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BY PETER ASHFORD Part II: Data Recorders: Built, Tested to Remain Intact After a Crash

Editor’s note: This is Part II of a extremes of tons of pressure. damage occurred during testing. two-part series examining flight data Using three layers of material, the There are several tests carried out recorders. Part I appeared in the CSMU in a solid-state flight data recorder to simulate the crash-survival sequence, February 2010 issue of News. insulates and protects the stack of mem- including: ory boards storing the digitized inputs. • Crash Impact: The CSMU is shot olid-state recorders are consid- The materials providing a barrier for down an air cannon to create an impact ered much more reliable than their the memory boards, starting at the inner- of 3,400 g. At 3,400 g, the CSMU hits an Smagnetic-tape counterparts. They most and working outward, are: aluminium honeycomb target at a force use stacked arrays of memory chips, hence • Aluminium housing: A thin layer of 3,400 times its weight. This impact force no moving parts, and have fewer mainte- aluminium surrounds the memory cards. is equal to or in excess of what a recorder nance issues. With solid-state recorders, • High-temperature insulation: A could experience during a crash. there also is less chance of something 1-inch thick (2.54 cm) dry-silica mate- • Pin Drop: To test the unit’s penetra- breaking during an accident. rial provides high-temperature protec- tion resistance, a 500 lbs (227 kg) weight Data from a flight data recorder (the tion, which assists in the protection of the with a 0.25-inch steel pin protruding from “black box”) is stored on memory boards memory cards during post-accident fires. the bottom is dropped onto the CSMU inside the crash-survivable memory unit • Stainless-steel : A dry-silica from a height of 10 feet (3 m). This pin, (CSMU). The stacked memory boards are material is contained in a stainless-steel with 500 lbs behind it, hits the CSMU about 1.75 inches (4.45 cm) in diameter cast shell approximately 0.25 inches cylinder’s most vulnerable axis. and 1 inch (2.54 cm) tall. These memory (0.64 cm) thick. Titanium also can be • Static Crush: For 5 minutes, 5,000 boards can accommodate up to 25 hours used for this containment. psi of crush force is applied to each of the of flight data; in larger aircraft, recorders unit’s six major axis points. can track more than 700 parameters. Testing a CSMU • Fire Test: The unit is placed into a To ensure the survivability and quality propane-sourced fireball. The unit sits Built to Survive of a flight data recorder, the manufacturer inside the fire at 2,000 degrees Fahrenheit In many aircraft accidents, the flight vigorously tests the CSMU. Only the (1,100 degrees C) for one hour. The FAA data recorder’s CSMU is the only device CSMU needs to survive a crash; there- requires all solid-state recorders to be that survives. Generally, the rest of the fore, if accident inspectors can retrieve able to survive at least one hour at this recorder’s chassis and other components the CSMU, the information they need to temperature. are damaged beyond repair. analyze will be available. • Deep-Sea Submersion: The CSMU The CSMU is a large cylinder bolted To test the unit, engineers load data is placed into a pressured tank of saltwa- onto the flat portion of the recorder. into all the memory boards. After testing, ter for 24 hours. This device is built to withstand the the data is reviewed to determine if any • Saltwater Submersion: The CSMU

68 avionics news • march 2010 must survive in a saltwater tank for 30 underwater locator beacon (ULB), which Once a flight data recorder is recov- days. is attached to one end of the recorder. ered, it usually is kept in a container of • Fluid Immersion: Various CSMU While it can double as a carrying handle, cool water, which keeps the recorder in a components are placed into a variety of this cylinder is the beacon. similar environment until it is transported fluids, including , lubri- If an aircraft crashes into water, the to an area where it can be adequately dis- cants and fire-extinguisher chemicals. ULB sends out an ultrasonic pulse. This assembled. During the fire test, the memory inter- pulse cannot be heard by the human ear; face cable that attaches the memory however, it is detectable by sonar and Conclusion boards to the circuit board is burned acoustical locating equipment. On the side Following any aircraft accident, there away. After the unit cools, the unit is of the beacon, there is a “bull’s-eye” sub- are many unanswered questions as to taken apart and the memory module mergence sensor. When this sensor comes what caused the accident. Accident inves- removed. The memory modules are re- into contact with water, it activates the tigators turn to the flight data recorder for stacked and a new memory interface beacon. answers. However, the flight data recorder cable is installed and attached to a read- The beacon sends out pulses at 37.5 is only one tool that can assist investiga- out system to verify all pre-loaded data is kHz and can transmit from as deep as tors. The voice recorder is another accounted for. 14,000 feet (4,267 m). Once the beacon “black box” that can provide vital infor- begins “pinging,” it pings once per second mation to the investigator. Underwater Locater Beacon for 30 days. A battery with a six-year shelf- Hopefully, analyzing the information In addition to the flight data recorder life powers the beacon. On rare occasions, from “black boxes” translates into less being painted bright orange and having the beacon might snap off during a high- accidents and safer flying for all of us in reflective tape, it also is equipped with an impact accident. the future. q

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avionics news • march 2010 69