First off, there are two recorders: the cockpit voice recorder and the flight data recorded.
The voice recorder needs power which is provide by the aircraft and is a rolling 2-hour recording. If there is an incident, the captain will pull the breaker to this system to prevent the recording from being overwritten after on the ground, or, in the worst case, aircraft destruction will cause the severance of power to the device for a similar effect.
The flight data recorder a very dependent on all the systems of the aircraft, it listens on all electrical buses, senses the position of controls, and records datapoints at a defined rate for a rolling two hours of flight time. It has a small battery system to capture what it can, but if you lose engine generation and your APU, you either gliding to a crash landing in the best case or you are just hosed and it will be literally seconds before you’ve reached the ground.
Both of these things are not read only, they continually rewrite their memory because it’s usually the last bit of flight data that matters. There are pushes to make a system that can allow for 18-20 hours of flight data, but everything moves slowly in avionics.
This seems nuts to me. You want ALL the data transmitted off the vehicle to ground stations, once a second or something like that. Sure, keep on-vehicle for backup, but only for backup. You get a continuous data stream to the ground for every plane. I mean, how much data are we talking about here? A few 10s of kb/sec for voice, maybe the same for compressed sensor data? Here we are in 2023 and we can't get a 50 kb/s stream from each airplane to the ground? Really?
part of the problem is that it has to go to satellites since the Pacific exists. the other thing is that they aren't made to survive adversarial attacks by pilots. if the pilot wants to bring a plane down, they will, and a better blackbox won't tell you anything other than that you shouldn't have let them in the cockpit.
1- If the airline industry really had a problem about paying for a low bandwidth satellite data link for a 100MM $ aircraft, they could optimize things, such as using ground data links 90% of the time while switching to satellite only in the middle of the ocean.
2- If a pilot is suicidal, black boxes don't help either. It's like saying we don't a better car safety systems, if someone really wants to die they will smash their car to a tree. That's not why BBs exist.
Even knowing that a pilot was the cause of a crash helps immensely in analysing their mental state prior to the event, you know, to prevent it from happening again.
That's realy the key there, you have a 100+Tons of metal and fuel with 100:300 people on board going close to the speed of sound. It NEEDS to be safe, but unfortunately, accidents happen. In such an event you HAVE TO know what happened, know if it was an accident or a voluntary action, the fault of equipment, software, procedure, pilot, ATC , anything really. Every procedure/safety system/training/design specification/ecc.. is literally written in blood from past mistakes.
If i know I shouldn't have left that pilot in the cockpit, great! I'll make sure no other pilot gets in that same mental condition.
The advantage of a local storage is a ruggedized recorder will not need to maintain any sort of wireless com link, as it’s stored on the physical unit. If you introduce any number of factors such as in-air separation of the aircraft, trauma to any sort of connection, or just random stuff that will occur during a crash, the antenna (which will need to be mounted outside the aircraft) is very likely break or become disconnected.
Something physically attached (especially to the electrical system) can always theoretically interfere with the rest of the plane. If there is a fire, is the pilot just supposed to shrug as the plane goes up because he cannot interfere with the black box?
Optical isolators exist exactly for this purpose. They're common, cheap, only work in one direction and result in no electrical connections between both sides.
The voice recorder needs power which is provide by the aircraft and is a rolling 2-hour recording. If there is an incident, the captain will pull the breaker to this system to prevent the recording from being overwritten after on the ground, or, in the worst case, aircraft destruction will cause the severance of power to the device for a similar effect.
The flight data recorder a very dependent on all the systems of the aircraft, it listens on all electrical buses, senses the position of controls, and records datapoints at a defined rate for a rolling two hours of flight time. It has a small battery system to capture what it can, but if you lose engine generation and your APU, you either gliding to a crash landing in the best case or you are just hosed and it will be literally seconds before you’ve reached the ground.
Both of these things are not read only, they continually rewrite their memory because it’s usually the last bit of flight data that matters. There are pushes to make a system that can allow for 18-20 hours of flight data, but everything moves slowly in avionics.