Posts about: "Generators/Alternators" [Posts: 161 Pages: 9]

787 gear and flaps/slats are both on the centre system, powered by 2x big electric pumps and no EDPs, so retraction should be minimally impacted by engine failure assuming electric power was still available and reconfiguration worked. Note the 787 has two generators per engine so generator failure is also unlikely to contribute, unless both engines failed taking out all four generators (and presumably no APU running).

From that thread, I believe it was discussed that on most/all other large transports, deploying the RAT re-powers the CVR/FDR. The 737 didn't have that happen because no RAT. You may still get a few second gap while the RAT deploys.

The 787 has 2x Enhanced Airborne Flight Recorders (EAFR), which each record both cockpit voice and flight data. I expect they are also fitted with the dedicated batteries that the Jeju was a year or two too early to require. Per the NTSB , the forward recorder has a 10-minute backup battery.

Hopefully flight data is not going to be an issue for this investigation.

The suggestion is that the buzzsaw/propeller sound is the RAT; it does sound a bit like an interference pattern, but you don't get the engine roar with it.

It's also maybe visible in a few stills (e.g. post 64).

Two 225kVA generators per engine (plus two on the APU). Directly driven with no constant speed drives so they are variable frequency. That is converted to high voltage DC and distributed around the plane. So, four or six independant sources.

Several load distribution centers, where the DC is supplied to various loads and in some cases converted to 28Vdc, 400Hz AC, or other levels as required by the loads. The switching between alternate sources would depend on each load buses criticality. There are also those lithium ion standby/starting batteries available. So, theoretically very redundant. But highly complex systems also suffer from the possibility of hidden faults which may escape certification testing and analysis. We'll see.

Primary trigger: Loss of all four AC power sources.

• These include:
  • Left Integrated Drive Generator (IDG)
    
  • Right IDG
    
  • Left Backup Generator
    
  • Right Backup Generator
    Engine failure alone does not trigger the RAT, must be all of above

and people are saying this happened all at the same time within 30-45 seconds ?

Forgive me if appear to be being a bit pedantic but the 787 does not have IDGs and BUGs.
Each engine has two identical Variable Frequency Starter Motor Generators.
They are a combined starter motor and generator.

More in this ancient thread here-
787 electrical system - variable frequency generators?

Without getting into how an MEL actually works, here's an excerpt from an actual 787 MEL.



AGCU = APU Generator Control Unit, VFSG = Variable Frequency Starter Generator. IDK what exactly the AGCU does nor why the left one is important.

There are no IDGs on a 787. There are 4 identical variable frequency starter-generators.

About the only way that could happen would be some catastrophic software 'hole' in the GEnx-1B FADEC software. By design, the only thing the engine control really needs to adequately the engine is:
1) Fuel
2) Thrust lever position
Everything else is 'goodness'. The FADEC has its own dedicated (gearbox mounted) electrical generator (actually alternator), so even a 100% aircraft power loss wouldn't affect the FADECs ability to control the engine. It was right at takeoff - 'suction feed' would be more than sufficient if the aircraft fuel pumps failed, FMC and other aircraft inputs have only a secondary effect on the thrust setting, it's primarily determined the thrust lever position.
So there is no known way that a fault in the engine/aircraft interface could cause a large loss of thrust.

#3 would be the TAT and thus N1 Max on this very hot day. Nothing abrupt, but cumulative? Get hot enough and N2 limit can make hot day line steeper. But likely latched DT, which I recall was to deal with inversions. At 42C, likely used full-rated TKO. Also would be useful to know engine health, residual margins. Blast through EGT, stop at N2.

You are quite correct. Every wide body Boeing (and Airbus) twin plus the 747-8 has a RAT - Some drive a generator and/or some drive a hydraulic pump. The reason for the 748 having a RAT is that for a 3 or more engine flameout (Boeing speak for a 4 engine flameout) the EDP’s are depressurised to unload the gearbox for ease of windmilling. Hence, no engines = no hydraulics. Edited to clarify the different reasons for the RAT. Edited to add every “wide body”

A220 has a RAT - so does the E-jets and the Sukhoi Superjet. You're right on the 737 and I'd forgotten the 717...


I can only reiterate what I said, you can disagree if you like, I don\x92t have any current 767 documentation anymore (been off it for almost 10 years), I can 100% say that across all of the the 30+ airframes, 2 different models -200/300ER and 3 engine combinations (PW, GE, RR) that I flew... NONE OF THOSE 30+ airframes had a RAT. Maybe yours do? I don\x92t know. Feel free to post some 767-200/300 FCOM information if you have it.

What the 767s I flew did have, was a hydraulic generator (or 2 in some cases), but that sure ain\x92t a RAT.

TCMA\x85?

FR24 data appears to stop shortly after airborne but well before impact.
That would seem to align with the significant loss of electrics as a result of loss of engine generators theory?
Flaps prematurely retracted shouldn\x92t be a cause of loss of electrical power to the transponder. If electrical power was normal then one would have expected data info until impact, regardless of flap position.

Reading the various reports about electrical problems on the prior and this flight, such as flickering lights reminded me of the BMI A321 incident discussed here 15 years ago:

https://www.pprune.org/archive/index.php/t-433616.html

A faulty generator caused all sorts of problems with control of the aircraft. It is a reminder that complete electrical failure is not the only failure mode. Shutting down the faulty generator on that aircraft recovered the situation, but they had time and altitude on their side.

One thing which could cause simultaneous unexpected idle power is the autothrottle. I'm thinking about this, leading to a crew too startled to retract the gear and too distracted to push the thrust levers forward, as a possible cause. As others have said, the RAT could have been manually deployed - an action which would make sense to pilot convinced that he was about to lose both engine driven generators.

It's fine that the \x93Enhanced Airborne Flight Recorders\x94 have 10 minutes battery backup. If the bits of equipment/sensors sending data to be recorded don't have power, you will be recording 10 minutes of silence/blank data.

The concept of powering 'critical (sensor) equipment' has been floated - the problem being that it must be possible to power down malfunctioning equipment in case of fire - real or suspected. Having independent power supplies and battery back-ups all around the airframe, each with an ability to lose their magic smoke, is a poor idea.

Commercial passenger jet aircraft already have robust power supplies with multiple generators and emergency battery support. However, if one malfunctions, rather than fails completely, it can be difficult to decide which one to disable, as it can cause problems in all systems.

Especially when the video is clearly taken on the ground, when you could easily expect source switching due to shutting down an engine for single-engine taxi, then switch to APU, then ground power.

IIRC the CVR battery (in this case EAFR battery) is required to power at least the cockpit area microphone, if not the pilots' mics.

Once the RAT deployed at least some data should have come back.

This has been discussed upthread and has happened before (on a 777 IIRC) but did not result in a crash.

It does not explain the RAT and generally you would expect crews to shove the thrust levers fully forward.

Assumptions
30 secs to 100 kts from TO power set.and 200 kts after 60 seconds
Impact occurred 30 secs after Vr 1 nm out, so about 120 kts and no more than 300ft
The gear was not or could not be retracted.
Without doubt the crew knew impact was inevitable at least 10 seconds prior to impact noted by body angle change in video evidence
whether a Mayday Call was in fact made or not.

I think that the only thing that would matter for any of us in that 20 seconds would be THRUST and everything it's got.
Which occurred first, the loss of thrust on both engines causing all generators to go offline or a total electrical failure that caused flight Idle thrust.

There would be way much going on for anyone to even think about deploying the RAT. They've literally just left the ground and find themselves in a state where the plane is not climbing for a currently unkown reason. If you haven't thought to advance the thrust levers fully you definitely won't be looking up to the overhead panel to press deploy the ram air turbine during a critical phase of flight.