Originally Posted by
Old Ag
So I wont be accused of overreaching and parroting a parrot, here is an excerpt from NPR reporter Steve Inskeep's interview with the chair of the National Transportation Safety Board Jennifer Homendy on the topic of the warning lights. While not completely ruled out, the NTSB made it clear they don't see a linkage between the warning light and the incident event but will keep looking:
HOMENDY: "Well, those warning lights, we - first of all, we have a team that is looking at those warning lights. At this time, we have no indication that those warning lights were in any way related to the expulsion of the door. And let me just take a second to describe that. That system monitors and adjusts cabin pressure and - automatically. There's a primary system, there's a secondary system and there's a manual system. So there are two backups on the aircraft. It's a triple redundant system. We know the two other systems were working on the aircraft, and the Federal Aviation Administration allows airlines to continue flying the aircraft with those other backup systems. So in this case, what we want - we do want to make sure there was no linkage, so we are pulling the memory cards and looking at the maintenance and testing that was done on those systems."
So they are continuing to look at pressurization data, but the system the Chairwoman is talking about is the automatic pressurization system that threw the warning. The Chairwoman describes it as triple redundant with two automatic controllers and a manual control. The failure modes associated with the warnings generated by that system when one component fails and the others are working, as described above by the Chairwoman, have nothing to do with a loss or fluctuation of cabin pressure.
Again, the way the system works is that if one controller throws an error, and the others don't, the system illuminates the AUTO FAIL light and automatically switches to the alternate system as indicated by the ALTN annunciator. So I am saying that the ALTN light was illuminated.
Alaska chose not to perform ETOPS flights, but it wasn't due to any pressurization issue. It was due to the transient pressurization controller errors.
When I say the issue was resolved, I mean the Auto Fail light illumination and loss of automatic pressurization. Failover was automatic although It seems the AUTO FAIL light was extinguished by the flight crew, in at least one case, switching the mode switch to ALTN. It didn't magically fix the pressure controller that kept throwing errors, but the warning went away for the remainder of the flight with the green ALTN annunciator remaining illuminated.
And there was much histrionics about the "pressure warning light" which was suggested by the press early on to be a pressurization issue. That has been picked up here and elsewhere and incorrectly used to claim that the plug was causing pressurization issues prior to the incident flight.
Bottom line is this, the illumination of the "warning lights" has nothing to do with failure to pressurize, loss of pressurization or fluctuation of pressure. Thats not to say there weren't pressurization issues prior to the incident, but to say the "warning lights" might indicate a plug induced pressurization issue is simply not supported by the way the system functions and the facts as we know them now.
My read of that wall of text is that we are in full agreement that NTSB does not know and they are still investigating what, if any, relationship the prior pressurization fault indications have to the door plug departure.
By the way, in the quote you included, Homendy was responding to the question, "
Should this plane have been flying at all?"
Your conclusion, "Bottom line is this, the illumination of the "warning lights" has nothing to do with failure to pressurize, loss of pressurization or fluctuation of pressure" does seem like an overreach to me. But maybe you know more than me.
The link is here in case anybody wants to read what you quoted: Link