Introduction
Most people are aware that large commercial aircraft (and some smaller commercial, corporate, and private aircraft) are required by the FAA to be 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, the Flight Data Recorder (FDR), monitors parameters such as altitude, airspeed and heading. The older analog units use one-quarter inch magnetic tape as a storage medium and the newer ones use digital technology and memory chips. Both recorders are installed in the most crash survivable part of the aircraft, usually the tail section. Each recorder is equipped with an Underwater Locator Beacon (ULB) to assist in locating the unit in the event of an over water accident. The device called a "pinger" is activated when the recorder is immersed in water. It transmits an acoustical signal on 37.5 KHz that can be detected with a special receiver. The beacon can transmit from depths down to 14,000 feet.
Following an accident, both recorders are immediately removed from the accident site and transported to NTSB headquarters in Washington D.C. for processing. Using sophisticated computer and audio equipment, the information stored on the recorders is extracted and translated into an understandable format. The Investigator-in-Charge uses this information as one of many tools to help the Safety Board determine the probable cause of the accident.
What most people are unaware of is that, during the past decade, more than six million passenger motor vehicles sold in this country have been equipped with "black boxes" capable of providing similar types of information regarding the circumstance surrounding automobile crashes.
Background
The Event Data Recorder (EDR) in an automobile is based upon the sensors and microprocessor computer system that are used to activate the airbag in the vehicle during a crash.
General Motors introduced the first regular production driver/passenger air bag systems as an option in selected 1974 production vehicles. It incorporated electromechanical g-level sensors, a diagnostic circuit that continually monitored the readiness of the air bag control circuits and an instrument panel readiness and warning lamp that illuminated if a malfunction was detected. The data-recording feature utilized fuses to indicate when a deployment command was given and stored the approximate time the vehicle was operated with the warning lamp illuminated.
During the next two decades, as vehicles became increasingly sophisticated, more electronic systems and sensors were added to the automobiles. These included engine control modules that gathered information about throttle position, engine RPM and airflow. Acceleration sensors were added to activate airbags, wheel speed sensors were added for antilock braking systems (ABS) and traction control systems and vehicle yaw rate sensors were required for stability control systems.
Beginning in 1990, a more complex Diagnostic and Energy Reserve Module (DERM) was introduced by General Motors with the added capability to record closure times for both the arming and discriminating sensors as well as any fault codes present at the time of deployment.
For the 1994 model year, the multiple electromechanical switches previously used for crash sensing were replaced by GM with the combination of a single solid state analog accelerometer and a computer algorithm integrated in a Sensing & Diagnostic Module (SDM)."
The SDM also computed and stored the change in longitudinal vehicle velocity (Delta-V) during the impact to provide an estimate of crash severity. This feature allowed GM engineers to obtain restraint system performance data when a vehicle was involved in a deployment event or experienced an impact related change in longitudinal velocity, but did not command deployment (i.e. near-deployment event). The SDM also added the capability to record status of the driver's side switch belt (buckled or unbuckled) for deployment and near deployment events. This is what we now refer to as the "Black Box" (although it is actually metallic silver in color).
