The issue came to light within the last week during tests in Boeing’s MAX engineering flight simulator, or e-cab, a source with knowledge of the situation confirmed. The pilots were simulating a runaway stabilizer scenario and running through the requisite emergency-response checklist. A key early step is to use control column-mounted electric-trim switches to command horizontal stabilizer movement to counter the runaway. A subsequent step, if needed, is to toggle cutout switches that disable the trim motors.
According to the source, the FAA pilots found response to the electric-trim inputs took too long. “They had a difficult time quickly resolving the situation,” the source explained.
The issue has been traced to how quickly a specific flight control computer chip is processing data, the source said. What is not clear: whether the chip itself needs to be changed, or if a software update will address the issue. A second industry source said that a software fix is possible—and certainly would be preferable for Boeing, which suggested in a statement that a software modification will be sufficient. Changing chips could further delay the MAX’s return to service, as it would likely require new chip architecture as well as changing chips on nearly more than 500 MAXs in airline fleets or ready to be delivered.
Seems Boeing's suggestion that it can be fixed via software is yet another opportunity for Boeing to disappoint should it not be fixable via software.
If it is not fixable by software and a new chip with a new architecture is needed then this already enormous tragedy will go off the scales, and we'd be in that place where even Airbus didn't want to go, which is a total melt down of the 737 product line with dreadful knock on effects for world aviation.
The newly discovered issue came up during a very specific failure scenario, and it is not clear whether it has any link to either MAX accident sequence, the first source emphasized.
I don't know if this is a blessing (i.e. not related to MCAS) or a curse (a lack of processing resources needed to be addressed via software redesign or new hardware).
The software redesign is manageable especially if such was already begun eight months ago as hinted at by the Bloomberg piece.
A new processor chip would be an enormous increase in scope, especially if no ground work was already in progress for one. The hardware itself would need massive amounts of testing (for things like electromagnetic interference, power consumption under load, performance when blazing hot or freezing cold, etc) and then all the software from beginning to end would need to be retested. It would be a grounding measured in years rather than months.