By Richard Bond
Digital technology has the potential to enhance the accuracy and manageability of flight data recording while lowering the cost. Until recently, however, users have not been able to realize the benefits of digital technology because no widely accepted standard has been available.
During the first generation of digital recording products, individual manufacturers developed their own proprietary solutions without any means for interoperability and data interchange. Each type of flight recorder required its own custom analysis platform. This lack of flexibility prevented users from taking advantage of advancements in technology and competition between vendors.
That is all changing with the adoption of IRIG 106 Chapter 10, the Digital On-Board Recorder Standard, which is the culmination of several years of cooperative effort by the Range Commanders Council, manufacturers, and users.
This new recording standard is leading to a revolution in 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, IRIG 106 Chapter 10 provides well-defined control and download interfaces, as well as secure erase procedures.
Compatibility
The most obvious advantage of the new digital standard is the ability to take a recorded media cartridge from any vendor’s flight recorder, download it via a standard interface to a PC, and analyze it with a compliant software package from any other vendor.
This compatibility increases the return on investment in software packages, system integration, and training. Previously, several staff years of effort were necessary to integrate a new vendor’s recorder. Now, once an IRIG 106 Chapter 10-compliant recorder is integrated with an analysis system, only a minimal effort is required to integrate additional standards-compliant recorders.
Such intervendor compatibility increases reliability. Once the community establishes tried-and-true analysis methods, designers can reuse these standards confidently with any standards-compliant recorder. There is no need to start again at the bottom of the learning curve with an entirely new proprietary system.
Accessibility and distribution
Not only can a software system analyze data from different recorders, but the converse is also true with the new standard; many different software systems can analyze data from one recorder. 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 flow to several suppliers of the various components of the aircraft. Recipients can each employ their own standards-compliant decommutation and analysis systems.
One user can also use several analysis systems for the same data. For instance, a laptop can be used to quickly verify data immediately after a flight, and then later a workstation can be used to perform more extensive and detailed analysis.
A principal advantage of digital technology is the ease of distribution. Captured as bits and bytes, data can transfer onto a wide variety of low-cost media, including CDs and DVDs, and move over data networks and the Internet. Data can also post on a secure server to enable several users to access it.
IRIG 106 Chapter 10 requires the use of Telemetry Attributes Transfer Standard (TMATS), presented in Chapter 9, which provides metadata tags to identify and describe all data. TMATS includes information on the signal sources, and the configuration of the recording equipment that acquires the data. Because the TMATS tags are an integral part of the data, IRIG 106 Chapter 10 recordings can not become unlabeled or mislabeled during copying, distribution, and archiving.
Fusing many signal types
The standard supports acquisition of a wide range of signal types, including 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 defined for each signal type, thereby ensuring that compliant analysis and replay equipment will always recognize and interpret the data.
For users of analysis applications integrated with hardware-based data collection systems, the standard supports analog reconstruction of the original signal types while preserving time coherency between channels.
IRIG 106 Chapter 10 also supports simplifying airborne instrumentation. We increasingly see the combination of video, PCM and other signals, together with MIL-STD-1553 data, into the ultimate all-in-one recording system that offers fusion and separation of all data types with 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 critical for flight-data recording synchronize data from several sources on the same aircraft, as well as to correlate with recorders located on the ground or in other aircraft.
Digital technology has the advantage of recording timestamps based on an internal crystal controlled clock. IRIG 106 Chapter 10 defines the time source and a method of time, tagging the data that allows accuracy in absolute time and in relative time between signal channels.
Engineers at Heim Data Systems Inc. in Belmar, N.J., have invested several years in developing hardware and firmware ways to synchronize data time tagging and the reference clock across several channel types. The time delay experienced by a signal between reception at the hardware input and actual time stamping is different for each type of signal channel. Designers, therefore, must give careful attention to accurate compensation of this time variance to maintain channel-to-channel coherency.
The 10 MHz clock provides 100-nanosecond time-stamp resolution, which is significantly better than previous-generation recorders. The absolute clock is useful for correlating data captured on separate recorders, even at geographically-separate locations. Synchronizing the recorder’s internal clock with time signals from Global Positioning Satellites or other external reference clocks can enhance accuracy of the absolute clock.
Looking forward
The new IRIG 106 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 reconstruction of analog signals, video, and audio. Many users have a large investment in analog technology and the benefit of digital technology does not always outweigh the cost of replacing legacy systems. This calculus is changing for some, as the availability of analog tapes decreases.
IRIG 106 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 evolves, while still protecting their basic investment in software-based decommutation and analysis systems.
IRIG 106 Chapter 10 brings order to what has been a chaotic environment for users of first generation digital recording systems. There is no longer 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 at large and encourage better products through healthy competition between vendors.
Richard Bond is chief operating officer of Heim Data Systems Inc., a supplier of data acquisition equipment in Belmar, N.J. He holds an honors degree in electrical and electronic engineering and is a member of the United Kingdom IEEE. The company is online at www.heimdata.com.
