Posts about: "Switch Guards" [Posts: 87 Pages: 5]

As far as I know the flaps will stay where they are if hydraulic power is lost. There is an electrical over ride function as a back up but I doubt the crew would have used that as it's a guarded switch.

Two pieces of information have emerged in the last 24 hours which are, I think, indicative of where this will end up.

1. Pilot Comms reporting total loss of thrust
2. Survivor report of flickering green and white light

The first supports (and is supported by) the lack of apparent engine noise in the available videos

The second indicates an INTERMITTENT electrical fault of significant systems (emergency lighting being responsive to aircraft wide power issues and guarded in a way that IFE might not be)

[Speculation] Intermittent failure and transient loss/spike of current could overwhelm soft and hard controls against inappropriate engine cutout

Impossible. The switches are guarded. You need to pull them out to move them to Cutoff.

Exactly like the action of lifting the flap lever out of detent before moving it. What is significantly different is that you would have to do it twice. It is that which makes it improbable unless intentional.

Please read this thread first before asking a question, it has been answered several times.
Yes, the RAT will deploy automatically in the event of a loss of both AC Busses, both engines or all hydraulics.
It can be deployed manually via a guarded push button switch on the overhead panel.

Several hundred posts ago, a link to a PPrune thread re 787 RAT deployment was posted. I am sure everyone posting has at least seen if they have read the thread....

I apologise, if my thoughts have already been posted - please delete if this is the case, I cannot find them in the main thread though

None of us know if there was no engine failure, single engine failure or double engine failure.

If RAT was deployed, we do not yet know whether it was automatic or manually deployed by a very experienced captain because "We have no power. What harm can it do now?" (Electrical power, not thrust) Would the Captain also elect to start the APU in the few seconds he had?

In the thread re 787 RAT deployment, some one states that a single engine failure, due to the small rudder size on 787-8, automatically throttles back the remaining engine as the rudder will not be able to correct the course. I am not clear about the guards around this - be they height restrictions, speed restrictions or % of power delivery. If there are any guards in the software. It may have been stated and I missed it or didn't understand.

However, as someone involved with critical software design & development, if the generators were "playing up", which is highly possible given passenger observations on previous flights, could there be a window, if the aircraft experienced a problem with say no 1 engine ( suggested in video "analysis" despite the aircraft tracking right ) whereby the loss of electrical power triggered the software to "throttle back" No 2, and that again limiting any recovery of No 1, if the generators on 2 didn't perform/react as planned. Software always has holes.

The primary flight deck screens have battery backup - but do they lose power when the main buses go offline - and/or again when the RAT delivers? Or is it seemless? Previous posts mention both scenarios but with no answer. Are there flickers, resets, reboots? All distracting at best and time limiting at worst.

I think a pertinent point posted earlier, was that the problems seems to have begun with "gear up", a lot of load on the electrically driven, hydraulic pumps.
Seemingly started, but obviously not completed.

I believe the 2 guys sitting in row 0 dealing with this, were just passengers from the moment it left the gate - for whatever reason. The mayday call, by whichever pilot - although no transcript officially published - was probably a last ditch attempt to alert ATC asap to a situation with a clear outcome. Very sad. It is bad form to point the finger before any useful facts are confirmed.

So, I suspect generator problems & a hole in the software and/or logic due to timing issues caused by generators appearing to be on/offline -maybe rapidly - restricting thrust by design..

I saw earlier someone post about this and wondered how the drill would run and how/who performed memory items. On a past 4 jet type a double engine failure drill was done in the sim regularly and both had immediate actions as well as a number of confirmations but at least we still had two running😎. In this scenario of a twin jet where perhaps the PF noticed a major loss of thrust and called \x93Double engine failure drill\x94 would PNF confirm it then do the 2 switches and hit the guarded RAT button without identification and confirmation or is it whoever gets there first? Seems a free for all scramble would be a poor way to do it since latched and guarded switches could be operated incorrectly in a panic without deliberate and controlled movement backed up by confirmation of diagnosis and then the memory items?

Engineering function. You literally push the RAT guarded switch to on

As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch.
Very poor design. Would not pass `military-muster.`

They're guarded by the switch design/operation itself. To move one of them, the toggle handle has to first be pulled outward.

But what about whats inside and behind the switches? How is the signals from them transmitted to the valves? Analog? Digital? Software? They seem to be part of the same LRU, what does it look like on the inside? same multi-cable harness too? Same multi-connector? I believe this has not been touched upon.

Agree. The two most important controls in the aeroplane, sitting there in a wide-open, unprotected space. After an incident where a manual fell off the coaming (can't remember if a switch got bashed into the Off position), we put guards on our non-787 fuel switches:
Ours:

787:

The 787 fuel controls do have guards on each side but they're hard to see in the photo I posted. Here's a better angle:

Has this been discussed already?

https://ad.easa.europa.eu/blob/NM-18...SIB_NM-18-33_1

Does a Boeing 787 go from HOLD TO/GA to THR REF/VNAV SPD at 400' AGL/AAE, like older versions of the Boeing?

If so, what if the WoW stayed in ground mode, for whatever reason, how would that affect

1) Retraction of the landing gear (it didn't retract, as obvious in videos released)

2) The transition from HOLD to THR/REF at 400' (they reached just barely over 400' AGL before leveling, then descending)

I am also thinking that Air India would follow Boeing procedures in that the left seat pilot will move their right hand away from the thrust levers at V1, and thus, at 400', the thrust levers are not guarded or monitored?

Even if thrust levers were pushed forward, is there some kind of logic related to FMC and-or FADEC or other involved systems, which regardless of thrust lever position commands IDLE thrust to the engine?

Remember that Airbus accident where the aircraft thought it was landing, while the pilots wanted full thrust, and they crashed into a small forest because some kind of idle is all they were afforded by the system?

If the engines of this 787 thought it was in the rollout or final part of the flare, it might also command thrust levers to idle?

This does not explain the RAT, though, unless there is some weird combination of software working against each others logic.

Had the engines failed by some really random, odd reason, like birds, fuel contamination-vapor-starvation or such, wouldn't there be at least a slight bit of roll or yaw visible? Even with TAC or whatever they have on the 787, I would think even a 1 second difference in thrust reduction between the engines, a hint of yaw or roll should be visible ...

Thoughts, especially by someone who flies the 787?

Here we go again.
They are not "ground-only" levers, Why do you and MagPlug have this idea that the PF would not place their hand back on the thrust levers after the gear up call, or at least be guarding the throttles just in case, heaven forbid, they started to roll back?

That would be a stupid design. FYI, the old 787 FCOM I have says "Maximum rated thrust is available in any phase of flight by moving the thrust levers to the full forward positions".
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Irrelevant. They were doing a single-engine test and completely messed it up; nothing like what this crew would have been faced with. They were ta Idle because the captain pulled the TL back in an attempt to regain control. Nothing like you say.

I'd suggest not but the elephant in the room as far as you and Magplug goes... what are the pilots doing all this time? Just sitting there watching?

I agree to placing hands on, or behind to guard them, during many phases of flight. But when do your hands go back on the thrust levers after take-off, before 400' AGL? Would that be the left seat pilot, the PF or PM doing that?

It is noteworthy that the point that thrust is lost, is very close to 400' AGL, where at least on some other Boeing aircraft, HOLD changes to THR REF. It seems coincident with this height, the thrust is lost. And lost so closely, between the engines, that there seems to be neither yaw nor roll to see in the videos. Does the 787 have a system for asymmetric thrust, like the TAC on the 777? Even if it does, would the aircraft still not show at least a slight bit of yaw/roll before such a system kicked in, unless both engines lost thrust near simultaneously?

If all AC and DC was lost in an instant, then that would be within a split second for both engines, via the FSOVs, rendering FADEC powerless. If anything like birds, bad fuel, lack of fuel, vapour or all other things like that mentioned, the chances of no yaw seem only remotely possible.

Then there is the RAT and the landing gear.

Any indication from known videos as to what height the RAT comes on, around 400' AGL, or well before reaching 400' ?

15K hours, 5 companies, 7 types, JAA/FAA. All had something like "Below 2500' the PF will have hands on/guarding the flight controls" in the manual. Power/thrust levers/throttles are considered flight controls in this context. Vast majority opinion was that as soon as you were done rotating, and had asked for gear up, the PF would put their hand back on the thrust levers. I would think this would almost always be well before 400'. When I was on the 320 it would be about 50' because you only use one hand to rotate, now new on the 737 it takes (me) two hands and a bit longer to get rotation right, but probably almost always below 200'.

That's why Boeing put side guards on the panel.

precisely