Digital technology has the potential to greatly enhance the accuracy and manageability of flight data recording while significantly lowering the cost. Until recently, however, users have not been able to fully realize the benefits of digital technology due to the absence of a widely accepted standard.
During the first generation of digital recording products, individual manufacturers developed proprietary solutions without any means for interoperability and data interchange. Each type of flight recorder required a custom analysis platform. This lack of flexibility prevented users from taking advantage of advancements in technology and competition among vendors.
Courtesy of Eglin Air Force Base Multi-Media Center
That is changing with the adoption of IRIG106 Chapter 10. The Digital On-Board Recorder Standard is the culmination of several years of cooperative effort by the Range Commanders Council, manufacturers, and users.
This new recording specification is defining the way airborne telemetry data is captured, recorded, analyzed, and distributed by standardizing the digital data-recording directory and data format for random-access digital media. In addition to the standardized file structure and data format, IRIG106 Chapter 10 provides well-defined control and download interfaces and secure erase procedures.
Compatibility
The most obvious advantage of the new digital standard is the capability to download a recorded media cartridge from any vendor�s flight recorder via a standard interface to a PC and analyze it with a compliant software package from any other vendor. This compatibility increases the ROI in software packages, system integration, and training.
Previously, several staff-years of effort were required to incorporate a new vendor�s recorder. Now, once an IRIG106 Chapter 10-compliant recorder is integrated with an analysis system, only a minimal effort is required to add more standard-compliant recorders.
Such intervendor compatibility increases reliability. Once analysis methods are established, they can be confidently reused with any standard-compliant recorder. There is no need to start again at the bottom of the learning curve with a new proprietary system.
Immediate Accessibility and Easy Distribution
Not only can a single software system analyze data from different recorders, but the converse also is true with the new standard: Data from one recorder can be analyzed by many different software systems. This is especially important for airborne telemetry data because many different parties typically require access to the data.
For example, telemetry data from a test flight may be sent to several suppliers of the various components of the aircraft. Recipients can each use their own standard-compliant decommutation and analysis systems.
A single user also may use multiple analysis systems for the same data. For instance, a laptop can quickly verify data immediately after a flight, and then later a workstation can perform more extensive and detailed analysis.
A principal advantage of digital technology is the ease of distribution. Captured as bits and bytes, data can be copied onto a variety of low-cost media including CDs and DVDs and sent over data networks and the Internet. Data also can be posted on a secure server, allowing multiple users to easily access it.
IRIG106 Chapter 10 requires use of the Telemetry Attributes Transfer Standard (TMATS), presented in Chapter 9, which provides meta-data tags to identify and describe all data. TMATS includes information on the signal sources and the configuration of the recording equipment needed to acquire the data. Because the TMATS tags are an integral part of the data, IRIG106 Chapter 10 recordings cannot become unlabeled or mislabeled during copying, distributing, and archiving.
Accurate Fusion of Many Signal Types
The standard supports acquisition of a wide range of signal types including pulse code modulation (PCM), MIL-STD-1553, discrete data, video, computer-generated, and analog signals. The method of acquiring and multiplexing the digitized signals into the recorded data stream is fully defined for each signal type, ensuring that compliant analysis and replay equipment always will recognize and correctly interpret the data.
For users of analysis applications integrated with hardware-based data collection systems, the standard supports complete analog reconstruction of the original signal types while preserving accurate time coherency between channels.
IRIG106 Chapter 10 also promotes the trend toward simplification of airborne instrumentation. The combination of video, PCM, and other signals, together with 1553 data, is seen as an all-in-one recording system that conveniently offers fusion and separation of all data types and accommodates precise time-coherent analysis and playback. Such single-box solutions can replace two or more legacy recorders with savings in on-board resources and improved performance.
Time Coherency and Resolution
Time coherency is critically important to ensure synchronization of data from multiple sources on the same aircraft as well as to correlate with recorders located on the ground or in other aircraft. Digital technology can record timestamps based on an internal crystal-controlled clock. IRIG106 Chapter 10 defines the time source and a method of time tagging the data that allows accuracy in both absolute time and in relative time between signal channels.
We at Heim have invested several years in developing hardware and firmware methods to provide accurate synchronization between data time tagging and the reference clock across multiple channel types. The time delay experienced by a signal between reception at the hardware input and actual timestamping is different for each type of signal channel. For that reason, careful attention must be given to accurately compensate this time variance to maintain channel-to-channel coherency.
The 10-MHz clock has 100-ns timestamp resolution, significantly better than previous-generation recorders. The absolute clock provides a supplemental timing method that is highly useful for correlating data captured on separate recorders, even at geographically separate locations. The accuracy of the absolute clock can be further enhanced by synchronizing the recorder�s internal clock with time signals received from GPSs or other external reference clocks.
Looking Forward
The new IRIG106 Chapter 10 standard is accelerating the migration to digital recording as users recognize the benefits of digital technology. However, universal adoption will not occur overnight, and vendors need to continue to support the recording and reconstructuring of video and audio analog signals.
Many users have a large investment in analog technology, and the benefit of digital technology may not outweigh the cost of replacing legacy systems. This calculus is changing for some as the availability of analog tapes decreases.
IRIG106 Chapter 10 allows users to benefit from digital technology without being dependent on a single vendor. By lowering the switching costs, users can augment their capabilities or seek new solutions as their needs and the available technology evolve while still protecting their basic investment in software-based decommutation and analysis systems.
IRIG106 Chapter 10 brings order to a chaotic environment for users of first-generation digital recording systems. There no longer is the threat of expensive obsolescence or inferior performance through being tied to a single vendor�s proprietary digital data format.
The standard takes account of all steps in the acquisition process from signal source through to analysis software and provides an easily implemented means for interoperability and data interchange. This will bring comfort to the research, development, and test community and encourage better products through healthy competition among vendors.
About the Author
Richard Bond is the chief operations officer at Heim Data Systems. He began his nearly 30-year career in the data acquisition industry at Racal Recorders and was integral in Racal�s purchase of Joseph Heim GmbH, which brought about Racal-Heim and eventually Heim Data Systems. Mr. Bond holds an honors degree in electrical and electronic engineering and is a member of the UK IEE. Heim Data Systems, P.O. Box N, Belmar, NJ 07719, 732-556-2318, e-mail: [email protected]
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March 2007