The potential of digital flight data

 

This new recording standard is leading to a revolution in the way airborne telemetry data is captured, recorded, analysed, and distributed by standardising the digital data recording directory and data format for random access digital media.

In addition to the standardised file structure and data format, IRIG 106 Chapter 10 provides well-defined control and download interfaces and secure erase procedures.

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 analyse it with a compliant software package from any other vendor.

This compatibility greatly increases the return on investment in software packages, system integration and training.

Previously, several staff years of effort were required 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 standard-compliant recorders.

Such inter-vendor compatibility increases reliability.

Once tried and true 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 an entirely new proprietary system.

Not only can a single software system analyse data from different recorders, but the converse is also true with the new standard: data from one recorder can be analysed 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 employ their own standard-compliant decommutation and analysis systems.

A single user may also use multiple 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 employed 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 be copied onto a wide variety of low cost media, including CDs and DVDs, and sent over data networks and the Internet.

Data can also be posted on a secure server, allowing multiple users to easily access it.

IRIG 106 Chapter 10 requires the use of 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 used to acquire the data.

Because the TMATS tags are an integral part of the data, IRIG 106 Chapter 10 recordings cannot become unlabeled or mislabelled during copying, distribution and archiving.

The standard supports acquisition of a wide range of signal types, including PCM, MIL-STD-1553, discrete data, video, computer generated, and analogue signals.

The method of acquiring and multiplexing the digitised signals into the recorded data stream is fully defined for each signal type, thereby ensuring that compliant analysis and replay equipment will always recognise and correctly interpret the data.

For users of analysis applications integrated with hardware-based data collection systems, the standard supports complete analogue reconstruction of the original signal types while preserving accurate time coherency between channels.

IRIG 106 Chapter 10 also supports the trend towards simplification of airborne instrumentation.

We increasingly see the combination of video, PCM and other signals, together with 1553 data, into the ultimate all-in-one recording system that conveniently offers fusion and separation of all data types, with precise time-coherent analysis and playback easily achieved.

Such single box solutions can replace two or more legacy recorders, with great savings in onboard resources and significantly improved performance.

Time coherency is critically important for flight data recording, to ensure synchronisation 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 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 high 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 of providing accurate synchronisation 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 time stamping is different for each type of signal channel.

Therefore, careful attention must be given to accurate compensation of this time variance in order to maintain channel-to-channel coherency.

The 10MHz clock provides 100ns time stamp 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 synchronising the recorder's internal clock with time signals received from Global Positioning Satellites or other external reference clocks.

The new IRIG 106 Chapter 10 standard is accelerating the migration to digital recording, as users recognise the benefits of digital technology.

However, universal adoption will not occur overnight, and vendors need to continue to support the recording and reconstruction of analogue signals, video and audio.

Many users have a large investment in analogue 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 analogue 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.

IRIG106 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.