I suppose if worse comes to worse they can do some or all of the training on the actual aircraft

The ryanair max's need a locking mechanism for the extra door. At the moment that was not foreseen so any luny could open it. So a bit more work on integration in the PSEU... And certification.

I'm sure some way will be found aka fudge to enable the use of the existing NG simulators with a software upgrade.

Thanks. First factual response.

That will be a challenge because while the system (overhead) panels look quite the same on the Max and the NG, the instrument panels don’t.
The NG panels look like the B747-400 and B777, the Max looks like a B787.
I know a lot of people are led to believe that the cockpit layouts are the same, but they aren’t.
You will need a hardware upgrade as well to let it look like a Max.

Surely you mean "what did regulatory authorities already miss that makes trusting them a fool's errand"?

The MAX and classic were certified on the same cert but pilots could not have a common rating on both, no matter how much Southwest tried with the FAA. My wording was poor in the original post, should have said "ratings" rather than "certs".

The 'grandfathered' portion of the cert basis had nothing to do with the MAX problems. Everything that has been identified as a shortcoming in the MAX has been associated with new (e.g. MCAS) or significantly modified/affected systems (e.g. cable separation for rotor burst) needed to be certified to the latest regulations per the Changed Product Rule.
It's not the cert basis of the MAX that is a problem, it was the execution of the cert.

BTW, I'd bet good money that if you went through any other aircraft cert (Boeing, Airbus, etc.) with the same fine tooth comb that is being applied to the MAX, you'd find plenty of issues. Cert is done by humans, humans make mistakes and bad assumptions. Certifying a new (or major derivative) aircraft is a big, big job. To do that job perfectly, with no mistakes, bad assumptions or oversights, is basically a statistical impossibility. Most of the time those cert errors don't have a significant effect on safety. Occasionally they do - and that happened big time on the MAX.
My biggest criticism of the FAA over the years has been a horrible tendency to focus on minutia at the expense of the big picture (e.g. "missing the forest for the trees") - and EASA is just as bad. On the MAX, I watched them do this with "Uncontrollable High Thrust" - UHT. Both the FAA and EASA didn't just look at UHT, they dissected it to the Nth degree - far more than they did even on the 787 - even though UHT has never resulted in a fatal accident. Boeing probably spent more time/resources addressing UHT on the MAX they they did on any other Propulsion related issue. Had the FAA spent 10% of the time looking at MCAS that they did UHT, it would never have been certified in that configuration but instead they spent all their time staring at the tree...

Are you suggesting that it would be possible for the Max to be certificated as a new, clean-sheet design, with no reference to its predecessors ?

What is the holdup, everybody knows where the off switch is.

Most of the grandfathered regs relate to aircraft structure, and perhaps HIRF/Lightning protections of some of the electronics - at the time of the NG, there wasn't a FAR for HIRF - that was all certified by special condition. The FAR that was eventually implemented isn't the same as the SC so electronics that are unchanged from the NG are not certified to the HIRF FAR - they'd need to be retested. They'd probably pass - according to the HIRF/Lightning experts the additional requirements in the FAR are not difficult to meet relative to what was in the SC - but it's not the sort of thing that can readily be shown by analysis.
It probably could be shown to meet without significant changes, but it would require repeating a number of structural test (e.g. wing to failure, fuselage pressurization, fatigue, that sort of thing). So it would be expensive.
On the 747-8, a big part of the grandfathered cert basis was that the wing structural design wasn't changing (although beefed up for the higher weights) - just the aerodynamic profiling of the wing - since a truly new wing would have meant repeating all the structural testing at considerable time and expense. I know something similar was done on the 737NG - wing changed aerodynamically but not structurally. I don't know how much of that carried over to the MAX but without the original structural basis all that would need to be re-done.

They have 400 planes currently expecting scraping or upgrades in some ways. Why not take one or two for destructive structural tests? Or does Boeing fears the result?

Yes, I fear you may be correct, many of the issues found on the MAX may cause corrective actions to the NG as well..

Look at the manual trim wheel issue, redundancy in systems such as AoA and ADIRU,, and the FCC' protection as examples...

Would the MAX be able to be certified against the latest requirements if it was treated as a stand alone, brand new aircraft type with no reference to previous generations of the B737 ?

If you were going to build a brand new aircraft, you wouldn't have built something like the MAX.

See tdracer's post, 3 above yours.

There are 2 issues, one is in the event of rotor burst, the Max has a lack of control cable run protection ahead of the wing similar to the NG which Boeing claim has not proved to be a problem with the CFM56, but the LEAP 1B is a different engine in a different location with presumably a different rotor burst path and therefore could hardly be compared accurately to the NG....
The other issue is the lack of power cable separation for the electric trim control system which was also an issue on the NG and did not meet the relevant FAR when the NG was certified, but was missed by the FAA.

As DR notes, I've already stated my belief that the MAX could have been certified to the current regs with minimal changes. Oh, it would take quite a bit of of time and money to redo every last part of the cert, but it could be done. There isn't much of the non-structural cert basis that is carried over from original 737 cert (and the structural regulations haven't changed much). Further, no one is claiming the 737 MAX design is structurally deficient (and before anybody launches on the NG pickle fork issue - every indication is that the problem with the pickle forks is due to the build process causing fatigue cracks, not the basic structural design).

Of course a brand new, from the ground up design wouldn't have a lot in common with the 737 - there has been a considerable amount of technological change and advancement in the last 50 years. Heck, there isn't a lot common between the 767 and the 787, and that was only ~25 years.
I repeat, the issues with the MAX have nothing to do with the cert basis, they have everything to do with the cert execution. As hec7or notes, even items like rotor burst and wire separation should have been addressed per the Changed Product Rule. But they weren't.
BTW, with all the bitching and moaning about 'grandfathered' 737 cert basis, remember that the 'modern' A320 cert basis is over 35 years old, and there were not that many changes to the regulations between when the 737 was launched and when the A320 was launched...

Boeing announce production line restart including MAX.
Certification only a matter of time.

Time waits for no man.

Boeing have been saying that since March last year. Expect a tentative date and then have it postponed a couple of times before it happens.