patplan wrote:I am coming back to the CAPT log of the next-to-last flight of Lion Air PK-LQP...
===============CAPT LOG JT047=================
A: PK LQP, B737 Max 8
O: Airspeed unreliable and alt disagree shown after take off. STS was also running to the wrong direction, suspected because of speed difference. Identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree. Decide to continue flying to CGK at FL280, landed safely rwy 25L
R: DPS CGK LNI 043
R: Capt William Martinus/133031, FO M Fulki Naufan/ 144291
I put the CAPT description of STS behavior in BOLDFACE with huge Font because, IMO, he [and/or his FO] didn't realize that they had just encountered the stealthy and secretive [and "counter-intuitive"] MCAS in action. He tried to explain this strange trimming behavior as STS "running to the wrong direction suspected because of speed difference". Unbeknownst to him, he had actually confirmed and experienced the MCAS weird/counter-intuitiveness trait.
The fact that the CAPT, the FO had saved the aircraft [and ALL passengers] by consulting the NNC for "Airspeed Unreliable and ALT disagree", as explained in the log, will strongly suggest that whatever malfunctions on Lion Air PK-LQP's last flight were something different, something more complex. The crews of that fateful flight would've had the chance to study the JT047 log and had understood what the problems had been and how to overcome them as explained by the log. They might've followed that same procedures as pointed out by the previous crew, but, alas, they couldn't save the aircraft by using that same method.
The FDR shows airspeed indicator problems for the PK-LQP's last 4 flights. Yet, replacing the AOA sensor in DPS before its penultimate flight didn't solve that problem at all. Problems still persisted. Furthermore, flushing the pitot tube before its last flight also failed to fix that airspeed unreliability. Even more puzzling was apparently replacing the AOA sensor introduced an additional problem: AOA disagreement by about 20 Degree. More and more, these circumstances seem to point to either connection/cabling problems or a flight control system malfunction because all supposedly relevant remedies didn't seem to have worked at all.
In automation systems generally, multiple sensor faults at the same time typically point to a fault in the data acquisition unit itself or that a fault in one sensor / cabling disturbs the units power supply also to other signals connected to the same unit. In new systems, with low running hours, cabling is mostly in good condition and problems are often a result from wrong connections made during manufacturing the system.