The black box of the crashed Yeti Airlines aircraft was recovered from the accident site on January 16.

On January 15, a Yeti Airlines plane with 72 people onboard, including five Indians, crashed into a river gorge while landing at the newly-opened airport in the resort city of Pokhara, killing at least 68 people.

This was Nepal’s deadliest aviation accident in 30 years.

The data on the recorders may help investigators determine what caused the Yeti Airlines ATR 72 aircraft to crash in clear weather just before landing in the tourist city of Pokhara.

The black box of the crashed aircraft was found at the accident site and it was handed over to the Civil Aviation Authority of Nepal.

The cockpit voice recorder and the flight data recorder were recovered, as search and rescue teams rappelled down a 300-metre gorge to continue their efforts to locate the four missing persons.

What are black boxes in an aircraft?

• Aircrafts are usually equipped with two black boxes that record information about a flight. Both recorders are installed to help reconstruct the events leading to an aircraft accident.

• One of these, the Cockpit Voice Recorder (CVR), records radio transmissions and sounds in the cockpit, such as the pilot’s voices and engine noises. The other, Flight Data Recorder (FDR), monitors parameters such as altitude, airspeed and heading. Both recorders are installed in the most crash survivable part of the aircraft, usually the tail section.

• They are not actually black, but high-visibility orange. Experts disagree about how the nickname originated, but it has become synonymous with the quest for answers after crashes. Many historians attribute their invention to Australian scientist David Warren in the 1950s.

What are the parts of a black box?

It weighs about 4.5 kg and contain four main elements:

• A metal chassis designed to hold the recorder and facilitate recording and playback.

• An underwater locator beacon to assist in locating in the event of an overwater accident. The device called a “pinger” is activated when the recorder is immersed in water.

• The core housing or ‘Crash Survivable Memory Unit’, made of stainless steel or titanium, and designed to withstand equivalent to 3,400 times that of gravity.

• Inside that housing, circuit boards holding fingernail-sized recording chips.

• The CVR records the flight crew’s voices as well as other sounds inside the cockpit. The recorder’s “cockpit area microphone” is usually located on the overhead instrument panel between the two pilots. Communications with Air Traffic Control, automated radio weather briefings and conversation between the pilots and ground or cabin crew are recorded.

• The FDR onboard the aircraft records many different operating conditions of the flight. It monitors many important parameters such as time, altitude, airspeed, heading and aircraft attitude. In addition, some FDRs can record the status of more than 1,000 other in-flight characteristics that can aid in the investigation. The items monitored can be anything from flap position to auto-pilot mode or even smoke alarms.

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