Design Con 2015

Secrets inside an airplane’s black box

-March 14, 2014

On the minds of many these days, myself included, is the mystery of Malaysia Airlines lost flight MH370, a Boeing 777 that disappeared early Saturday morning on March 8th shortly after departure from Kuala Lumpur en route to Beijing. How does a plane just disappear into thin air? Recovering the flight data recorder (FDR), otherwise known as the flight’s black box (even though it is really orange), might be the only way to solve the plane’s mysterious disappearance. This got me wondering: just how does a black box containing electronic circuit boards remain intact during a catastrophic airplane crash? The truth is that the electronics are likely destroyed, but the recorded data is recoverable.

black box
Figure 1 Electronics inside an open flight data recorder box (Source AFP Photo/Jack Guez)

In fact, there are two data recording devices on-board an airplane: the cockpit voice recorder (CVR) that records dialogue in the cockpit such as communications between the pilots with air traffic control, and the FDR that records hundreds of different parameters about the airplane while in flight. Both devices are located in the tail of the plane to increase the chances of survival following a crash. Although earlier black boxes were in fact painted black, they are now painted bright orange to make them easier to locate in a plane’s wreckage.


Figure 2 Basic components and operation of an aviation recording system (source L-3 Communications)

A solid state flight data recorder (SSFDR) can store up to 25 hours of flight data. The main components of an SSFDR are an interface and controller board (ICB), power supply, crash survivable memory unit (CSMU) and an optional under water locator beacon (ULB). The ICB is a single circuit board that controls the SSFDR and provides data processing capabilities. It enables front-end data conditioning, recording, and monitoring and ensures that up to 700 different parameters associated with an airplane’s operating conditions are recorded by the CSMU.


Figure 3 Main components of a solid state flight data recorder (source Visual Journalism of Honeywell’s SSFDR)

The CSMU of the FDR is often the only device that survives a plane crash and holds the secrets of what went wrong. The CSMU is designed to be resistant to shock, temperature extremes, and pressure according to EUROCAE ED-112 standard for Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems. Even so, if investigators cannot find the FDR, it is of little use.

The ULB will send out a ping signal for at least 30 days that can be detected from up to two miles away. However, there are several instances where the flight data recorders are never recovered such as the ones from the Boeing 767’s that hit the World Trade Center in New York on 9/11. This leaves many people wondering why given all of our technological advancements flight data is not uploaded in real-time.

In fact, all airplanes do have a system called Aircraft Communications Addressing and Reporting System (ACARS) that sends critical information about the airplane to the ground in real-time. However, only basic information is sent such as whether or not the doors are closed and the plane’s altitude and location.  Plus, ACARS data is typically only sent during events such as takeoff and landing and not continuously during the entire flight. The amount of data recorded by the FDR during the entire flight that would need to be uploaded in real-time would be immense. Although I think we have the technology required to support the bandwidth and storage capacity needs, the real question is at what expense?

It is well known that traveling in an airplane is far safer than driving in a car. According to the National Safety Council (NSC), the lives lost on US roadways each year are equivalent to the lives that would be lost from a 100-passenger jet crashing every day of the year. Is the extra expense of real-time data transfer from a plane in flight really worth it? I am sure that if we asked that question to those waiting to find out the fate of their loved ones on Malaysia Airlines flight MH370, they would say that it is.

Unfortunate events such as these are prompting people to rethink airplane communications and tracking. For example, a Canadian company named Flyht has developed a portable satellite communications device based on global positioning system (GPS) to monitor and stream critical data in real-time from anywhere in the world. Makes sense to me since GPS signals are already found in many devices that we use everyday such as our cell phones and cars. Do you think that with continued improvements to GPS systems they will offer a viable alternative to the infamous black box?

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