[Jeroen]

Originally Posted by fhdowntheline

I am sure the real pilots will corroborate on this, but 170Kt is a pretty darn high speed for any regular commercial airliner to land at..

Concorde, being a delta wing design was probably the jet liner with one of the highest, if not highest landing speeds. Typical about 160 knots.

Of course, landing speeds vary depending on type of plane, but also amongst others, on weight and flap setting.

A 737 Max would be somewhere in the 125-145 knots range I guess.

For airplanes two different speeds matter. Speed through the air and speed across the ground. The difference being the wind speed.

All the above speeds are air speeds. So if a plane comes in in to land it typically does so against the wind. So the speed over the ground is less.

Just for context as not everybody might be aware. Aircraft speeds are measured in nautical miles per hours. Also known as knots, identical to seagoing vessels. A nautical mile is slightly longer than a regular mile. A nautical mile is 1852 meter, versus 1609 meters for a regular or statute miles.

Jeroen

[arijitkanrar]

Originally Posted by PistonRing

A very nice review. And a lot of interesting comments. I would like to add to the same with the following:

The 737 MAX ain’t going to change even with the second AoA sensor. It still is dynamically unstable beyond a certain pitch and the MCAS will still cut in for an actual event. The details can be found on the internet but majorly: The 737 was designed with a lower height to aid loading/unloading at remote locations. The newer highly fuel efficient geared turbofans have a much larger frontal dia and thus in a 737 need to be placed higher on the wing (look at it and compare with a A320 the next time you fly Akasa). This is what makes the 737 unstable at high pitch and requires a MCAS. A fact hidden by Boeing till the two crashes. The addition of the second AoA sensor has added to the safety but the inherent problem remains.

The second AoA sensor was always present but the FCC (Flight Control Computer, which houses the MCAS software) was designed to use only 1 depending on which of the 2 FCCs, left or right, was active for the flight.

Now, as part of the fixes implemented, the values of both the sensors are used and the AoA is calculated using a Mid-Value-Select logic.
Also the AoA values are monitored and if they deviate by some margin continuously for some time, the MCAS is disabled.

In the future, a third synthetic AoA source will be added (means the AoA will be computed by other means). This will enable the FCCs to single out and isolate a faulty AoA sensor as now there is a third reference value to compare against.

Then as part of the fixes, MCAS will only operate once every time it senses a high AoA instead of operating continuously till it senses high AoA.

Also its important to understand why MCAS was required in the first place.
Any airframe type as it goes through upgrades will face changes which will affect the flying characteristics. For e.g. re-engines which is what was the case with the MAX series when combined with the new LEAP engines.
In the case of the 737, the altered characteristics are in the form of a higher pitch up tendency at some AoA and airspeed regions.
This also would cause a reduction in stick force on the control columns for the pilots while pitching up towards a stall.
This is not allowed by regulation. (The regulations are listed as 14CFR §25.203 for whoever interested).
Here is the relevant text in bold.

(a) It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.

Does it mean that the MAX would stall because of the pitch up? Yes, just like any other aircraft would.
Does it mean that the pilots wouldn't be able to prevent the stall by regular means. No, they can easily counteract it, but it goes against the regulation for the aircraft to have this pitch up behaviour and the resulting reduction in stick force.
To meet the regulation, the MCAS was added.

The closest analogy that I can think of is if we have improperly aligned wheels (maybe due to a tyre upgrade for e.g.) in our car and it causes the car to drift left or right. Now suppose the car drifts left, you will need to use less force that normal on the steering wheel to make the car go left (reduction in control force).
This is forbidden by the rules because if you were to use the same amount of force on the steering wheel, you can make the car drift more left than you intended.

The media hysteria has made it look like the MAX actively tries to go against the pilots wishes and kill them

Boeing later increased the scope of conditions in which MCAS can operate and also to what degree it can move the stabiliser and apparently did not inform the regulating authorities about this change. Also the implementation was, shall we say, not well thought out and did not consider the other factors that can come into play due to an inadverdent pitch down command issued by MCAS. These came to light after the Ethiopian crash and have since been accounted for in the procedures, trainings and type certifications.

All things said, the MAX should be just as safe as any other aircraft to fly.

[PistonRing]

The analogy to a car with misaligned wheels explains things better. However, I wouldn't equate an incident happening because of misaligned wheels to what happened to the MAX.Boeing played with the trust of people flying their machines as well as the travelling public. It will take more than what has been done till now to exonerate itself. No one has been penalised for what happened. What kind of an example does this set for Boeing employees. Just added scrutiny by FAA won't stop them from going down the juicy path again. The informed traveller understands this and will take travel decisions accordingly.

[vignesh207]

Excellent review of the 737MAX of Akasa Air. I flew on their MAA-BLR sector every week for few months and consistently had excellent experience with Akasa Air. I hope they are here to stay and their service doesn't go bad over time as they grow.

And the technical details in this thread by all the AvGeeks of the forum made me squish my eyes and double check if I'm in team-bhp or in some Aviation related forum. Great to see this thread.

Originally Posted by ricky_speed

The problem with 737 MAX is that it needs MCAS in the first place.

The inherent flaw here is that Boeing didn't want to develop a brand new Fly-by-wire aircraft to replace the decades old 737 because they were running out of time while the A320Neo was penetrating into their stronghold markets (aka US). Trying to fit the relatively larger CFM LEAP on a older design frame, then trying to compensate that with a MCAS and confusing pilots with a hybrid Fly-by-wire and conventional controls all culminated into a disaster.

The two crashes and subsequent grounding of the MAX worldwide and then the rigorous testing and certification everywhere to get the MAX up on the air now means it might actually be one of the safest aircrafts to fly on, in my opinion.