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How does a plane's black box work?

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Quick answer

A plane's black box is two orange recorders: one logs flight data such as altitude, speed and control inputs, and the other records cockpit audio. Both keep data on memory chips sealed inside an armoured, heat-insulated case, with an underwater beacon, so investigators can recover and read them after an accident.

A plane's black box is actually two crash-protected recorders: a flight data recorder that logs instrument readings and a cockpit voice recorder that captures crew audio. Both store data on solid-state memory inside armoured, insulated cases, and investigators read them after an accident to reconstruct what happened.

Step by step

  1. Sensors across the aircraft measure values such as altitude, airspeed, heading, engine power and control positions.
  2. A data acquisition unit collects those signals and passes them to the flight data recorder in digital form.
  3. Cockpit microphones and radio channels feed the voice recorder, which keeps a rolling record of recent sounds.
  4. Both recorders store data on solid-state memory inside armoured, insulated casings built to survive impact and fire.
  5. After an accident, investigators recover the units, download the memory in a laboratory and rebuild the flight's final moments.

Key things to understand

  1. Sensors throughout the aircraft send hundreds or thousands of readings, such as altitude, speed and control positions, to a data acquisition unit.
  2. The flight data recorder writes those parameters continuously, keeping at least the most recent 25 hours.
  3. The cockpit voice recorder captures pilots' microphones, radio calls and cockpit sounds, overwriting its oldest audio as it goes.
  4. The memory chips sit inside a crash-survivable unit wrapped in steel or titanium and thick thermal insulation.
  5. An underwater locator beacon starts pinging when the recorder is submerged, helping search teams find it.

Labelled diagram

  1. Sensors and microphones

    Capture flight parameters and cockpit sounds throughout the entire flight.

  2. Data acquisition unit

    Gathers sensor signals and converts them into a digital stream for recording.

  3. Memory module

    Solid-state chips store the latest hours of data and audio.

  4. Armoured casing

    Steel or titanium shell and insulation protect the memory from impact and fire.

  5. Locator beacon

    Sends ultrasonic pings underwater so search teams can track the recorder down.

Inside an aircraft flight recorder

Real-world examples

  • After the 2020 Air India Express accident at Kozhikode, investigators recovered both recorders to study the landing.
  • Recorders from Air France Flight 447 were found on the Atlantic seabed nearly two years after the 2009 crash.
  • Malaysia Airlines Flight 370's recorders were never found, which is why investigators still lack a full explanation.
  • Airlines also download flight data routinely after normal flights to spot hard landings and improve training.

Common mistake

✗ Myth: The black box is a single device that films and records everything on board.

✓ Fact: Most airliners carry two separate recorders, one for flight data and one for cockpit audio, and neither records video of the passenger cabin. Some newer aircraft combine both functions in one unit.

People also ask

How does a black box survive a crash?
The memory chips sit in a crash-survivable unit made of steel or titanium, packed with thermal insulation. Certification standards require these units to withstand an impact of thousands of g, intense fire and deep-sea pressure. The rest of the recorder may be destroyed while the protected memory core stays readable.
What does a black box record?
The flight data recorder logs parameters such as altitude, airspeed, heading, vertical acceleration, engine settings and the positions of controls and flaps. The cockpit voice recorder captures the pilots' headsets, radio exchanges and background cockpit sounds like alarms, switches and engine noise, which help investigators interpret the data.
Why don't they make the whole plane out of black box material?
A recorder's armoured core is small and very heavy for its size. Building an entire airliner that strong would make it far too heavy to fly. Survival in a crash also depends on deceleration forces on the human body, which a rigid airframe would not reduce.
Why is a black box orange, not black?
The recorders are painted bright orange with reflective strips so searchers can spot them among wreckage. The name black box most likely comes from early jargon for any sealed electronic unit, not from its colour.
Where is the black box kept on a plane?
Recorders are usually mounted near the tail, because that section tends to suffer less direct impact in many accidents. Wiring links them to sensors and cockpit microphones throughout the aircraft.
How long does a black box beacon ping underwater?
Older underwater locator beacons were required to transmit for at least 30 days, and newer rules extended this to 90 days. The beacon sends an ultrasonic pulse that ships detect with special listening equipment.
Who reads the black box after a crash?
The national accident investigation agency takes charge, such as the Aircraft Accident Investigation Bureau in India. Specialists download the memory in a laboratory, often with experts from the manufacturer and the country where the aircraft was built.

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