Posts by user "Someone Somewhere" [Posts: 44 Total up-votes: 79 Pages: 3]

Originally Posted by EDML

Once again tdracer confirmed the PMGs for the FADECs in the first AI171 thread. He even explained the logic behind it and the connections with the onboard electronics:
- Each engine has a PMG for the FADECs
- Only for engine start the FADECs are powered by the aircraft
- Once the engines are running, this connection is opened
- It is verified, that the FADECs are then no longer connected to the aircraft electrical system. A failure to open the connection triggers a "No dispatch" message
- In case the PMG fails, the FADECs are once again powered by the aircraft electrical system

Originally Posted by Util BUS

Based on my previous speculation regarding a BTB short, I wonder how aircraft engines might react in a situation where initially a transient power fault is followed by only battery power being available? As I understand it, there are no longer cable connections to the engines, given no valid inputs from the.thrust levers, what thrust mode would the FADEC's revert to?

Originally Posted by EEngr

A different set of PMGs.

Originally Posted by EDML

I still think that the small black area is the back of the engines visible through the small gap of the extended flaps.

Furthermore: The small hydraulik pump of the RAT only powers some of the flight controls that are powered by the center hydraulic system. The ones powered by the engine driven pumps will not work once the engine(s) failed.

Originally Posted by StudentInDebt

No, it doesn’t “only” happen in these cases!

Originally Posted by Lead Balloon

Just so I have this clear, are you saying that the implementation of the TCMA functionality involved no new components being added to the pre-existing FADEC? Are you saying, in effect, that the two switch relays described in the TCMA patent application, which relays and their configuration achieves the described two channel redundancy, were already there as components or are mere depictions of what the software does itself?

I am not suggesting you are wrong and, as I've said before, the descriptions and schematic in the patent application are just 'big hands / small maps' concepts. However, if TCMA functionality "is simply a bit of software in the FADECs", merely sending a 1 or 0 or other signal into a point in the pre-existing FADEC that already had control over fuel cutoff (with the TCMA software merely monitoring data busses, rather than direct sensor outputs, to work out thrust lever position and whether or not the aircraft is 'on the ground' for TCMA purposes) I for one would really like to know that for sure and get my head around the implications.

Originally Posted by ignorantAndroid

In general, we can classify computer errors into 3 categories:

1. Errors in system design, specifications, or algorithms. These are cases where the computer does exactly what it was designed to do, but the design itself was flawed or inadequate, or had unforeseen consequences. This would include things like MCAS on the 737 MAX.
2. Software errors. These are cases where the computer does exactly what the code tells it to do, but not what the designers wanted it to do. This results from mistakes in writing the actual code, and this is usually what we'd refer to as a "bug." This includes things like race conditions, loops that fail to terminate, incorrect type conversion, etc.
3. Hardware malfunctions. These are cases where the computer does something different from what the code instructs. It can involve memory corruption or data bus corruption. It can result in a system that appears to work, but returns incorrect outputs, e.g. a calculator saying 2+2=5. It can also cause the computer to execute valid instructions, but at an inappropriate time. It can result from manufacturing defects in components, cosmic rays (SEU or SEE), radiofrequency interference (HIRF), moisture ingress, failed solder joints, and numerous other things.

Originally Posted by martinebrangan

I would, of course, presume, that take-off roll performance was within expected limits, otherwise they would have aborted by V1. They reached VR before running totally out of runway, and achieved a short-lasting climb. What one single point of failure occurred very shortly after aircraft went nose-up and would it be possible that the fuel feed in some way affected by virtue of that angle in the context of some failure?

Originally Posted by Capn Bloggs

The bleeding obvious didn't work on the Jeju Air 737.

The 787s recorder/s have obviously been damaged so much/missing data they are being taken to the US.

Originally Posted by MaybeItIs

On that point, the gear, as far as I can establish (not openly published according to Google), weighs around 8-odd to 10 tonnes. Typically, retracts in about 10 seconds. I estimate it's no more than a 2 metre lift. As far as I can work out (using 3m to make the value higher), that requires about 30kW (rough estimate, budgetary figure, not accounting for it being a curved path, so it's probably higher closer to fully up), but whether wind pressure affects it, I have no idea. Anyway, 30kW isn't a huge (additional) load on a 225kVA alternator. Less than I'd imagined.

Now I'm wondering how big (power ratings) the hydraulic pump and motor are? No doubt, they're driven by a VSD. Can anyone comment, please?

Originally Posted by Icarus2001

Always possible, however since a pilot made a radio call there was some emergency leve l power available, which suggests the EAFR would be powered.

The Jeju recorders were okay if I recall correctly, they just had no input, was that the case?

Somoeone made a good point above about the German Wings FDR/CVR being available the next day after the aircraft was aimed at the ground like a missile. These things are built tough, as you know, this may be type specific but….

Originally Posted by mh370rip

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.

Originally Posted by FullWings

That\x92s the nature of a common mode bug. If the software was vulnerable to Mars being in the house of Uranus, the scent of lilacs and the DOW being less than 42,000 then you\x92d expect the failure to occur everywhere when these conjoined. Same when an aeroplane\x92s systems and/or the environment present data that triggers an unplanned/unforeseen response in something like an EEC/FADEC. The experts still appear to think that this is unlikely but we have been presented with an unlikely occurrence...

Originally Posted by Roo

Thanks for doing this.
Someone else created an external page a few days ago that indexed and sorted all the topical posts in this thread and the original one under major headings.
I can no longer find it. Did that get deleted by mods for non compliance or is it still around somewhere?

Originally Posted by Sailvi767

I suspect both recorders will contain the same data. Given the radio transmission after the loss of thrust the aircraft still had at least the emergency electrical bus powered. This should have kept both recorders online. It is however possible given the 10 minute battery backup that Boeing chose to put the the recorders on another bus but that\x92s not the norm.

Originally Posted by Loose rivets

I was puzzled by the total absence of replies to Godfrey's talking heads post way back in a main thread. He talked with clarity and implied authority but I was left wondering if people discounted him because of his research into encoded data in radio waves and its connection to the 370 search.

One thing he claimed, in a log of several 171 flights, was that the runway used was greater on the crash flight. Not huge, but significant since the other 6? listed were all about the same. On PPRuNe threads it has been repeatedly stated that the runway used was not unusual.

Originally Posted by megan

Hold your horses there Bloggs , I didn't say they did, I said centre tanks were typically turned on at that altitude (using a certain 737 operator as a guide). As the check list that you posted shows the centre pumps will automatically turn off because of load shedding once an engine is started.