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Originally Posted by Lonewolf_50
(Post 10435349)
I have experienced weird wiring anomalies in a number of aircraft, and a few avionics systems, that frustrate the maintenance troubleshooters for days and weeks.......
As somebody has already suggested; one wonders if all the AoA probes on the grounded aircraft will be tested by hand : moving them back and forth, clockwise and anticlockwise by engineers through their whole range to see if there are any bad data spots or signal interruptions? |
Redundancy and experience!
What it all boils down to is triple redundancy on all levels critical!
Two engines and the last ultimate mode : Gliding! Which brings me to training and experience, Gimli 767 crew was **** at Imperial gallon to Kg conversion via Lbs BUT excellent at adapting to glider pilots. Airtransat , slow to realize fuel leak was the main problem,BUT again great glider pilots. Point: Engine on fire- useless Shut Down AOA faulty - Shut down. BTW . The AOA is of no use to me whatsoever on normal ops with a working Pitot Static system! 3 sensors and a auto shutdown system is clearly needed as standard from what I have read the last 5 months. Just my 2 cents of common cents Regards Cpt B |
The eventful flight before the crash flight, had the Jump-Seat pilot save the day by giving an independent assessment of the situation, and finding the correct solution.
Maybe an independent electronic Jump-Seat computer could have done the same job by evaluating the overall picture... IF Airspeed increasing and Window not full of sky and Sense of Negative Gee and Trimwheels going the wrong way and Pilots obviously struggling with controls THEN Advise, Turn off all automatics. Or maybe the Jump-Seat passenger was just lucky, such as 'What happens if we turn this off..?' |
Scifi, you are 100% right.
That would be the way to go. More intelligent software. 100 times more than 737's, still 100 times less than any os or car. But that I think is scifi in the aviation industry as we know it. |
Originally Posted by Uplinker
(Post 10437371)
An airship I was once working in (but not piloting - during my television engineering years), had Porsche flat six engines driving the ducted fans. One of the engines had a persistent but intermittent slight misfire. The engineers eventually found that a coaxial cable which carried the ignition signal to that engine had somehow been wired wrong, so the earth was carried by the centre conductor and the signal by the outer screen. A coaxial cable is supposed to have the outer screen earthed so that the signal carried by the inner is screened against external interference. As somebody has already suggested; one wonders if all the AoA probes on the grounded aircraft will be tested by hand : moving them back and forth, clockwise and anticlockwise by engineers through their whole range to see if there are any bad data spots or signal interruptions? Or did the LOCO airline (Lion Air) go cheap and not buy that? (Did Ethiopian Airlines have a field servicde package, and of what kind?) The other issue of "why was the AoA cockpit thing an option rather than standard kit" has been done to death in the R&N thread, so I won't go there. The root problem, bad AoA signal getting to the electronic brain, has to be remedied down in detail from AoA probe to the connector at the flight computer. GIGO. |
Originally posted by DaveReidUK (Post 137):
“All of the above are theoretically possible. None have actually been demonstrated to be the case”. Originally posted by ecto1 (Post 139): “I don't particularly fancy the theory of a mechanical offset because of loose bolt (slipping shaft). People do know how to manufacture square shafts and splines and keyed shafts and safety wire and plenty of other tricks. I don't know how much is one of those vane things, but no less than 3000 dollars for sure. Probably way way more. Two cylindrical shafts with a screw tightening one against the other is not a proper way to do the job of critical torque transmission without slipping (well, maybe in toys)”. “In other words, I would not expect any connecting part of a rotary sensor with an all round shaft. Proper way: Splined (if it needs adjusting), keyed, or at least with a D shape”. Originally posted by JRBarrett (Post 140): “I have replaced RVDT sensors of similar electrical design (with a sin/cos output), used for elevator or aileron position feedback for the autopilot on various aircraft. They have always used a splined shaft. I’ve never seen one with a round shaft held with a set screw. I would think that the internal mechanical connection in an AOA sensor would be similar”. In response to the above comments regarding Double07’s posts suggesting that the two B737MAX incidents may have been caused by a defective AoA sensor, please read the recent FAA Emergency Air Worthiness Directive No. 2019-08-51, for the Cirrus SF50 aircraft, dated April 18, 2019. (I can’t post this AD because of my PPRUNE newbie status, but you can search for it on Google). This emergency AD describes three incidents with the Cirrus Model SF50 aircraft that are astonishingly similar to the incidents with the B737 MAX aircraft. Quoting from the FAA document: “This emergency AD was prompted by Cirrus reporting three incidents on Cirrus Model SF50 airplanes of the stall warning and protection system (SWPS) or Electronic Stability & Protection (ESP) System engaging when not appropriate, with the first incident occurring in November 2018 and the latest in April 2019. The SWPS or ESP systems may engage even when sufficient airspeed and proper angle of attack (AOA) exists for normal flight. The SWPS includes the stall warning alarm, stick shaker, and stick pusher. The ESP includes under speed protection (USP). The SWPS system engaging inappropriately could potentially result in a STALL WARNING crew alert (CAS) message activation, accompanied by an audio alarm and stick shaker activation, followed possibly by either low speed ESP/USP engaging, and/or the stick pusher engaging. The pilot will also observe the dynamic and color-coded (Red) airspeed awareness ranges displaying the stall band, regardless of actual indicated airspeed.” The AD goes on to state: “Cirrus and Aerosonic (manufacturer of the technical standard order AOA sensor) have identified the probable root cause as an AOA sensor malfunction due to a quality escape in the assembly of the AOA sensor at Aerosonic. Two set screws that secure the potentiometer shaft to the AOA vane shaft may have improper torqueing and no application of thread locker (Loctite) to secure the two set screws. The AOA sensor with this quality escape is labeled with part number 4677-03”. So, even though the AoA sensors in these two aircraft have different manufacturers and designs, they are sufficiently similar that they can be affected by the same type of defect. And in both cases, this defect can cause an offset in the AoA sensor output leading to a false triggering of the stall warning system. |
Originally Posted by Double07
(Post 10454865)
So, even though the AoA sensors in these two aircraft have different manufacturers and designs, they are sufficiently similar that they can be affected by the same type of defect. And in both cases, this defect can cause an offset in the AoA sensor output leading to a false triggering of the stall warning system.
Other than that obvious fact, I don't see any other common factors between the Cirrus events and the Max accidents, at least none that I would describe as "astonishingly similar". |
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