Posts about: "Parameters" [Posts: 71 Pages: 4]

How horrible. From what has surfaced so far, it does appear that the aircraft became airborne and got to a reasonable height and groundspeed, within parameters for a normal takeoff. The video with RAT-like audio and the snapshot from another video showing hints of RAT deployment seem to be the biggest clues so far: flaps and gear are a minor issue compared with a serious power loss, although loss of electrical power would trigger the RAT if it uses the same logic on the 787 as earlier Boeings.

That you can hear the RAT on the video over what should be engines at takeoff thrust at that point adds credence to the theory, as does reports of a MAYDAY.

The audio is not great and kind of whiny. Even at the end when the crash happens, it does not sound robust.

Likely: this is not the RAT sound; it is just poor audio pickup.

Wow love the theories. Ok why was the gear still down. Under all circumstances that comes up with positive rate. Can\x92t see the flaps but sure looks like they were retracted instead of gear coming up.

engine failure. Sure that would suck lift out but all parameters take thay into effect with the proper flap setting. And you can\x92t take off without the right flap setting per the performance data unless you ignore it.

Loss of lift. VNAV engages at 400 ft and targets airspeed in MCP.

Airboard, do you fly the 787?

I understand that the FDR has been recovered from the crashed 787.
Could anyone tell me how many engine parameters are recorded and what is the sample rate.
Thank you.

What will that give you?

Most likely anything between 256 and 1024wps, individual parameters will vary with regards sample rate. Not au-fait with 787 but other Boeing aircraft may have dataframes relative to the original owner requirements (though this is unlikely to vary much given my experience with Boeing aircraft). I\x92m not sure if GE have a real time EHM feed like RR? Anyhow, and not wanting to speculate too much, if there was anything engine related it would certainly show up on the DFDR and GE could possibly even know that by now if they are equipped with real time health monitoring. In my opinion, for what it\x92s worth, the CCTV footage is consistent with flap retraction instead of gear, something that would also be easily identifiable upon review of the FDR which will be reported upon in due course.

Not yet seen a response to my question about which engine parameters are recommended by the FDR and what is the sample rate.
Hopefully you might be able to answer this.
Many thanks.
I am a retired gas turbine engineer who worked on safety systems and assessments and assisted on a number of accident investigations (military fast jets) and would be interested to know this.

I can't tell you off the top of my head. I was an engineer at final assembly (mostly final body join and functional testing) and then did support for airlines post delivery (working with their engineering teams on maintenance and operation) so I wasn't intimately involved in anything data wise on the FDR. My personal belief is that it should end up being glaringly obvious why the engines stopped working with the data they have, just to many coincidences happening at literally the exact same time for it to be some minuscule problem never envisioned before. Pretty sure FDR and CVR will tell all.

OK, another hour spent going through all the posts since I was on last night...
I won't quote the relevant posts as they go back ~15 pages, but a few more comments:

TAT errors affecting N1 power set: The FADEC logic (BTW, this is pretty much common on all Boeing FADEC) will use aircraft TAT if it agrees with the dedicated engine inlet temp probe - but if they differ it will use the engine probe . The GE inlet temp probe is relatively simple and unheated, so (unlike a heated probe) a blocked or contaminated probe will still read accurately - just with greater 'lag' to actual temperature changes.

TCMA - first off, I have to admit that this does look rather like an improper TCMA activation, but that is very, very unlikely. For those who don't know, TCMA is a system to shutdown a runaway engine that's not responding to the thrust lever - basic logic is an engine at high power with the thrust lever at/near idle, and the engine not decelerating. However, TCMA is only active on the ground (unfamiliar with the 787/GEnx TCMA air/ground logic - on the 747-8 we used 5 sources of air/ground - three Radio Altimeters and two Weight on Wheels - at least one of each had to indicate ground to enable TCMA). TCMA will shutdown the engine via the N2 overspeed protection - nearly instantaneous. For this to be TCMA, it would require at least two major failures - improper air ground indication or logic, and improper TCMA activation logic (completely separate software paths in the FADEC). Like I said, very, very unlikely.

Fuel contamination/filter blockage: The fuel filters have a bypass - if the delta P across the filter becomes excessive, the filter bypasses and provides the contaminated fuel to the engine. Now this contaminated fuel could easy foul up the fuel metering unit causing a flameout, but to happen to two engines at virtually the same time would be tremendous unlikely.

Auto Thrust thrust lever retard - the TO lockup in the logic makes this very unlikely (it won't unlock below (IIRC) 400 ft., and even that requires a separate pilot action such as a mode select change or thrust lever movement). And if it did somehow happen, all the pilot needs to do is push the levers back up.

Engine parameters on the FDR: I don't know what exactly is on the 787 FDR with regards to engine parameters, but rest assured that there is plenty of engine data that gets recorded - most at one/second. Getting the FDR readout from a modern FDR is almost an embarrassment of riches. Assuming the data is intact, we'll soon have a very good idea of what the engines were doing

The speed at which there was a complete loss of thrust and electrical power degrading to the point of flickering lights and RAT deployment suggests to me an actual engine shutdown rather than anything linked to auto thrust or fuel contamination. There are not many things which can cause an engine to shut down: LP valves, FADEC incl TCMA, crew action\x85

In my opinion ( and we all know the cliche about opinions ), there are only two plausible explanations.
1. Dual engine failure/damage due to multiple bird strikes somewhere immediately after V2 and liftoff.
Given the suddenness of the situation the gear could well have been overlooked by the PM who would be checking out the engine parameters only at this point in time. Flaps were in 5 position. No doubt about that.
Take off thrust used was for Optimum thrust
( meaning minimum thrust for take off given runway and environmental conditions ). That accounts for the full runway length being used. This is policy. That means minimum thrust used for take off to meet 2nd segment climb gradient at almost MTOW.
Loss of total thrust, RAT may or may not have deployed. At 650, AMSL no chance of any relight or turn back. Rest is history.
This also corresponds to the thud heard by the survivor about 30 seconds after takeoff.

2. Loss of thrust in only one engine and degraded performance in the other. Again, due to bird strike. Thereby not allowing even level flight.
Gear staying down could have been overlooked by mistake OR left down intentionally forseeing an impending ground contact by PIC and trying to minimize damage to his airplane.
Eitherways it added to additional drag and if anything, only accelerated the process of ground contact.
Given the above conditions safe flight would have been close to impossible. If not completely impossible. He neither had the airspeed not the altitude to make a 180 or even look for a safer place to put her down.
Refer the last Concorde flight/crash.

A very very sad day for aviation indeed \x85 🙏

Woulda shoulda coulda and might not have changed this particular outcome, but is there a case in taking off with APU ON? It would give some level of redundancy for electrics and hydraulics and perhaps avoid the added shock and workload of losing thrust, electrics and hydraulics pretty much simultaneously in a rare scenario like this one. During Hudson river accident, APU ON was the first thing Sully did (apart from saying \x91my aircraft\x92) but he had more altitude and speed and electrics and the gear up. I know there are other considerations for using or not using APU depending on flight phase, but if it is safe and within design parameters, perhaps SOPs should give pilots discretion on whether or not they use the APU for critical flight phases? Just a thought.

If it was a software fault or even strongly suspected there would be a worldwide 787 groundstop. Or at least a urgent engineering works package.
investigators on the ground likely know the cause already. Engine manufacturers also remotely monitor all engine parameters worldwide so they\x92d also know.

Good point.
GE already knows and so does Air India.
For the SLF, GE will call my employer and paraphrasing here: this airframe that engine needs attention because of the following.

Engine parameters are generally data linked in bursts. Usually every 30 minutes. If an engine parameter goes out of limits normally an alert will de sent immediately but in this case I doubt the alert would gave been sent before the power interruption. The black box will tell the story.

Yes, in one in a million (billion?) cases. If every take off and landing would be with the APU runing, there would be [some small number] of cases where the APU would shutdown at the critical moment causing electrics to reconfigure or the APU could shed a blade or catch a fire. Those events should not cause an accident, but then aircraft shouldn\x92t just fall out of the sky 30 seconds after lift off.

Furthernore mandating use of the APU would be quite hyppocratic, if reduced thrust take-offs, single engine taxi outs, landing with less than maximum available flap or other cost saving measures were still allowed.

About software (and TCMA). This a/c is in service around the world since some time. I understand that, for "something bad" to happen, then two independent conditions A and B must be (incorrectly) determined to be met. By now, rather than simply saying "very very unlikely", surely there Must be actual data of how often either A or B had been triggered (incorrectly). Not just for TCMA but any other feature with multiple protections. I would be curious to learn how the knowledge of the systems is actually improved with time, and how the 'Never' probabilities change (or not).

Regarding this TCMA, from what I think I understood, (A) would be some discrepancy between commanded thrust and actual thrust (and this requires calibration based on many engine and environmental parameters) and (B) would be the Aircraft on Ground. Maybe overly simplistic but roughly true?

777/787 driver here.

Reading a few posts about an APU-to-pack takeoff, or a packs off takeoff on a 787, because of the hot weather, makes me shake my head.
There is no bleed air on the 787. A packs off takeoff, or an apu to pack takeoff, is never done. There isn’t a procedure in the fcom to describe it. It is also pointless. The packs are electrical.

Then the gear.
When you lift off the runway, the gear doors open REGARDLESS of gear lever position. If you do not raise the gear within 30 seconds, the gear doors close again and you keep the gear down as you apparently desire. In the video, the gear doors are closed again as the airplane flies into the suburb. This requires normal hydraulics in system C, which was apprently available as the doors are closed again.

takeoff performance:
I entered all relevant weather parameters into my performance tool for Ahmedabad VAAH, rwy 23, 42 degrees C and no wind, qnh 1005.
It comes up with flaps 10 as optimum, albeit for a 787-9 (don’t have the possibility to calculate for the 787-8) But even the 787-9 is able to depart with flaps 5 in those conditions. Max tow around 230tons.

Isn\x92t the gear door feature exclusive to the -9 and -10 variants, not on the -8?