I was reading about the missing of the Malaysian flight 370 and was wondering if it would have been helpful if the cockpit would have a live streaming service where they live stream what's happening to the tower. I think it's too much bandwidth and data but was wondering why people haven't implemented.
Sure. A stream of security-cam footage might have been helpful.
It wouldn't have been helpful for the Tower, certainly. The Tower is mainly responsible for ensuring safe operations on the runways of an airport. Any airspace they do own is unlikely to extend beyond five miles in any direction of the airport.
And it wouldn't have been that helpful for the radar controllers either; the most it would have done is confirmed whether the pilots were unresponsive on purpose or due to some mishap. It wouldn't have changed the fact that they were unresponsive on the radios or that they changed their flight path.
It wouldn't have been helpful for Malaysia Airlines dispatchers or operations personnel either, except to (again) point to a possible reason for what was occurring, and for the same reason it wouldn't have been helpful for security personnel.
It might have been helpful for the lawyers, to assist in assigning blame for the incident; this could have had an effect on how much monetary compensation the next-of-kin received and who was responsible for paying it.
In general, such a livestream would be useful "in the moment" only in very limited situations. There are only two I can quickly think of:
- The aircraft is in trouble and the pilots are talking to ATC, but ATC does not yet understand the magnitude of the trouble or the magnitude of the pilots' workload. Viewing the livestream might help them understand better what the pilots are facing and avoid asking unnecessary questions.
- In a talk-down landing, having a video feed to confirm that the proper controls are properly selected could be very valuable. However, (1) it is unlikely that a general security-cam view of the flight deck would provide the resolution and focus necessary to confirm that and (2) while there have been examples of talk-down landings they are exceedingly rare, and even more so on airline-transport category aircraft.
Having such a system available for live viewing means there needs to be someone trained in what "normal" and "abnormal" flight deck activity looks like, and they need to be actively monitoring video feeds from (ideally) more than one aircraft at once (or else things will get even more expensive than such a system would already be). This person should not be a controller, who already has a lot of other duties, so now you have to hire a wholly new position or else put the responsibility on what is, in all likelihood, an already-overworked dispatcher at the airline. And as you say, such a system would cost a lot of money in equipment and bandwidth, and coverage over the open ocean would be limited to (even more expensive) satellite links.
Besides, every electrical system on an aircraft needs to be wired into a circuit breaker, for very valid safety reasons. Fires on an aircraft are much more common than hijackings, and generally more dangerous. And as Ron Beyer points out, if the pilots are able to switch off a feature (which there are valid reasons for doing; see also this answer regarding the transponder for the flight in question) then having that feature is not a safeguard against a malicious pilot.
So in all, such a system would provide extremely limited benefit in exchange for quite a lot of added complexity and cost. That is why it does not exist. (That and the fact that pilots' unions oppose the idea as an invasion of privacy for little added benefit.)