After AF447 and again after MH370, the same question was asked publicly: aircraft have satellite links, so why is the flight data not simply sent to the ground continuously, making the recorders redundant? The answer is not that nobody thought of it.
The volume problem
A modern flight data recorder captures well over a thousand parameters, many of them several times per second. That is a continuous stream per aircraft. Multiply by roughly 100,000 commercial flights a day worldwide.
Satellite bandwidth over oceans — where this would matter most — is the scarcest and most expensive kind. The infrastructure to carry all of it continuously would be substantial, and it would be carrying data that is discarded unread for essentially every flight.
The cost-benefit shape
The benefit is real but concentrated: it materialises only when an aircraft is lost somewhere the wreckage cannot be recovered. That is a very small number of events. Aviation safety spending is allocated by expected lives saved per unit cost, and continuous streaming scores poorly against alternatives — better fire detection, better icing certification, better crew training — that address accidents that happen far more often.
This is an uncomfortable argument to make to a family whose relative is on a seabed, and it is the actual reason.
The other objections
Cockpit voice. Pilot unions have consistently opposed continuous transmission of cockpit audio, on the grounds that it constitutes permanent workplace surveillance and would change how crews speak to each other — which would itself be a safety loss. The value of a CVR depends on crews behaving normally in front of it.
Data protection. Recorder data is tightly restricted to accident investigation for good reason. A continuous stream creates a store of operational data that would be far harder to protect from other uses.
What was adopted instead
The compromise is triggered rather than continuous, and it addresses the actual failure mode.
Aircraft on oceanic routes must report position at least every 15 minutes. Autonomous distress tracking transmits position at least once a minute once the aircraft enters an abnormal state — a steep bank, an unusual descent rate, a loss of power — independent of anything the crew does. Recorder beacons now last 90 days rather than 30, and long over-water aircraft carry an additional low-frequency beacon on the airframe.
The reasoning is that the problem was never a shortage of data. It was not knowing where to look for the box that already had it. Narrowing the search area to a few kilometres achieves the same end at a fraction of the cost.
Where it is heading
Some regulators have moved further, requiring newly designed aircraft to carry a deployable recorder — one that separates from the airframe on impact, floats, and transmits. That approach has been used in military and some helicopter applications for years and is being brought into commercial transport, which may make the streaming question moot.