ANA 787 Engines shutdown during landing

[Someone Somewhere]

Originally Posted by Leonakua

If "Lighting your "Wingman" is not "Communicating", then I've got CPR all wrong...

Besides I am referring to a "Common Core" Consultation, not a party line.
We are discussing something that should NOT have happened...you don't get there by defending what was supposed to happen...

My point is that here, TCMA WAS ENGINEERED to prevent Overboost, or throttles incorrectly misaligned. Not to second guess the crew. Crew will bounce, it happens.
QF32 could have used a precautionary shut down on #2. ANA was doing just fine.
IMO,
Should TCMA BE Transferred to cover TOC? Leave landings alone?

TCMA?? Arse about? Should it be prohibited below 10k AGL?? Like sterile cockpit. I will tell you this rotor burst at altitude could have killed every body

Overboost on the roll also, but some will live, and after rotation it is supposed to mind its own business....supposed to...

I'm pretty sure you're BugBear under a different name, so I suggest you re-read and re-interpret this post again:

Spoiler

 

 

Originally Posted by Someone Somewhere

Again, you're smushing everything into one big mass of 'stuff I don't understand'. These systems are discrete, each with their own triggers and actions taken.

It is like wondering why your smoke detectors didn't save you from electric shock: they have no means to detect it, and the effect they have has no impact on the thing you wanted them to prevent. The fact that people sometimes put two or more safety devices in one box, or that they might look the same, doesn't really make a difference.

Safety systems generally detect a specified sequence of events, and then take a specified action when those events are detected.

• Smoke detector:
  • Detects smoke
  • Action: makes loud noise
• RCD/GFCI:
  • Detects unequal/residual current, indicating a possible shock
  • Action: cuts power
• Conventional circuit breaker or fuse:
  • Detects:
    • way too much current for a short time, or
    • a bit too much current for a long time (inverse curve)
  • Action: cuts power
• Surge protector:
  • Detects: excess voltage
  • Action: Draws a lot of current to limit that voltage
• TCMA (in FADEC):
  • Detects:
    • Commanded thrust (thrust lever position) low, and
    • Actual thrust from engine high, and
    • Actual thrust from engine not decreasing, and
    • On ground (WoW)
  • Action: Shut down engine by closing HP fuel valve
• Turbine/N2 Overspeed (in FADEC):
  • Detects spool spinning way too fast, at risk of rotor burst
  • Action: Shut down engine by closing HP fuel valve
• Loss of thrust lever position detection (in FADEC)
  • Detects that both thrust lever resolver signals are missing (or impossible?)
  • Action: Maintain last valid thrust setting (on some previous aircraft)
  • Action: Set engine to idle (on other previous aircraft)
  • Action: shut down engine (on 787/GEnx? Why?)
• Fire shutdown switch
  • Detects crew pulling fire handle
  • Action:
    • Disconnect generators
    • Shut off hydraulics to engine
    • Shut HP & LP fuel fuel valves
    • Shut off bleed air (not on 787)
    • Arm exinguisher squibs.

N2 Overspeed (and various equivalents) are designed to prevent a rotor burst by shutting the engine down if a particular rotor overspeeds. The Trent 900 on QF32 didn't have overspeed protection on its N2 rotor because it was thought that it was impossible for that rotor to overspeed without also overspeeding N3, which was protected. I expect that's fixed now.

Overboost is where the engine as a whole is running at too high a power setting, shortening engine life and risking failure. That's avoided by the control loops in the FADEC under normal conditions. If the FADEC thinks it's partially damaged and unable to properly determine some factors (usually sensor failures), the FADEC ends up in an alternate mode without overboost protection, which becomes the crew's problem. Overboost is a minutes problem, not a seconds or split-second problem.

TCMA shuts the engine down if it continues producing high thrust but the crew has that same engine set to/near idle. It only does this on the ground, because uncommanded high thrust in the air isn't a major hazard - there's always more sky above you, you can reduce thrust on the other engine to maintain altitude/drift down, and there's little time pressure.

TCMA doesn't care about throttle split. One engine operating and one engine stopped is a pretty big throttle split.