Posts about: "Water Ingress" [Posts: 23 Pages: 2]

Would anyone know whether this AD is relevant?

FAA Orders Boeing 787 Inspections to Fix Water Leak Issues

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I add this note: the background on this AD is here:
https://www.federalregister.gov/docu...pany-airplanes
T28B

Water ingress into the E/E bay is a serious issue. The B744 had this issue in the past causing serious problems, one of which was fortunate to not lead to a loss of the aircraft, on a B744F. The B744 pax aircraft had a number of water problems related to the toilets and the galley. The forward galley on the B742/3s had many issues.

Any large aircraft going through maintenance is interesting to observe the extent of corrosion that occurs near toilets and galleys, and from water lines.

The B777 was not immune to this either. The potable water tank failing caused one of our aircraft to have 6.5 tons of ice accumulating in the underfloor area of the aft cargo hold, which we detected on a preflight walk around as a series of water streams from the drain holes in one area of the aircraft. This was an interesting item for CG, a note on weight, but only affected the electrical services related to the aft cargo systems.

Water accumulations on the B744 came to light at rotate, and took out a lot of electrical services.

My suspicion is some cause such as this will come to light shortly.

The water leak issues with the B787 go back to in service reports in 2014 and before, considered an unsafe condition in 2016, and were covered by AD 2016-14-04. This latest AD is curious as it stems from an administrative oversight in the drawings of the aircraft, that arose on aircraft manufactured from 2018 onwards. 2025-09-12 stands alone related to missing sealant, following the drawing oversight in production. It did not affect all aircraft. The earlier AD, 2016-14-04 was related to water line coupling issues, and is in Service Bulletin B787-81205-SB380009-00 WATER/WASTE - Water System- Potable Water System - Couplings Replacement. It notes on page 21 of 229 the reason for the work

The latest AD and the earlier AD highlight that problems can occur, and have done so in the past. Both of the E/E bays contain stuff that is nice to keep dry and operating, and prior events have shown that multiple system failures can and have occurred when a flood is added to all the black boxes sitting innocently on their racks.

The ADs are not necessarily directly related to the specific cause, they highlight the potential for water damage and that bad stuff happens. In two cases I investigated, the event occurred at rotate. Both were B744's one pax, one F.

Compound, unrelated system failures at rotate? Single cause? Water in the E/E bay.

The amount of flooding that occurs in the toilet cubicles is unfortunate, apparently towels still fit well into toilet bowls, signs are disregarded etc. Coffee grounds block galley drains with monotonous regularity, the planes are only as good as we care for them, and passengers seem to have odd ways of treating the conveniences.

Potable/waste water leakage into the forward EE Bay is a potentially fascinating fit. Rotation sloshes water onto a critical wiring junction resulting in dual simultaneous engine shut down as well as cascading electrical failure throughout the aircraft. The hard part is thinking that Boeing's engineers would permit such a failure mode in their design. It would seem to require a substantial volume of liquid.

See tour of forward avionics bay, Boeing 787:
May the victims rest in peace and their families find enduring comfort.

- Ed

Retired RAF avionics technician, PPL / Glider pilot with ~ 700 hrs. VC10 double EFATO survivor.

The TCMA system should be inhibited when Air / Ground logic is in Air mode.
I understand that it has Inputs from RadAlt, Weight on Wheels, etc.
This airframe was reported to have had a history of significant electrical / electronic problems, including on the prior inbound flight.
There may have been water ingress in the E&E bay, likely causing corrosion or other damage.
Chafed or damaged wiring / cable insulation within looms is possible. Including the landing gear microswitches.
The landing gear may have been interrupted in the cycle.
BOTH engines are reported to have shut down, so whatever happened is a system common to both engines.
TCMA failing at the moment of gear retraction appears to fit with the available evidence.

A Qantas 747-438 suffered an 'Electrical System Event' when on approach to Bangkok airport on 7 January 2008. The following extracts are taken from the report:

"System malfunctions

Between 0846 and 0852, 4 after passing FL 100 and when the aircraft was turning
onto an extended left downwind leg for runway 01 Right (01R), the EICAS, flight
displays and automated systems showed faults of numerous electrical and other
aircraft systems, including:
\x95 AC buses 1, 2 and 3 not powered
\x95 autothrottle disconnected
\x95 autopilot disengaged
\x95 some fuel pumps not operating
\x95 weather radar not operating
\x95 automatic cabin air conditioning and pressurisation system not operating
\x95 right (FO\x92s) displays blanked
\x95 between three and five pages of messages on the EICAS display
\x95 lower EICAS display blanked.
The CSM contacted the flight crew and advised that the cabin lighting had failed."

"Origin of Generator Control Unit (GCU) faults

Post-incident examination of the GCUs revealed corrosion of the internal circuit
boards in all three of the GCUs that shut down. Analysis of the corrosion materials
observed in GCU 3 showed evidence of long-term exposure to water, including
evidence of acids and carbohydrates that are present in beverages such as coffee,
fruit juice and soft drinks. Those findings indicated a fluid source originating from
the aircraft\x92s galley drains or from spilt liquids in the cabin, and also suggested that
liquid ingress had been occurring over an unknown, but extended period of time."

https://www.atsb.gov.au/sites/defaul.../ao2008003.pdf

This link to the report includes diagrams of where the 747 forward galley was located, directly above the Main Equipment Centre and the E1/E2 racks.

The phtographs show how ineffective the dripshield was in protecting the electrical equipment and the extent of corrosion and damage.

The aircraft was 17 years old at the time of the incident and had completed a C-check approximately three months before the incident.

As FDR notes, this issue seems to have carried over to the 787-8 with Airworthiness Directive AD 2016-14-04 ( https://drs.faa.gov/browse/excelExte...A0058AF6B.0001 )

"We are issuing this AD 2016-14-04 to prevent a water leak
from an improperly installed potable water system coupling, or main cabin water source, which could
cause the equipment in the EE bays to become wet, resulting in an electrical short and potential loss
of system functions essential for safe flight"

AD 2016-14-04 mirrors precisely what occurred to the Qantas 747 on 7 January 2008. It is possible something similar may have occurred on take-off of AI171, with water causing the equipment in the EE bays to become wet resulting in electrical short and potential loss of system functions

Adding to your response TD, there is no time in this event where a high AOA arose prior to the final moments, around 13 seconds after the problem has occurred. AOA, intake separation is not a factor.

Going back to your prior comments on FADEC and TCMA; these are independent systems to each engine, however the event indicates a symmetric loss, and the potential of water ingress from a failed E/E sealing from the main cabin services remains a single causation that could result in multiple failures at the same moment. The last time I assessed issues in the E/E bay related to unauthorised inflight access to the fwd E/E of a B777 it was sobering how many irreversible conditions could arise. The B744 water inundation cases I was involved in were both on TO, the QF event was during deceleration. We are looking at vectors that come from outside of the normal assumptions in the SSA's, water fits that bill.

One related question: since it was reported that the packs were not functional on the previous flight and were (presumably?) fixed before the accident flight, could condensation of excess humidity in the E/E bay be a relevant mechanism?

Adding to your response TD, there is no time in this event where a high AOA arose prior to the final moments, around 13 seconds after the problem has occurred. AOA, intake separation is not a factor.

Going back to your prior comments on FADEC and TCMA; these are independent systems to each engine, however the event indicates a symmetric loss, and the potential of water ingress from a failed E/E sealing from the main cabin services remains a single causation that could result in multiple failures at the same moment. The last time I assessed issues in the E/E bay related to unauthorised inflight access to the fwd E/E of a B777 it was sobering how many irreversible conditions could arise. The B744 water inundation cases I was involved in were both on TO, the QF event was during deceleration. We are looking at vectors that come from outside of the normal assumptions in the SSA's, water fits that bill.

True, I would bet that the voltage regulating architecture of the voice recorder at least will give useful information for a short time around the loss of power, as it did for the Lockerbie CVR using far less sophisticated recorder systems. That was sufficient to show the pressure pulse in the fuselage and to give a fairly good idea of where the explosion had emanated from. TWA was similar, a bigger bang though. Would be listening for any mechanical noises related to the fuel switches, and frankly I doubt that they existed, but they would be recorded.

If the cause is what I have suggested it will dificult to get direct evidence of that case, as it was for the QFA072 event as well. Like icing cases, a water ingress into the avionics is going to be a tough investigation, water would have been sprayed all over the wreckage in the aftermath. Dousing the E/E bay with 20 or 30 gallons of water will be an expensive investigative exercise to do in a real plane, with engines running. Would not want to be observing up close.

CALLOUT TO MAINTENANCE CREW!

Can we please have a productive discussion on maintenance, to examine a new area and avoid the hamster wheel? Can someone from turnaround crew working on 787's generally (or ex A-I staff) comment on what standard checks are performed in the allocated time?

PAX have reported cabin issues on the inbound flight, (and other A-I flights), from no aircon for the whole flight to unresponsive screens etc. TDRacer has explained that the FADEC is shielded from other electrical systems. However, is there ANY correlation with these cabin malfunctions and the crash other than 'poor maintenance' we can find here? E.g. what if one of Air Canada's 787's entered YYZ with the packs malfunctioning - what inspection and maintenance would be performed? C ould a maintenance engineer working on fixing the packs do something to trigger a later plane-wide power loss? Or could non-functioning cabin electrics give us a clue as to other more fatal issues present? Could the system isolation protections have failed somehow? E.g. water ingress?

*Each time I post this, it gets ignored, but it's an unexplored area and my view is maintenance may have played a large part in this crash, - please help to narrow it down. Thanks.

Water was mentioned earlier in the previous iteration of this thread, as I recall by one of the most well respected contributors on the forum and an expert in flight testing and certification issues. There have been a couple of well known incidents of flight deck screens going blank due to all sorts of electrical problems caused by water ingress into the E&E bay, fortunately in daytime vmc and not on particularly electric jets, and both I believe at rotation. The one I recall had it’s L1 door left open during a black rainstorm in Hong Kong. It’s also been said that total electrical failure can’t result in in a double engine failure on the 787, but I wonder what multiple sequelae could result from such water contamination with an aeroplane that relies so much on electrical power and software? Another very remote probability but many accidents and incidents are. I don’t even know if there was any inclement weather before this flight, maybe someone could confirm?

Just looked…..none by the looks of things so skip that theory, apologies.

SLF Engineer(electrical -not aerospace) so no specialised knowledge of any kind.
The TCMA discussions on here seem clear that in normal operation the TCMA functions should not
operate in air mode and the TCMA has multiple inputs from various sensors (Rad alts, WOW sensors).
My query is to how these signals are routed to the engines, are they compared/aggregated in or routed through
the EE bays. If they are present in the EE bays then fdr's idea of a water leak at rotate into the EE bays
could generate shorts from the HV buses to the TCMA units.
Are the TCMA units designed to cope with 400V AC inputs where a low voltage input is expected.
I appreciate that the TCMA has to physically power a valve closed but applying high voltage to low voltage
logic circuitry might have unexpected consequences.

The TCMA runs on the FADECs (Full Authority Digital Engine Control). There is one per engine, located inside the nacelle. Each one has a dual channel design inside, to compare computations, inputs etc. and generally provide redundancy (but I don\x92t know further details on the design/logic).

The sensors and actuators related to that engine (pressure, temperature sensors, various valves etc.) are most likely directly connected to it. The two throttle position sensors per engine are also directly cabled to it according to tdracer. No idea how other inputs like WoW and RADALT are connected. The FADECs don\x92t necessarily need much else, as apparently Autopilot etc. always move the actual thrust lever.

There must also be a communication channel back to the flight recorders. No idea if it gets thrown into a comms bus or there is direct wiring.

In terms of power, each FADEC has its own alternator driven by the engine. But there\x92s a failover connection to the AC bus of the plane. Not sure if there\x92s a physical relay keeping it disconnected in normal operations.

SLF Engineer (electrical - not aerospace) so no special knowledge

Perceived wisdom may be applicable in normal circumstances but not when all the holes line up.

For example I've seen it quoted many times that the engine FADECs are self powered
by the engines, the TCMAs-whether part of the FADEC or a separate unit, similarly self contained
within the engine. The perceived wisdom seems to be that there is no common single fault
which can take out both engines.

And yet we're also told that the TCMA function can only function in ground mode and receives ground-air
signals from a combination of inputs from Rad Alts and WOW sensors.
There is therefore a connection from the central EE bay to the engine.

Yes I'm sure the Rad/Alt and WOW sensor processing will use different sensors for each side and powered from different
low voltage buses.
However as an analogy, in your house your toaster in the kitchen may be on a separate circuit from the water heater in
the bathroom, each protected by a fuse at the main switchboard. In normal operation a fault in one cannot affect the other.
However a lightning strike outside the house can send much higher voltages than normal operation throughout the entire
system and trash every electrical appliance not physically disconnected at the time.

Now I'm not suggesting the aircraft was hit by lightning but FDR has proposed a single event, buildup from a water leak entering
one of the EE bays at rotate. It would be possible for one or more of the HV electrical buses to short so that all the low voltage
buses go high voltage. I have no knowledge of how the FADEC / TCMA systems connect to or process the Ground-Air signals but
there is a single fault mechanism whereby high voltage could be simultaneously and inappropriately applied to both engine control systems.
It would be unfortunate if this failure mechanism did cause power to be applied to drive the fuel shut off valve closed.

Since the likelihood is that we're looking at a low probability event then perceived wisdom about normal operations and fault modes
might not be applicable.

The equipment on RAT/battery is limited:


(from the online 2010 FCOM)


(from the maintenance training )

The 787 battery fire report says the two recorders are on the left and right 28VDC buses. I don't think those get powered on RAT by the looks of it. I would wager you get whatever is on the 235VAC 'backup bus', plus the captain's and F/O's instrument buses via C1/C2 TRUs. You won't get all of that (like the F/O's screens) because the 787 energises/de-energises specific bits of equipment, not just whole buses.

Losing recorder power looks entirely expected.


400VAC/540VDC (+-270V) is not really known for blowing past input protection in the same way as actual HV or lightning. I would expect some optocouplers and/or transformers to be both present and adequate. There's definitely some big MOVs scattered around the main 235VAC buses.

Weight on wheels appears to go into data concentrators that go into the common core system (i.e. data network).

Presumably there is a set of comms buses between the FADECs and the CCS to allow all the pretty indicators and EICAS alerts in the cockpit to work. The WoW sensors might flow back via that, or via dedicated digital inputs from whatever the reverse of a data concentrator is called (surely they have need for field actuators other than big motors?). Either way, left and right engine data should come from completely different computers, that are in the fwd e/e bay (or concentrators/repeaters in the wings, maybe) rather than in with the big power stuff in the aft e/e bay.

...by the FAA

"This AD was prompted by reports of water leakage from the potable water system due to improperly installed waterline couplings, and water leaking into the electronics equipment (EE) bays from above the floor in the main cabin, resulting in water on the equipment in the EE bays"

The FAA is saying it's a problem . Any suggestion that it's related to this incident is pure speculation. Possibly brought on by that slop 'report', which may have itself been somewhat inspired by the ADs.

The engines controllers are powered internally, and the control signals appear to be redundant wiring to the thrust lever module. Perhaps there are joints in the E/E bays (probably to be avoided) but asserting liquid intrusion would cause simultaneous loss of all four signals seems laughable.

Flight controls are primarily in the fwd E/E bay but there is a set of actuator control electronics in the aft E/E bay. So even if one bay gets a deluge, it shouldn't take out all flight controls. And the flight path isn't consistent with uncontrolled flight, much less uncommanded flight with high thrust.

Consider that there's standby instruments with independent sensors and computing and mostly independent power. Thrust and flight control is subject to greater scrutiny and requirements.

Agreed. But the FAA itself does speculate - on what basis, I have no idea. They use the word "may", see here, last sentence (and in other ADs in the sequence):

https://www.federalregister.gov/d/2022-26933/p-18

This paragraph (and one before) is/are also worth a read - they see no rush to fix, obviously. https://www.federalregister.gov/d/2025-08346/p-20

100% Agree: any suggestion that it's in any way related to 171 is pure speculation. Sounds like these ADs apply only to small numbers of 787s. Don't even know if 171 was one of them.

But installing lavatories directly above EE Bays? Who's the genius...? .

Anyway, I make a point of not going 'there' during the last half of any long flight. They are frequently "awash" and unpleasant places to be. The washbasins themselves are also prone to the ejecting of water onto the floors. Agreed, it's a ####ty problem.

Every commercial airliner I've ever been on - with the exception of a short-range regional jet (only lav in the back) - has at least one lav immediately aft of the flight deck. Especially post 9/11, putting the most forward lav any further back would become a nightmare when the pilots need to relieve themselves (presumably, they expect the pilot to be able to 'hold it' on a short range regional jet).
And every commercial airliner I'm familiar with has the prime electronics bay below the flight deck - for what should be obvious reasons.

There is absolutely nothing unusual about the 787 arrangement in this regard.