Posts about: "MLG Tilt" [Posts: 76 Pages: 4]

I'm sure it's not the case, but if an attempt was made to raise the gear with the pins still fitted, you would see the main gear doors open as part of the normal gear retraction sequence.

This applies equally to a normal gear retraction: the centre hydraulic pumps must have stopped very early for the trucks to be in that position on an "interrupted" gear retraction, with the main gear doors still closed (and presumably locked). Seems unlikely.

The tilt and stow positions are definite hydraulically achieved positions of the truck positioner actuator. I don't think the actuator is spring-loaded to the stow position on the 787, though perhaps they move that way given my earlier statement...

Alternate extension appears to rely on the truck positioner remaining in its previously "positioned" state - stowed - where it has been sitting cold, unloved and unpowered since the gear was previously retracted. Like other Boeing types, the wheel well has some bars to stop the truck moving while it's up and stowed.

It's remotely possible the main gear priority valves may have prevented more gear movement in the absence of good hydraulic pressure - however this wouldn't stop the nose gear from operating, so not likely.

Well, could be that. Or...

Could be that the gear is quite clearly in the forward tilt position (indicating initial gear retraction has commenced), but then the gear never goes up. How does that occur? The gear in the 787 is driven in retraction by the center hydraulic system. How is the center hydraulic system powered? Electrically, via C1 and C2 EMP's. How are those EMP's supplied with power? Engine 1 and 2 (via a bootstrap from L1/2 R1/2 gens). The rat also connects to the center hydraulic system, but importantly, it does not supply hydraulic power to the gear. Only a select number of flight control surfaces.

So, my question to you is, given you're claiming there is zero evidence of electrical failure, how did the gear move into the forward tilt position, but then not retract?

Me too. Including the 787-8. Do you fly the 787-8?

I see the YouTube influencers are now shifting their speculation to the RAT deployment and loss of thrust theory.

we have to look at the limited evidence and stop
speculating on things that have no evidence yet (like the flaps). Aside from RAT deployment the other red flag here is the partial gear retraction. On the 787-8 the bogey will tilt forwards first, before gear doors opens. Not to be confused with the -9 and -10 variants where the gear doors automatically open after liftoff.
This is an important distinction because the Center hydraulics which is solely electrically pump driven (not engine) only had enough power to tilt the bogey, not open the doors.

so the question is, did the electrical failure (and loss of Center hydraulics power) happen before or after loss of thrust?

There was some debate earlier in the thread about whether the actuator was there to tilt the bogie or to untilt it. I don't recall that having been resolved, but I may be wrong.

I'm posting some YT-links to show that 787-9 gear doors indeed open on lift-off, while the -8 gear doors open only when gear up is actually selected. I also include links to a 787-8 and a -9 that keep their LG down after departure. The 8 doors are not opening. The 9 doors do open again regardless and indeed close again about 30 seconds after lift-off.

1. 787-8 LG retraction: boogies tilt forward, doors open, boogies tilt inward: 2. 787-9 LG retraction: doors open on lift-off, boogies tilt forward before inward: 3. 787-8 LG kept down: doors remain closed: 4. 787-9 LG kept down: doors open and close again about 30 secs after lift-off:

The caption seems to be in conflict with the video sequence. The caption, which may be all that is read/viewed, should be "bogies tilt, doors open, gear retracts.

Regarding the flashing green and white lights. On Airbus aircraft the emergency exit lights come on when the gear is down, and goes out when the gear is raised. Is this also the case on the 787?
if so, if the gear is/stays in transit (as the gear tilt may suggest) can this make the exit lights cycle on and off?
Just a thought.

Experienced 777 driver. Have tried to solve the puzzle. Looked carefully at the video in this article many times - see below and use full screen.

I might see a small puff of smoke and a smoke-ring just before they pass the shed. Indications of en enginefailure. I also see the wings tilt briefly - a few degrees - towards left. Correct procedure after enginefailure is to tilt the wings about 3 degrees toward the engine that is still running. I also see them climb at a - it seems - too high angle for the actual conditions if engine has failed. That will kill the nescessary engineoutspeed in a few seconds and be hard to recover from. If - and I say if - they in this stressed situation managed to shot down the wrong engine following the engineout procedures the RAT would come out. That would probably preoccupy them so much they forget everything about gear and flaps.. It is a situation I believe most experienced 777 / 787 pilots would recognise as a possibility and would explain everything. But this is pure speculation. Lets wait and see what the investigation teams find out...

https://www.aerotime.aero/articles/a...w-so-far-crash

While you are still on the ground or on lift-off? In the air yes, to be able to use slightly less rudder but not while on the ground.

Who would start the engine out procedure at just 100-200ft AGL? No airline teaches that and it doesn't have any advantage. You would only get the gear up. The shutdown can wait until at least 400ft AGL and once in a stable OEI climb.

Also there is no asymmetry visible in any of the videos.

Every airline training course I have had stressed never touching a critical item below 400 feet. That was later changed to 1000 feet at my airline. . I can\x92t conceive of the crew shutting a engine down in the first 8 seconds of flight.

According to the MMEL available on the FAA website there are 8 air/ground sensors on the main gear. Two tilt sensors and two compression sensors on each strut. Can be dispatched with just one tilt sensor and one compression sensor working on each side.

@T28, sorry, I wasn't questioning the "experience" of Seven-Five, I was questioning his comment about doing (and messing up) the engine failure drills with the jet barely of the ground, as if it was SOP for him or his operation. That's crazy. As for an experienced airline referring to bank angle as "tilt", I'll say no more!

Increasingly, the posts in this thread are becoming more ridiculous as time goes on. The hampsterwheel bearings will soon explode. IMO it should be locked.

What if I were to tell you that I think that our esteemed colleague isn't a native English speaker, as you and I are?
(I raise this point based on what's in the profile).
Would that change your desire to engage in a bit of eye gouging of over that particuar detail?

Full disclosure: most of the posts you have offered in this long and painful thread have hit the "makes sense" threshold with me.

But you and I have not read the same thread.
I have had to read all of it.
You've only been exposed to some of it.

I am about out of patience with the mutual eye gouging bit (most of which has been scrubbed) but at the moment thread closure isn't in the offing.
SP closed it when it had run amok.
If it does so again, it will be doubtless be closed for a breather.
That's for the Mod/Admin team to assess.

"I might see a small puff of smoke and a smoke-ring just before they pass the shed."

I originally wondered about that ... until an old colleague sent me this short clip of a triple kicking up dust rotating in the same location

For your consideration: (20 second clip)

If you read the thread, you would know:

The RAT was almost certainly deployed. 4 different sources.
The Flaps were not retracted. Visible at the accident site plus many other sources agreeing they were indeed down.
APU will autostart when all engine power is lost. Potentially explaining why the inlet door was open or partially open at the accident site. Mentioned in several previous posts
On a 787-8, the main bogies tilt as the 1st action of the gear retract sequence. As stated in previous posts. I don't think this happens unless gear is selected up. So the conclusion was, gear was selected up. One caveat, IIRC, there was some discussion around a failure could have caused the bogies to tilt without Gear up being selected but I don't recall the outcome.
As for the Air France remark, un-necessary IMHO. Let's respect the crews please.

On item 1, the TCMA issue should have been fixed, it does fit the sort of issue that occurred here. TDRACER can talk to that, and has done in 2019 and again in post 792. As to flap auto retraction, the B787 like all Boeings has a gated flap lever, and the flaps are only able to move independent of the lever by flap load relief. That would not have caused a loss of thrust, and in this case it is evident that the event is a thrust loss not a CL loss.

On item 2, the video shows no asymmetry at any time, so there is only a symmetric failure of the engines possible. Back on a B747 classic, you could chop all 4 engines at the same time with one hand, on a B737, also, not so much on a B777 or B787. I would doubt that anyone used two hands to cut the fuel at screen height. Note, there was a B744 that lost one engine in cruise when a clip board fell off the coaming. Didn't happen twice, and it only happened to one engine.


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Neila83 is correct, the gear tilt pre retraction is rear wheels low, and at the commencement of the selection of the retraction cycle (generally), the first thing that happens is the inboard MLG doors start to open below the wheel well and then the bogie is driven to front wheels low. (There is also an option that the inboard gear doors start to open early as a result of WOW sensing to improve the SSL climb limit). [my bad, for the B788 Capt Bloggs informs us the gear door sequence is after the tilt, not before, the B789 has the before tilt, the option for the door open at rotate is separate]

The inboard doors do not appear to have opened in this case, yet, the gear is forward wheels down. This appears to be out of sequence. TD may have better knowledge on the options that exist with the B788, but this is not looking good at this time.

There is enough in the way of anomalies here to end up with regulatory action, and airlines themselves should/will be starting to pore over their systems and decide if they are comfortable with the airworthiness of the aircraft at this moment. A latent single point of failure is not a comfortable place to be. Inhibiting TCMA might be a good interim option, that system could have been negated by having the ATR ARM switches....(Both)... ARM deferred to the before takeoff checks. The EAFR recovery should result in action within the next 24-48 hours. Boeing needs to be getting their tiger teams warmed up, they can ill afford to have a latent system fault discovered that is not immediately responded to, and the general corporate response of "blame the pilots" is not likely to win any future orders.

I think we are about to have some really busy days for the OEM.


Not sure that Neila83 is that far off the mark at all.

Every airline training course I have had stressed never touching a critical item below 400 feet. That was later changed to 1000 feet at my airline. . I can\x92t conceive of the crew shutting a engine down in the first 8 seconds of flight.

"I might see a small puff of smoke and a smoke-ring just before they pass the shed."

I originally wondered about that ... until an old colleague sent me this short clip of a triple kicking up dust rotating in the same location

For your consideration: (20 second clip)

If you read the thread, you would know:

The RAT was almost certainly deployed. 4 different sources.
The Flaps were not retracted. Visible at the accident site plus many other sources agreeing they were indeed down.
APU will autostart when all engine power is lost. Potentially explaining why the inlet door was open or partially open at the accident site. Mentioned in several previous posts
On a 787-8, the main bogies tilt as the 1st action of the gear retract sequence. As stated in previous posts. I don't think this happens unless gear is selected up. So the conclusion was, gear was selected up. One caveat, IIRC, there was some discussion around a failure could have caused the bogies to tilt without Gear up being selected but I don't recall the outcome.
As for the Air France remark, un-necessary IMHO. Let's respect the crews please.

I previously speculated the forward truck tilt was proof the gear had been selected UP and the retraction sequence was interrupted.

I’m not so sure now and believe there is a different conclusion from this non-normal gear position.

In normal retraction sequence the gear doors open almost instantaneously after the forward truck tilt. It does seem coincidental the tilt was completed while no indication of the doors opening is visible on the rooftop video, which would suggest hydraulic failure at that exact moment; this precise timing of interruption in the retraction sequence feels unlikely. So is there a more likely answer for the forward truck tilt that does not involve movement of the gear lever?

I suspect it’s more likely that C hydraulics lost power prior to rotation, as a consequence the truck could not tilt rearward during rotation as it normally should. Therefore it’s probable it always stayed in a neutral or forward tilt position from the take off run until we see it in the rooftop video. If the gear was behaving normally, and the crew had omitted to retract, it should be hanging rearwards. Watch any 787-8 takeoff video and you can see at rotation all 4 main wheels stay on the runway as the aircraft rotates. Just after wheels up they tilt rearwards. It’s a very subtle position change.

If the gear was always in a neutral or forward truck tilt position then this undermines the theory that retraction sequence was interrupted. It insinuates the C hydraulic and electrical failure happened prior to main wheels lift off.

For this reason I believe we cannot assume that gear UP was selected nor that retraction was interrupted. I’m seeing lots of social media posts which suggest the forward tilt means gear was in retraction and I don’t believe it was now.

I think the truck tilt position is key to understanding the timeline of system failures and whether the automatic RAT deployment was triggered by power failures or engine(s) failure. The question remains, did loss of center hydraulics happen before or after loss of thrust?