Soldato
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It's an emergency power supply.
Air India Crash
- Thread starter Grim5
- Start date
It's an emergency power supply.
Soldato
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It does the same thing all turbines do - generates power, in this case its generating power when the plane's main power systems fail
Bit of a tangent, but I always thought of 'ram air' being when pressure is increased as air is forced into a smaller space. Hence 'ramjet' which follows that principle.
Feels like an odd term to use for a prop just spinning in the airstream. The air isn't being 'rammed'.
Feels like an odd term to use for a prop just spinning in the airstream. The air isn't being 'rammed'.
If its the same as the Airbus (I don't know about the Boeing as not flown one but assume it would be similar), the RAT doesn't directly generate power but drives a hydraulic pump, which can pressurise a hydraulic system, and also drives a generator to provide electricity.
It is because its attached to something that's moving. Unlike a wind turbine for example that's static.
It provides electrical power to the flight controls & instruments.
Caporegime
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You are increasing the dynamic pressure to the propeller by the fact the airplane is moving through the air compared to the propeller being on the ground stationary. That increase in dynamic pressure is what causes the blades to spin because that is part of the equation for the coefficient of lift as a propeller is essentially a wing on its side.
Just the movement of the plane flying through the air is ramming high dynamic pressure to the RAT which it otherwise wouldn't have on the ground as it has no way of providing its own power to generate thrust.
It generates enough power to support instruments, flight controls, and hydraulics.
I'm gonna guess it's called Ram because the airflow is not naturally blowing into the turbine as would be the case for a static wind turbine on a hill, but instead the plane is moving propelled forwards by it's jet engines which is forcing airflow over the turbine. If the RAT itself was propelling the plane forward then it would not be Ram anymore, it would just be a propeller powered engine but the RAT is not connected to an engine and is not generating thrust or any forward momentum
Last edited:
Soldato
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I found an interesting comment on this by
@savvas0711
under video:
As I couldn't link to it, I'm posting their comment here, hope that's ok. Obviously he's speculating, but he seems to have a lot of knowledge and it's interesting reading.
---- COMMENT STARTS ----
Speculation and only a theory.
I call a total electrical failure on the Air India 787. The 787’s electrical system powers not just flight controls but also engine control units (FADEC) and support systems like cooling and anti-ice. A failure could disrupt engine operation, throttle response, and control surfaces simultaneously — a deadly combination unique to the 787’s more-electric design. If the battery buses or power distribution system are compromised, battery power can’t reach the systems it’s meant to support.
The battery alone isn’t capable of powering the whole aircraft — it only supports a limited number of essential systems, and only for a short period.
Yes, the battery provides backup to critical systems like engine control (FADEC), emergency power (via RAT), and minimal avionics in an emergency.
But if the failure extends into the distribution network or control logic, even those backups may not function — leaving the aircraft unable to restart engines or control flight surfaces.
That’s why a full electrical failure on a 787 is uniquely dangerous.
Yes, GE engines (like the GEnx on the 787) have dual-channel PMAs (Permanent Magnet Alternators) to power the FADEC — independently of the main aircraft electrical buses.
But here's the problem unique to the 787:
The aircraft's entire operational dependency is on electrical distribution. You don’t need all four engine-driven generators to fail — you just need a distribution bus failure, a short, or software fault (as seen in prior 787 incidents) to cut off those FADEC PMAs from delivering usable output to where it's needed.
Also:
If cooling fans, inverters, or control relays in the Integrated Modular Avionics (IMA) racks fail — the FADECs can overheat or shut down.
Boeing centralizes too much through software-managed buses, meaning a corrupted logic path can trigger a false overload or trip entire buses offline.
So while it’s “hard to lose 4 sources,” it’s much easier to:
Lose access to them, or
Render their output useless, through faulty routing, sensor misreadings, or control logic errors.
That’s the Achilles’ heel of the 787’s “more-electric” design — the power might still be there, but you can’t get to it.
A total electrical failure on a Boeing 787 would be catastrophic — not just inconvenient. The 787’s “more-electric architecture” replaces traditional pneumatics and hydraulics with electrically powered systems. So let’s unpack what a true electrical failure would imply, how it could happen, and why it's a nightmare scenario:
What Does the Electrical System Power on the 787?
The 787 relies on electricity for:
Primary flight controls (via electro-hydrostatic actuators)
Engine control units (FADEC) – fully electronic, no mechanical backup
Throttle response – digitally linked
Air conditioning, pressurization, anti-ice
Fuel system pumps and valves
Lighting, avionics, and displays
It uses six generators — two on each engine (IDGs plus backup permanent magnet generators), and two from the APU. These are controlled via power distribution units and software-managed electrical buses.
---
What Happens in a Total Electrical Failure?
If all six generators and distribution systems fail, you'd lose:
Fly-by-wire controls (control surfaces powered by electric hydraulic actuators)
Thrust lever control (since FADEC relies on power)
Engine restart ability, unless batteries intervene
Displays, communications, and navigation — effectively blind
A scenario like this would render the aircraft unflyable, even if the engines continue producing thrust briefly.
---
What About Batteries?
Yes — there is a lithium-ion battery backup system. In an engine-out or generator failure:
Batteries provide limited power for essential systems (e.g., standby instruments, communications, FADEC during restart)
They power the Ram Air Turbine (RAT) deployment logic, which can supply hydraulic and limited electrical power
However, battery capacity is short — minutes, not hours. It buys time, not recovery. If the failure involves power distribution buses, battery power might not even reach critical loads.
---
Dual Engine Failure ≠ Total Electrical Loss
In a typical dual engine flameout:
The APU can auto-start in flight and restore electrical buses
Batteries support FADEC and ignition for relight
The RAT provides hydraulic backup for flight controls
But in a total electrical collapse, even with engines running:
FADEC may become unresponsive
Engine control and restart may be impossible
The aircraft may be intact but uncontrollable — effectively in free fall
---
What Could Cause This?
Some plausible or previously documented causes:
1. Massive bus failure or software corruption in power distribution
2. Multiple generator failures (including APU) from a short circuit or surge
3. Physical damage from lightning or undiagnosed maintenance issues
4. Improper grounding, bonding, or flawed assembly (as alleged by whistleblowers)
5. Severe thermal event — fire affecting electrical wiring or the EICAS bay
---
Final Word – Unique to the 787
This vulnerability is specific to the 787’s more-electric architecture. Older jets like the 777, A330, and 747 rely heavily on pneumatic and hydraulic backups. The 787 replaced those with electrics — and if those electrics fail, the entire aircraft goes dark.
---- COMMENT ENDS ----
@savvas0711
under video:
As I couldn't link to it, I'm posting their comment here, hope that's ok. Obviously he's speculating, but he seems to have a lot of knowledge and it's interesting reading.
---- COMMENT STARTS ----
Speculation and only a theory.
I call a total electrical failure on the Air India 787. The 787’s electrical system powers not just flight controls but also engine control units (FADEC) and support systems like cooling and anti-ice. A failure could disrupt engine operation, throttle response, and control surfaces simultaneously — a deadly combination unique to the 787’s more-electric design. If the battery buses or power distribution system are compromised, battery power can’t reach the systems it’s meant to support.
The battery alone isn’t capable of powering the whole aircraft — it only supports a limited number of essential systems, and only for a short period.
Yes, the battery provides backup to critical systems like engine control (FADEC), emergency power (via RAT), and minimal avionics in an emergency.
But if the failure extends into the distribution network or control logic, even those backups may not function — leaving the aircraft unable to restart engines or control flight surfaces.
That’s why a full electrical failure on a 787 is uniquely dangerous.
Yes, GE engines (like the GEnx on the 787) have dual-channel PMAs (Permanent Magnet Alternators) to power the FADEC — independently of the main aircraft electrical buses.
But here's the problem unique to the 787:
The aircraft's entire operational dependency is on electrical distribution. You don’t need all four engine-driven generators to fail — you just need a distribution bus failure, a short, or software fault (as seen in prior 787 incidents) to cut off those FADEC PMAs from delivering usable output to where it's needed.
Also:
If cooling fans, inverters, or control relays in the Integrated Modular Avionics (IMA) racks fail — the FADECs can overheat or shut down.
Boeing centralizes too much through software-managed buses, meaning a corrupted logic path can trigger a false overload or trip entire buses offline.
So while it’s “hard to lose 4 sources,” it’s much easier to:
Lose access to them, or
Render their output useless, through faulty routing, sensor misreadings, or control logic errors.
That’s the Achilles’ heel of the 787’s “more-electric” design — the power might still be there, but you can’t get to it.
A total electrical failure on a Boeing 787 would be catastrophic — not just inconvenient. The 787’s “more-electric architecture” replaces traditional pneumatics and hydraulics with electrically powered systems. So let’s unpack what a true electrical failure would imply, how it could happen, and why it's a nightmare scenario:
What Does the Electrical System Power on the 787?
The 787 relies on electricity for:
Primary flight controls (via electro-hydrostatic actuators)
Engine control units (FADEC) – fully electronic, no mechanical backup
Throttle response – digitally linked
Air conditioning, pressurization, anti-ice
Fuel system pumps and valves
Lighting, avionics, and displays
It uses six generators — two on each engine (IDGs plus backup permanent magnet generators), and two from the APU. These are controlled via power distribution units and software-managed electrical buses.
---
What Happens in a Total Electrical Failure?
If all six generators and distribution systems fail, you'd lose:
Fly-by-wire controls (control surfaces powered by electric hydraulic actuators)
Thrust lever control (since FADEC relies on power)
Engine restart ability, unless batteries intervene
Displays, communications, and navigation — effectively blind
A scenario like this would render the aircraft unflyable, even if the engines continue producing thrust briefly.
---
What About Batteries?
Yes — there is a lithium-ion battery backup system. In an engine-out or generator failure:
Batteries provide limited power for essential systems (e.g., standby instruments, communications, FADEC during restart)
They power the Ram Air Turbine (RAT) deployment logic, which can supply hydraulic and limited electrical power
However, battery capacity is short — minutes, not hours. It buys time, not recovery. If the failure involves power distribution buses, battery power might not even reach critical loads.
---
Dual Engine Failure ≠ Total Electrical Loss
In a typical dual engine flameout:
The APU can auto-start in flight and restore electrical buses
Batteries support FADEC and ignition for relight
The RAT provides hydraulic backup for flight controls
But in a total electrical collapse, even with engines running:
FADEC may become unresponsive
Engine control and restart may be impossible
The aircraft may be intact but uncontrollable — effectively in free fall
---
What Could Cause This?
Some plausible or previously documented causes:
1. Massive bus failure or software corruption in power distribution
2. Multiple generator failures (including APU) from a short circuit or surge
3. Physical damage from lightning or undiagnosed maintenance issues
4. Improper grounding, bonding, or flawed assembly (as alleged by whistleblowers)
5. Severe thermal event — fire affecting electrical wiring or the EICAS bay
---
Final Word – Unique to the 787
This vulnerability is specific to the 787’s more-electric architecture. Older jets like the 777, A330, and 747 rely heavily on pneumatic and hydraulic backups. The 787 replaced those with electrics — and if those electrics fail, the entire aircraft goes dark.
---- COMMENT ENDS ----
It's quite possible there was some kind of electrical failure but not a total failure as the Captain was able to get off a MAYDAY. So the radio had power. And if the radio was powered, even in the worst case scenario (considering electrical failures), then so would other essential systems.
Also, unless the 787 is uniquely different to the aircraft I have flown, then is should be possible to fly on battery power alone - not for minutes as stated, but somewhere between 30-90 minutes depending on exactly how the aircraft was certified.
And the wings were level, with the pitch of the aircraft being sensible, so I would guess the flight controls were working and the aircraft was under some kind of control as it went down.
There is a lot of guesses in that analysis with not much to back them up.
So
1. electrical system has a secondary back up bus.
2. Engines can suction feed and bypass the electrical fuel pumps: https://kb.skyhightex.com/knowledge-base/how-to-master-b787-fuel-system/ where in the event of a electrical AC power (this is the power direct from the engine and not the distribution board) then each engine can suck fuel directly from his own wing fuel tank.
Now if there was an electrical short on both AC generators in each engine, and both primary and back power distributed failed.. then it would still suck fuel from its respective wing tank. Only caveat is at high altitude when it may not have the rate todo that.
The engine turbine shaft oiling line is a separate system from the main hydraulic. Insufficient oil could result in essentially the turbine shafts binding up and the engine attempting to shut down. However each engine has its own oil tank, and the pumps (bot main and scavenger oil pumps) are mechanical drive off the engine.
So, short of a turbine blade coming off and going through and hitting the other engine.. or the AC generators acting like electronic brakes, there's very little to stop the engine functioning as instructed by the control system.
Unless there's a serious wiring problem - like someone hot wired the distribution to have a single bus as it's failed previously and wasn't repaired, then it seems to be a wait until we see what the black boxes provide.
This assumes no foul play by a hacked firmware update - to update you'd need to (a) verify the plane with Boeing to get the encrypted start key for that particular flight and (b) you'd need access to the control systems which tend to be locked away.
On that link there's also information about the electrical system failure modes:
Also if the electrical power fails to the flight crew displays.
1. electrical system has a secondary back up bus.
2. Engines can suction feed and bypass the electrical fuel pumps: https://kb.skyhightex.com/knowledge-base/how-to-master-b787-fuel-system/ where in the event of a electrical AC power (this is the power direct from the engine and not the distribution board) then each engine can suck fuel directly from his own wing fuel tank.
Now if there was an electrical short on both AC generators in each engine, and both primary and back power distributed failed.. then it would still suck fuel from its respective wing tank. Only caveat is at high altitude when it may not have the rate todo that.
The engine turbine shaft oiling line is a separate system from the main hydraulic. Insufficient oil could result in essentially the turbine shafts binding up and the engine attempting to shut down. However each engine has its own oil tank, and the pumps (bot main and scavenger oil pumps) are mechanical drive off the engine.
So, short of a turbine blade coming off and going through and hitting the other engine.. or the AC generators acting like electronic brakes, there's very little to stop the engine functioning as instructed by the control system.
Unless there's a serious wiring problem - like someone hot wired the distribution to have a single bus as it's failed previously and wasn't repaired, then it seems to be a wait until we see what the black boxes provide.
This assumes no foul play by a hacked firmware update - to update you'd need to (a) verify the plane with Boeing to get the encrypted start key for that particular flight and (b) you'd need access to the control systems which tend to be locked away.
On that link there's also information about the electrical system failure modes:
| In case of all generators fail and the APU is not available | The RAT will deploy automatically |
Also if the electrical power fails to the flight crew displays.
Last edited:
I haven't seen mention of it in here yet, but a second Air India 787 Dreamliner has had technical issues today:
www.lbc.co.uk
Air India Boeing 787-8 Dreamliner flight forced to turn back with 'technical issue' | LBC
An Air India Boeing 787-8 Dreamliner heading for Delhi has been forced to turn back after the pilot said the aircraft was facing technical issues.
www.lbc.co.uk
I haven't seen mention of it in here yet, but a second Air India 787 Dreamliner has had technical issues today:
Air India Boeing 787-8 Dreamliner flight forced to turn back with 'technical issue' | LBC
An Air India Boeing 787-8 Dreamliner heading for Delhi has been forced to turn back after the pilot said the aircraft was facing technical issues.
Probably an abundance of caution. If I was a 787 pilot right now, I'd be a little bit skittish. And aircraft have minor technical issues all the time - it's normal.
My wife used to be cabin crew. Return to airport, aborted landings, and aborted take offs are extremely common.
Soldato
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Blimey, I thought all India 787s at least were grounded until report of the trajedy in this thread!I haven't seen mention of it in here yet, but a second Air India 787 Dreamliner has had technical issues today:
Air India Boeing 787-8 Dreamliner flight forced to turn back with 'technical issue' | LBC
An Air India Boeing 787-8 Dreamliner heading for Delhi has been forced to turn back after the pilot said the aircraft was facing technical issues.
You know, that's something I hadn't considered. Some kind of bodge job to get the aircraft back in the the air. It would indicate astonishing incompetence and criminal negligence but not beyond the realms of possibility. I guess it's just wait and see....