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

Aerospace101 post makes a good point about the gear tilt. When jacking an aircraft with hydraulics off the trucks will often self-rotate with the heavier end obviously going down. Since the 787 truck position actuator is on the forward end of the truck it is probable that is the heavier end therefore the truck is likely to rotate nose down without hydraulics.

Not to mention aerodynamic forces as well.

I originally was onboard with the truck tilt seen in the one video being proof that the gear handle was selected rather than the flap handle. But after watching several videos and an "endless" web search for info, I also have started to think that there was a problem before the gear handle was moved.

In a normal retraction, the main gear doors begin to open before the truck tilt is complete (roughly when the gear trucks are "level", seen around 8-10 second marks of this video ). The nose gear doors open at the same time the main gear tilt starts (seen in Jetstar video linked below). It's too blurry in the video/stills of the accident aircraft to definitively say the nose doors are not open, but I'd say no. And it's pretty much a certainty that the main gear doors are not open. And finally I think it is also pretty clear that the main gear trucks are tilted down to the retract position.

I have no confirmation of this, but I read (or heard someone say in a video) that the truck tilt actuator was a "single acting" actuator, meaning hydraulic pressure held it in the toe up position and it was spring loaded to the retract position. Which means if hydraulic pressure was lost due to loss of power to the electric driven center hydraulic system, then the main gear trucks would tilt forward on their own without moving the gear handle. The Jetstar burst tire video somewhat backs this up, in that the blown tire caused a leak to the center hydraulic system and an alternate extension was required (thus the reason the main doors are down during the landing). No hydraulic pressure means the main gear trucks remained pointing nose down during the landing. Video here

The doors on a 788 don't open prior to tilt. The gear doors open for 30 seconds automatically after takeoff on the 789 and 78-10 in anticipation of selecting gear up, but not the 788.

There are eight air ground sensors. Two truck tilt sensors and two strut compression sensors on each main gear.

Thanks. Do we know that these are monitored by TCMA for air/ground state and if so, do we know the logic used to make a determination based on those inputs? Alternatively, do you know where we should be looking for those answers?

If a gear retraction remains in "tilt", then what does that interregnum status say in response to various systems' interrogations of the WoW sensors? Is it stuck in the Netherworld of betwixt and between ?
Perhaps the safer solution should be an additional circuitry micro-switch feed of all three "up and locked"? (that agrees with the gear-handle).
Also waiting to hear what the 787-8 RADALT status is? Was it ever 5G emanations-proofed?
Is there any software provision for the TCMA to know for sure that the gear is neither up nor down? I would doubt it. Does that uncertainty affect the thrust-lever's positional input?

Are you saying that the RAT cannot power retraction of the gear, neither via its own hydraulic pump nor via its generator providing power to the centre system pumps?

Or could it be that it's capable of delivering enough power (via either route) to move the tilt actuator but not a humungous retraction jack?

If the 787 is not different to all other aircaft, the WoW senses and putouts only one parameter that is always 1 or 0. There is no netherlands in between. The physical motion the switch is sensing migh have not reach it other end at the time the switch changes its output, but it is irrevelant. If there is a requirement to know that the motion has reaches it\x92s other end, another switch (or other type of sensor) is needed.

Using up and locked as signal to prevent TCMA activation is obviously more dangerous as it allows TCMA to function while the aircraft is in the air.

Even in the same aircraft there might be different logics to determin if the aicraft is on the ground or in the air, depending what is the priority. Is the priority to know that the aircraft is in the air or on the ground or even NOT in the air. Some of those logics could use up-and-locked sensors and the gear handle position.

The RAT provides hydraulic power only to the flight control portion of the C hydraulics. Wing and tail flight controls only. Non return valves prevent power to other C hydraulic powered systems like the gear.

The RAT provides electrical power only to critical flight instrumentation (mostly Captains), navigation and communication. The same critical equipment that the Battery will provide. If all electrics was lost, the main Battery would provides standby power until RAT is fully deployed. The RAT electrical power would not be able to power C hydraulic electric pumps.

How does this explain the unusual forward tilt of the gear trucks as seen in the roof top video?

I appreciate some don\x92t want to speculate on the RAT deployment or APU auto start until further evidence, but the gear truck tilt is a massive clue to a non-normal hydraulic issue, most likely caused by electrical power problems since C hydraulics is only electric pump powered.

If power was lost at the moment gear was selected ‘up’ it would have started the process only for it to stop, hence why the forward tilt was present - perhaps

That is one conclusion (which I now suggest is unlikely), because you are assuming:

1. The hydraulic failure happened exactly when the truck had tilted forward but the split-second before the gear doors could open. That exact timing seems too coincidental.
2. The crew selected Gear Up. We have no proof of this. I speculate the crew never got as far as "Positive Rate...Gear Up" because they were already engrossed in flying the aircraft and processing their thrust problem. If an electrical problem had developed (as evidenced by the RAT deployment) the flight instrumentation would have been flickering and a flurry of silent master caution alerts would be very distracting.

I suggest it's more likely that the truck remained in a forward tilt from the takeoff run because the hydraulic failure happened prior to rotation, therefore keeping it in this unusual position. This answer does not rely on the gear lever position either. It also insinuates that their hydraulic problems occurred probably between V1 and VR. See my earlier post .

yeah the low MCP alt setting/alt capture doesn\x92t make a whole lot of sense- the plane didn\x92t pitch forward it just failed to climb/lost lift

that\x92s not conducive with what happened nor does it explain why the gear is still down (although seemingly selected up given the boogie tilt) or the RAT deployed (if it really was)

I still consider the forward truck tilt is a massive clue to a C system Hydraulic failure prior to wheels-up, which must have been caused by loss of electrics (since C is solely electrically powered), so I am still wondering if hydraulic failure happened before or after the loss of thrust.

While thinking about the consequences of a total hydraulics failure around time of rotation (caused by a suspected dual engine failure), here is a new observation. I searched the previous threads to see if anyone lese had noticed it.





In the rooftop video, as it's just approaching the treeline, there are spoiler deflections visible just behind the engines on each wing.

With a total hydraulics failure, the pilots control column using direct wiring, will only control this spoiler pair and the stabiliser. The RAT does not control this spoiler pair (hydraulically), only the most inboard spoilers pair. Its an interesting observation because it means this spoiler pair were being deflected electrically, either by the battery or RAT. But if the RAT provides emergency C hydraulic power why didn't the RAT powered spoilers deflect instead? Does this mean the RAT was unable to provide emergency hydraulic at such low airspeed?

I think this also re-affirms the critical loss of power (dual engine failure), and rules out many other theories. It tragically lost all power, both engines, all hydraulics and electrics (apart from battery and RAT).

I am wondering if anyone else has noticed other flight control deflections?

(Tried posting link to youtube but unhelpfully frames entire video)

The 787-8 landing gear retraction is primarily hydraulic, using the center hydraulic system for the main operation. However, the alternate gear extension system utilizes a dedicated electric pump to pressurize fluid from the center hydraulic system for gear extension. Obviously due its size and weight and staged retraction, the effort required to raise and stow the gear greatly exceeds that required for extension.

The main gear retraction/extension is controlled by the center hydraulic system.

It is apparent that the hydraulics failed when the engines shut down after breaking the down-locks and leaving the Main Landing gear bogeys in the tilt position, ready for a next step internal stowage and door closure (that was now never to happen). It is therefore apparent that the dual engine failure and consequent automated RAT extension was precipitated by this gear selection or retraction cycle and thus likely to be either WoW micro-switch or 5G Radar altimeter-effect associated. Due to accumulator depletion, the electric pump load would have spiked to replenish it. This may have precipitated the dual engine shutdown due to an unfiltered electrical surge affecting the Ground/Air microswitches (or a local 5G transmission affecting the RADALT) and resetting the TCMA.

The RADALT? Another plausibility? Because of the furore over a spasticated frequency allocation by the US FCC, the US FAA had finally “bought in” and declared that individual nations and their airline operators were responsible for their own 5G frequency spectrum allocations and for taking essential steps to ensure mitigation of the interference effects upon aircraft automated landings and other critical systems caused by their own national approved 5G spectrum decisions. It was admittedly a situation calling for extensive modifications to (and shielding for) the three radar altimeters fitted for redundancy considerations to all modern airliners... for Category 3 ILS approach and landing in zero/zero visibility conditions. The RADALT also features in many air-ground sensing applications. (eg the 747-8).

This was an unusual FAA “passing of the buck” to manufacturers such as Honeywell etc. (to sort out with client operators). But then again, it was not the US FCC’s right to dictate the specific 5G frequencies internationally. These spectrum allocations now vary over the wide selection of 5G phones available (and also nationally). 5G Radar Altimeters constitute a part of the ground/Air sensing that changes the TCMA from ground mode (able to fuel-chop engines) to the air mode (inhibited from doing so)... Ground activation is acceptable ...where fuel chopping of uncommanded thrust can prevent runway sideways excursions or runway length overruns. The question now becomes: “Is it more (or less) safe having an automated fuel-chopping capability on BOTH your left and right, rather than leaving it to the pilot to react via his center console fuel cut-off switches... in the unlikely event of a runaway engine after landing (or during an abandoned take-off)?

5G Frequency Variations

The frequencies of 5G phones vary nationally based on the frequency bands allocated and used by different carriers in each country. In the United States, for example, carriers such as AT&T, Verizon, T-Mobile, and others use a combination of low-band, mid-band, and high-band 5G frequencies. Low-band 5G frequencies typically range from 600 MHz to 1 GHz, mid-band 5G frequencies range from 1.7 GHz to 2.5 GHz, and high-band 5G (mmWave) frequencies start at 24 GHz and go up to 40 GHz . These frequencies are allocated by regulatory bodies such as the Federal Communications Commission (FCC) and can vary between countries based on spectrum availability and regulatory decisions. In other countries, the specific frequency bands used for 5G may differ, leading to variations in the frequencies supported by 5G phones. Additionally, the deployment of 5G networks can also influence the frequencies used, with some countries focusing more on sub-6 GHz bands while others prioritize mmWave technology.

5G interference? It may be an avenue worth exploring?

I too watched his explanation with interest. However I believe he is not considering the possibility of C hydraulics failure prior to wheels lift-off, because I speculated this is the more likely reason the gear trucks remained in a forward tilt position, see my earlier post here . I believe the crew never got as far as calling for the Gear Up... many possible reasons for this, flickering instrument screens during the electrical switchover to battery power, flurry of EICAS messages. For any of those things happening around time of rotation, I would be advocating delaying gear up decision until safely climbing away above AA and as a crew you have chance to discuss safest course of action. Not putting the gear up shouldn't kill you.

Point is the gear truck tilt is a clue of a C hydraulics failure, but we cant determine if hydraulics failed prior to wheels off runway or prior to gear doors opening in retraction sequence.

Presumably the RAT was deployed (with an "humungous" bang) when the residual pressure in the "C" hydraulic system decayed to zero: there was initially enough to tilt the trucks but thats it.

In a video of a 787 gear swing on jacks the trucks start moving to the nose down tilt position at the same time as the door starts to open so if the door did not open it is unlikely the gear was selected up and the truck tilt was more likely a result of C system failure. The front end of the truck is the heavier end because of the truck position actuator location so along with air loads, a nose down position is the result.

Loss of only C hydraulics is not enough to auto deploy the RAT.