Posts about: "RAT (All)" [Posts: 683 Pages: 35]

Non-aviation engineer here: I have a question about the low level altitude capture theory that I've been a bit hesitant to ask, since no-one else seemed to be bringing it up.

My understanding of altitude capture is that the autopilot will automatically adjust both thrust and pitch to intercept the requested altitude. However to my eyes there is very little pitch adjustment in the CCTV video of the plane taken from behind, until the very end of the video when it pitches up somewhat (obscured by buildings, more visible in the smartphone video). Please correct me if I'm wrong but I'd have thought that if the autopilot was trying to capture a very low altitude it would start pitching down (quite noticeably!) to do so, not remain at what looks like 10+ degrees nose-up. I honestly struggle to reconcile what I'm looking at in the video with an attempt to level off at 0ft, 200ft, or any of the other mentioned low-level altitudes.

Also maybe I'm missing something 787-specific but generally doesn't the autopilot have to be activated for the aircraft to automatically attempt to capture the pre-selected altitude? That was the case in this incident involving a Dash 8 and a target altitude of 0 feet that I am reading about ( https://www.gov.uk/aaib-reports/aaib...-dash-8-g-ecoe ). I'd have thought the PF would still be hand-flying the departure at the point that things went wrong, considering that the gear hadn't even been retracted yet...

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?

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.

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

100%. As pointed out many times, this accident just doesn\x92t fit with either performance errors, flap/gear mis-selection or inappropriate AP/AT modes. The flightpath was as expected until shortly after liftoff, then we see/hear RAT deployment and an unpowered descent into the ground. There are still plenty of possible reasons as to why this occurred but to date we can\x92t really narrow it down any more.

I wasn\x92t going to jump on the hamsterwheel, but\x85

Those takeoff FMA annunciations look similar to all previous Boeings and I think all of us would have slammed the thrust levers forward as soon as the speed and climb rate started decaying, where presumably they would have stayed in THR HOLD no matter what the TCMA/FADECs were doing?

Would \x93top of the amber band\x94 or equivalent have been less than RAT stall speed? If the RAT stalled as the speed decayed depriving the pilots of all control, that\x92s a horrible end. Those of us who have had to perform non-normal landings at least had a runway or clear area to aim for, and the means to do it. They didn\x92t.

Which perhaps explains why we\x92re all honouring the crew by trying to understand what happened, even with the stupidest posts about autopilots etc.

Jumping off the hamsterwheel now\x85

No, very unlikely the pilots lost all control. In a total power failure (hydraulics and electrics) the pilots can control roll (by a specific spoiler pair) and pitch through the stabiliser. All electrically powered through wiring direct to control column.

It's possible the RAT was not providing correct power in the last moments, remember RAT provides Hydraulic (C system flight controls only) and Electrics. The evidence is the spoiler pair deflection behind the engines prior to impact. See earlier post . . That specific spoiler pairing is only controlled by electrical power (directly connected to pilot control column). We should see other flight control deflections if the RAT was powering hydraulics. In the final moments I would speculate the flight controls had only emergency electric power from the battery.

I still think that the small black area is the back of the engines visible through the small gap of the extended flaps.

Furthermore: The small hydraulik pump of the RAT only powers some of the flight controls that are powered by the center hydraulic system. The ones powered by the engine driven pumps will not work once the engine(s) failed.

Engines generally deliver hydraulics while running down, as they operate down to a much lower speed than the generators do. Useful flight control power might be available from windmilling alone (hence why the 747 didn't have a RAT until the -8). That's subject to similar speed issues to the RAT but the engines have much more inertia. The Virgin Atlantic 024 report (A340 partial-gear-up landing at Heathrow) notes an expected 25-30 seconds of useful hydraulics after engine shutdown.

This doesn't apply if the pumps are depressurised by a fire handle, or to allow easier engine relight.

Very subjective, and I agree it it could look like a slotted gap between the wing and flaps, except the shadow is confined to exactly where that spoiler pair is located. You don't see it where the rest of the flap is. It would be good to hear other opinions about what we are seeing here . Is it wing, flap, gap or spoilers?


I don't understand your point here. The RAT hydraulic powers very specific flight controls like the stab, rudder, outboard ailerons and one specific pair of spoilers - the inboard most spoilers. Have a look at this schematic (at 3:55) youtu.be/DFbOLNduutI?si=siPnQ9oHMbLgp64K&t=235 (not publishing link as it fills the frame). The spoiler pair I mentioned above (visible in the video) are only powered by L hydraulics and electrical. Assuming L hydraulics was lost by dual engine failure, then this spoiler pair can only have been electrically powered...hence the conclusion it's either powered electrically by the Battery or electrically powered by the RAT. That spoiler pair is not connected to the RAT hydraulics.

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?

Well said thanks &
“A ram air turbine (RAT) pump converts mechanical input power into hydraulic power for the center system flight controls. The RAT is in the right, aft wing-to-body fairing.”

To make things clear, just check this B787-related alert service bulletin dated 25 Nov 2014 (my bold):



787 RAT hydraulic pump location

RAT types vary significantly by aircraft family. The 777 and 787 types (along with most BBD aircraft) are indeed dual hydraulic-electric (lifted from the 2010 FCOM available online):


Other types are different. The A350/A380 do have an electric-only RAT with adequate electric flight controls.

The A320/A330 have a hydraulic-only RAT with a separate hydraulic-driven electrical generator. The 757/767 are similar except the generator is optional.

Some used an electric RAT to drive an electric hydraulic pump.

Be careful when attempting to transfer knowledge from one type to another.

The RAT (unverified source):

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' ?

Has anybody the skill, knowledge, hands-on system familiarity or diagrammatic access to examine the
Ground/Air,
gear-handle,
gear doors
gear position lights
emergency extension,
Throttle lever position and
W.o.W. circuitry - in any sanguine detail?
What for? It could possibly reveal some abstract relationship flaw between microswitches, RadAlts, and/or even shock-strut extension or travelling gear or door position that allows for an effect dependent upon the high ambient temperature-dictated interrelationship?
Why ferret thusly? Many latent gremlins reside in complex circuitry. It is very hard to get away from the logical proposition that gear selection / travel (or possibly the earlier G/A transition) predicated the double flame-out and RAT deployment. The 787 was always ever described as an electric airplane and I see that as a harbinger - not of doom, but of inspiration.
I personally have never trusted electro-mechanical devices such as micro-switches... or for that matter, solenoid-operated relays. Or travelling further afield, those fiendish devices called circuit-breakers (thermal or otherwise). And a description of an RCD as a "safety switch" sends a shiver up my spine. They are really just a potential annoyance and an ongoing expense. As I have found again and again, their reliability and test functions are no guarantee of serviceability. A ceiling fire cured me of that fantasy.
You might also reflect deeply upon the following observation:
From the outset, this electric airplane had electrical issues. The Lithium Ion battery fires were never really resolved. They just re-housed it in a very stout titanium box - one that can only breathe a fiery breath overboard I believe... as if it was a slice of thorium always threatening to turn into lethal plutonium. The 787 designers convinced the regulator that their electric airplane could only become an industry steed if it had the power of such a battery. Unsure whether there's since been any ongoing issues (or if there had been, would it become a "known" event - now that this malignant potency has been robustly "contained"?). So what happens when a fire breaks out inside that titanium box and all its volts are discharged overboard? Are any battery-powered holding relays released at that point? i.e. is there a damning catch? Pandora's stout box may prove to be a gift-horse.

I haven't seen any videos, or heard of any, that might tell us when the RAT deployed. It was definitely below 400' AGL, because the airplane never got that high.

OK, enough quick, consecutive, posts from me for now. Off to do required chores.

If we accept that the RAT was deployed, then my understanding is that this would only occur if both engines were fully shutdown, not just reduced thrust or idle.

I have read most of the thread (old and new). As a lawyer working in forensic investigations, I am constantly involved in problem-solving. My field of work also includes complex investigations related to insolvencies, which almost always require an analysis of the causes behind a specific, established outcome. In doing so, I naturally also have to deal with probabilities. However, it often turns out that the most likely or plausible explanation does not reflect what actually happened.

Many of the considerations I’ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable.

With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought—and it was nothing more than that—was that their activation becomes more probable if it can occur accidentally. That’s how I came across SAIB: NM-18-33.

Another user then brought up an iPhone. That notion would, of course, be dramatic—but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the “Off” position. Due to the buttons on top of the switches, which provide some resistance, it’s even possible that the object both pulled and pushed them.

But all of this is speculation. The investigation report will bring clarity.

Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety—especially considering that the FCS are protected laterally by metal plates.