Comment by rob74 | Hacker News Reader

Comment by rob74 | Hacker News Reader

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> There are elements of the 737 design that still exist on every new MAX coming off the line that would completely doom the certification chances of any new design, but are still there because they got grandfathered in for 737.

Not only that, but Boeing is actually limited in how much they can "modernize" the 737, because doing too much might exceed the limits of the 737's type certificate. This is the reason behind the current engine inlet overheating worries, which has led to an airworthiness directive for the 737 MAX (https://aerospacenews.com/faa-airworthiness-directive_boeing...) and is also one of the reasons for the delay certifying the MAX 7 and MAX 10. This would be a complete non-issue for other planes, because all modern designs have a switch position that only turns on the engine anti-ice system when it's needed, but the 737 MAX can't have that because the 1967 737 didn't.

This sounds odd, they're able to certify the crazy MCAS but not a simple anti-ice switch?

I know that it's a complete nightmare to certify anything. However I apparently don't understand some underlying principle that allows to certify some things and not the others.

The constraint here (entirely self-imposed by Boeing's sales strategy) is that the newer models have to basically behave like the older models to avoid needing a new type certification. (See https://en.wikipedia.org/wiki/Supplemental_type_certificate) The aircraft behavior, and pilot procedures and training have to be substantially similar. That was the whole point of MCAS, to make the plane fly as-if it were an older model, despite the significantly different aerodynamics. Changing anti-icing procedures is apparently too big a difference to maintain the original type certification.

> That was the whole point of MCAS, to make the plane fly as-if it were an older model, despite the significantly different aerodynamics.

MCAS was implemented to make sure the control forces increase going into a stall, this is a requirement in the regulations. Without MCAS the control forces would drop on the way into a stall, which is an issue that would prevent certification of the aircraft.

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