Posts by user "fdr" [Posts: 33 Total up-votes: 201 Pages: 2]

Adding to your response TD, there is no time in this event where a high AOA arose prior to the final moments, around 13 seconds after the problem has occurred. AOA, intake separation is not a factor.

Going back to your prior comments on FADEC and TCMA; these are independent systems to each engine, however the event indicates a symmetric loss, and the potential of water ingress from a failed E/E sealing from the main cabin services remains a single causation that could result in multiple failures at the same moment. The last time I assessed issues in the E/E bay related to unauthorised inflight access to the fwd E/E of a B777 it was sobering how many irreversible conditions could arise. The B744 water inundation cases I was involved in were both on TO, the QF event was during deceleration. We are looking at vectors that come from outside of the normal assumptions in the SSA's, water fits that bill.

Insufficient data. There is cooling in the bay and that can be affected by aircon problems. High humidity and temp can lead to moisture in the area, however, the events I had involvement with were massive amounts of water from various sources. One was a failure from the toilet system, and the other was related to cargo loaded on the main deck via the NCD, and that had pallets that had turned into swimming pools that made a fashion statement when rotated. The QF event was similar, water accumulated in a damaged barrier.

Yes.
1250m from the end of the runway, between high speed C and D, adjacent to the closed high speed.
There is nothing unusual with the rate of acceleration that is observable ninth video. You can work that out using google earth and the Indian AIP and/or state airport charts. The weight of the plane can be estimated by the flight time and pax load and an allowance for cargo. The simplified TO performance is in the inflight performance section of the FCOM, which you may find a copy on line.
The aircrafts rotation has no obvious issues, until a few seconds after achieving an attitude that is consistent with the V2+15-25 range, at which point the ROC visibly starts to decay.

True, I would bet that the voltage regulating architecture of the voice recorder at least will give useful information for a short time around the loss of power, as it did for the Lockerbie CVR using far less sophisticated recorder systems. That was sufficient to show the pressure pulse in the fuselage and to give a fairly good idea of where the explosion had emanated from. TWA was similar, a bigger bang though. Would be listening for any mechanical noises related to the fuel switches, and frankly I doubt that they existed, but they would be recorded.

If the cause is what I have suggested it will dificult to get direct evidence of that case, as it was for the QFA072 event as well. Like icing cases, a water ingress into the avionics is going to be a tough investigation, water would have been sprayed all over the wreckage in the aftermath. Dousing the E/E bay with 20 or 30 gallons of water will be an expensive investigative exercise to do in a real plane, with engines running. Would not want to be observing up close.

Views from outside the box will likely be worthwhile in this case.

Re E/E environmental, no sensors incorporated, and they probably would not help in the type of problem that I have concerns with. The crew get an idea of a problem as multiple systems fail at the same time from water inundation. This is way outside of the DO-160-G requirements taht the electronics are certified to. Pouring a kiddy pool worth of water that is sitting above the bay in the moisture barrier awaiting a suitable opportunity to become evident is outside of expected behaviour, but has happened at least 3 times with major impacts on other aircraft.

Pooled water around the moisture barrier is just looking for a suitable access point to drain into. The 3 events I am aware of in the B744 were all during manoeuvring, 2 at rotate and one during a descending turn.


PBL is a globally recognised authority on complex faults, and his teams papers are great reading. He is also associated with the Functional Resonance work from Erik Hollnagel. FRAM does not reduce the workload for SMS managers, but it has the potential to increase the reliability through understanding how our systems work. PBL W-B analysis is elegantly simple but gives complex system understanding in a logical manner.

...Yet...

The state is not yet required to report more than the preliminary report IAW Annex 13, however, the observations that are readily available to the investigators and the OEM teams will not be conducive to good nights sleep by any of them.

The regulator is not in a position to make an EAD or other airworthiness directive without a justifiable basis, and the very fact this is suggestive of a failure mode that is catastrophic, even though obviously low probability doesn't permit the risk to be accepted. With the system architecture on the B787, if viewed as a Bayesian assessment, the highest probability remains an environmental item outside of the design as approved. The problem with that area as we have seen before, it is very difficult to prove events with icing (Roselawn etc) or moisture ingress in most cases, it will likely require a forensic teardown of the control systems of the engine to determine what damage may have occurred before impact. That is a daunting proposition when the area involved has been at the center of the impact and post impact fire. I have more confidence in the systems engineers and software than the ability to maintain an environment that does not cause adverse outcomes.

Crossky, welcome to this hamster wheel.

If you go and chat to the engineers, have a look in the IPC or MM I Ch 28, you should find a good description of the fuel boost pumps. It's been a while but I recall they are Eaton designs, the general arrangement is similar to the B777. They both have a suction feed that permits fuel feed in the event of a loss of all boost pumps. The only impact of that arises at high altitude and high thrust levels, where the engine driven fuel boost pumps may capitate and reduce the available fuel feed resulting in a lower thrust level.

Refer page 12.20.02 in the TBC's B787 FCTM, or search for "SUCTION FEED".

At sea level, full thrust will be achieved without any boost pump on the aircraft. Recall that the CWT boost pumps are known as Override boost pumps, they are feeding from the CWT when there is fuel and they are running, as the output pressure is higher from these pumps than the 2 wing boost pumps. Whether there is fuel in the CWT or not, or the CWT pumps are energised, is immaterial to whether fuel will be supplied to the engine driven fuel pumps.

Note that with BA038, the fundamental problem was blockage of wax/ice formed in the piping that blocked the FOHE, and that will cause a problem with those engines that have such architecture, but is not associated with the availability of the boost pumps themselves. Even then, the engines did not technically fail, as they have both done simultaneously with the B788 of AI 171, BA's engines were running but not able to provide significant thrust due to the FOHE blockages.

The available video and trajectory information are quite conclusive that both engines stopped producing thrust within 12 seconds of the main wheels leaving the ground. Had partial power of any level remained, the aircraft impact would have been further away from the departure end of the runway. The NE end camera shows by using transit sightings against identifiable structures, that the failure occurred while the aircraft was still within the airport boundary area. The energy state of the aircraft at that time trades off to impact at the correct time and place.

On departure at these weights the aircraft would have some assumed temperature thrust reduction from max available on the GEnx -1B70, Unless they were carrying lead, they were around 30,000 or more below the limit weight for a flaps 5 TO. At that weight, around 440k lbs, they would have had a fair OEI climb gradient on one engine, certainly a positive gradient with the gear down, so they lost more than 50% of total thrust. There is no yaw or roll, or inputs to counter a yaw or roll moment so the aircraft was symmetrical at all times, that means losing absolutely no less than 50% of total available thrust at that point on each engine. At 50% reduction. the aircraft would have continued a positive gradient with the gear down and the flaps at the TO setting. It did not, it decelerated at around 1meter sec, or 0.1g deceleration for just maintaining level flight, but it also had to descend and that was worth around 0.05g as well. Instead of having any positive thrust margin, the guys were needing to descend to balance the decrement in thrust of around 0.15g, and that means it has negligible to no thrust from the engines. The full analysis takes more effort as the AOA has increased over the 15-20 seconds to impact, which is increasing the drag of the aircraft rapidly towards the end. For the first 5-10 seconds however, it is not such a great change, but it is still increasing.

In level flight, the aircraft would accelerate level at around 0.3-0.4g gear down with both engines running at max chuff. Lose one, and you are back to 0.05-0.1g or so. These guys had far less than one engine remaining, gravity was all that they had going for them.

To that end, there is no requirement to have the EAFR readout of the N1, N2, FF, or EGT, the video shows they had no puff going worth a darn. That is basic back of the envelope physics and anyone who does aircraft performance testing would be able to get that answer straight from the video without using a calculator, by the time they had watched the video a couple of times in replay.

I have no qualms on stating that the engines are not operating, the RAT, gear tilt are consistent with the dynamics of the aircraft. This is far simpler to determine the energy state than that of the B738W at Muan, the lack of early video required a couple of iterations of the kinetic energy of the aircraft at Muan to end up with a probable flight path, and most likely estimate of the thrust remaining for those most unfortunate souls.

regards,


FDR

The first B744 flood event in the E&E was 25 years into the operation with one airline, and the other 2 occurred over 30 years into the operation of the type, one was uniquely a cargo loading event, and how the OEM would have guessed that some carrier would enter a wading pool worth of rain water into the E&E, they had and have my sympathy. We took action after that to avoid a repetition, but it wasn't on the radar before it ended up with a bit of excitement for the crew. They happened to have a nice clear evening when the whole cockpit went darl. The B787 has a AD out since 2016 which was added to last year related to unwanted leaks. My own event with a B777 ended up with over 6 cubic meters of ice in the belly of the B773ER, and was only found doing a walk around where there was a number of the belly drains drooling onto the ramp, which happened to be dry. An event external to the system architecture remains a high probability, and as unusual as that may be it is not without precedent, with existing AD's related to such matters extant.

When pax flush clothing and other rubbish down a vacuum toilet system, the potential for stuff to not work as advertised is not zero.

However, a roll back on its own to idle would not give the evidenced gear behaviour nor the RAT (I happen to concur that the RAT was deployed and probably automatically). Given the gear tilt, it is safe to assume no engine is at idle, the normal electrical systems are not functioning at all.

Elmer Fudd (an alternative spelling of "PhD") by all accounts knows a thing or two about a thing or two, aerodynamics of ducks, and ballistics, at the 12-Ga, birdshot level at least. That is a step above GT.

1. There is zero reason for the engines to have to be DOA before rotate. A point of note will be a close look at the elevator deflection at rotate, and that alone would put paid to such a position.
2. The engines being lost shortly after rotate is consistent with the video from the NE met sensor camera.
3. Determining the liftoff point by ADSB without adding a correction for the flow change at the PS sensor due to AOA is going to give nonsense, and that appears to be the case. The video gives a fair, not brilliant geometry to shoot a transit sighting of the aircraft at liftoff, and that is before the point that GT states.
4. I am impressed that GT has the deceleration rates for a B787 gear down, flaps at 5, for zero thrust. I know what it is for gear up, gear down, not so much, but it will be on the prompt side of ugly.
5. Undertaking an MLE estimate of the kinematics, do add the change for AOA if assuming a deceleration rate. You can get away with a rough overall estimate, but then lets not "gild the Lilly" by assuming accuracy at the decimal point level.
6. Every sensor has measurement errors, position errors, and granularity factors when converting to an output, accuracy to multiple decimal points just looks tacky.
7. The weight of the aircraft, if it is within +/-2% of the actual is doing pretty well, we have analysed baby puppy FAA aircraft that alter their actual weight by over 6% depending on whether they are using EASA weights for PLD, or FAA, or maybe the aircraft just happen to suffer from Coriolis.
8. GT's heart is in the right place, I don't agree with much of what he says, but then my wife doesn't agree with me often either, so maybe that is inconclusive.

We remain in the same holding pattern with a curious event that was recorded in daylight, and from which the recorders are recovered. The answers will start "flowing" "short"ly I guess.

For the past 30 years, we have collectively bagged Boeing in increasing measure, for doing what all corporations are obliged to do; the board is answerable to the investors, and the investors have a "10-second Tom" event horizon when it comes to their earnings. It is little wonder that the race to the bottom is being won by Boeing, it is what Wall Street demands, and in the end, after the bones of the OEM are picked clean by those that do such things on the carcasses of once great US engineering giants, then they will bitch and moan about the losses to shareholders while they pocket the profit of their profession, fleecing the investors. L-M has been better in managing the milking of the public purse, and maybe that is the way it should be.