Posts about: "Gear Retraction" [Posts: 243 Pages: 13]

I agree with this. For all the SLF reading and not posting ( good work!) there is a delay between the end of the takeoff run and the gear being selected up. I fly 737’s so any 78 folk feel free to correct me but it looks like this;
PM: “ V1 ….Rotate”
The PF then begins to rotate the aircraft up to a pre determined attitude which is normally between 13 and 15 degrees. They do this at a rate of between 2 and 3 degrees per second so about 5 or 6 seconds later the aircraft is at its climb out attitude. The PM is then looking at their instruments to confirm that the aircraft has a positive rate of climb, this takes a moment, maybe 1 to 3 seconds then;
PM “ positive rate”
PF: “ gear up”.
So minimum 8 seconds but probably longer between the PM calling “rotate” and the gear being selected up.
The relevance of all that is to say that if you suspect that the gear up cycle has been interrupted by a dual engine failure, then the engines may well have been producing thrust up to an altitude of 50-100ft or so, which ties in nicely with the max height reached, distance travelled etc.
Mods this is clearly not a theory, just info for those who don’t fly airliners to aid understanding.

The landing gear is run off of the center hydraulic system which is pressurized by electric pumps. The left and right hydraulic systems run their respective thrust reversers and some flight controls, and that is it.

Thankyou I didn't know that and I'm not questioning you. I guess it doesn't matter electrically driven or engine driven, they cannot share the same power supply the gear must be retracted within 12 seconds. this in my opinion improves the argument for total electrical failure. Unless of course gear up was never selected..There must also have been a substantial loss of thrust on at least one engine.

Capn Bloggs We shall see!

A mate tried gear/flap scenario in the sim earlier. Selecting flaps up (all the way) instead of the gear did not predjudice the flight path at all. They selected flaps up at normal gear retraction height and punched the AP in. The Slats remained out until 225kts (as per my post about 50 pages ago) and the aircraft climbed happily away clearing all obstacle by a good margin.

Was that using the same aircraft weight, same flaps, same ambient temperature and with the same de-rate(s) as the accident flight? Presumably he had inside information to find the appropriate numbers?

I am a software engineer, I find it alarming that the power control unit had the ability to command all AC generator control units to effectively shut down - regardless of that being the side-effect of a bug, or an ability of the system to call on in appropriate scenarios.

Integer overflow is a specific type of issue common to many systems, but like you said - it is something that should be found with robust QA and analysis. The ability to shut down all generators at once from a single source seems like a risky design decision to me and I agree with your point about different software on 2 or more redundant sub systems.

My theory is that this was an accepted risk because the engine-driven fuel pumps would be more than enough in most phases of flight to keep the engines running, and you would still have 2 engines for redundancy. The APU would also restore AC power in lets say 30 seconds and you would then have electric fuel pumps as well.

I think there are several factors that could explain how loss of all AC power during takeoff could lead to a crash:

• The crash happened within 30 seconds - possibly too short for the APU to start, and the RAT doesn't power the AC electric fuel pumps
• The engine driven fuel pumps even if sufficient in level flight may have struggled during rotation - has Boeing tested an actual takeoff with only EDP feeding the engine while the fuel tanks are rotating and in extreme environments, or, have they only tested this statically?
• The takeoff was hot and heavy - combined with the landing gear stuck down and reduced thrust from loss of electric fuel pumps could this be enough?

can you ask him by any chance what the outcome would be with f15 or 20 speeds, but in a F5 config and a rotation at VrF15 ?
and retract the flaps to 1 instead of gear ?
sorry I don\x92t know if that has been tested already.

I need to correct one of my previous posts, I was going down the path of a mismanaged engine failure after V1, however it's been demonstrated to me that this aircraft will fly away on one engine even with the gear down with better than minimum climb gradient requirement. Quite astonishing actually.
That just leaves deliberate act not necessarily intentional, fuel vapour lock and automatically commanded engine shutdown.
I hope the rat is found soon so we know for sure if both engines were in fact lost.

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?

@ferry pilot and others who mentioned the seat back collapsing: That was from an entirely unrelated incident on Air India Express flight 611 in 2018 which got poorly rehashed / fakenewsed into a bogus theory over the last week. It was a 737. It did *not* happen on AI171.

For what it's worth, the AIX 611 story in 2018 involved a 737 captain's seat back being overtightened and suddenly collapsing backwards during the takeoff roll. He had been guarding the thrust levers and reflexively grabbed them when falling back, causing a thrust reduction from 98% N1 to 75% N1 or thereabouts. Control was immediately transferred to the other pilot but the inadvertent thrust change was not corrected immediately, and the plane took off a few seconds later with a tail strike, scraping the runway, flying through the localizer and demolishing part of the airport perimeter wall with its landing gear. During the climb, the flight crew ran several system checks and landing gear tests to reassure themselves the plane was fine, then proceeded with the flight, pressurizing the aircraft and whatnot. They evidently did not consult the tail strike procedure. Many hours later they were ordered by company to divert and land quickly after the damage was seen at the airport. After landing, the plane was found to have a fair bit of damage, including part of the perimeter wall's barbed wire fencing material wrapped around the landing gear. But zero injuries, and the plane was fixed and flew again.

It's an entertaining story because of the cause and the happy ending, but had nothing to do with AI171, for which we all await the preliminary report.

Very interesting. Pal of mine used to fly. Caught up with him last night over text. This is what he said:

\x93An aircraft can be in service for many years before supposedly 'random' failures are discovered. We had a 747-400 departing JNB many years ago, and during the take off roll, the inboard leading edge flaps (flaps on the Jumbo, not slats) retracted. The only indication of this was the flaps secondary display popping up and crosses appearing over the inboard LE flaps. No Master Caution, no warnings of any kind. Apparently the system was working exactly as 'designed\x92!

During the landing roll, when Reverse is selected, the inboard LE flaps automatically retract, to avoid damage from any debris blown up by the effect of the reverse thrust.

In this take off scenario, due to maintenance work being carried out earlier in the day, the aircraft thought the reversers had been selected, and 'correctly' retracted the flaps. At rotation, the stick shaker activated, and the aircraft struggled to get airborne. The passengers got lucky, as the First Officer, who was Pilot Handling, was an experienced aerobatic pilot, and was able to keep the aircraft airborne, flying in heavy buffet and with the stick shaker activated until the air-ground logic finally caught up after gear retraction, and the LE flaps deployed again.

Not something that most regular guys would cope with, particularly at night, with no outside horizon for reference. Pilots who\x92ve operated around Africa will know what I'm talking about.

They dumped fuel and returned to JNB.
This happened on May 11th 2009 (Google it) - just how long had the Jumbo, of all variants, been in service before this 'glitch' was discovered?

The actual issue was that during the earlier maintenance, the engineers had cycled the thrust levers, with the engines off, all the way through the reverse gates, and back again (the aircraft had arrived earlier that day, and a reverser had failed to deploy). What no one knew, was that the action of moving the thrust levers through the reverse gate, would latch a bit of software logic in one of the computers on board, causing a near catastrophic sequence of events.

We all know and love the Jim Reason Swiss cheese model - I suspect we're going to discover some previously unknown holes.\x94

I find it rather a coincidence that this aircraft had so many electrical problems, had, not been retrofitted to solve one electrical issues like all 787s in the US had, and suffered what appears to be some kind of electrical failure.

I recommend that everyone look at the video posted by Sawbones62 in this post . The video (Stig Shift #76) is by a qualified B787 engineer and he looks at the various aircraft systems that are being discussed in the Air India accident. With respect to the landing gear, he concludes that the landing gear handle must have been selected up for the bogies to have been tilted front down.

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.

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?

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 hope/wish. I accept that it's not at all likely that TCMA is the/a culprit in this crash, but it is, like the cutoff switches, one of the few things designed and intended to shut down an engine in a very big hurry. It would be good to know as much as possible about how it determines the aircraft's ground/air state.

And add the radio altimeter(s). I think, but don't know, that they provide inputs to the FADEC TCMA function also.

SLF but: I still really don't understand how this is supposed to happen, not merely hypothetically, but congruently with how short and low the flight we can actually see is.

My understanding (and others have corroborated this) is that in a standard departure the autothrottle is armed and starts the takeoff roll in THR REF mode. It goes into HOLD mode when the IAS passes 80 knots (obviously still on the ground). While it is in HOLD mode, the autothrottle is physically inhibited from moving the thrust levers. It then automatically re-engages at 400ft AGL (though I am not sure how the altitude is measured), and begins to operate as requested by various human and computer systems.

If something about my explanation is wrong, please let me know - but if it is correct, then how would the autothrottle roll back thrust drastically in what looks like the first few seconds of the flight? I do understand that what you describe is how the autothrottle would behave when it is active, but it sounds to me like it is by design not supposed to actually be active during the critical time that we are looking at no matter what automations are armed to be activated once the aircraft is safely away from the ground. Unless the crew did something to cause it to engage - and I'm not sure what that would even be. What would they plausibly be doing before even retracting the landing gear?

My only guess was that depending on how the altitude is measured to determine whether the 400ft gate has been passed (radio altimeter? pressure altitude?), the autothrottle might have come out of HOLD mode (along with VNAV if armed) at a lower altitude than it was supposed to due to some mechanical fault or crew error. But that's already a bigger kettle of fish than just altitude capture...