Good day all
After reading Epsilon's earlier post about commercial aircraft I felt I wanted to share some avionics details for those of you, like me, who like to take the lids off of things:
This is the best, highest resolution image of a DFDR I've ever seen. Taken from a real, bona fide crash.
A commercial jetliner has two such recorders, one is the Cockpit Voice Recorder, or CVR, the other is the Digital Flight Data Recorder, or DFDR.
As the names imply, the CVR records all voice communications, including ambient noise, in the cockpit via several microphones and usually mixed down to one single track. They have a long history, being initially implemented with recording wire, then magnetic tape. Due to the fact that tape is susceptible to sea water when planes crash into the sea, the newest recorders are solid-state and digital, some models even compress the audio or encrypt it to prevent unauthorized disclosure. In the past, recording durations of 30 minutes used to be the norm, on an endless tape. Nowadays, and with pending new FAA/CAA regulations, newer recorders are capable of recording audio covering several complete flights.
The DFDR, is a relative newcomer to aviation, being deployed somewhere in the late 1970's. These units digitally record data, onto magnetic tape, some of the aircraft's parameters, such as air speed, flap position, throttle position, aileron position, engine load and sometimes a few additional parameters. The new regulations require recording as many as 96 parameters, covering everything including heading and possibly GPS co-ordinates.
The data retrieved can be "played back" in computer software which will then show exactly what the plane was doing and when.
As can be seen above, the unit is quite tough, but not tough enough, as we know many recorders have been destroyed beyond use, and/or never recovered. The latest CVR/DFDR models are of such a nature they can withstand incredible forces, and can now, for the first time, withstand being burnt for several hours. Additionally, all recording is now done with flash memory, which is housed in what I like to call a supercell, which is a very tough compartment in metal as thick as 12 millimetres, lined with silica and other compounds which keep the inner temperature at 30-40 degrees C whilst the outside has been in fire for several hours.
Now, you might wonder, where are the recorders installed in the plane. The answer is simple, right at the back of the plane.
Now why would they install it there? Well simple really, it has the best chance of survival in a crash as usually, in most crashes, the tail of the plane sustains the least amount of damage. The big drawback of this is, that a fire can burn through the wiring, resulting in the loss of those precious final moments before a plane crashes. A bomb can also inflict similar damage resulting in the loss of much vital data.
