Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

737NG Complete loss of electrical power.

Tech Log The very best in practical technical discussion on the web

737NG Complete loss of electrical power.

Old 19th Mar 2021, 22:41
  #21 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 66
Posts: 3,368
Originally Posted by excrab View Post
I only have experience of one company’s ETOPS requirements on the NG so it’s not definitive, but we couldn’t dispatch an ETOPS flight unless both engine generators and the APU generator was serviceable. In flight the APU had to be started prior to the ETOPS entry point and if it didn’t start or one of the engine driven generators failed prior to the entry point then we had to re-route to ensure we remained within one hour of a suitable airfield. I would imagine that would apply to most ETOPS aircraft unless they have a RAT that can provide sufficient power if one of the other sources fails.
ETOPS MEL's are more restrictive - I don't think any MEL for ETOPS allows dispatch with only two generators - regardless of aircraft type.

Banana Joe, I should have specified 'commercial jetliner'. The point remains - jetliners having to ditch is very, very rare. Compare that to spacial disorientation leading to a loss of control - multiple crashes in just the last decade. Sim time can be better spent.
tdracer is offline  
Old 20th Mar 2021, 00:21
  #22 (permalink)  
 
Join Date: Dec 2006
Location: Whanganui, NZ
Posts: 223
Originally Posted by tdracer View Post
Banana Joe, I should have specified 'commercial jetliner'. The point remains - jetliners having to ditch is very, very rare. Compare that to spacial disorientation leading to a loss of control - multiple crashes in just the last decade. Sim time can be better spent.
Apart from Capt Sullenberger's remarkable display of skill, how many jet aircraft with underslung engines have been successfully ditched? I think the answer is "none", and that the number of attempts can be easily counted on the fingers.
Yes, IMHO sim time can be much better spent.
kiwi grey is offline  
Old 20th Mar 2021, 03:05
  #23 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 264
Originally Posted by Gin Jockey View Post
Engine fuel spar valve has its own battery so can always shut engine down.
I’m pretty sure that’s not correct. You reading that in a Boeing manual of some kind?
Dave Therhino is offline  
Old 20th Mar 2021, 03:12
  #24 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 264
Originally Posted by FlyingStone View Post
You're talking about a triple failure to get there, after which the aircraft is still flying normally, albeit for a limited period of time, and is then still controllable with extremely limited instrumentation.

737 has been flying for more than 50 years and I haven't heard of any incidents where all three AC sources have failed. If you know of any, please share, it would be an interesting read.
There have been several events of loss of all normal AC power on the 737NG. Also at least two on the 767 I can recall.

Generator failures are almost never completely independent. Failure of the first one usually causes an increase in load on the remaining generator(s), often to their load limit, which can cause another generator or switching equipment to fail. Also, on an NG the third source is the APU generator. APU inflight start reliability is at best in the 99% range.

Also, adding to the list of what doesn’t work when all normal ac power is lost, add the fuel pumps. You are on suction feed if AC power is lost. If you are at high altitude with warm or unweathered fuel when this happens, you may experience a flame out on both engjnes.

Last edited by Dave Therhino; 20th Mar 2021 at 03:35.
Dave Therhino is offline  
Old 20th Mar 2021, 06:20
  #25 (permalink)  
 
Join Date: Feb 2008
Location: earth
Posts: 67
Originally Posted by Dave Therhino View Post
I’m pretty sure that’s not correct. You reading that in a Boeing manual of some kind?
the FCOM makes no mention of it.

Both iPad apps for 737 I have mention it (737 cockpit companion and 737 MRG)

“spar valve mounted on the front spar outboard of each strut
- access is through an access panel on the leading edge
- has backup nicad battery to make sure it always has power to close
- the fuel spar valve actuator is interchangeable with the crossfeed valve actuator”

“a dedicated fuel spar valve battery ensures electrical power to close the valves should the hot battery bus become unpowered”

I’ll ask an engineer when I am at work tomorrow.
Gin Jockey is offline  
Old 20th Mar 2021, 07:54
  #26 (permalink)  
 
Join Date: Jan 2014
Location: Melbourne
Age: 65
Posts: 2
Originally Posted by Dave Therhino View Post
There have been several events of loss of all normal AC power on the 737NG. Also at least two on the 767 I can recall.

Generator failures are almost never completely independent. Failure of the first one usually causes an increase in load on the remaining generator(s), often to their load limit, which can cause another generator or switching equipment to fail. Also, on an NG the third source is the APU generator. APU inflight start reliability is at best in the 99% range.

Also, adding to the list of what doesn’t work when all normal ac power is lost, add the fuel pumps. You are on suction feed if AC power is lost. If you are at high altitude with warm or unweathered fuel when this happens, you may experience a flame out on both engjnes.
BS

Name one.

I have flown many thousands of hours on the NG and never heard of one.
The NG has one of the simplest and most robust electrical systems there is.
I’ve been hit several times by lightning and it was not an issue.
Just lots of paperwork.
George Glass is offline  
Old 20th Mar 2021, 10:23
  #27 (permalink)  
 
Join Date: Feb 2003
Location: Blue sky
Posts: 123
I only know one case on a B727 where a water leak whiped out the complete electrical system, and that was pretty much in the departure sequence so the aircraft was back on the ground in little time.

In the simulator I have seen many bus failures, for some reason my company loved these during recurrents as for the "pilot side", there are a lot of little unrelated issues to deal with, some more apparent than others. But the result is always a no rush situation...

As for reality: single drive failures, gen failures, I remember somebody had a battery bus failure in the UK with some smoke?

So a full and non-recoverable loss of all AC power generation is really lottery level stuff.
BraceBrace is offline  
Old 20th Mar 2021, 11:23
  #28 (permalink)  
 
Join Date: Feb 2008
Location: FLORIDA
Age: 67
Posts: 15
UAL 854 on April 13, 2004. My younger brother Brian Witcher was Captain. ALPA Superior Airman awarded to the crew. Root cause was corrosion at the AC/DC grounding bracket which caused a nearly continuous loss of electrical power. This was an ETOPS aircraft (B767-300) and if not for the emergency landing at BOG after 42 minutes it would have been a disaster. There is a good read on this in the October 2005 ALPA magazine. What I never quite understood was the inability to select the HMG or RAT on the 767 although due to the nature of the failure (total loss of the grounding of current) I believe it would not have made any difference. I myself flew for EAL from 1979 to the strike in 1989 on the 727, A-300 and the DC-9. Not pertinent to this topic but I just retired this month from a single corporate job I held from 1990. Flew the CL60, GV and G550.
RAWLAW is offline  
Old 20th Mar 2021, 14:32
  #29 (permalink)  
 
Join Date: Apr 2000
Location: FL, USA
Posts: 385
Originally Posted by BraceBrace View Post
So a full and non-recoverable loss of all AC power generation is really lottery level stuff.

Maybe, maybe not. As I mentioned, I don't know the exact numbers, but there is another consideration, the numbers across the civil aviation fleet might not be well known since a loss of Engine and APU generators has been a non-event in most aircraft types. Lottery level failures would probably apply to the 4 and 3 engine types where one has 4-5 Generators and maybe RAT backup. On the 2 engine types, the older 767/757 ER aircraft were equipped with hydraulic generator backup, providing 4 sources of flight display redundancy. On 2 engine Airbus, my understanding is the the RAT will provide the same.

The 737NG/MAX have reduced the number of electrical backups to 3. What I don't pretend to know is the MTB failure design specs on the NG/MAX. Have they improved significantly over the years? Hopefully yes. One still has to admit that no matter how good the odds, the aircraft is unflyable IFR after the IFSD battery dies after a loss of all generators. On other civil types with electric RAT options, not so much. The MAX also requires significant runway length in that scenario.

The Lottery jackpots for 3 numbers are significantly less than those for 4 or 5 numbers
WhatsaLizad? is offline  
Old 20th Mar 2021, 18:04
  #30 (permalink)  
 
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 1,126
Originally Posted by WhatsaLizad? View Post
One still has to admit that no matter how good the odds, the aircraft is unflyable IFR after the IFSD battery dies after a loss of all generators. On other civil types with electric RAT options, not so much.
If I'm not mistaken, the ISFD is normally powered by the DC standby bus, which will be powered by battery in the event of loss of all AC power. I'd guess that most 737NG aircraft (and certainly those that are ETOPS certified) are equipped with two batteries. So we are talking 60 minutes on batteries + another 150 minutes on the ISFD battery, total of 210 minutes. 737 NG/MAX are certified to ETOPS-180, so even if the loss of AC power would be at the critical point, it would still give crew a 30 minute margin, assuming battery capacity is what it should be. Note that very few (my guesstimate would be sub 1%) 737 flights worldwide include an ETOPS segment to begin with.

It's a pretty much very hypothetical scenario at best. Remember, at the end of the day, even the most modern aircraft only have dual-redundancy when it comes to pilots on board. And dual pilot incapacitation due to oil fumes is probably much more likely than a full electrical failure exactly when the aircraft happens to be far over the ocean.
FlyingStone is offline  
Old 20th Mar 2021, 18:37
  #31 (permalink)  
 
Join Date: Apr 2000
Location: FL, USA
Posts: 385
FS,
Not sure of battery power on STBY. I've never seen the 60 minute number for two. As for the IFSD, the extra time is nice, but without any Nav or Comm source, the 737 is less redundant than other aircraft. There seems to be a common theme that it's never happened so it's not a problem. If so, perhaps the other fleet types can deactivate the backup generator option of their RAT's to save maintenance costs.
WhatsaLizad? is offline  
Old 20th Mar 2021, 18:46
  #32 (permalink)  
 
Join Date: Oct 2019
Location: north of Harlow and south of Cambridge
Posts: 0
“Power
The integrated standby flight display (ISFD) gets 28v dc from the ISFD dedicated battery/charger.
The ISFD dedicated battery system gets 28v dc from the battery bus. The battery/charger sends the 28v dc power to the ISFD. The battery/charger also uses the 28v dc power to charge its internal battery.
A signal from the battery switch on the electrical meters, battery, and galley power module goes to the battery/charger. When the battery switch is on,the battery/charger supplies 28v dc power to the ISFD. When the battery switch is off, the ISFD does not receive 28v dc power.
The ISFD gets 5v ac for the front panel lights from the master dim and test circuit.”
70 Mustang is offline  
Old 20th Mar 2021, 18:48
  #33 (permalink)  
 
Join Date: Apr 2000
Location: FL, USA
Posts: 385
70 Mustang,

Great info, thanks!

Our manuals including the QRH have been dumbed down so much that information is excluded. While flying in the Domestic US? So what? Plenty of options within 30 minutes. In other areas such as over the Amazon, 60 minutes of Nav and Com along with the IFSD backup time after that should cover the areas of concern in my earlier posts.
WhatsaLizad? is offline  
Old 20th Mar 2021, 18:53
  #34 (permalink)  
 
Join Date: Oct 2019
Location: north of Harlow and south of Cambridge
Posts: 0

70 Mustang is offline  
Old 20th Mar 2021, 20:20
  #35 (permalink)  
 
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 1,126
Originally Posted by WhatsaLizad? View Post
If so, perhaps the other fleet types can deactivate the backup generator option of their RAT's to save maintenance costs.
I'm not sure how well FBW works without any electrics.
FlyingStone is offline  
Old 20th Mar 2021, 21:57
  #36 (permalink)  
 
Join Date: Jul 2009
Location: USA
Age: 75
Posts: 131
Everybody talks about Sully but didn't Captain Rozaq ditch his 737 Classic with both engines out due to intense rain - 1 fatality out of 60 on board. And although the gear was down, Air Niugini also made a water landing, 1 fatality out of 47 on board. If I recall on the Garuda incident, the battery was in poor condition so all electrical power was lost prior to ditching.
NWA SLF is offline  
Old 20th Mar 2021, 22:12
  #37 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 264
Originally Posted by Gin Jockey View Post
the FCOM makes no mention of it.

Both iPad apps for 737 I have mention it (737 cockpit companion and 737 MRG)

“spar valve mounted on the front spar outboard of each strut
- access is through an access panel on the leading edge
- has backup nicad battery to make sure it always has power to close
- the fuel spar valve actuator is interchangeable with the crossfeed valve actuator”

“a dedicated fuel spar valve battery ensures electrical power to close the valves should the hot battery bus become unpowered”

I’ll ask an engineer when I am at work tomorrow.
What you quoted seems quite clear. If it's in a system description or training material that came directly or indirectly from Boeing, then I think you can assume it's accurate. I just don't remember seeing reference to a dedicated battery for the spar valve in the engineering documents covering the fuel system description, the rotorburst safety analysis, or powerplant fire safety. Learned something new today. Thanks.
Dave Therhino is offline  
Old 20th Mar 2021, 22:15
  #38 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 264
Originally Posted by FlyingStone View Post
I'm not sure how well FBW works without any electrics.
I'm only familiar with the 777 FBW, which has dedicated generators on the engine gearbox for the FBW system. That system will function if all normal AC power is lost, and even if standby DC is lost. I imagine the 787 and the Airbus systems are the same, but don't know that for a fact.
Dave Therhino is offline  
Old 20th Mar 2021, 23:12
  #39 (permalink)  
 
Join Date: Jan 2014
Location: Melbourne
Age: 65
Posts: 2
The NG only has a useful endurance of around 6 hours.
The ETOPS sector of 99% of flights is usually short.
There is no need for more redundancy.
Running the APU during the ETOPS sector is enough.
Same reason it only has 2 IRSs.
In fact my operator requires me to turn the APU off exiting the ETOPS sector to save fuel.
George Glass is offline  
Old 20th Mar 2021, 23:24
  #40 (permalink)  
 
Join Date: Feb 2003
Location: Blue sky
Posts: 123
Originally Posted by WhatsaLizad? View Post
The Lottery jackpots for 3 numbers are significantly less than those for 4 or 5 numbers
Don't understand me wrong, I understand what you are trying to say. But you are talking about non-recoverable failures. The B767 had a common cause which is (probably) a result of non-bullet-proof failure analyses (well failure analyses will never be bullet proof). But such discoveries will certainly lead to modifications to aircraft or maintenance changes and hence shouldn't happen anymore.

The Boeing checklists in these cases aim at recovery of systems: they isolate and try to re-establish step by step. Ie, it's a known basic sim-scenario on the B737 to trigger a complete loss through an AC demand system (hydraulic pump), and have the crew walk through the checklists and identify the cause. The reasoning is 3 or even 2 different generators (power generation) on themselves don't fail around exactly the same time, those do require lottery number chances. A user can trigger the failure, but in these cases generators should be recoverable.

I do have to say I started on non-EFIS classic 737's. The "one fails, one overloads" could indeed be a problem because the APU generator did not have the same output as an engine driven generator, and the APU itself was dodgy to start... You also had 30' of battery life (if the battery was new) and if you wanted to start a dodgy APU you lost a couple of minutes already... Meanwhile, the flying pilot was looking at tiny standby dials. At a certain point he would discover the trim is not working, you are on manual trim now. And when you've finally "composed yourself", the dreadfull "tuut tuut tuut" comes on and you have to reach for the oxygen mask. How much time left now? About 20 minutes to land? Then came the EFIS (hey look the captain has good instruments to fly these 20 minutes!).

This sounds like story telling, but I only mention it to point out that - even on battery only - it's not that easy. The captain is flying and pretty much has to do... everything.

Then came the NG... 60 minutes battery? Holy moly... So it is 60 minutes to reach an airport but more importantly... 60 minutes to try to recover something. Because chances are big that one of those 3 generators will be recoverable. Non-recoverable power generation - IS a case of lottery numbers...

But I'll take the NG any day, beats the 30 minute battery classic ;-). Same rules did apply though.

Last edited by BraceBrace; 20th Mar 2021 at 23:47.
BraceBrace is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.