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Comment by mjevans | Hacker News Reader

Alternate, non Twitter, link.

https://katu.com/news/local/alaska-airlines-flight-1282-retu...

The nomenclature is interesting. In my mind, a "depressurization event" would imply that the biggest problem was the depressurization. In other words, that there was not a big gaping structural hole.

If there can be a big hole in the plane and we can call that a "depressurization event", I would like to advocate for changing how we describe this.

Man gets shot in the leg. Femoral artery hit. Cause of death: "hypotensive event"

I know you're kidding, but we're trained to avoid making that mistake in assignment of cause of death (and in states where I've lived, they give clear instructions on the death paperwork to remind you not to make that kind of mistake)!

this is extremely common in the US, look at almost any headline in a mainstream newspaper about the police murdering someone.

Aviation is very careful to use specific phraseology. It's a Big Deal(tm) to avoid ambiguity.

Isn't this phrase generating ambiguity, in this circumstance, where a better description would not be ambiguous?

Yes. I think the aviation community would use something like "explosive uncontrolled depressurization", to distinguish from e.g. someone forgetting to arm the pressurization system.

You can't depressurize what isn't pressurized. Also, there isn't a "if you forget this everyone suffocates" button. The controls are multiply guarded and "normally closed".

That sounds lovely, but over here in reality we have:

https://en.wikipedia.org/wiki/Helios_Airways_Flight_522

> An investigation into the crash by the Air Accident Investigation and Aviation Safety Board (AAIASB) concluded that the crew had neglected to set the pressurization system to automatic during the take-off checks. This caused the plane not to be pressurized during the flight and resulted in nearly everyone on board suffering from generalized hypoxia, thus resulting in a ghost flight [..] eventually crashed near Grammatiko, Greece, killing all 121 passengers and crew on board. It is the deadliest aviation accident in Greek history.

That's pilot error. You have to move multiple safeguards and covers to move it OUT of auto in the first place. There is a reason (very poor training and safety practices, often government corruption as well) that you hear about accidents like that happening in Greece, Vietnam or Ethiopia, not the US.

I feel like you should retract:

> Also, there isn't a "if you forget this everyone suffocates" button.

(Also note that the pilots did not move the pressurization system out of AUTO; you are blaming them for not discovering that a ground engineer had done so, mostly while they fought hypoxia.)

I retract nothing. The cause of that crash was pilot error. They ignored written procedure, and did not react to multiple serious warnings, including the master caution. Which is something you do not ignore. Also note this was still only an issue because the pilots ALSO refused to verify the position of the aft outflow valve. It was the combination of all these things. So no, there absolutely is not a "press this button every flight or everyone suffocates" button.

So, what you are trying to say there is no button but a "don't switch this off or everyone suffocates" switch.

more like a "don't throw BOTH of these at the same time, while also ignoring every warning device in the cockpit". The master caution will both flash and say "CAUTION! CAUTION! CAUTION!" You can't miss it.

You are simultaneously arguing that it's not possible to accidentally kill everyone by having a switch be in the wrong position, and also that when this actually happens in reality it shouldn't count because "that was pilot error".

Yes, it was! Those pilots should totally have put that switch in the position that doesn't kill everyone! But they didn't, and then they got too hypoxic to fix it and now everyone's dead. It's almost like there's a switch that it's a really bad idea for pilots to forget about..

It is not possible for one switch to kill them.

It is possible for two switches, and multiple external factors including scandalous levels of procedural error by the Captain, First Officer, and maintenance technician to kill them.

The key with these things is something can be BOTH pilot error AND manufacturing design defect.

The MAX itself is an example of this. Both famous crashes definitely were pilot error AND were a bad design allowing that pilot error to occur.

>Isn't this phrase generating ambiguity

it's not generating ambiguity for the people who need to know

for example, air traffic control and other pilots listening on the radio will know that this aircraft needs to be cleared to descend to a lower altitude and other traffic needs to get out of the way, be alert, etc.

> not a big gaping structural hole.

It's an exit door opening, not some random part of the fuselage developing a potentially structure-compromising hole...

Bad wording on my part since I implied but didn't state the alternative. In my mind, the alternative scenario that would create a depressurization event would be a small hole or a hole that is not visible from the passenger compartment. I.e., a hole from which a passenger or attendant could not exit the plane.

I'm no expert, but I've always assumed these pressurized cabins aren't exactly hermetically sealed, so a small invisible hole wouldn't noticeably depressurize the plane.

My assumption has been there's always fresh air actively added continuously at a rate that can compensate for such small leaks, and that it's just an automatically regulated thing. Maybe a gauge/alarm visible to the pilots would indicate an out of spec level of fresh air entering to maintain pressure, without actually being a "depressurization event"...

But a door-sized hole is a whole (har har) different story.

Edit: https://aviation.stackexchange.com/questions/53831/are-press...

Your assumption is correct - air is pushed into the cabin by the engines, and the pressure is controlled by an outflow valve. An unanticipated hole, assuming it was small enough, would just be compensated for.

It wouldn’t take much of a hole to depressurize the plane. And unplanned holes in a pressure vessel have a tendency to rapidly get larger.

> unplanned holes in a pressure vessel have a tendency to rapidly get larger.

I suspect that's only an issue on airliners when the hole happens in a window.

There's no shortage of search results confirming that something like gunfire on an airliner likely won't depressurize the plane unless it hits a window....

Wouldn't a small hole quickly become a large gaping hole anyway, if it's large enough to affect the cabin pressure?

I suppose if the small hole had existed since before takeoff, you could avoid catastrophic damage as the aircraft will not be pressurized at all. I wouldn't call it a depressurization event, though.

if the big gaping hole is only a problem because it causes a "depressurization event", then categorizing it as a depressurization event make sense?

seat you are sitting on gets literally ejected from the airplane

"Man, it's unfortunate that there's a problem with the pressurization system in this.. sky."

Disturbing the peace? I got thrown out of a window! What's the fucking charge for getting pushed out of a moving car, huh? Jaywalking?

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