yup…Heinlein fan are you 
Seems a definitive thread to follow
Thanks. I have not looked at the thread but will probably do so tomorrow. Ironically enough, while passengering home from a long weekend road trip.
IME Pprune is an odd place. Supposedly most posters are pro pilots at some level. But the ignorance on display in most accident threads is still colossal. There might be a lot of signal, but there’s also a lot of loud noise.
Wheat and chaff …twas ever thus online tho the science forums are a bit better.
If Boeing designed the speculated one-way gate valve then they are aware of the possible reason for the crash and are actively designing an immediate replacement to a two-way valve that is connected directly to a battery.
One thing I haven’t heard about is the APU. Shouldn’t that have been running so there was air conditioning after they left the gate in 110 degree heat?
Even the maintenance manuals are massively simplified. It’s the engineering drawings, analyses and reports that contain all the functional details, hazards, failure modes and rationale for mitigation. Often times to understand an unexpected behavior you have to bring it back to first principles, assessing whether the part(s) in question are actually meeting all the necessary design requirements. This is the space where you find an overlooked detail, or a change that invalidated initial assumptions, etc. If your widget was programmed to react at an input value of X+/-0.02 and it actually performs at X +/-0.03, that could cascade to another seemingly unrelated part failing or allowing a condition that is hazardous, etc. Your fuel system engineer may not know or assume that their new widget causes an issue in an adjacent electrical component. Unless you test to rule that out, it’s easy to overlook.
This is why things often take years to certify in the first place (initial design or design changes). You can’t assume everything will be fine, you have to demonstrate it. But people are people and can’t know or remember every feature of every component, so a robust development process needs to capture it all and that’s incredibly hard to put in place and maintain. “Lessons learned” have to actually be learned by other people, and not just the one old guy who’s about to retire. But now I’m ranting in general…!
What is plausible?
Good rant.
You remind me of that mystery of , I think it was early 737s were crashing at random and one pilot managed to figure out the controls were crossing…all others crashed.
The engineers flat out denied it was possible but after a couple years they sorted it that yes indeed that actuator could reverse under certain temperature conditions…stuck with me.
You just can’t test for everything …this might be one of those. 
The explanation in the accompanying video.
No. Typically the APU is shut down a few seconds after the second engine is started.
On airplanes other than 787s, the air conditioning system is supplied by bleed air from the engines OR from the APU, but never both. On older now-obsolete airplanes, e.g. 727, MD-80, original 737s, the APU often put out more air than did the engines at idle/taxi power. So APUs were often used during taxi-out. On 737s NGs and MAXes, and 757, 767, 777 the engines at idle usually put out more air than the APU. So you get better results with APU off than on.
The 787 is different. The entire HVAC system is electric; there is no bleed air. The 4 engine-driven electrical generators are more than powerful enough to fully power the HVAC system with the engines idling. Again no value to running the APU. At least not as to HVAC.
But …
At one of the places I worked, it was a common technique, though not procedural, to leave the APU running if taking off into truly awful weather, or an especially demanding departure track. Likewise to start it partway through an approach into very low Cat II or III weather. The thinking being to have full electrical backup instantly if an engine generator (or engine) chose to crap out at this especially inopportune time. In the case of the Cat II/III arrival, having the APU running would be the difference between landing out of the approach versus needing to go around if the subsequent failure occurred in the last ~10 minutes of flight. When the weather really sucks, often you’ve already used up most of your fuel margin with holding, vectoring, etc. That small incremental improvement in success probabilities was deemed worthwhile. By pilots who didn’t have to pay for the fuel the APU burned the thousands of times over the years it was run but unneeded.
When I changed carriers, they thought this idea was simply nuts. I suspect it was probably a good idea for 1960s reliability equipment that had outlived its engineering usefulness and had also become unfashionable in a deregulated industry that was no longer operating on a cost-plus basis.
In any case running the APU as an electrical backup on a routine departure on a sunny day would never have occurred to anyone.
A really interesting right up. thanks. I had no idea any aircraft HVAC was driven off of electrical motors. that was an eye opener.
Actually, electric HVAC harks back to the way it worked on prop airliners like the Douglas DC-6/7, Boeing 337 & Lockheed Constellation. They had no source for bleed air and relied on electrically driven air compressors to do HVAC. With a very low PSID this was practical, barely, w the wimpy electrics of the day.
The 707 & Convairs took a hybrid approach: hot compressed air was bled off the engines but was used to drive a turbocharger that ingested and compressed fresh air that was in turn stuffed into the HVAC system. Engineers were kinda squeamish about pushing engine air onto the cabin. They got over thst a few years later & breathing bled engine air directly became the norm until tbe 787 came along.
Along w composite wings and fuselage, the idea of a no-bleed “more-electric” airplane was an experimental leap into the future. If it worked / works well, the next step is to eliminate hydraulics for an all-electric airplane.
The sorta-early returns on the 787s innovations are broadly favorable. We shall see.
Make that “377”. Oops.
Boeing factory workers told NTSB investigators they felt pressured to work too fast and were asked to perform jobs they weren’t qualified for. None of the 24 people on the door team were ever trained to remove a door plug before working on the plane in question and only one of them had ever removed one before. That person was on vacation when it was done in this instance.
No one from the door team was working when the plug was reinstalled.
Well, it’s a good thing the wings-stay-on guy wasn’t on vacation!
We may find the “engines stay running” guy was absent during the 787’s design process. I hope not, but I’m becoming more skeptical about their ability to design software-heavy airplanes all the time.
Y’know, I used to say that by now it would have cost them less to have actually created a properly designed 797 instead of futzing around with MAX-ing the 737. But now that would just mean the plug would have blown off that airplane.
…who am I kidding, it would probably still be 5 years away from certification.
There’s a LOT of chicken and egg there.
The MAX crashes are the reason the FAA has decided to slow Boeing certification efforts to the crawliest of crawls. Had those accidents not occurred, so the MAX’s MCAS was tweaked for greater redundancy (as was already in progress) before anyone got hurt, then the 777X would long ago have been in revenue service and the truly next gen 737 replacement aircraft would be moving along smartly about now.
Xyla Foxlin starts to build a Pietenpol Air Camper.
Part 1:
Part 2:
Brian
Bernard would be intrigued to see his plans in use 100 years later.