Posts by user "mh370rip" [Posts: 7 Total up-votes: 0 Pages: 1]

SLF engineer ( not aerospace)
so nothing to contribute but a query. I've read the first thread since it started and then this one and the best suggestions I've seen which seem to fit multiple failures at rotate and shortly after (gear mid cycle or failed hydraulics, RAT out, emergency lights on, lack of thrust) involve some catastrophic failure in the electrical systems. My query is will the investigators be able to establish this, are there environmental sensors in the EE bays which might detect and record water presence (steam, excessive humidity) before there are cascading and otherwise unrelated failures in a variety of systems.
Obviously a long term leak would leave corrosion residue but a recent burst build-up with a dam overwhelmed at rotate might be more difficult.

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.

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 phrase in the report is "switches transitioned from RUN to CUTOFF position".
Does the FDR actually have some input of the physical position of the switches or is it just measuring the output signal voltage
which might be changed by a momentary short from liquid or swarf.
Both signals go to cutoff within 1 second but then one recovers four seconds after the other.
Surely a pilot discovering a turned off switch would have both back on in less than four seconds.

Surely when the switches turn off there would be an EICAS warning (I didn't see any mention in the report of what messages were being displayed) to the effect that switches were in CUTOFF which might have prompted the query.

In this case it was spectacular but gliding in just off the airfield from a few hundred feet up is not guaranteed to result in total loss whereas spearing in from a few thousand feet would be a sure end. Why take the chance if you're determined to end your life.

A query, the FO was pilot flying and the Captain was pilot monitoring. Is it SOP that pilot flying sits in the LHS at takeoff? As I understand it the situation on power failure is that the battery backup will keep the displays alive until the APU comes online but only on the LHS. Trying to maintain best gliding performance and look for best landing site without any instruments to show speed or attitude would be more difficult. Captain taking over and swapping roles at 200 feet mid crisis is disruptive.

Tdracer has certainly explained that separation of cabling runs etc would have it very improbable that a single cable fault or short would impact both engines simultaneously in the same way. The CVR data is derived from local sensors with a dedicated battery backup, however all the FDR data and the fuel shut off commands are electrical signals which ultimately have a common source in the aircraft power buses. A water ingress into the EE bay at rotate which momentarily shorted all the low voltage buses to higher AC voltage is unlikely but is it unlikely to the same extent.

Quote from 2025-06420.pdf
AD 2021-15-05 requires initial and repetitive replacement of the full authority digital engine control (FADEC) integrated circuit (MN4) microprocessor.

The MN4 is part of the FADEC in the engine, the probability of both engines having identical unrelated failures at the same time is very unlikely.

Edited: I see katekebo has already raised this as very unlikely