Flight Data Recorders Advance

A flight data recorder (FDR) is an electronic recording device placed in an aircraft to help investigate aviation accidents and incidents. They are used not only for flight evaluation after an unexpected event, but also for a pilot training, pilot skills assessment, diagnostics of onboard systems, and evaluation of aircraft systems as a whole. Often referred to as a black box, an FDR consists of two devices that can be combined into a single unit. The FDR preserves the recent history of the flight through the recording of dozens of parameters collected several times per second, while the cockpit voice recorder (CVR) preserves the recent history of the sounds in the cockpit, including the conversation of the pilots.

Since their inception as a photograph-based flight recorder (the record was made on a scrolling photographic film) developed by François Hussenot and Paul Beaudouin in 1939 at the Marignane flight test center in France, FDRs have advanced and become more sophisticated. They have evolved to meet new regulatory mandates, exploit new technologies, and increase the amount of information available to accident investigators. Even their nickname “black box” has become outdated; FDRs are now required to be painted bright orange to aid in their recovery by making them more visually conspicuous in accident debris.

Generational Progress

The first real generation of FDRs was introduced in the 1950s. Many first-generation FDRs used metal foil as the recording medium, with each single strip of foil capable of recording 200 to 400 hours of data. This metal foil was housed in a crash-survivable box installed in the aft end of an airplane.

Second-generation FDRs were introduced in the 1970s as the requirement to record more data increased, but they were unable to process the larger amounts of incoming sensor data. To remedy this, the flight data acquisition unit (FDAU) was invented. A flight data acquisition unit receives various discrete, analog and digital parameters from a number of sensors and avionic systems and then routes them to a flight data recorder (FDR) and, if installed, to a Quick Access Recorder (QAR). Information from the FDAU to the FDR is sent via specific data frames, which depend on the aircraft manufacturer.

The digital world signaled another generation for FDRs. FAA rule changes in the late 1980s required the first-generation FDRs be replaced with digital recorders. Many of the older FDRs were replaced with second-generation magnetic tape recorders that can process incoming data without an FDAU. Most of these second-generation digital FDRs (DFDRs) can process up to 18 input parameters (signals). This requirement was based upon an airplane with four engines and a requirement to record 11 operational parameters for up to 25 hours.

“Recording media/storage has evolved very significantly, moving from tapes to solid state media providing large capacity,” says Dror Yahav, CEO, Universal Avionics, Tucson, Ariz. “Digital recording support provides much more flexibility to operators, supporting more exhaustive aircraft data collection over an extended period. Data retrieval interval can be extended when aircraft are not easily accessible while ensuring no recorded data loss. In addition, Universal Avionics has introduced much faster download speed with its Kapture recorders.”

FDR Advances

Robert Zehnder, director of sales airborne solutions at HENSOLDT, Immenstaad, Germany, explained some of the advances FDRs have made in the past 30 years. Zehnder says the requirements of the minimum performance specifications (MOPS); the requirements for crash survival increased; the high temperature fire test (1100°C) increased from 30 minutes to 60 minutes; a new low temperature fire test (260°C for 10 hours) was incorporated; the duration of sea water immersion test changed from 30 to 90 days; and new shear and tensile test, which will guarantee that in the event of an accident the ULB will not be separated from the crash protected memory unit within the recorder.

He stated that the recording capacity (e.g., two hours of audio versus 25 hours, or also the amount of flight data) has increased. Data acquisition units (DAU) are now often integrated into the CVR or FDR or CVFDR. The size and the weight have decreased and the read-out process is now easier and faster, Zehnder said.

Zehnder adds that the first generation of solid-state recorders have continued with a legacy ARINC 573, later ARINC 717 format which was originally based on Harvard Biphase encoding to record a signal directly onto magnetic tape. “This has finally been superseded with new interface types such as CAN-Bus and Ethernet, although legacy formats such as ARINC 717, ARINC 429, Discrete Analogue / Frequency Inputs are still supported for earlier generation aircraft.”

Componentry Advances

Improvements in lithium battery technology, specifically power density and thermal runaway protection have enabled CVR/FDRs flight recorders to meet the FAA TSO-C121b mandate for Ultrasonic Locator Beacons (ULBs) to transmit for a minimum of 90 days when activated. “In addition, ULBs feature thermal runaway protection when using lithium batteries in order to meet the DO-227A requirement,” Zehnder says. “Furthermore, design improvements have reduced the quantities of lithium below thresholds for transportation — i.e., ULBs shipped separately from recorders as spares — where additional precautions would be required for transporting hazardous materials.”

HENSOLDT’s Lightweight Crash Recorder (LCR) combines all acquisition and recording functions that were previously spread across different devices into one single box. Its smaller dimensions and reduced weight makes it ideal for small aircraft platforms, helicopters and UAVs. HENSOLDT image.

Universal Avionics’ Kapture Recorders contain an innovative Recorder Independent Power Supply (RIPS) which is internal to the CVR unit. Yahav says this all-inclusive, internal RIPS eliminates weight and cost of an external LRU or bolt-on RIPS unit.

Universal Avionics say their KAPTURE Cockpit Voice and Flight Data Recorder is designed for operators seeking a recording solution that meets all of the latest certifications and requirements around the world and can hold 25 hours of data. Universal image.

Advances in memory technology, such as single-level cell (SLC) flash devices have sufficiently fast read/write times that enable imagery from multiple video sources such as cameras and multi-function displays to be recorded alongside voice, datalink and flight data parameters. Zehnder explains this meets new Airborne Image Recording System (AIRS) requirements for certain categories of Part 23 airplanes and Part 25 helicopters.

Advances in Micro Electro Mechanical Systems (MEMS) technology has produced highly accurate 3-axis gyros and accelerometers in devices packages that can be built into flight recorders. This can eliminate, in some cases, the need to install a separate data acquisition unit. It can reduce the installation cost of wiring to the AHRS (Attitude Heading Reference System) and the corresponding certification effort required when connecting to a mandatory aircraft system.

Zehnder says semiconductor and manufacturing technology, such as high-density FPGAs and memory devices, along with multi-layer printed circuit board technology have made it possible to create very lightweight units: ED-155 recorders such as SferiRec LCR 100 weighing less than 1 kg. “This is an advantage especially on smaller helicopter, fixed-wing aircraft, eVTOLs and UAVs where weight, space and electrical power are at a premium.”

Aircraft have migrated from conventional point-to-point data buses, such as ARINC 429, toward CAN and Ethernet networks. These operate at significantly higher data rates, e.g., 100Mbps Ethernet versus 100 kbps ARINC429, allowing significantly larger parameter sets to be recorded at higher sampling rates. The networking approach also reduces aircraft wiring considerably and can eliminate the need to fit a separate Data Acquisition Unit.

Zehnder explains high-capacity SD cards, built into the recorder, are providing an ultra-low cost Quick Access Recorder (QAR) solution for flight data monitoring programs, such as FOQA (Flight Operations Quality Assurance).

Reliability and Maintenance Advances

FDR’s Mean Time between Failure (MTBF) has increased considerably over the last 30 years when tape-based recorder achieved around 5,000 hours before failure. Latest generation recorder routinely achieve >25,000 hours MTBF.

Mean Time between Unscheduled Removal (MTBUR) has been a historical issue with flight recorders. Often, flight recorders would be removed from an aircraft if a parameter was not functioning correctly or flatlining. “Often the recorder was merely recording outputs from failed sensors and the so-called “bad pulls” resulted in high No Fault Found (NFF) rates,” Zehnder says. “Today’s recorders feature power-on, pilot initiated and continuous Built in Test (BIT) features that rapidly identify and report any fault conditions or bad sectors due to memory degradation over long-term use. Fault conditions are reported over an Onboard Maintenance (OMS) system, as part of a Central Maintenance Computer (CMC) used by pilots for tech log write-ups and by line maintenance engineers for ground troubleshooting.”

There have even been advances that give operators secure and reliable maintenance records compliant with aviation’s highest standards, including all FAA, EASA, and ICAO mandates for flight data recorders. Dallas-based Flight Data Systems’ SAFR Readout is a state-of-the-art secure Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) data analysis service addressing the requirement for aircraft operators to perform periodic maintenance readouts on flight recorder systems at least once a year.

Flight Data Systems’ Readout analysts examine all recorded parameters for their validity and serviceability and create recognized CASA or EASA readout reports that state the condition of the aircraft’s flight recorder system serviceability. By generating all necessary reports and documentation required by aviation authorities, Flight Data Systems’ SAFR Readout services take the guesswork out of this process and help eliminate the operators’ costly in-house troubleshooting process.

The above FDR advances have all been evolving the aviation and aircraft industry toward safety. Furthermore, aircraft modernization programs are further anticipated to propel the growth of the flight data recorder market. The rise in the demand for situational alertness, the increase in aircraft deliveries worldwide, the upsurge in air traffic, and the adoption of high-tech commercial aviation technologies have been major driving factors.