3MilesToWRO
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LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 1:14 pm

First report was issued about last month Warsaw belly landing of LOT 767. The document is in Polish so far but I guess some automatic translator will be sufficient if anyone is interested.
http://bi.gazeta.pl/im/3/10739/m10739573,RAPORT.pdf

In short: just after take off hydraulic system C lost pressure. After consultation with ground the crew decided to keep flying. Upon approach in Warsaw the gear did not come out. Approach was aborted, again of course ground consultation and fighters checking from outside. Finally there was the landing everyone saw, I guess.
Inspection after landing revealed that on panel P6 circuit breaker C829 BAT BUS DISTR was in "off" position and breaker C4248 LANDING GEAR – ALTN EXT MOTOR was in "on" position. State of C829 is not reported to the crew nor written to FDR.
After lifting the aircraft ground power was connected, (A1) BAT BUS DISTR breaker switched on and the gear was extended successfully.

Faulty hydraulic hose was identified and sent to NTSB.
 
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Starlionblue
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 2:50 pm

Quoting 3MilesToWRO (Thread starter):
After lifting the aircraft ground power was connected, (A1) BAT BUS DISTR breaker switched on and the gear was extended successfully.

So if I'm reading that right, if the crew had set the breaker to "on" they would have landed normally? Is the breaker easily accessible and is it on the gear fault checklist?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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longhauler
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 3:10 pm

The breaker is just to the right of the F/O at floor level, easily accessible and visible.

But would you reset it?

First, one would have to determine when it popped. Did it pop before the first attempted Alternate Gear Extension, or did it pop as a result of it? Big difference!

Secondly, if you could determine it was popped all along, (you couldn't, but playing "what if"), then yes a reset is a possibility. But if it did pop when first attempting an Alternate Gear Extension, would you risk resetting it? Why re-energize an electrical system (with a known electrical problem) possibly sitting in a pool of flammable hydraulic fluid?
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Okie
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 3:16 pm

Quoting Starlionblue (Reply 1):
So if I'm reading that right, if the crew had set the breaker to "on" they would have landed normally? Is the breaker easily accessible and is it on the gear fault checklist?


That is kind of unusually worded.
If the breaker had been "on" then they would have been able to successfully lower the gear by alternate means would be the correct statement.

I can not answer that if after several changes, cycles, of the gear lever and tries of the manual extension if that would allow the manual extension of the gear if controls were out of sequence even if the breaker was returned to the on position.
However the brief explanation above indicated that it could have been accomplished.

The real question here is that even with Mx involved, QRH and the pilots and a with time to spare that the circuit breaker was overlooked for the alternate extension.


Okie
 
roseflyer
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 4:21 pm

Thanks for the article and translation. The center hydraulic system is what normally operates the gear on a 767. They lost that system shortly after takeoff, so primary extension is effectively dead. It appears that for some reason the alternate system was not working. It's hard to know why since the circuit breaker could have been popped when it was attempted to be used, it could have been inadvertently left open, something else could have happened. It sounds like one of those once in a billion scenarios where two faults happened that are unrelated to each other which happened to disable the landing gear.

Landing gear typically only has two methods of extension unlike primary flight controls which have triple redundancy. It looks like the odds were not in the favor of that airplane on that day. I wonder if the airplane had been flying with a problem in the alternate extension system for a while and it was only found out when the primary system was disabled due to a hydraulic failure.
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EGGD
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 6:01 pm

I wonder had it not been a technical fault that caused the breaker to trip, whether it was pulled by accident? The panel where it is situated is not ideally sighted and I've known of people to pull circuit breakers by accident when moving crew bags or when accessing charts that are sometimes placed in front of it. If that was the case then it would have been a real unfortunate chain of events but I suppose that is how incidents and accidents of such a low-probability scenario occur.
 
767eng
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 6:09 pm

Quoting EGGD (Reply 5):
I wonder had it not been a technical fault that caused the breaker to trip, whether it was pulled by accident? The panel where it is situated is not ideally sighted and I've known of people to pull circuit breakers by accident when moving crew bags or when accessing charts that are sometimes placed in front of it. If that was the case then it would have been a real unfortunate chain of events but I suppose that is how incidents and accidents of such a low-probability scenario occur.

Too true, some airlines have bars across the front of the P6 circuit breaker panel between rows of breakers to stop them accidentally being knocked by crew bags. Ours don't and it is a place where the chart bags are normally kept on longhaul flights.

There is always a risk in pushing in a popped circuit breaker in flight as already damaged wiring may spark causing a fire to start. Tough call to make but from the report it does sound like the c/b was reset on the ground and stayed reset.
 
474218
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 6:59 pm

So "normal" gear extension failure can be traced back to a:

Quoting 3MilesToWRO (Thread starter):
Faulty hydraulic hose was identified and sent to NTSB.

and "alternate" gear extension failure was due the a pulled (by something or someone unknown) CB!

Kind of "anti climatic"!
 
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Jetlagged
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 7:23 pm

Some other Battery Bus powered equipment must have been unpowered as a result of C829 being pulled. Wasn't that noticed or indicated to the crew in some way? Does anyone here have access to 767 wiring information to check what other systems would be affected?
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MD11Engineer
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 7:39 pm

Quoting longhauler (Reply 2):
The breaker is just to the right of the F/O at floor level, easily accessible and visible.

This C/B (and others) on the P6 panel is in a location where it easily gets bumped when the F/O puts his flight bag into it´s stowage place.
Boeing has some stupid locations for C/Bs on the B737, B747, B757 and B767.

Jan
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Jetlagged
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 7:51 pm

Quoting Jetlagged (Reply 8):
Some other Battery Bus powered equipment must have been unpowered as a result of C829 being pulled. Wasn't that noticed or indicated to the crew in some way? Does anyone here have access to 767 wiring information to check what other systems would be affected?

To answer my own question, here's the report in English. It includes a list of the CBs which would lose power if C829 was pulled, together with photos of the CB location.

http://www.transport.gov.pl/files/0/30680/20111400RWenglish.pdf

Apparently none of these would show up to the crew as a caution on EICAS or be recorded in the FDR.
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Tristarsteve
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RE: LOT 767 Belly Landing First Investigation Report

Thu Dec 01, 2011 8:11 pm

Quoting Starlionblue (Reply 1):
So if I'm reading that right, if the crew had set the breaker to "on" they would have landed normally? Is the breaker easily accessible and is it on the gear fault checklist?

Yes, and it would not be on a gear fault checklist.

Quoting okie (Reply 3):
The real question here is that even with Mx involved, QRH and the pilots and a with time to spare that the circuit breaker was overlooked for the alternate extension.

The pilots and the QRH had no chance at all.
Maint had a very small chance. The CB concerned is not in Chap 32 Gear, it is in Chap 24 Electrics.
If you go to the FIM for the alt gear, the elect diagram says power from Batt. To find out more would take time (and more fuel onboard!)
If you don't know which CB you are looking for, I would not expect a pilot to find any tripped CB on P6.
 
Okie
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 12:12 am

http://www.transport.gov.pl/files/0/...0RWenglish.pdf

See if this works.

Quoting Tristarsteve (Reply 11):
If you go to the FIM for the alt gear, the elect diagram says power from Batt. To find out more would take time (and more fuel onboard!)
If you don't know which CB you are looking for, I would not expect a pilot to find any tripped CB on P6.


Thanks Tristar,
The more I think about it even if the F/O had noticed the breaker was tripped the F/O would not necessarily know that it was involved with the alternate extension.
Ok, here it comes............. but a F/E probably would.

Okie
 
KELPkid
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 5:56 am

Quoting okie (Reply 12):
The more I think about it even if the F/O had noticed the breaker was tripped the F/O would not necessarily know that it was involved with the alternate extension.
Ok, here it comes............. but a F/E probably would.

Okie

What do you want to bet we will see an accident board recommendation that a tripped breaker will trigger an EICAS alert when the primary extension hydraulic system is INOP   
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
tdscanuck
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 6:05 am

Quoting KELPkid (Reply 13):
What do you want to bet we will see an accident board recommendation that a tripped breaker will trigger an EICAS alert when the primary extension hydraulic system is INOP

I'll take that bet...you won't see that recommendation. You'll probably see a guard on the breaker.

Tom.
 
T prop
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 6:31 am

So if a C/B is out, and the crew knows about it, they have the choice of trying to reset it and see if the gear comes down, or belly it in. Why wouldn't they reset it? Try it once, if it pops again, well there's a short somewhere, now you have to deal with it. If it stays in and the gear comes down, this thread doesn't exist.

Quoting longhauler (Reply 2):
Why re-energize an electrical system (with a known electrical problem) possibly sitting in a pool of flammable hydraulic fluid?

To set Skydrol on fire, you have to try real hard, you'd have to do something like land with the wheels up, slide along on the belly with sparks and flames emitting from where the airframe is dragging on the ground, grind holes through the skin and... hey wait!
 
3MilesToWRO
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 9:07 am

Considering that THE circuit breaker was not included in checklist for landing gear I guess that most useful recommendation would be to to expand this checklist (and all others, actually) with information about all breakers potentially involved. This way they would not be omitted like this one.
There is, indeed, some danger of fire since the breaker goes off for some reason. But I guess that balancing the risks is the job of people who write the flight manuals anyway.
 
Tristarsteve
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 9:38 am

Quoting KELPkid (Reply 13):
What do you want to bet we will see an accident board recommendation that a tripped breaker will trigger an EICAS alert

What like an Airbus?
The A320 says CB tripped on rear or overhead panel.
A330 says which CB and which system.
 
tdscanuck
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 2:12 pm

Quoting T prop (Reply 15):
So if a C/B is out, and the crew knows about it, they have the choice of trying to reset it and see if the gear comes down, or belly it in. Why wouldn't they reset it?

They certainly might...but do we have any indication that the crew actually knew the CB was open in this case?

Quoting 3MilesToWRO (Reply 16):
Considering that THE circuit breaker was not included in checklist for landing gear I guess that most useful recommendation would be to to expand this checklist (and all others, actually) with information about all breakers potentially involved.

Flight crew checklists don't generally include circuit breakers, especially not as troubleshooting steps; the crew isn't supposed to have to screw with them in flight. They're supposed to be notified of any that are open during the dispatch process and anything that trips in flight 1) has a reason for tripping that the crew probably can't diagnose and 2) will generate an EICAS indication if it impacts a system that the crew needs for continued safe flight and landing. In this case, the gear (correctly) indicated on EICAS that it was still up.

This was one of those corner cases of the intersection of two totally unrelated failures impacting two redundant systems at the same time.

Quoting Tristarsteve (Reply 17):
What like an Airbus?
The A320 says CB tripped on rear or overhead panel.
A330 says which CB and which system.

What level ECAM message are individual circuit breakers on an A330?

Tom.
 
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longhauler
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 2:19 pm

Quoting T prop (Reply 15):
So if a C/B is out, and the crew knows about it, they have the choice of trying to reset it and see if the gear comes down, or belly it in. Why wouldn't they reset it? Try it once, if it pops again, well there's a short somewhere, now you have to deal with it. If it stays in and the gear comes down, this thread doesn't exist.

Because they have no way of knowing that the circuit breaker didn't already pop, and that there isn't already a short somewhere, and that the circuit breaker isn't already doing what it is supposed to do ... and that is protect the rest of the aircraft.

If there is a short somewhere, and now "You have to deal with it", it may not be something you can handle. One of the odd quirks about these breakers is that normally they don't just power one system, and this one is a prime example. Have a look at the list at what this breaker powers. It is a lot more than just the Alternate Gear extension. In fact, the "short" might have been somewhere other than the Alternate Gear Extension itself, and powering up an unknown already shorted system is never a good idea.
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yeelep
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 3:04 pm

Here's the FAA's take on circuit breakers. I'm not sure if its the latest version. Each operator will have there own policy on resetting circuit breakers.

FAA Aviation Safety
SPECIAL AIRWORTHINESS INFORMATION BULLETIN
SAIB: CE-10-11
SUBJ: Electrical: Fire Hazard in Resetting Circuit Breakers (C/Bs) Date: December 23, 2009
This is information only. Recommendations aren%u2019t mandatory.

2. Essential C/Bs should be reset in flight only once:
a. after at least one minute;
b. if there is no remaining smoke or burning smell and
c. the affected system and equipment is needed for the operational environment.
3. Do not reset any non-essential C/Bs in flight.

From my airlines QRH manual 737-400/NG:

Circuit Breakers
WARNING! Opening, resetting or cycling of CBs is prohibited
except when following an approved QRH, Flight
Handbook, MEL procedure or in the Captain%u2019s
judgment an extreme condition exists which
makes it necessary for the safety of flight.
WARNING! Do not reset a tripped Fuel Pump, Fuel Quantity
Indication System, or (400) Lavatory Flush Motor
circuit breaker under any circumstance.
If a tripped circuit breaker needs to be reset, a two-minute cooling
period should be observed before resetting. If the circuit breaker
trips again, do not attempt another reset.
A Maintenance Logbook write-up, including a description of the
exact conditions when the trip occurred, when the CB was reset
and the results of resetting the CB, is required and may provide the
key to effective troubleshooting and corrective action by
Maintenance.
2/15/

[Edited 2011-12-02 07:06:21]
 
767eng
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 3:38 pm

Quoting Tristarsteve (Reply 17):
What like an Airbus?
The A320 says CB tripped on rear or overhead panel.
A330 says which CB and which system.

Not all circuit breakers are monitored on the A320 though , only the green ones.
 
Tristarsteve
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 4:29 pm

Quoting tdscanuck (Reply 18):
What level ECAM message are individual circuit breakers on an A330?

Master warning with Amber caution and single chime
for all cbs except commercial ones.
Pushing CB button on ECAM control panel (in front of throttles)
will list all tripped cbs by name, position and FIN number.

But remember on A330 and also B777 and later aircraft, all the CBs are downstairs and
are not really accessible in flt.
 
roseflyer
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 4:52 pm

Quoting T prop (Reply 15):
Quoting longhauler (Reply 2):
Why re-energize an electrical system (with a known electrical problem) possibly sitting in a pool of flammable hydraulic fluid?

To set Skydrol on fire, you have to try real hard, you'd have to do something like land with the wheels up, slide along on the belly with sparks and flames emitting from where the airframe is dragging on the ground, grind holes through the skin and... hey wait!

Skydrol will only burn when in mist form and exposed to continuous source of ignition and it will not burn continuously. Flammability is a major reason why the nasty stuff is used over the much more mundane Mil Oil of the past. I don't think that's a concern.
If you have never designed an airplane part before, let the real designers do the work!
 
SAAFNAV
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 5:38 pm

Quoting yeelep (Reply 20):

WARNING! Do not reset a tripped Fuel Pump, Fuel Quantity
Indication System, or (400) Lavatory Flush Motor

I understand the Fuel Indicators and Pumps CB's. We have the same SOP's, but why the Lav Flush Motor?

Regards,
Erich
On-board Direction Consultant
 
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litz
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 7:17 pm

Quoting Saafnav (Reply 24):
I understand the Fuel Indicators and Pumps CB's. We have the same SOP's, but why the Lav Flush Motor?

That probably comes from the DC9 that burned out due to a fire caused by an overheated lav flush motor ...
 
MD11Engineer
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 7:31 pm

Quoting 3MilesToWRO (Reply 16):
Considering that THE circuit breaker was not included in checklist for landing gear I guess that most useful recommendation would be to to expand this checklist (and all others, actually) with information about all breakers potentially involved. This way they would not be omitted like this one.
Quoting litz (Reply 25):
Quoting Saafnav (Reply 24):
I understand the Fuel Indicators and Pumps CB's. We have the same SOP's, but why the Lav Flush Motor?

That probably comes from the DC9 that burned out due to a fire caused by an overheated lav flush motor ...

I once had a 737NG with a popping lav flush motor C/B, which was resetted repeatetely by the pilots. The reason of the C/B popping was a badly routed wireloom chaffing against the housing of the cockpit zone temperature fan above and behind the captain´s seat. Due to the repeated arcing (115V AC system), the area was already nicely black and the insulation of other wires in the same wireloom was damaged. Remember SR111?

Jan
Je Suis Charlie et je suis Ahmet aussi
 
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longhauler
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 8:37 pm

Quoting litz (Reply 25):
That probably comes from the DC9 that burned out due to a fire caused by an overheated lav flush motor ...

If you are referring to AC797, DFW-YYZ that ended up in CVG ... it was the other way around. The fire caused the flush pump to pop the circuit breakers. The cause of the fire was never determined.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
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Jetlagged
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RE: LOT 767 Belly Landing First Investigation Report

Fri Dec 02, 2011 11:10 pm

Quoting Tristarsteve (Reply 22):
But remember on A330 and also B777 and later aircraft, all the CBs are downstairs and
are not really accessible in flt.

True, but what was needed in this case was an attention getter to alert the crew that an important CB is tripped (whether that's because of an electrical fault or a flight bag knocking it). CBs in the lower lobe are unlikely to be tripped accidentally. Of course if the CB has tripped for a genuine fault and shouldn't be reset then it's of no help unless you allow it to be reset only to operate the alternate gear motor.

Maybe the simplest solution of all would be to move C4248 ATLN EXT MOTOR from the SEC circuit (protected by C829) to the PRIM one coming straight off the bus.
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tdscanuck
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 5:15 am

Quoting Jetlagged (Reply 28):
True, but what was needed in this case was an attention getter to alert the crew that an important CB is tripped

I would say the lack of landing gear coming down was a pretty serious attention getter. Even if they'd known exactly why (CB open) they wouldn't know why the CB was open and may or may not have been allowed to reset it. For certain failures, resetting a tripped CB could kill you. A gear up landing, though really ugly, is unlikely to be fatal.

Quoting Jetlagged (Reply 28):
Maybe the simplest solution of all would be to move C4248 ATLN EXT MOTOR from the SEC circuit (protected by C829) to the PRIM one coming straight off the bus.

Then you run the risk of losing your battery due to a short in the alternate extension motor...fault protection for backup systems is always an ugly tradeoff.

Tom.
 
zanl188
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 12:15 pm

Quoting tdscanuck (Reply 29):
I would say the lack of landing gear coming down was a pretty serious attention getter. Even if they'd known exactly why (CB open) they wouldn't know why the CB was open and may or may not have been allowed to reset it. For certain failures, resetting a tripped CB could kill you. A gear up landing, though really ugly, is unlikely to be fatal.

Could they have setup a CB reset while on, say a 5 mile final, try the gear and then land whatever the result? If the fault that tripped the CB starts a fire they'd be on the ground shortly.
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vc10
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 12:47 pm

I feel very sorry for the crew, who no doubt will be blamed. Before my retirement if the drill was completed with no success, assuming time is available, all CBs would be checked in and if one was found out it would be reset once to see if rectified the problem. If it popped again then it would be assumed that it was the source of the problem and left out,

I think you have to assume that this crew did not do a CB check which they seem to have had time to do, or surely they would have reset the CB just prior to trying alternate lowering . If the gear goes down and you are still worried about why the cb popped then pull it for the rest of the flight. If it pops on lowering then you have tried your best

It is very easy to be wise after the event,and whilst I advocate the use of checklist, however perhaps it is time for basic airmanship to return to the flight deck.

littlevc10
 
Tristarsteve
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 1:47 pm

Quoting vc10 (Reply 31):
all CBs would be checked in and if one was found out it would be reset once to see if rectified the problem.

I work on ramp maintenance. I trip and reset CBs every day.
Quite often I will trip a CB, do something, then go and reset it, but can't see where it is.
I have to go back to the CB list to find the CB that is out.
And this is on an overhead, or rear wall panel.
This tripped CB was an inch off the cockpit floor just outboard of the co-pilot seat,
behind his flight bag. He did not know what he was looking for.
Maint had probably told him to check the Alt Gear cb that was higher up
on this panel, and finding it OK, they didn't look any further.
All aircraft have hidden CBs. There are a lot in the EE bay, and the fwd equip bay
and the fwd freight, etc etc. The only cure is the monitored CB with a cockpit
display like the A330 has.
But the B767 is 10 years older technology and this wasn't available in 1982.

The answer to me is to reintroduce the hatch in the cockpit floor, and a big lever on the
alt gear quadrant for manual operation, like the original B767 had.
 
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747classic
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 2:31 pm

Quoting vc10 (Reply 31):
I feel very sorry for the crew, who no doubt will be blamed. Before my retirement if the drill was completed with no success, assuming time is available, all CBs would be checked in and if one was found out it would be reset once to see if rectified the problem. If it popped again then it would be assumed that it was the source of the problem and left out,I think you have to assume that this crew did not do a CB check which they seem to have had time to do, or surely they would have reset the CB just prior to trying alternate lowering . If the gear goes down and you are still worried about why the cb popped then pull it for the rest of the flight. If it pops on lowering then you have tried your bestIt is very easy to be wise after the event,and whilst I advocate the use of checklist, however perhaps it is time for basic airmanship to return to the flight deck.

I couldn't agree more.

Not at our proficiency checks but during the type recurrent simulator checks we always got the more complicated, time consuming, failures and it was Standard Operating Procedure -SOP- (time permitting) to do a complete cockpit CB check after the abnormal QRH procedure(s) were not succesful.
Most of the time the tripped or pulled CB was at a hard to spot location (behind your flightbag at the lower P6 panel of the 742, or at another aux. CB panel).
But that was at a time with far less automatisation, three man crew and basic airmanship at the flight deck.

[Edited 2011-12-03 06:32:04]
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tdscanuck
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 6:25 pm

Quoting ZANL188 (Reply 30):
Could they have setup a CB reset while on, say a 5 mile final, try the gear and then land whatever the result?

Yes, that would technically work, but it would be against procedure at some airlines.

Quoting ZANL188 (Reply 30):
If the fault that tripped the CB starts a fire they'd be on the ground shortly.

True. The thing you really worry about, and what's behind the original regulatory guidance material on the subject, is resetting circuit breakers on tripped fuel boost pumps. Done wrong, this can detonate the ullage space in the wing (think TWA-800).

Tom.
 
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RE: LOT 767 Belly Landing First Investigation Report

Sat Dec 03, 2011 9:18 pm

Quoting Tristarsteve (Reply 32):
All aircraft have hidden CBs. There are a lot in the EE bay, and the fwd equip bay
and the fwd freight, etc etc. The only cure is the monitored CB with a cockpit
display like the A330 has.
But the B767 is 10 years older technology and this wasn't available in 1982.

This is why I love the MD-11. Except for a handfull of APU related C/Bs (located in the center equipment compartment), all C/Bs are located in the cockpit and aranged in a very logical manner. No craling around in E/E tunnels like on the 757 or 747, or crawling between the seats like on a 747.

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Jetlagged
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RE: LOT 767 Belly Landing First Investigation Report

Mon Dec 05, 2011 5:30 pm

Quoting tdscanuck (Reply 29):
I would say the lack of landing gear coming down was a pretty serious attention getter. Even if they'd known exactly why (CB open) they wouldn't know why the CB was open and may or may not have been allowed to reset it. For certain failures, resetting a tripped CB could kill you. A gear up landing, though really ugly, is unlikely to be fatal.

It wouldn't be at all obvious that as well as the ALTN EXT MOTOR CB a battery bus CB had also to be checked. Alternate gear extension is something you'd expect to work under almost any circumstance. I guess we'll have to wait for the full report to know if the crew were aware the CB was tripped.

The alternate gear motor only needs to operate long enough to unlock the gear. There would be "unlock" indications within seconds of resetting the CB and operating the switch. If not then the CB could be pulled again to isolate the SEC CBs. It's only a few seconds.

If that distribution CB tripped due to an electrical fault it must be from the battery side of the circuit, as the CBs it supplies weren't tripped. Without other signs of trouble on the battery bus what risk would there be in resetting it?

Quoting tdscanuck (Reply 29):
Then you run the risk of losing your battery due to a short in the alternate extension motor...fault protection for backup systems is always an ugly tradeoff.

Why? Surely the ALTN EXT MOTOR CB would provide the same protection to a motor short circuit? The two CBs are effectively in series. In fact the bus distribution CB must be higher rated, so the motor CB would be the first to trip in the event of a motor short.

The APU DC fuel pump motor and the eng fuel control valve power supplies are not given the belt and braces protection that the alternate gear motor is.
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RE: LOT 767 Belly Landing First Investigation Report

Mon Dec 05, 2011 6:34 pm

Quoting yeelep (Reply 20):
Here's the FAA's take on circuit breakers. I'm not sure if its the latest version. Each operator will have there own policy on resetting circuit breakers.

And to take it one step further, the FAA has been rather paranoid about in-flight circuit breaker resets after the AS261 accident.
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ADent
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RE: LOT 767 Belly Landing First Investigation Report

Wed Dec 07, 2011 5:19 am

There was that NASCAR Cessna 310 that went down to resetting a circuit breaker. Good article here: http://www.airforce.forces.gc.ca/dfs...sv/pub/nr-sp/index-eng.asp?id=9943 .

That says the FAA issued guidance ( AC 120-80 ) on not resetting breakers due in part to the SR 111 crash.
 
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RE: LOT 767 Belly Landing First Investigation Report

Wed Dec 07, 2011 9:54 am

Quoting Goldenshield (Reply 37):
the FAA has been rather paranoid about in-flight circuit breaker resets

Understandably for Chapter 28 related pop outs,but why the rest.
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RE: LOT 767 Belly Landing First Investigation Report

Wed Dec 07, 2011 10:12 am

Quoting HAWK21M (Reply 39):
Understandably for Chapter 28 related pop outs,but why the rest.

This is th FAA we're talking about. When AREN'T they paranoid? However, ADent provides a great example why.

I don't know too much about it myself, since I only got an overview as to why it's done, but most all (U.S.-based) airline MX people should be able to answer your question.
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