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A mysterious voice is haunting American Airlines’ in-flight announcements

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Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#231

Post by nullc »

mirker wrote: post #172
Nextgrid wrote: post #102

Earlier quoted context omitted.

Is it really analog though? The audio might be analog, but they still have to "key" the mic which would be a digital input at the very least, or something even more complex such as a phone-like system where handsets have actual keypads and internal numbers. I wouldn't expect the amplifier to be active at all unless a "call" is in progress (otherwise you might hear a constant noise, plus energy saving/thermal concerns…

Yeah, I don’t believe the system is analog end-to-end. Moving the audio signal to every speaker across the entire length of the plane with analog seems like a fight against physics.

what? analog PA systems that cross giant buildings or even campuses have been a thing for a long time.

The traditional design uses a 70v or higher bus and a transformer at each speaker.

I would be really surprised if the PA speakers we anything but that-- electronics at each speaker is a repair/failure rate headache.

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#232

Post by mhh__ »

echelon wrote: post #94
mhh__ wrote: post #83

Earlier quoted context omitted.

It tries to show me people talking about maths and finance and programming but they're all either infantilising themselves for some reason or not very good at it. And anyway I have a fair amount of karma here so what does that say about hackernews if your implication is correct...

> I have a fair amount of karma here so what does that say about hackernews That you (in)frequently post spicy hot takes.

I've mellowed a lot in my old age

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#233

Post by tl90 »

dont know anything about the sound systems of aircrafts, but why can’t they switch off each sound system one by one and see which one causes it and then see the possible inputs to the one where the sound is played? I assume it cannot be that hard to do during maintenance period especially if this happens on multiple planes.

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#234

Post by onionisafruit »

mindcrime wrote: post #169
sidewndr46 wrote: post #5

I doubt the veracity of this account, at all. The liability from flying a malfunctioning, compromised plane is way too high for this to happen more than once.

Anecdotal, but... I was on a flight from Chicago to Raleigh a few years ago, and we were just starting to taxi out to the runway when the plane stopped and the pilot got on the PA and said something like "Sorry folks, we have a maintenance indicator (kind of like a 'check engine' light) that has come on. We have to go back to the terminal and get maintenance to check things out." So we go back to the terminal, wait a…

My mother was a flight attendant on a flight where they thought the front landing gear didn’t come down. There were three independent systems on an L-1011 to detect this and all three agreed that the landing gear failed to extend. They did a tower flyby, and the tower said the wheels were down, so they operated under the assumption it wasn’t locked into place. The plane circled for a long time while emergency crews foamed the runway and positioned themselves for an emergency landing.

It turns out that all three independent systems malfunctioned and the landing gear was fine.

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#235

Post by duckqlz »

The sounds probably aren't a prank or a recording of a human at all. I am guessing it is just a resonant frequency of a standard part being picked up as a feedback loop due to some component which was recently exposed after a change in maintenance protocols. (or something similarly mundane) I have heard all sorts of ghoulish sounds picked up while tinkering with RF and old microchips. Our brains tend to anthropomorphize such sounds when we have never experienced them before. Going straight to the wildest explanations like "hacking" or "ghosts" is fun for our brains but further reinforces the inaccurate picture we had painted for ourselves initially.

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#236

Post by stonegray »

camkego wrote: post #206
stickfigure wrote: post #165

Earlier quoted context omitted.

A bit of searching for airplane medical communications jacks turned up this picture: https://aviation.stackexchange.com/questions/12776/how-are-t... Jacking into that would not be inconspicuous.

If those are 1/4" or 6.35mm audio phone jacks, I'm sure there are lots of electrical engineers who could design a pre-recorded player that would fit ENTIRELY inside the jack without protruding outside the jack whatsoever.

Eh, only one way to find out.

An ESP32-PICO-D4 is 7mm wide, but based on internal images it appears you can safely grind it down to ~6.35mm. It contains a DAC, 4MB flash, and all needed peripherals plus bluetooth. The quality [1] would be poor, but this matches what we observed.

A circuit board would probably be out of the question given the size. Even 0.8mm would have very little usable area. Flex PCB could work well, but is probably overkill for the complexity required. I'd expect a project like this to be hand soldered, given the low (less than 6?) component count. It wouldn't be easy, but well within the capabilities of a hobbyist at home with a cheap USB microscope.

For power, I could imagine a repurposed AirPod battery (they fit in the 0.235 inch diameter "stem" of the headphone) with a deadbugged switching or linear regulator fitting both the power budget and the size constraint.

From a physical design perspective, a lot of traditional methods seem impractical. With this size constraint one possibility could be placing requisite components into a 1/4" jack shaped mold, and casting it in epoxy in a vacuum, completing the conductive surfaces with copper tape.

1. https://www.youtube.com/watch?v=lgDu88Y411o

I could definitely make one as a demo.

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#238

Post by Waterluvian »

iudqnolq wrote: post #200
Waterluvian wrote: post #99

Earlier quoted context omitted.

I don’t deny that it’s an important safety system. I’m curious, though, if they’re treated like safety critical systems in design or if emergency training covers how to act if the PA is down. I’ve got to believe it’s safety critical.

I'd assume it's important to safety, but they have slightly less effective backups like yelling. I think the backup systems on aircraft are often things you'd rather not need to use.

I was thinking about yelling. I wonder if yelling on the larger planes is even viable. Especially in an emergency.

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#239

Post by RC_ITR »

stonegray wrote: post #236
camkego wrote: post #206

Earlier quoted context omitted.

If those are 1/4" or 6.35mm audio phone jacks, I'm sure there are lots of electrical engineers who could design a pre-recorded player that would fit ENTIRELY inside the jack without protruding outside the jack whatsoever.

Eh, only one way to find out. An ESP32-PICO-D4 is 7mm wide, but based on internal images it appears you can safely grind it down to ~6.35mm. It contains a DAC, 4MB flash, and all needed peripherals plus bluetooth. The quality [1] would be poor, but this matches what we observed. A circuit board would probably be out of the question given the size. Even 0.8mm would have very little usable area. Flex PCB could work wel…

The only problem, though, is then there need to be dozens of these because that airpod batter lasts maybe what, 2 flights?

Re: A mysterious voice is haunting American Airlines’ in-flight announcements

#240

Post by Crashbat »

jrootabega wrote: post #229

Unsatisfying, Hanlon-style prediction: no one involved had any notable malice or competence. Maintenance and cleaning crews love to listen to radio/music on speakers while working. Someone from this staff plugged in a receiver to listen while servicing the plane, and forgot it. Or they left it there for convenience and didn't think anyone would notice. Someone else unrelated, while on the flight, found this receiver…

This seems like the most likely explanation. Whoever left the device in the plane isn't likely to own up to it (if they even remember where they left it!) since they may lose their job.
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