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Fly-by-wire & Total Electric Failure  
User currently offlinenipoel123 From Netherlands, joined Jan 2011, 269 posts, RR: 0
Posted (2 years 7 months 2 weeks 3 days 18 hours ago) and read 8698 times:

What would happen if an aircraft equipped with fly-by-wire systems would experience a total electric failure? I suppose there's some sort of backup system. I find it hard to believe that the plane would become uncontrollable, especially ith these days of redundancy and safety.


one mile of road leads to nowhere, one mile of runway leads to anywhere
20 replies: All unread, jump to last
 
User currently offlinetravelavnut From Netherlands, joined May 2010, 1612 posts, RR: 7
Reply 1, posted (2 years 7 months 2 weeks 3 days 16 hours ago) and read 8659 times:

Differential thrust, in some cases like A320s and early A330/A340s (IIRC) you have manual reversion on the elevator. In other cases like the A380 and I guess also the 777 and 787 you're dead.

Quoting nipoel123 (Thread starter):
especially ith these days of redundancy and safety.

Well, the systems are extremely redundant. I cannot recall any crashes because of a total electic failure on an FBW aircraft, none, nada, zip.

If you have total hydraulic failure on most large airliners you're just as dead (or almost certainly dead, Sioux City DC-10 comes to mind)

I'm no expert but the chance of having all the generators, APU, RAT and all the busses fail is like 1 to a bazziljoin.



Live From Amsterdam!
User currently offlinetravelavnut From Netherlands, joined May 2010, 1612 posts, RR: 7
Reply 2, posted (2 years 7 months 2 weeks 3 days 15 hours ago) and read 8595 times:

Quoting travelavnut (Reply 1):
Differential thrust

Come to think of it, all modern airliners use FADEC for engine control. So I guess with a total electric failure using differential thrust is also out of the window.



Live From Amsterdam!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17039 posts, RR: 66
Reply 3, posted (2 years 7 months 2 weeks 3 days 11 hours ago) and read 8453 times:

Quoting nipoel123 (Thread starter):

What would happen if an aircraft equipped with fly-by-wire systems would experience a total electric failure? I suppose there's some sort of backup system. I find it hard to believe that the plane would become uncontrollable, especially ith these days of redundancy and safety.

If you lose all electrics on 380 and so forth you are toast. However there is lots of redundancy so getting to that stage is probably more unlikely than losing everything on an older airliner with manual reversion.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 4, posted (2 years 7 months 2 weeks 3 days 9 hours ago) and read 8357 times:

Quoting travelavnut (Reply 2):
Come to think of it, all modern airliners use FADEC for engine control. So I guess with a total electric failure using differential thrust is also out of the window.

AFAIK FADECs are powered completely independently from all other electrics in the airplane.



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlinePositiveClimb From Germany, joined Jun 2004, 214 posts, RR: 0
Reply 5, posted (2 years 7 months 2 weeks 3 days 8 hours ago) and read 8306 times:

Hi there,

as already stated, if you really loose all electrics, you have a very bad day. But given the design of the electrical power system the probability of this is close to zero.

For power generation, you have one VFG (variable frequency generator) per engine, so a total of four, which would all have to fail.
Then you have two generators on the APU (of which either one can be used in flight). These have to fail as well.
The most likely scenario would be an out-of-fuel situation, I suppose, killing al engines and the APU. This happened for example in the famous Gimli Glider and the Azores Glider events.

In this case (as for other airliners), the RAT (ram air turbine) swings into action to save the day. For the A380, the RAT is delivering electrical power (not hydraulic power as in other a/c) and the output is around 70kVA (in comparison: each VFG delivers around 150kVA, the APU generators 120kVA). This is still enough to power all essential loads on the emergency bus.

Bottom Line: In case all engines, the APU and the RAT fail, then you are in trouble (you still have the batteries and the static inverter, but with an output of around 2,5kVA this won't be too much of a help..). But this is the same for all other aircraft as well.

On the other hand, if one would worry about the control input side (as all commands are done through fbw without a hardware link between sidestick and control surfaces) then keep in mind that there is quite a bit redundancy as well:

You have three primary systems (PRIMs), each of them able to do the work (compute the needed surface deflections and execute the commands). If all of them fail, you have three secondary systems (SECs), of which again each one is able to do the work (only thing you loose are the flight envelope protections, as SECs will only provide direct law). If these fail as well, you still have the electrical backup system, with which you still can control all surfaces.
Anyway, this backup still needs electrical power, which is generated by hydraulic pressure from both (green and yellow hydraulic system), so it would work as long as the engines run and at least one of the eight engine driven hydraulic pumps (2 per engine) works.

Anyway, when one faces a total electrical failure, all engines and the APU are dead, RAT won't deploy, with no more electrical power anywhere on board that won't be too much of a help. But as hopefully pointed out, this shouldn't happen in any thinkable scenario...

Best regards,
PositiveClimb 



Proud Airbus employee
User currently offlinelonghauler From Canada, joined Mar 2004, 4982 posts, RR: 42
Reply 6, posted (2 years 7 months 2 weeks 3 days 8 hours ago) and read 8261 times:

Quoting travelavnut (Reply 1):
If you have total hydraulic failure on most large airliners you're just as dead (or almost certainly dead, Sioux City DC-10 comes to mind)

This is an important point in my opinion. Aircraft built with no manual reversion for total hydraulic loss, ie. the DC-10 and later, is a much more serious situation. And those beasts have been flying around since the 1970s.

Quoting Fabo (Reply 4):
AFAIK FADECs are powered completely independently from all other electrics in the airplane.

That is right, for the most part, as long as the engine is turning, FADEC is powered by the rotation of the engine itself.

Quoting PositiveClimb (Reply 5):
Anyway, when one faces a total electrical failure, all engines and the APU are dead, RAT won't deploy, with no more electrical power anywhere on board that won't be too much of a help. But as hopefully pointed out, this shouldn't happen in any thinkable scenario...

Another important point. The odds of absolutely everything ... every source failing, every bus shorting and every relay failing, as less likely than getting hit by an undetected meteor!



Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offlinecraigpc01 From United States of America, joined Jun 2009, 31 posts, RR: 0
Reply 7, posted (2 years 7 months 2 weeks 2 days 2 hours ago) and read 7835 times:

I thought the 777 had an actual cable attaching the yoke to the elevator, and pedal to the rudder, for redundancy?

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 8, posted (2 years 7 months 2 weeks 2 days ago) and read 7785 times:

Quoting craigpc01 (Reply 7):
I thought the 777 had an actual cable attaching the yoke to the elevator, and pedal to the rudder, for redundancy?

It has actual cables to some of the spoilers (roll control) and the stabilizer trim (pitch control). I don't believe there is any rudder or elevator in the event of total FBW failure on a 777.

Something to keep in mind is that FBW systems are about the most reliable parts of what is already a very reliable system. There has never been a full FBW failure of any commercial airliner ever, as far as I know...you can't even say that for engines (there has never been a fully independant multi-engine failure but there have been common mode failures).

Similar to what was posted earlier for Airbus, total failure of the FBW on a Boeing would require completely failure of three primary flight computers (PFC's) *and* three actuator control electronics boxes (ACE's), and each one of those boxes is a triple-channel architecture so there's really nine independent control loops, any one of which is capable of safely operating the aircraft. Those six computers are fed by four primary generators (main engines), two auxiliaries (APU), three permanent magnet generators (redundant generator on the engine generators), the main battery, and the RAT. Any one of those power source is enough for continued safe flight and landing and five of them don't depend on fuel (the PMG's run even if the engines are windmilling, the RAT runs if you're simply flying, and the battery doesn't care at all). It is really really really really hard to completely kill off a modern flight control system.

Tom.


User currently offlinecraigpc01 From United States of America, joined Jun 2009, 31 posts, RR: 0
Reply 9, posted (2 years 7 months 2 weeks 1 day 23 hours ago) and read 7727 times:

Tom, thanks. Is this the same situation with the Airbus (cables to a few flight controls)?

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 10, posted (2 years 7 months 2 weeks 1 day 20 hours ago) and read 7660 times:

Quoting craigpc01 (Reply 9):
Is this the same situation with the Airbus (cables to a few flight controls)?

The implementation is different but the concept is still there...an A320 has mechanical control of the stabilizer and rudder. So you've got pitch and, through roll-with-rudder, roll. Although I suspect it's probably not fun to fly. Lots of good info on the A320 flight controls here:
http://www.smartcockpit.com/pdf/plane/airbus/A320/systems/0031/

Tom.


User currently offlineALTF4 From United States of America, joined Jul 2010, 1212 posts, RR: 4
Reply 11, posted (2 years 7 months 2 weeks 9 hours ago) and read 7279 times:

Just out of curiosity, how long would the main battery last in flight? Thinking about the US A320 in the Hudson - obviously the battery has plenty of juice for that. How about at 30,000 feet? Enough for a glide down and landing?

Of course, at 30,000 feet you'd have time to deploy the RAT, start the APU, or similar; plus the engines would be windmilling, as opposed to the Hudson river incident, where I would assume that the engines were not windmilling normally given the bird strikes.

I'm not suggesting that the Hudson river incident was anywhere near close to losing electrical power; just that I doubt they bothered to start backup electrical generation and just used the battery, which then makes me curious as to how long the battery will last in such a situation?

[Edited 2012-02-06 07:23:53]


The above post is my opinion. Don't like it? Don't read it.
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6858 posts, RR: 75
Reply 12, posted (2 years 7 months 2 weeks 7 hours ago) and read 7224 times:

Quoting ALTF4 (Reply 11):
Just out of curiosity, how long would the main battery last in flight? Thinking about the US A320 in the Hudson - obviously the battery has plenty of juice for that. How about at 30,000 feet? Enough for a glide down and landing?

For the 320...
Electrical Power:
GEN1 (Engine), GEN2 (Engine), APU GEN, & EMER GEN.

GEN1,2 and APUGEN goes to AC BUS1 and 2, from there, it goes to AC Essential Bus, TR1 and TR2... TR1 and TR goes to DC BUS 1 & 2, which then goes to DC BAT BUS.

The AC Essential Bus normally take power from AC Bus 1, but can be from AC Bus 2... and when the normal gens fail, it takes power from the EMER GEN.

AC BUs and EMER GEN also supply ESS TR, that goes to DC ESS BUS.

EMER GEN is a HYD Powered GEN from the Blue System... the Blue HYD is essentially the last line of defence in terms of HYD (there's the Green HYD and Yellow HYD systems too)

Now... RAT automatically drop when AC BUS 1 and AC BUS 2 Fail or loses power... it pressurizes the Blue HYD, which also powers the EMER GEN. The process is automatic and takes about 8 seconds (time to couple the EMER GEN, during this time, BAT 2 powers the DC ESS Bus, BAT 1 Powers the AC ESS Bus through thestatic inverter) As long as speed is above 100kts, the RAT has enough rotation to power the HYD and the EMER GEN.

So when both engines fail, once Both AC BUS 1 and AC BUS 2 Fail, RAT gets deployed and power gets generated through the AC ESS BUS and DC ESS BUS, which charges the respective batteries when needed, and the DC BAT BUS gets powered.

If all else fail, the batteries will provide about 30 mins of flight battery only flight. On older 320s, the RAT can stall (risk is significantly higher below 145kts if I remember correctly), when that happens, AC SHED ESS and DC SHED ESS Buses are shed immediately (so that the AC and DC essential buses, I mean, the truly essential stuff, still gets power from the batteries).

It's been a while since I read this stuff, till tonight...

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineBoeingGuy From United States of America, joined Dec 2010, 3074 posts, RR: 7
Reply 13, posted (2 years 7 months 2 weeks 6 hours ago) and read 7190 times:

Quoting ALTF4 (Reply 11):
Just out of curiosity, how long would the main battery last in flight?

Normally 30 minutes.

The 767 has an option to wire it in parallel with the APU battery that would give about 90 minutes standby battery power.

However on the 777 and 787 the RAT generates electric power also, so it would give standby power for any length of time.

All overwater equipped 757s and 767s have a Hydraulic Motor Generator (HMG) that is powered from the Center Hydraulic system, which in turn can be pressurized by the RAT. So the RAT sort of indirectly provides standby power, again for unlimited time.

Hope this helps.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 14, posted (2 years 7 months 2 weeks 5 hours ago) and read 7164 times:

Quoting ALTF4 (Reply 11):
Of course, at 30,000 feet you'd have time to deploy the RAT, start the APU, or similar; plus the engines would be windmilling, as opposed to the Hudson river incident, where I would assume that the engines were not windmilling normally given the bird strikes.

In that particular case, the engines weren't so badly damaged that they weren't still turning over, they just weren't providing useful thrust. I haven't seen the FDR data off that event but I suspect they never went over to battery power.

Tom.


User currently offlinetravelavnut From Netherlands, joined May 2010, 1612 posts, RR: 7
Reply 15, posted (2 years 7 months 2 weeks 2 hours ago) and read 7076 times:

Quoting tdscanuck (Reply 14):

Also Sully started the APU early on



Live From Amsterdam!
User currently offlineBoeingGuy From United States of America, joined Dec 2010, 3074 posts, RR: 7
Reply 16, posted (2 years 7 months 1 week 5 days 21 hours ago) and read 6842 times:

Quoting travelavnut (Reply 15):
Quoting tdscanuck (Reply 14):

Also Sully started the APU early on

On the 777 and 787, Sully wouldn't have needed to start the APU. It starts automatically, in addition to the RAT automatically deploying, when both engines go sub-idle.


User currently offlineB777LRF From Luxembourg, joined Nov 2008, 1359 posts, RR: 3
Reply 17, posted (2 years 7 months 1 week 5 days 15 hours ago) and read 6759 times:

Quoting travelavnut (Reply 1):
If you have total hydraulic failure on most large airliners you're just as dead (or almost certainly dead, Sioux City DC-10 comes to mind)

Unless, of course, you've been hit by a SAM climbing out of SDA, your left wing is on fire, all hydraulics are gone but you just happen to go by the names of Eric, Mario and Peter and are flying an A300 ....



From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
User currently offlineBoeingGuy From United States of America, joined Dec 2010, 3074 posts, RR: 7
Reply 18, posted (2 years 7 months 1 week 5 days 6 hours ago) and read 6648 times:

Quoting B777LRF (Reply 17):
Unless, of course, you've been hit by a SAM climbing out of SDA, your left wing is on fire, all hydraulics are gone but you just happen to go by the names of Eric, Mario and Peter and are flying an A300 ....

Or you are a AA DC-10 flying over Windsor and the cargo door blows out and takes out on the controls but you manage to land at DTW by uncanny use of the throttles only (unlike the similar TK DC-10 that took a nosedive into a forest near ORY). Or you are flying an EA Lockheed Constallation that collides mid-air with a TW 707 and takes out pretty much all flight controls and still manages to use the four throttles to make an extremely skilled controlled crash landing on the side of a hill in which everyone survives the initial impact.

In each case, extremely well done.


User currently offlineB777LRF From Luxembourg, joined Nov 2008, 1359 posts, RR: 3
Reply 19, posted (2 years 7 months 1 week 4 days 4 hours ago) and read 6426 times:

Indeed, BoeingGuy, indeed. UA232 is very well known, and the crew did a very good job in the circumstances they were in, but its final outcome is very far from being the best demonstrated.


From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
User currently offlineBoeingGuy From United States of America, joined Dec 2010, 3074 posts, RR: 7
Reply 20, posted (2 years 7 months 1 week 4 days 4 hours ago) and read 6426 times:

Quoting B777LRF (Reply 19):
ndeed, BoeingGuy, indeed. UA232 is very well known, and the crew did a very good job in the circumstances they were in, but its final outcome is very far from being the best demonstrated.

Neither of those were references to UA 232, but in each case the crews did outstanding jobs with what they had.


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