power/control systems cutting in and out. Those lights would be battery backed and would stay illuminated if the primary power/control permanently ceased. Just a few thoughts for consideration.
I have looked at the electrical systems on the B787 and this is my source. Book 1 Introduction to B787 Avionic/Electrical. Tried to post the URL but was unable to do so as I haven't made many posts.
I wonder if there may have been some kind of complex fault in the electrical system that day. The incoming flight passengers reported faults with the air conditioning and IFE. The electrical power system block diagram is on p. 84 mentioning engine generated power and the RAT which, if deployed, feeds a backup power bus. There is a power limit on the RAT system of 10kVA which probably isn't enough to retract the undercarriage (correct me if I am wrong). The main electrical system is 235V ac from the engines which is converted to DC using ATRU units (Auto Transformer Rectifier Unit) - see p. 95. These systems get very hot so there is a liquid cooling system called PECS. If there were malfunctions in ATRU units that may explain the air conditioning issues on the incoming leg. So, what exactly triggered the deployment of the RAT?. I'd be looking at the whole electrical network and not just the engine generation systems. The emergency lighting system (p. 146) is called WELS (Wireless Emergency Lighting System). The survivor mentioned that was flickering. Power/control systems cutting in and out. Those lights would be battery backed and would stay illuminated if the primary power/control permanently ceased. Just a few thoughts for consideration.
15 users liked this post.
2025-06-13T15:59:00
permalink Post: 11900654
Retired engineer here.
I have looked at the electrical systems on the B787 and this is my source. Book 1 Introduction to B787 Avionic/Electrical. Tried to post the URL but was unable to do so as I haven't made many posts.
I wonder if there may have been some kind of complex fault in the electrical system that day. The incoming flight passengers reported faults with the air conditioning and IFE. The electrical power system block diagram is on p. 84 mentioning engine generated power and the RAT which, if deployed, feeds a backup power bus. There is a power limit on the RAT system of 10kVA which probably isn't enough to retract the undercarriage (correct me if I am wrong). The main electrical system is 235V ac from the engines which is converted to DC using ATRU units (Auto Transformer Rectifier Unit) - see p. 95. These systems get very hot so there is a liquid cooling system called PECS. If there were malfunctions in ATRU units that may explain the air conditioning issues on the incoming leg. So, what exactly triggered the deployment of the RAT?. I'd be looking at the whole electrical network and not just the engine generation systems. The emergency lighting system (p. 146) is called WELS (Wireless Emergency Lighting System). The survivor mentioned that was flickering. Power/control systems cutting in and out. Those lights would be battery backed and would stay illuminated if the primary power/control permanently ceased. Just a few thoughts for consideration.
I have looked at the electrical systems on the B787 and this is my source. Book 1 Introduction to B787 Avionic/Electrical. Tried to post the URL but was unable to do so as I haven't made many posts.
I wonder if there may have been some kind of complex fault in the electrical system that day. The incoming flight passengers reported faults with the air conditioning and IFE. The electrical power system block diagram is on p. 84 mentioning engine generated power and the RAT which, if deployed, feeds a backup power bus. There is a power limit on the RAT system of 10kVA which probably isn't enough to retract the undercarriage (correct me if I am wrong). The main electrical system is 235V ac from the engines which is converted to DC using ATRU units (Auto Transformer Rectifier Unit) - see p. 95. These systems get very hot so there is a liquid cooling system called PECS. If there were malfunctions in ATRU units that may explain the air conditioning issues on the incoming leg. So, what exactly triggered the deployment of the RAT?. I'd be looking at the whole electrical network and not just the engine generation systems. The emergency lighting system (p. 146) is called WELS (Wireless Emergency Lighting System). The survivor mentioned that was flickering. Power/control systems cutting in and out. Those lights would be battery backed and would stay illuminated if the primary power/control permanently ceased. Just a few thoughts for consideration.
Last edited by Saab Dastard; 13th Jun 2025 at 16:49 . Reason: full quote included
1 user liked this post.
2025-06-13T23:58:00
permalink Post: 11901012
The B787 is a way way different and much more complex and sophisticated plane than your Gulfie. The B787's two outermost (left & right) hydraulic systems are primarily driven by the engines, mechanically driving the hydraulic pumps. The center hydraulics are primarily electrically driven, and power the main flight controls, amongst other things like the gear. The left and right ones power the main flight controls as well, some of the less important flight control surfaces like spoilers and thrust reversers -- pardon me for not having the exact list of things. They also have a backup/supplementary electric pump each. Each of the two main engines has redundancy for the power plant a.k.a. VFSG (and motor-driven pump?) in its own right as well. All three hydraulic systems work together in a redundant fashion when it comes to the primary flight controls. The RAT can provide both electrical and mechanical sources of hydraulic support, if I'm not mistaken. The flight instrument and information systems can also be powered from two backup batteries, the APU power plant itself, and/or the RAT.
2 users liked this post.
2025-06-14T00:22:00
permalink Post: 11901021
The B787 is a way way different and much more complex and sophisticated plane than your Gulfie. The B787's two outermost (left & right) hydraulic systems are primarily driven by the engines, mechanically driving the hydraulic pumps. The center hydraulics are primarily electrically driven, and power the main flight controls. The left and right ones power the main flight controls as well, some of the less important flight control surfaces like spoilers and thrust reversers -- pardon me for not having the exact list of things. They also have a backup/supplementary electric pump each. Each of the two main engines has redundancy for the power plant a.k.a. VFSG (and motor-driven pump?) in its own right as well. All three hydraulic systems work together in a redundant fashion when it comes to the primary flight controls. The RAT can provide both electrical and mechanical sources of hydraulic support, if I'm not mistaken. The flight instrument and information systems can also be powered from two backup batteries, the APU power plant itself, and/or the RAT.
1 user liked this post.
2025-06-14T12:24:00
permalink Post: 11901432
The B787 is a way way different and much more complex and sophisticated plane than your Gulfie. The B787's two outermost (left & right) hydraulic systems are primarily driven by the engines, mechanically driving the hydraulic pumps. The center hydraulics are primarily electrically driven, and power the main flight controls, amongst other things like the gear. The left and right ones power the main flight controls as well, some of the less important flight control surfaces like spoilers and thrust reversers -- pardon me for not having the exact list of things. They also have a backup/supplementary electric pump each. Each of the two main engines has redundancy for the power plant a.k.a. VFSG (and motor-driven pump?) in its own right as well. All three hydraulic systems work together in a redundant fashion when it comes to the primary flight controls. The RAT can provide both electrical and mechanical sources of hydraulic support, if I'm not mistaken. The flight instrument and information systems can also be powered from two backup batteries, the APU power plant itself, and/or the RAT.
The Global Express has 4 engine driven generators, one APU generator, one RAT generator that provide AC and DC power to the aircraft's systems. On the hydraulic side, the aircraft has 3 fully independent and redundant hydraulic systems which power all flight control surfaces the exception being, the slats and flaps are AC power driven and are available even with only the RAT providing power. The 3 hydraulic systems are powered from each engine backed up by 2 EDPs (system 1 and 2) and system 3 is powered by 2 EDPs only. The RAT powers system 3 via one of its EDPs. In the event of a dual engine failure the RAT would deploy automatically and power the AC essential plus DC essential busses and one EDP on system 3. The APU is available to you up to FL450 and will supply full AC power but bleed air only up to FL300.
5 users liked this post.
2025-06-15T11:03:00
permalink Post: 11902361
Retired engineer here. Following my post a while ago on the avionics electrical system I have read all the posts and also noticed mention of the hydraulics system.
Returning to my original source, which is Book 1 Introduction to B787 Avionic/Electrical, I read on p. 96 that the RAT will deploy if any of three conditions are met.
https://fliphtml5.com/quwam/qhdw/Boo...ics_Electrical
These conditions for deployment of the RAT specifically are:
Loss of both engines
Loss of power to the instrument buses
Loss of all three hydraulic systems
The latter one may be worth a close look because it would appear that problems took place when the wheels left the runway and I assume there was a change of states in various sensors. I surmise these sensors are different from the engine systems where both commands and power are needed to force a change of state in, say, fuel pumps. Is it the same for thrust control?
It says there are three hydraulic systems but is there a common reservoir? I'm not an expert in that field but google tells me that B787 has a bootstrap reservoir system which I understand to mean that a pressure of 5000 psi is maintained using a piston arrangement.
At this point think timeline, and changes of states.
There is an operational change when the wheels leave the ground. The associated sensors would send that data to the CCS. What was sent? Maybe the CCS read Hydraulic L + Hydraulic R + Hydraulic C = incorrect or fail, which would trigger deployment of the RAT. What would the electrical and control system do then? More importantly what exactly did all the systems do on this aircraft following such an event.
Was there a problem with the fluid in the hydraulics? Does hydraulic fluid ever 'go off' in very hot conditions. Or maybe there wasn't as much fluid in there than there should have been? How would hydraulics systems be compromised if indeed that was the case.
All speculation - but forensic system analysis is a bit like that.
Finally - what was the noise the survivor heard? Was it before or after the lights flickered? It may have been a bit of the airframe hitting something and snapping.
The survivors in the doctor's hostel heard a noise too which may be jet engines running. They would know the difference between that and other noises being close to an airport. Need a timeline for everything here.
Apologies for the long post. Just my thoughts.
RIP to all who didn't survive.
Returning to my original source, which is Book 1 Introduction to B787 Avionic/Electrical, I read on p. 96 that the RAT will deploy if any of three conditions are met.
https://fliphtml5.com/quwam/qhdw/Boo...ics_Electrical
These conditions for deployment of the RAT specifically are:
Loss of both engines
Loss of power to the instrument buses
Loss of all three hydraulic systems
The latter one may be worth a close look because it would appear that problems took place when the wheels left the runway and I assume there was a change of states in various sensors. I surmise these sensors are different from the engine systems where both commands and power are needed to force a change of state in, say, fuel pumps. Is it the same for thrust control?
It says there are three hydraulic systems but is there a common reservoir? I'm not an expert in that field but google tells me that B787 has a bootstrap reservoir system which I understand to mean that a pressure of 5000 psi is maintained using a piston arrangement.
At this point think timeline, and changes of states.
There is an operational change when the wheels leave the ground. The associated sensors would send that data to the CCS. What was sent? Maybe the CCS read Hydraulic L + Hydraulic R + Hydraulic C = incorrect or fail, which would trigger deployment of the RAT. What would the electrical and control system do then? More importantly what exactly did all the systems do on this aircraft following such an event.
Was there a problem with the fluid in the hydraulics? Does hydraulic fluid ever 'go off' in very hot conditions. Or maybe there wasn't as much fluid in there than there should have been? How would hydraulics systems be compromised if indeed that was the case.
All speculation - but forensic system analysis is a bit like that.
Finally - what was the noise the survivor heard? Was it before or after the lights flickered? It may have been a bit of the airframe hitting something and snapping.
The survivors in the doctor's hostel heard a noise too which may be jet engines running. They would know the difference between that and other noises being close to an airport. Need a timeline for everything here.
Apologies for the long post. Just my thoughts.
RIP to all who didn't survive.
2 users liked this post.
2025-06-15T11:16:00
permalink Post: 11902370
Retired engineer here. Following my post a while ago on the avionics electrical system I have read all the posts and also noticed mention of the hydraulics system.
Returning to my original source, which is Book 1 Introduction to B787 Avionic/Electrical, I read on p. 96 that the RAT will deploy if any of three condions are met.
Maybe the URL will work this time
https://fliphtml5.com/quwam/qhdw/Boo...ics_Electrical
These conditions for deployment of the RAT specifically are:
Loss of both engines
Loss of power to the instrument buses
Loss of all three hydraulic systems
The latter one may be worth a close look because it would appear that problems took place when the wheels left the runway and I assume there was a change of states in various sensors. I surmise these sensors are different from the engine systems where both commands and power are needed to force a change of state in, say, fuel pumps. Is it the same for thrust control?
It says there are three hydraulic systems but is there a common reservoir? I'm not an expert in that field but google tells me that B787 has a bootstrap reservoir system which I understand to mean that a pressure of 5000 psi is maintained using a piston arrangement.
At this point think timeline, and changes of states.
There is an operational change when the wheels leave the ground. The associated sensors would send that data to the CCS. What was sent? Maybe the CCS read Hydraulic L + Hydraulic R + Hydraulic C = incorrect or fail, which would trigger deployment of the RAT. What would the electrical and control system do then? More importantly what exactly did all the systems do on this aircraft following such an event.
Was there a problem with the fluid in the hydraulics? Does hydraulic fluid ever 'go off' in very hot conditions. Or maybe there wasn't as much fluid in there than there should have been? How would hydraulics systems be compromised if indeed that was the case.
All speculation - but forensic system analysis is a bit like that
Returning to my original source, which is Book 1 Introduction to B787 Avionic/Electrical, I read on p. 96 that the RAT will deploy if any of three condions are met.
Maybe the URL will work this time
https://fliphtml5.com/quwam/qhdw/Boo...ics_Electrical
These conditions for deployment of the RAT specifically are:
Loss of both engines
Loss of power to the instrument buses
Loss of all three hydraulic systems
The latter one may be worth a close look because it would appear that problems took place when the wheels left the runway and I assume there was a change of states in various sensors. I surmise these sensors are different from the engine systems where both commands and power are needed to force a change of state in, say, fuel pumps. Is it the same for thrust control?
It says there are three hydraulic systems but is there a common reservoir? I'm not an expert in that field but google tells me that B787 has a bootstrap reservoir system which I understand to mean that a pressure of 5000 psi is maintained using a piston arrangement.
At this point think timeline, and changes of states.
There is an operational change when the wheels leave the ground. The associated sensors would send that data to the CCS. What was sent? Maybe the CCS read Hydraulic L + Hydraulic R + Hydraulic C = incorrect or fail, which would trigger deployment of the RAT. What would the electrical and control system do then? More importantly what exactly did all the systems do on this aircraft following such an event.
Was there a problem with the fluid in the hydraulics? Does hydraulic fluid ever 'go off' in very hot conditions. Or maybe there wasn't as much fluid in there than there should have been? How would hydraulics systems be compromised if indeed that was the case.
All speculation - but forensic system analysis is a bit like that
Left and right hydraulics have an engine driven pump that will keep turning as long as the engine is turning unless explicitly disabled.
Low reservoir levels are both a maintenance check and something that will raise an EICAS warning.
2 users liked this post.
2025-06-17T09:28:00
permalink Post: 11904137
Are you saying that the RAT cannot power retraction of the gear, neither via its own hydraulic pump nor via its generator providing power to the centre system pumps?
Or could it be that it's capable of delivering enough power (via either route) to move the tilt actuator but not a humungous retraction jack?
Or could it be that it's capable of delivering enough power (via either route) to move the tilt actuator but not a humungous retraction jack?
The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps.
8 users liked this post.
2025-06-17T12:43:00
permalink Post: 11904270
The RAT provides hydraulic power only to the flight control portion of the C hydraulics
2025-06-17T13:06:00
permalink Post: 11904288
The RAT provides hydraulic power only to the flight control portion of the C hydraulics. Wing and tail flight controls only. Non return valves prevent power to other C hydraulic powered systems like the gear.
The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps.
The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps.
3 users liked this post.
2025-06-17T13:32:00
permalink Post: 11904305
2 users liked this post.
2025-06-17T14:54:00
permalink Post: 11904372
Simply that the RAT is an electrical generator, that is all. What the electricity it generates powers is a downstreamm issue. The absolute rubbish being spouted on here is unreadable\x85viz\x85
Why? To achieve what? The people who write this have no clue about two crew jet operations. It is so sad. No crew would pull a shut off immediately after rotation. It makes no sense. Just stop with all this rubbish.
I am going to have a lie down.
Why? To achieve what? The people who write this have no clue about two crew jet operations. It is so sad. No crew would pull a shut off immediately after rotation. It makes no sense. Just stop with all this rubbish.
I am going to have a lie down.
2025-06-17T14:56:00
permalink Post: 11904373
8 users liked this post.
2025-06-19T11:34:00
permalink Post: 11905954
The RAT is an electrical generator, not a hydraulic pump. How many times does this need to be said?
This service bulletin provides instructions to replace the Ram Air Turbine (RAT) Pump and Control Module
Assembly to prevent failure of the hydraulic pump at low air speed. The RAT Assembly provides an emer-
gency source of electrical and hydraulic power for the primary flight control if the left, center and right main
hydraulic systems fail. Loss of the RAT Pump and Control Module Assembly could lead to loss of control
of the airplane when emergency power from RAT Assembly is needed. If this change is not incorporated
on the RAT Assembly and hydraulic power is lost on the left, right and center main hydraulic systems, then
the RAT Assembly may not provide sufficient hydraulic power which could result in the loss of many critical
control systems that are necessary for safe flight.
Assembly to prevent failure of the hydraulic pump at low air speed. The RAT Assembly provides an emer-
gency source of electrical and hydraulic power for the primary flight control if the left, center and right main
hydraulic systems fail. Loss of the RAT Pump and Control Module Assembly could lead to loss of control
of the airplane when emergency power from RAT Assembly is needed. If this change is not incorporated
on the RAT Assembly and hydraulic power is lost on the left, right and center main hydraulic systems, then
the RAT Assembly may not provide sufficient hydraulic power which could result in the loss of many critical
control systems that are necessary for safe flight.
787 RAT hydraulic pump location
Last edited by Senior Pilot; 19th Jun 2025 at 11:40 . Reason: Image
6 users liked this post.