I had no idea what NTO was and had to google it: Nitrogen Textroxide. Apparently used as an oxidizing agent for some rocket propellant.
FWIW, all of the legacy players and in space have plenty of experience with hypergols, most (all?) of which use N2H4 as the oxidizer. Its nasty nasty stuff (the barrels have a sticker that says "you will die if...") and there's an absurd amount of regulations/procedures around its handling/use.
Boeing has a long history of NTO on both their commercial and defense platforms (which are probably similar variants of each other, if not exactly the same...), and certainly the components on the Starliner system (and the team that designed/assembled them) would have, at a minimum, significant commonality with that heritage. They would have long standing processes covering all aspects of their propulsion systems that would have certified these valves for flight that would include multiple verification points where the valves go through activation/leak/flow testing [for ground testing the prop system is typically pressurized with helium], and test results like voltages, response times, calculated flow rates, measured leak rates, etc. would all be trended to ensure in-family performance over time. While not common, valves and even thrusters will be cut out of a propulsion system and replaced with properly functioning units if they fail these tests or their trends are too divergent from the family.
In other words, Its not like Boeing just bolted the Starliner jalopy on top of a rocket with a FIFI stamp on the door...and that's actually what's most concerning about this escape. This isn't just one statistical anomaly that just happened to lottery ticket its way through a full test campaign only to fail at the last second.
Someone mentioned somewhere humidity might be a cause. That's plausible if not likely--along with unintended impact from temperature--as those are likely the only two major variables relative to previous hardware Boeing has flown. The twist is that pretty much the entire life of Starliner, including the above noted tests, would have been within a temp and humidity controlled cleanroom environment. No doubt there was some analysis and (hopefully) actual testing in the "its not just another 702" environments, but that...at least it would seem....was likely done in a less than comprehensive manner at the engineering level, not the production level. One could imagine some lower level analysis/testing being focused on the parts themselves and maybe not fully contemplating the complexity of the system level environment when strapped on top of a rocket in Florida.
The good news is that Boeing has (as do all big aerospace entities) plenty of root cause analysis capability, so--embarrassment cover-ups aside--they should be able to get to the bottom of it and provide all of us a sufficient explaination. IMHO at this point, they best they can hope for is to trace it back to some lot problem at the valve manufacturer, AND find a smoking gun that shitcans that lot while exonerating the rest of the products that mfg pushes out onto the dock.
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