Why is the black box orange?

A requirement, not a fashion

The colour is written into the rules. ICAO's Annex 6 requires non-deployable flight recorder containers to be painted a distinctive orange colour and to carry reflective material; earlier wording also accepted yellow. In the United States, the requirement for bright orange or bright yellow, with reflective tape, entered the certification rules in 1977, and the wording has not changed since. EUROCAE ED-112B, the European performance standard, asks for a high proportion of the outer surfaces of the recorder and of its armour to be bright orange.

Bright colours were in use before they were required. A British recorder of the late 1960s, nicknamed the Red Egg, was bright red, and the aviation press of 1967 already described recorders as fluorescent flame-orange.

Why orange?

Because almost nothing else at a crash site is orange. Aircraft debris is grey, white or burnt; vegetation is green or brown; the sea is blue or grey. A bright orange surface stands out against all of them, in daylight and in the beam of a torch, and a reflective strip sends that beam back to a searcher or a diver. Investigators put it plainly: the colour makes recorders easier to find at a crash site.

Where the name comes from

Nobody can prove it, but the trail is well documented. In the 1940s, British aviation slang called any sealed electronic unit a black box, and the American press of the 1930s and 1940s already wrote about "little black boxes" of electronics. The phrase reached flight recorders around 1960: the earliest press uses found date from 1961. David Warren, whose Australian prototype was shown on British television in 1958, believed the name came from the journalists of those first interviews.

Two popular explanations have no support: that early recorders were painted black, and that the name comes from boxes charred by fire.

The lettering: do not open

Colour is not the only marking. ED-112B requires the words FLIGHT RECORDER DO NOT OPEN on the outer surfaces, in black letters at least 25 mm high, legible after every crash test except the fire tests. The instruction is meant for whoever finds the box first. The memory inside is recovered in a laboratory, with procedures that preserve the data; a recorder opened in the field can lose exactly what the investigation needs.

Under water: the beacon

• Every fixed recorder carries an underwater locator beacon that starts on contact with water and emits at 37.5 kHz. Its life was long 30 days.
• Air France 447 showed the limit. The beacons were not heard when detectors passed near the wreck in June 2009; the wreck was found in April 2011, 3,900 m deep, and the recorders were raised in May, 23 months after the accident.
• Since 1 January 2018, ICAO requires recorder beacons that last at least 90 days and, on aeroplanes over 27,000 kg flying long over water, a second locator at 8.8 kHz, fixed to the airframe but not in the wings or the tail fin, that lasts at least 30 days.
• Time still matters. After a 2018 accident at sea, the voice recorder was found buried in mud on the seabed two and a half months later, as its beacon neared the end of its life.

The beacon must stay on

In June 2009, after another accident at sea, the beacons were found on the seabed but had come off the memory modules; a remotely operated vehicle needed eight days to bring the modules up from about 1,200 m. A beacon is only useful attached to what it is meant to locate. ED-112B therefore fixes the beacon to the crash-protected part of the recorder, never to the chassis that is expected to break, and tests its attachment with a shear and tensile load of 26.7 kN in each direction before the impact and fire tests.

In the tail, and now in the front too

Recorders sit in the most survivable part of the aircraft, usually the tail: the US rules ask for them as far aft as practicable, but not where rear-mounted engines could crush them. For aeroplanes over 15,000 kg whose type certification was applied for from 2016, ICAO calls for two combination recorders, one near the cockpit and one as far aft as practicable. The forward one has shorter wires to the cockpit microphones, which are less likely to be cut in a fire or a break-up; the aft one keeps the best chance of surviving the impact.