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Qantas jumbo's water leak knocked out systems: report

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Qantas jumbo's water leak knocked out systems: report

Old 13th Dec 2010, 09:38
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Qantas jumbo's water leak knocked out systems: report

Sydney Morning Herald reporting following at:
Qantas 747's galley leak caused system failure: ATSB report

A water leak in the galley of a Qantas 747 jumbo jet knocked out electricity to a series of systems during a flight to Bangkok, leaving pilots just minutes to land on battery power.

Water flooding in the galley knocked out three of the four on-board power generators, including all AC-powered systems, as the plane was on descent 25 kilometres from Bangkok airport.

Air investigators say that if the flooding had occurred more than 30 minutes' flying time from an airport or had there been a delay in landing, it would have placed the plane — carrying 346 passengers and 19 crew — "at considerable risk" as more systems were likely to fail.

The leak had already knocked out power to radar, cabin pressurisation, autopilot, auto-throttle and some fuel pumps as the plane descended from 21,000 feet and passed through 10,000 feet. The batteries, which were designed to last a minimum of 30 minutes before depletion, had been running for 21 minutes when the aircraft landed and taxied to the terminal building, investigators found.

The drama began when the galley flooded on the Qantas Boeing 747 due to ice formation that blocked a drain pipe after an anti-ice heater failed.

A build-up of water flowed forward and cascaded through a decompression panel into the aircraft's main equipment centre, leaking onto three of the jumbo's four generator control units, causing them to malfunction and shut down.

The 114-page Australian Transport Safety Bureau report released today into the January 7, 2008 incident said plane was reliant on its battery back-up for the last 15 minutes of flight.
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Old 13th Dec 2010, 09:53
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Not a very good couple of months for QANTAS. Is this another maintainence issue for this revered airline. They may well have not lost any aircraft however their incident rate is telling me its only a matter of time. Or is it someone elses fault again??
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Old 13th Dec 2010, 09:59
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So what maintenance procedure was not followed? Looks to me like a drain mast failure to me!
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Old 13th Dec 2010, 10:04
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3 years ago!
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Old 13th Dec 2010, 10:20
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Water leak in 747 galley - long long ago this dripped onto the aileron control rods and quite literally froze the controls. Fatal crash. Cause not published until much later. During which interval I was SLF on a TWA 747 LAX-LHR, we got into a slow roll oscillation, about ten degrees each way, mid Atlantic. I was sat over the wing and could see the ailerons not moving, whilst a small inboard surface was flipping up and down. I guess this was all that was keeping us right way up. After landing I saw a member of the crew being wheeled in a wheelchair with his arm in a sling, possibly fatigue from the constant effort. My thanks to the crew for managing to avert what had been catastrophe in the previous occurrence.

PS - Sorry, have searched for citations and am unable to substantiate original fatal crash.

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Old 13th Dec 2010, 10:43
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Best source is the ATSB.
Aviation safety investigations & reports:
Electrical system event - Boeing 747-438, VH-OJM, 25 km NNW of Bangkok International Airport, Thailand, 7 January 2008

Final Report
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Old 13th Dec 2010, 10:48
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Wonder what the outcome would have been in the 'all-electrical' 787?

G-S
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Old 13th Dec 2010, 10:49
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whilst a small inboard surface was flipping up and down

Mike. For info, big jets use these 'inboard ailerons' in the cruise since the outboard ones are too severe at high speed. It is quite normal not to have the outboard ailerons working during the cruise.
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Old 13th Dec 2010, 13:26
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mike-wsm --

To build on blue up's comment, on 747 Classics the outboard ailerons are locked out (do not move) when the flaps are up. Roll control in cruise is provided by the inboard ("high speed") ailerons and spoilers.

In fact it is a bit of a problem if the lockout fails.
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Old 13th Dec 2010, 13:30
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Not a maintenance issue as the heater is an 'on condition' item used to happen fairly often on the classics but never heard of it knocking out any systems though.
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Old 13th Dec 2010, 16:44
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Would you call it a maintenance issue if the drip trays were cracked/torn?
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Old 13th Dec 2010, 16:44
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At the time there was talk here on PPRuNe about it just having come out of maintenance (somewhere in the FE?) and a drip shield not having been installed back where it should have been in the below decks area between doors 1L and 1R. And or it having been cracked.
Hence the drastic effects.
Any word on that in this final report?

There was also talk of 'lazy FAs' having caused a blockage of the galley drain by pouring coffee grounds down it.
Drain mast heater failure is a very different beast.

original thread
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Old 13th Dec 2010, 22:02
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Originally Posted by Juud
At the time there was talk here on PPRuNe about it just having come out of maintenance (somewhere in the FE?) and a drip shield not having been installed back where it should have been in the below decks area between doors 1L and 1R. And or it having been cracked.
Hence the drastic effects.
Any word on that in this final report?

There was also talk of 'lazy FAs' having caused a blockage of the galley drain by pouring coffee grounds down it.
Drain mast heater failure is a very different beast.
Just read through the report, and I would say "all of the above".

Drain mast heater failure leading to ice blocking at altitude.
Possibly assissted by ye olde coffee grounds which were indeed down the drain...
Liquid backs up to level of galley floor
Where it leaks out through damaged drains (some damaged by impact from the cart...)
It then leaks through inadequately sealed galley floor
Through bad joints and cracks around fasteners in the drip tray
And finally onto, and into, the unsealed GCUs which are redundant but all nicely located under the same drip...


Three GCUs had corrosion damage, and failed, but all four had evidence of liquid ingress. I'm not sure on first reading why the three GCUs failed at the same time from what was a chronic liquid / corrosion problem - maybe one tripped and then the others failed trying to switch the additional load.

At the pointy end, neither the QRH or the cockpit displays gave the crew any indication of battery time remaining, and the fact that they werew on battery was only a low priority message anyway

The crew gave up going through the messages and checklists and elected to just continue with landing (ok, good idea with hindsight). They elected not to inform ATC...

On the ground, they taxied to stand as normal, ground power was connected to the failed electrics (is it just me, or ummm...?), and then found they had no evac ability as pressurisation systems failed and cabin was overpressure.


The cracked drip tray turns out to be another aircraft - the drip trays were checked across the fleet:

The high proportion (52 out of 69) of damaged dripshields or gutters in the
operator‘s 747-400 fleet of aircraft indicates that the issue was widespread, even
though that particular problem could have been readily identified by a visual
inspection during regular maintenance activities
Ouch. Bit of a struggle to blame this one on RR
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Old 14th Dec 2010, 02:05
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design fault?

hindsight is a wonderful thing.

if you were going to design a large machine today, which you wanted five-9s reliability on, would you put mission-critical triple-modular-redundant circuit boards under a drip-tray?

argument 1) you can bet sod's law means no matter where you put it, poo will settle there sometime, for some condition of age/manoeuvrings/circumstance

argument 2) deliberately invoking the god of gravity seems to be taking liberties with foreseeable problems

argument 3) how come the TMR circuit has all three redundant circuits on the one board? isn't this a common-failure which means it either votes 2 out of 3 or fails, but cannot actually survive a board failure?
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Old 14th Dec 2010, 06:14
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As we slowly drift off topic I thought I would add a little.

As a result of the incident on the QF flight Boeing released a all operators telex informing them of the findings and as a result other operators found defects with the E1/E2 drip shield. This resulted in the Boeing SB being released which reinforces the drip shield gutters and the top of the drip shield which forms part of the E/E cooling plenum on top of the E1/E2 shelves.

The most significant damage I found was not to the gutters but to the top of the plenum. But to find this you had to boroscope the plenum so it is not readily visible to maintenance staff. So how can it be a maintenance issue?

By the way to repair this you have to remove the Galley complex at door 1 so not an easy task to do.
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Old 14th Dec 2010, 07:07
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Nice one, Clandestino!
 
Old 14th Dec 2010, 08:07
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infrequentflyer - Thanks very much for your admirable precis of the report.

As humble SLF it has always struck me that incidents such as these always tend to be a whole series of seemingly small events which culminate in a serious problem -- as you have highlighted.

But at least the plane had four engines, now if it had had only two.....

and was on a conveyor belt....
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Old 14th Dec 2010, 08:41
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Perrin

I would like to have cash whatever the type for the times I have had problems as a engineer after continued coffee spills in the cockpit. After all the skill to build and test A/C something simple causes problems.
Another thing well done flight crew (engineers don't say that much).
Keep them up boys
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Old 14th Dec 2010, 10:59
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Hi

Long time reader here. IT professional by trade but have air-transport engineering degree experience back in the early 90s so some mech eng knowledge.

The report made really interesting reading. The report identifies that the modification to incorporate the Y piece could/did allow the upstairs galley to backflow into the lower galley in the event of a blockage between y and drain mast. It also states that the modification from dual to single nozzle drain mast was done for purely cosmetic reasons. It has now been shown that this has introduced the potential for a significant spill into the lower galley and hence the electrics bay. My feeling is that it would be prudent to revert the plumbing to its original configuration.

Question for the techs: is it typical for transport aircraft to have all the generator control units and TRUs in one place? It seems like physical separation of these components into two bays would likely eliminate a single flood causing so many electrical systems going offline. Hydraulic lines are , where possible, routed so as to prevent the confluence of all systems in at-risk areas of the aircraft - we should do the same with the electrical system too.

Cheers

James

Last edited by rottenlungs; 14th Dec 2010 at 11:01. Reason: Edited to correct crummy splelng..
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Old 15th Dec 2010, 09:45
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Question for the techs: is it typical for transport aircraft to have all the generator control units and TRUs in one place?
The generator Control Units are on the same equipment rack, but they are quite far apart (two on each side of a rack which is maybe 3 metres across). The TRU's (AC to DC converters) are in a different area, but they use generator power.

Perhaps Boeing might consider putting a monitoring circuit on the drain mast heaters to sense failure (in their next gen aircraft)?

Is the problem really a maintenance issue... or a design issue. The problem is not really a "maintenance issue" if the heaters are routinely inspected every x months. A heater could fail the day after. How do you know when a light bulb will fail? Aircraft are not immune to the laws of physics (as some people think)

I wonder how many other airlines found cracked drip shields? They are not the most robust of things. I suspect all would find a few cracked shields if the inspections were done properly.
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