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Flight 370: What exactly is a Black Box?

March 24, 2014 • Features, Top Stories

The search for Malaysia’s missing Flight 370 is entering its third week, and as the hunt expands to a much wider area than first covered, investigators and rescue teams are hoping to make a breakthrough – by finding the cockpit voice recorder and the flight data recorder. These two devices are housed in what is collectively called the Black Box – and every plane in the world today is fitted with one.

A number of nations are involved in searching for Malaysia's Flight 370 (image: Media Info)

A number of nations are involved in searching for Malaysia’s Flight 370 (image: Media Info)

What exactly are they, and how do they work?

Cockpit voice recorder

The Cockpit Voice Recorder (CVR) is a device used to record the conversations and sounds from an aircraft’s cockpit. It continuously records the pilots’ conversations, noises from the aircraft and whether switches and knobs are tuned or turned.

Early CVRs make use of magnetic-tape technology, much like normal music tapes from yester-year. While they are still in operation in some planes, CVR manufacturers have stopped producing them. The magnetic-tape has been discontinued in favour of digital, solid-state hard drives, which can hold a lot more data.

The modern chassis that houses the Black Box and the crash-survivable memory units (image: file)

The modern chassis that houses the Black Box and the crash-survivable memory units (image: file)

Where magnetic-tape CVRs only record the last 30 minutes of a flight on a continuous loop, recording over the previous 30 minutes, solid-state drives can hold up to two hours of data before it starts to record over the previous two hours.

This is especially important to Flight 370, as data from satellite tracking shows that the plane made a sharp turn to the south-west, and continued to fly for hours. Since the CVR only holds two hours of conversations and sounds, investigators might not be able to find out why the unscheduled turn occurred.

Flight data recorder

Similar to the CVR, the Flight Data Recorder (FDR) records a number of things in an aircraft related to its flight. “There are sensors that are wired from various areas on the plane to the flight-data acquisition unit, which is wired to the FDR. When a switch is turned on or off, that operation is recorded by the FDR,” HowStuffWork explains.

While the solid-state FDR can record up to 700 parameters on an airplane, some of the most important include:

  • Time
  • Pressure altitude
  • Airspeed
  • Vertical acceleration
  • Magnetic heading
  • Control-column position
  • Rudder-pedal position
  • Control-wheel position

Because solid-state drives make use of better technology, they can store up to 25 hours of data, which is much longer than the average flight time. Investigators are hoping to recover the FDR to ascertain the circumstances under which Flight 370 operated, and to give valuable insight into its course, operational well-being and eventual demise.

Built for a crash

Since it is retrieved after a crash, how is it possible that the blackbox survives to tell the plane’s tale? While the recorders’ chassis and inner components are mangled, the hard drives are built to be crash-survivable memory units (CSMUs).

“The CSMU is a large cylinder that bolts onto the flat portion of the recorder. This device is engineered to withstand extreme heat, violent crashes and tons of pressure. In older magnetic-tape recorders, the CSMU is inside a rectangular box,” according to HowStuffWorks.

While the CVR and FDR is housed in a bright orange container, observers often mistake that to be the Black Box, making a joke that the Black Box is actually orange. Well, the aforementioned CSMU is the actual Black Box, housed inside the large cylinder – which is orange in color.

Using three layers of materials for protection, the black box is there to fully insulate and protect the CVR and FDR’s memory banks. Comprised of a layer of High-temperature insulation, the dry-silica material forms the middle layer of protectio. It’s what protects the data in a fire. The outer-most layer of protection is a Stainless-steel shell and is about 0.25 inches thick. Titanium is sometimes used as well, and serves as protection during an impact.

Underwater Locator Beacons

Before searchers and investigators can get their hands on the wreckage and the black box, they have to locate the plane first – and this is where the Underwater Locator Beacons (UBL) come in.

Unofficially known as pingers, this small device sends out a steady ping, about one ping per second, which helps to locate a lost aircraft. One pinger is attached to the CVR, while another is attached to the FDR.

Once the pinger comes in contact with water, it emits an ultrasonic pulse of 37.5 kHz at an interval of once per second – which is inaudible to the human ear. Locating the pingers for Flight 370 also forms a major part of the search, as the pingers only have a battery life of about 30 days – after which it is lost forever.

The UBL acts like sonar, which is picked up and tracked using specialized technology. But one aspect of finding the UBLs for Flight 370 that is hindering the search, are their range. A 37.5kHz pinger can only be detectable 4-5km from the surface in good conditions, while a 37.5kHz transponder pinger has a range of 6-7km in good conditions.

According to a CNN report- “To detect the signals, searchers drag hydrophones behind boats, drop them from ships or planes, or use specially equipped submersibles. Under favorable sea conditions, the pingers can be heard 2 nautical miles away. But high seas, background noise, wreckage or silt can all make pingers harder to detect.”

As the battery runs out, the pings fade in volume, and eventually will emit no ping at all. So for Malaysia Airlines and the many nations involved in the search, it truly is a race against time.

Charlie Fripp – Consumer Tech editor

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