A black box survives a plane crash because the part that matters, a small stack of memory chips, sits inside an armoured and insulated case designed for the worst. The NTSB says flight recorders are built to withstand an impact of 3,400 g for 6.5 milliseconds and a fire of 1,100 °C for 30 minutes, and to survive at great depth under water. They are also mounted in the tail, which is usually the part of an aircraft that suffers least in a crash.
Despite the nickname, they are bright orange, and there are two of them.
Two boxes: the flight data recorder and the cockpit voice recorder
An airliner carries two crash-protected recorders.
- The flight data recorder (FDR) stores measurements from the aircraft’s systems: altitude, airspeed, heading, control positions, engine settings and much more. The NTSB says newly manufactured aircraft must record at least 88 parameters, and some recorders track more than 1,000. The FDR on Helios Airways Flight 522, a Boeing 737-300, recorded 254 parameters and could hold 50 hours of data.
- The cockpit voice recorder (CVR) records the pilots’ voices, radio transmissions and other sounds in the cockpit, such as warning horns, switch clicks and engine noise. For an investigation in which the cockpit recording was central, see Germanwings Flight 9525: Mayday on the Cockpit Recorder Evidence.
Older recorders used magnetic tape. Modern ones store everything on solid-state memory chips, which are far more robust.
Why they are orange, and where the name came from
They are orange so that searchers can find them among wreckage or on the sea bed. US certification rules for airliners, in 14 CFR 25.1457, require the voice recorder’s container to be bright orange or bright yellow, with reflective tape on its outer surface to help locate it under water. The same rule says it must be mounted as far aft as practicable, to reduce the chance of it being crushed or burned.
“Black box” is a nickname, and official sources do not record where it came from. Investigators and regulators call the units flight recorders.
How they are built to survive
Each recorder has two parts: the electronics that collect the data, and the crash-survivable memory unit that stores it. Only the memory unit is armoured. Inside it, the memory boards are wrapped in thermal insulation and enclosed in a thick shell.
The NTSB lists three survival tests:
| Test | NTSB figure |
|---|---|
| Impact | 3,400 g for 6.5 milliseconds |
| Fire | 1,100 °C for 30 minutes |
| Water pressure | Submerged to the equivalent of 20,000 feet |
Fixed to the front of each recorder is an underwater locator beacon, often called a pinger. It switches on when it is immersed in water and transmits at 37.5 kHz. The NTSB’s description says the beacon can be detected from depths down to 14,000 feet and runs for 30 days. Europe has since raised that: an EU regulation required recorder beacons to transmit for at least 90 days from 2018, and large aircraft on long over-water flights had to carry an additional long-range locating device from January 2019.
The protection is not perfect. On Helios 522, the impact separated the voice recorder’s memory module from its protective case. Searchers found the module five days after the crash, using a photograph of what it looked like, and the data was recovered.
How long they record
Flight data recorders hold about 25 hours or more, so a whole flight and usually several earlier ones are on them.
Voice recorders have always held much less, because they record over themselves in a loop. The old tape units kept 30 minutes. Solid-state units kept two hours. That made a difference in long emergencies: by the time a recorder was recovered, the early part of the story could have been recorded over.
The rules are now changing:
- Europe: aeroplanes with a maximum take-off mass above 27,000 kg, manufactured from January 2021, must have a voice recorder that holds at least 25 hours.
- United States: an FAA final rule published on 2 February 2026 raises the requirement from 2 hours to 25 hours for newly manufactured aircraft, as Congress required in Section 366 of the FAA Reauthorization Act of 2024. The rule does not require existing aircraft to be refitted.
What investigators do with the data
The recorders go to a specialist laboratory. Damaged memory boards may be cleaned and connected to an undamaged reader. On Helios 522, both recorders were read out by France’s BEA for the Greek investigators.
The data recorder lets investigators rebuild the flight second by second and animate it. The voice recorder is transcribed, and the two recordings are synchronised. For Swissair Flight 111, Canada’s TSB matched the two to within one second.
Recorder data is checked against everything else: radar, air traffic control tapes, the wreckage and witness accounts. A recorder shows what happened. Working out why still takes the rest of the investigation, as our guide How Plane Crash Investigations Work explains.
Accidents the recorders explained
Helios Airways Flight 522, 2005. The Boeing 737 flew on autopilot for almost three hours with no response from the cockpit before it ran out of fuel and crashed near Athens, killing all 121 people on board. The voice recorder held the last 30 minutes. It recorded two Mayday calls that were never transmitted by radio, made by the one person who had entered the cockpit near the end. Colleagues identified the voice as that of the male flight attendant, Andreas Prodromou, which helped the investigators establish who had tried to control the aircraft.
Swissair Flight 111, 1998. A fire spread above the ceiling of an MD-11 off Nova Scotia. Both recorders lost electrical power at about 10,000 feet and stopped at 22:25:41 local time. The aircraft flew on for about five and a half minutes before it struck the sea, and nothing of those final minutes was recorded. The voice recorder held only 30 minutes, which met the rules at the time. In March 1999 the TSB recommended two-hour voice recorders and an independent power supply so that a recorder keeps running when aircraft power is lost.
Delta Air Lines Flight 191, 1985. On final approach to Dallas/Fort Worth, the voice recorder caught the first officer saying “lightning coming out of that one” at 18:04:18, 98 seconds before the crash. The recorded flight data, together with the weather analysis, let the NTSB work out the microburst the L-1011 had flown into, with a horizontal wind shear of at least 73 knots. Those findings helped drive the wind shear warnings and training that followed.
TWA Flight 800, 1996. Both recorders and the transponder lost power at the same second, 20:31:12. That simultaneous loss pointed to a sudden, catastrophic event. The wreckage later showed it was an explosion in the nearly empty centre fuel tank.
When they are not found. The recorders of Malaysia Airlines Flight 370, which disappeared in March 2014, have never been recovered. Those of Air France Flight 447 lay about 4,000 metres down in the Atlantic until May 2011, nearly two years after the crash; the search is covered in Air France Flight 447: Mayday and the Search for the Recorders.
CVR privacy: why the audio is rarely released
Voice recordings capture people in the last minutes of their lives. In the United States, federal law (49 U.S.C. 1114(c)) bars the NTSB from releasing any part of a cockpit voice or video recording. The Board does publish a transcript of the parts relevant to the investigation, either at a public hearing or when most of the other factual reports go into the public docket.
That is why documentaries that quote a crew’s words are reading from the official transcript, or using actors, rather than playing the real audio.
Questions people ask
How does a black box survive a plane crash? Its memory chips sit inside a crash-survivable unit with an armoured case and thermal insulation, mounted in the tail where impact forces are usually lowest. The NTSB says recorders are built to withstand 3,400 g for 6.5 milliseconds and a fire of 1,100 °C for 30 minutes.
Why is the black box orange? So searchers can find it. US certification rules require the recorder container to be bright orange or bright yellow, with reflective tape to help find it under water. “Black box” is a nickname; investigators call them flight recorders.
How long can a black box survive underwater? The recorder’s memory is protected against deep-sea pressure. Its underwater locator beacon starts pinging when it gets wet. Older beacons ran for 30 days; EU rules required 90-day beacons from 2018.
Can the public hear cockpit voice recordings? In the United States, no. Federal law bars the NTSB from releasing any part of the audio. It publishes a transcript of the relevant parts, at a public hearing or when most of the factual reports go into the public docket.
How long does a cockpit voice recorder record? Older tape recorders kept 30 minutes and solid-state units two hours. In Europe, new large aeroplanes built from January 2021 must record 25 hours, and a US rule of February 2026 requires 25 hours on newly manufactured aircraft.
For the terms used here, such as CVR, FDR and underwater locator beacon, see our Aviation Glossary. To see how recorder findings are written up, read How to Read an Air Accident Final Report.
Watch in the library
- Air France Flight 447: Mayday and the Search for the Recorders
- Germanwings Flight 9525: Mayday on the Cockpit Recorder Evidence
- Malaysia Airlines Flight 370: Radar, Satellite Data and WSPR
Sources
- NTSB, Cockpit Voice Recorders and Flight Data Recorders.
- 14 CFR 25.1457 (recorder container colour, location and locating device).
- 49 U.S.C. 1114(c) (disclosure of cockpit recordings).
- FAA final rule, 25-Hour CVR Requirement, New Aircraft Production, 2 February 2026.
- EASA, “New regulation, new timings”, 13 September 2016.
- TSB Canada A98H0003, Swissair Flight 111.
- AAIASB report 11/2006, Helios Airways Flight 522.
- NTSB/AAR-86/05, Delta Air Lines Flight 191.
- NTSB/AAR-00/03, TWA Flight 800.