Primarily for general aviation discussion, but other aviation topics are also welcome.
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NigelC wrote:Aircraft are bought by accountants, no option which doesn't increase revenue by more than it costs will ever be ticked.

That sounds like a darned good reason for why flight safety/competency features shouldn't be manufacturer's optional extras in the first place.
Iceman, NigelC, Stu B liked this
Iceman wrote:Certification requirement, a bit like a stick shaker for an impending stall.

Iceman 8)

I’m not sure that’s correct, and certainly not to the speed and magnitude to which it could operate.

From wiki
On the Boeing 737 MAX, MCAS was intended to mimic pitching behavior similar to aircraft in the previous generation of the series, the Boeing 737 NG...

During the certification of the MAX in 2017, Boeing removed a description of MCAS from the flight manuals, leaving pilots unaware of the system when the airplane entered service.[1][2] The Wall Street Journal reported that Boeing had failed to share information about that issue for "about a year" before the crash of Lion Air Flight 610.[3] Twelve days after the Lion Air accident, on November 10, 2018, Boeing publicly revealed MCAS in a message to airline operators, noting that the system operates "without pilot input."[4][5] A recovery procedure highlighted by Boeing and the U.S. Federal Aviation Administration (FAA) after the Lion Air accident failed to prevent another accident: Ethiopian Airlines Flight 302. Before that crash, the FAA anticipated that Boeing would deliver a software update to MCAS by April 2019.[6][7] Boeing admitted that the MCAS played a role in both accidents and asserted that MCAS is not an anti-stall system.

I thought it was a system introduced purely to prevent any requirement for ‘expensive’ conversion to that series of 737? It was a cost saving item that turned out to be rather costly.

Indeed the only ‘certification standard’ Boeing were concerned with was to limit conversion training for NG pilots to level B. But to achieve that they couldn’t even describe MCAS as a ‘new’ or ‘novel’ system to the 737.

That’s why they hid it away as simply an extension of the NG’s Speed Trim System. But it wasn’t!

If it was a certification requirement, why would they hide it from pilots and operators?
@Iceman is correct; it was a means of providing longitudinal stability characteristics that met Certification requirements.

A4 Pacific wrote:Indeed the only ‘certification standard’ Boeing were concerned with was to limit conversion training for NG pilots to level B. But to achieve that they couldn’t even describe MCAS as a ‘new’ or ‘novel’ system to the 737.

That's not right. From here: wrote:MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation.

The LEAP engine nacelles are larger and had to be mounted slightly higher and further forward from the previous NG CFM56-7 engines to give the necessary ground clearance. This new location and larger size of nacelle cause the vortex flow off the nacelle body to produce lift at high AoA. As the nacelle is ahead of the C of G, this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to inadvertently pull the yoke further aft than intended bringing the aircraft closer towards the stall. This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics". Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.

(I think there's a post from a while ago by a 737-rated forumite (@Josh, perhaps?) elsewhere on this site that goes into detail building on the above.

A4 Pacific wrote:If it was a certification requirement, why would they hide it from pilots and operators?

There are lots of design solutions to meet certification requirements that aren't typically passed on in detail to operators: Structural elements may be a good example. Operators should have been able to take the Certification as read, including that any information they do need to know has been included in the operating and maintenance material. That didn't happen here.
As I explained.

For the magnitude the system was eventually designed to operate to, there was no certification requirement.

From memory a displacement of something like 0.6 degree of the tail plane solved the pitch stability problem. That’s certainly all that the manufacturer declared. But as released the system had authority (in repeated ‘bursts’) for full travel of the horizontal stab. Somewhere in excess of 5 degrees? All driven by a single sensor!

That degree of authority was not required for certification. Indeed it could never have been certified in that state.

Whichever way you look at it, it is one of the most disgraceful episodes in aviation history!
There was a brilliant little aeroplane that the CAA limited to three seats, and only allowed a Special Category CxA. It was the Wassmer WA51A Pacific and WA52 Europa. Very nice to fly and very stable... Flew on rails in IMC, very nice.
But refused full certification as it was said to be unstable on an ILS when fully loaded.
I never found this.

So here we are with an airliner that does not have enough natural stability and so it requires an electronic sensor system with a control system to overcome a pilot, and it is certified by EASA and hence the CAA.
Should not be!

The next fatal accident this aeroplane has is likely to cost the manufacturer and all its customers a lot.
Is it worth the risk for an airline to take a chance on it?
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