View: https://www.youtube.com/watch?v=VswFVpyg5ew
This video highlights another user, probably into aircraft maintenance, telling that -
- There are known cases of 787 & 777 of total electrical failure.
- FSOV (Fuel Shut Off Valve) are spring-loaded & not powered by engine's PMA (Permanent magnet Alternator) but by aircrafts DC system.
- Aircraft loses electricity, FSOV shuts off.
- FSOV designed to protect airframe, not engines.
- Boeing thinks it is safer to shut down engine than to keep feeding fuel into a potential fire.
- BUT, for both FSOVs to close, A/c should lose both AC buses, DC buses & Battery backup.
- RAT would take 2 seconds to deploy & start giving electrical power
- when switching power sources, system can behave unpredictably - especially if one source is competing with RAT or is unstable, causing delays & closing FSOVs.
Well, we do notice in homes, offices, when voltage fluctuates then switching from main power to UPS/Invertor can be some times like ping-pong. But a S/w controlled switching can keep the power to backup/secondary only.
- So in 787 the FSOVs power is from DC but not with DIRECT battery backup, like in A320 for example. It is INDIRECT, the batteries support DC but FMC prioritizes flight critical systems 1st. If power limted or unstable then less critical FSOV can be deprioritized.
- From 2015-2020, 3 ADs (Air-worthyness Directive) were issued.
- 787 continiously powered for 248 days can lose all AC power due to GCUs (Generator Control Unit) going into fail-safe mode, the S/w counter is local to GCU.
- On ground, power cycling or reboot of main electrical power &/or to Contol Modules required.
- All 3 Control Modules might reset together if powered for 22 days.
- Stale data monitoring function of Common Core system (CCS) may be lost if powered for 51 days, leading to loss of Common Data N/w (CDN) message age validation, combined with CDN switch failure. IDK what is this.
- Google search on FSOV, in the video show that FSOV will close when -
- Inlet or outlet temp. beyond limit.
- Bleed air pressure is lost, probably due to compressor stall, fire, etc.
- electricity to FSIV lost.
- ANA 787 incident where Over-thust protection by
TCMA or Thrust Control Malfunction Accommodation system. I mentioned this already.
QUESTIONs:
- In those known cases, what caused a massive electrical failure taking out 3 redundant supplies - AC, DC, batteries?
- Why EEC & its PMA doesn't have at least secondary control over FSOV?
- Why the electrical switching in such critical machine is not instantanious?
- How can FSOV be deprioritized when A/c needs fuel to fly?
- Does the FMC check the GCU counter & Control Modules before flight, detect interception with flight, display caution on MFD?
- Is GCU connected to EEC or no need?
- What powers GCU - A/c's AC or DC, EEC's PMA?
- We now that battery can be shut down by cockpit overhead panel. Perhaps after 1 day of duty the A/c might be given few hours of rest, IDK. So, does the maintenance crew power cyce the main power or the sub-systems?
- Did the ground crew address th CDn issue.
- All types of planes fly in MEA region (Middle-Eastm Africa) with hotter climate. So what about inlets & outlet temp limits there?