Dumb question perhaps...related to Flight 447

[S_E_Fudd]

Any aviation experts out there...

Why aren't the black boxes constructed in such a way as they will float on water...?

[renegade000]

1. Not a dumb question.

I've thought about that as well. I'm definitely not an expert, but I would surmise that since the main requirement of the black box is to survive a catastrophic impact into land (being the hardest surface the plane would hit, plus usually most crashes occur while landing/descending over land), one of the only solutions would be an incredibly study steel case...which is just not conducive to floating well. any potential flotation devices you attach on this thing would probably be sheered off during an impact. any mechanism you place inside that inflates after impact would probably compromise the integrity of the box somewhat.

:shrug:

[TexasProgresive]

2. Back when the Wright brothers were still around

I was an avionics tech in the Air Force. (yes that's a joke about the Wright brothers) Anyway we had a thing call a CPI Crash Position Indicator. If I remember correctly it mounted near the rear and top of the plane. It was designed to eject and glide to the earth when the plane experienced strong acceleration/deceleration such as in a crash. Once released from the plane it sent out a radio beacon. This divice was very light weight and shaped as an airfoil so that it could glide safely.

Black boxes are quite different since they are very heavy. To eject them during rapid descent would likely destroy them when they hit solid ground. There would have to be some sort of chute to slow them down. Also some critical data might be lost if they leave the plane before impact. This is mostly guess work on my part.

Now about the CPI I don't know why those aren't on all commercial aircraft. I suppose the airlines don't want to do the regular maintenance on them. There are some DUers who fly maybe they could comment about the CPI's. Seems like a no brainer to me.

I think that the data stream needs to be sent out to satellites or whatever but I agree with the air crews nixing the voice being recorded full time. That would create a daunting environment for the crew.

[timeforpeace]

3. Not all crashes occur in water.

And who's to say they will float free of whatever part of the aircraft they are attached to when it goes down?

[Xithras]

4. As two others have mentioned...

The boxes are inside the aircraft, surrounded by metal. Flight recorders typically have to be cut from the twisted wreckage before they can be analyzed.

Someone upthread mentioned ejecting the boxes, but that introduces two additional problems. First, you'd need an automated way to determine that the aircraft was actually crashing. That's not nearly as easy as it sounds. Second, you'd lose all records of what happened between the point of ejection and the point of impact. There are plenty of cases where aircraft experienced horrific levels of damage, and yet the flight crews still managed to muscle the aircraft through the air for dozens of miles before crashing or even landing them. At what point do you decide to blow the boxes overboard?

Remember United 232? The plane had a massive engine failure which caused a massive hydraulic failure and a loss of all flight control. Despite that, the flight crew muscled the aircraft down from 30,000+ feet to final approach using only engine thrust controls. The loss of control that caused the final crash happened mere seconds before they hit the ground. And what about 1549 in the Hudson? The recordings right up to the moment of impact provided valuable information.

A better idea would be a two-phase real-time broadcast. Burst transmit flight data from all aircraft periodically, and automatically activate realtime streaming any time a serious problem is detected by a sensor. That way, the onboard black box merely becomes a backup.