> 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.
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?
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.
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.
Jokes aside... I'm certainly part of the intended audience: point me at an interesting rabbit hole, and there I gooo.
A RAT provides backup electrical and/or hydraulic power for control surfaces (and other goodies). A RAT would certainly be inspected during a heavy check and likely even during line checks (e.g. an "A" check or equivalent). How often is gonna depend on the airplane. But to suggest that a critical piece of equipment isn't checked regularly is just silly.
Additionally, it's pretty much guaranteed that if an airplane comes with a RAT the RAT is required to be functional for ETOPS flights. That alone means you're gonna be inspecting it pretty frequently. ETOPS certification has three parts: airplane, airline, and humans. You'd want to look at the ETOPS Maintenance Document at whatever airline to be sure.
Outside of Asia (where domestic widebody flights are still common) I'd guess many if not most 787 flights are ETOPS flights.
I remember a decade or more ago I was on a US domestic flight - I forget exactly what, I think it was American from SFO to LAX - so I doubt it needed ETOPS. But the captain announced - while we were still at the gate - that he was getting an error in the cockpit saying the RAT was faulty. And he called maintenance, and they told him to try resetting something (a computer or circuit breaker or whatever) to see if that cleared the error - and when it didn’t, he announced we could not take off and would all have to go back into the terminal. Thankfully they had a spare plane a few gates over and they put us all on that (same crew, same passengers) so we only lost an hour or two.
Back to your flight, both the FAA and EASA require airliners to have a minimum equipment list (MEL). It's entirely unrelated to ETOPS (overwater flights). This list describes what equipment is required to be functional, what you can fly without and when. What's on the list is all going to come down to what kind of plane we're talking about. Could be you're not allowed to fly without a functional RAT ever. Could be that you can fly without a RAT as long as something else (e.g. APU) is functional. Could be you can only make a certain number of flights with a non-op RAT.
A real world example is that ATR 72 crash in Brazil recently. One of the PACKs (air conditioning / cabin pressurization) was not functioning on the accident plane. Per the MEL you can dispatch an ATR in that condition, but you're limited to a service ceiling of 17,000 ft. Unfortunately that put the flight in direct conflict with the weather.