[jszymborski]

It's apparently quite loud

> After starting the descent, the flight crew made an announcement to the passengers; however, unbeknownst to the flight crew, the noise generated by the RAT (because of its high rotation speed) prevented the passengers and the cabin crew from hearing the announcement.

https://asn.flightsafety.org/wikibase/187755

[Filligree]

Oww. Seems they got lucky.

It always surprised me that there aren’t small, local lithium batteries to provide backup power for critical components like the smoke detectors. Is the risk of those catching fire considered too high?

[mrguyorama]

>It always surprised me that there aren’t small, local lithium batteries to provide backup power for critical components like the smoke detectors

There is, well, only lithium on the 787. If all power generation is dead, then the most critical flight instruments and gauges get about 20-30 minutes of power from the plane's batteries, things like your backup old fashioned gauges, the engine computers, and maybe some basic flight computer on newer planes. The RAT is intended to keep flight surfaces operational when everything else is utterly fucked, so it usually produces the same kind of energy as whatever the primary flight control system uses, which until recently was hydraulic power. On civilian airliners they generate tens of kilowatts. Airliners do not want to carry around an EV sized battery for the extremely rare occasions when you lose all systems, because that's a waste of gas. The RAT provides the same functionality for lower weight.

When the RAT is deployed, you do not care much whether a smoke detector is powered, you are already vectoring towards an attempted landing.

[jszymborski]

I know next to nothing about planes, but I think another comment here suggested some newer planes do have a large Li-ion battery banks.

That said, a household smoke detector runs on next to no power. Obviously not the same device but surely it can operate on the same principle.