Several ‘low speed’ flight design flaws causing Boeing 737 MAX fatal crashes
Is it true that the Boeing 737 Max is highly unsafe and risk riddled but its manufacturer is reluctant to call it back owing to the huge cost considerations?
Yes there are several low speed flight design flaws in the Boeing 737MAX which Boeing test pilots did not discover until they were test flying the prototype.
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Test pilots found the MAX had a reluctance to flare above the runway. Changes from the previous NG version made the aircraft nose heavy and hard to stall but also much harder to recover from a stall, thus Boeing developed MCAS as a technological fix to digitally restore the old feel of the previous type.
Problems stem from the new engines being positioned further forward with a higher thrust-line compared to previous Classic or 737NG series.
MCAS fixes however only masked the real handling of the aircraft, not just from pilots, but also from the Federal Aviation Administration who certified the aircraft safe to fly. When there are electrical or data problems the “mask” drops off.
MCAS works fine in practice until there is an electrical failure, or a digital signal encoding error, for example a failure by the Angle of Attack sensor.
Though in the case of Lionair there were a series of digital electrical errors. Boeing are essentially bluffing that they understand the original cause of Lionair JT610’s crash to maintain market confidence in the 737MAX brand.
Boeing are also busy trying to shift blame to Lionair’s maintenance or to blame pilots who were never aware about the existence of MCAS:
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Boeing’s response is unethical and merely kicks the can down the road in the hope that they can somehow cover up the real problem. Boeing are throwing dice hoping the odds favour them solving this.
If you study the succession of faults suffered by Lionair’s ill fated 737MAX registed PK-LQP you will notice that the crash of JT610 was not caused by a faulty Angle of Attack sensor. The suspect Left hand AoA sensor was replaced two flights previously following even earlier roller coaster flights.
It is statistically implausible that Lionair maintenance replaced a previously faulty AoA sensor with a faulty brand new AoA sensor.
For example a faulty AoA sensor would not also cause faulty airspeed readouts experienced on previous flights: JT43 and JT776. The AoA sensor was replaced after flight JT776.
Nor was the crash caused by a runaway Stabilizer Trim (Stab Trim). Lionair pilots were trained how to disconnect Stab Trim, but for some as yet not understood reason they elected to reverse every nose down trim by commanding a nose up trim each time to follow that commanded by the Flight Control Computer (FCC).
Boeing have yet to understand the real cause. They have used a sales tour of 737MAX customers to convince the industry they have a simple software patch that can nullify a problem with the AoA sensor but this is just unethical sales talk. By inference the software patch appears to disable the software logic which disconnects the Autopilot when AoA data disagrees.
There are valid reasons why an Autopilot should disengage when data disagrees, so solving that problem potentially only creates another safety problem.
Also analysis of the FDR data shows that the originating problem preceded the automated Stab Trim issue:
What Boeing have done is to conflate the symptoms to suggest they were the original cause. Boeing also brazenly suggest that Lion Air failed to fix the AoA fault, when in fact Lion Air Engineers followed the Boeing maintenance manual to the letter and did replace the suspect left hand AoA sensor.
Boeing do not have a handle yet on how Lionair JT610 went out of control. On the previous flight before the accident JT43, pilots reported a FEEL DIFF PRESS warning which suggests PCU failure of the Mach Trim Actuators.
Since the previous NG version was vulnerable to a nose-over problem called “Nip-Tuck” or “Mach-Tuck” at speeds as low as 0.615 Mach it is possible that FAA’s failure to properly test the 737MAX before certification failed to uncover a propensity by the nose heavy 737MAX to Mach Tuck at lower Mach speeds.
At 5,200ft Altitude JT610 was flown to 334kt Groundspeed/345kt TAS or Mach 0.528. Boeing and the FAA need to explain whether the 737MAX is vulnerable to Mach tuck at 0.528 Mach speed?
A final point. Unlike previous 737 models the 737MAX has a Wi-Fi system called CWLU directly connected to the Digital Flight Data Acquisition Unit (DFDAU). It is known that at least one passenger Mr Deryl Fida Febrianto was texting his wife Lutfinani from inside the cabin early in the flight. Neither Boeing nor the FAA have tested the MAX to establish whether the on-board CWLU maintenance Wi-Fi system is resistant to electronic interference?
What the Wi-Fi link can perform is a BITE diagnostic test during a flight which confuses the DFDAU or the Flight Control Computer (FCC) by asking too many questions when these systems were trying to concentrate on flying the plane.
My belief is that a passenger with a cell phone inadvertently accesed the CWLU system and sent one or more onboard systems haywire.
I would suggest at the very least there is a failure by FAA to properly certify the 737MAX design.