DIGITAL FLIGHT DATA RECORDERS

Digital Flight Data Recorders.

A flight data recorder is a system designed to collect and record data from a variety of sensors. These sensors are mounted throughout the aircraft structure picking up data from appliances- components and co-dependent systems that tell their story of how they were configured- and being used during the time before- and at the time of an accident. All of this data is collected and stored digitally within a reflective- fluorescent yellow or orange crash-proof container.

The collected data is critical in assisting accident investigators to try and understand what went wrong to cause an aircraft accident- especially if there are no survivors. Obviously without this information- there is a high probability that the same accident might reoccur on another aircraft under similar circumstances.

With Digital Flight Data Recorder data available- the faults that were to blame in causing the catastrophe might well be designed or trained out of the system- thus eliminating a disastrous repeat of history. Another benefit of a modern DFDR system is that it can become a crucial component within a condition monitoring and reliability program.

A DFDR must obviously have a high degree of ‘crashworthiness.’ The first units were required to withstand a momentary shock force of 1-000gs- the latest test standards now call for a test to 3-400gs for a duration of 6.5 milliseconds. The units also have to withstand a static crushing force at all of its six axis points of an applied load force of 5-000lbs for 5 minutes on each axis. Third- it must withstand a 500lbs piercing force test conducted by dropping it onto a ¼ inch steel pin from 10 feet. Lastly it must withstand a 1-100°C fire test for 60 minutes- and a 260°C oven test for 10 hours.

It is also required that these units are mounted within the tail area of an aircraft- away from the potential crushing force of any engines mounted nearby. The DFDR must be watertight to a depth of 20-000 feet in sea water- and survive at this depth for 30 days - and it must be fitted with an underwater locator beacon which will act like a sonar transmitter- by ‘pinging’ a signal through the medium of water that it might be laying in.

HISTORY- AND THE FOIL FDR
The Flight Data Recorder (FDR) has been around for more than 70 years. The first unit was invented in 1939 and slowly developed into a useable flight unit in the late 1940s. It wasn’t until 1954 that the Cockpit Voice Recorder (CVR) was invented.

The first FDR systems were quite simplistic because they were entirely electro-mechanical units which utilized inconel foil as the recording media which motored between spools- and had five styluses that scratched readings for Heading- Altitude- Airspeed- Vertical Accelerations and Time (five parameters) on one-side of the foil. Soon this system was enhanced by adding three more styluses on the opposite side of the foil- thus adding Pitch- Roll and Flap information (total of eight parameters).

I remember back in the late 1980s removing and replacing the foil cartridge in one of the 1960s/early 1970s Dassault Falcon 20 aircraft that I maintained. I would take the used foil roll to a desk- and using a Plexiglas screen held over the foil- read the highs and lows of all of the traces - looking specifically for any flight anomalies that the flight crews had failed to mention to any one of us in the maintenance department.

These spools of foil would contain 300 hours of recorded data. They were not reusable unlike the magnetic tape or wire units that were introduced to our industry next.

THE MAGNETIC TAPE/WIRE FDR
These newer units that utilized Mylar- or stainless steel magnetic tapes or wires as the recording media- were able to record 25 hours of data- and continually re-record over the data that was older than 25 hours. Virtually all were of an endless loop- single spool design- which normally allowed 16 parameters of data to be recorded.

In 1982 the International Civil Aviation Organization (ICAO) recommended that all Flight Data Recorders should have 32 parameters- and subsequently in 1989 the FAA called for the retrofit of all Foil Recorders and units that only recorded five parameters with at least 10 parameter tape units by May of 1994.

THE DIGITAL FLIGHT DATA RECORDER
With the arrival of the Solid State - or more accurately- the Digital Flight Data Recorder - both the survivability and reliability of this valuable monitoring system leapt- thanks to the elimination of tapes- drive motors- drive belts- and all other moving parts that were necessary with all previous versions.

Prior to the introduction of the DFDR- all recorded and stored data was in an analog format. Analog data transmission systems easily pick up any noise along its transmission wiring caused by poor insulation- local interference and also the random thermal vibrations of the atomic particles in the wire conductors.

All variations to the original analog signal will appear as noise. As the signal is transmitted over long distances- this noise if not filtered- will ultimately degrade the data signal sent from the parameter sensor. Digital data transmission systems convert the base data inputs into a binary signal- i.e. a ‘square-wave’ signal that is a pulse that represents either an “on” or “off”- or specifically a “1” or a “0.” This digital signal is not affected by noise- and therefore delivers pure- unaltered data to the receiving DFDR without the need of filtration- and the fear of lost or scrambled signal data.

ARINC SETS THE STANDARD
In 1929 the Federal Radio Commission - today’s Federal Communications Committee (FCC) - endorsed that Aeronautical Radio Incorporated (ARINC) be established as the sole conduit for aviation communications standards- and the principle industry advocate for development in communications technology.

Today- the internationally recognized standard for digital data transmission on-board aircraft through an open digital-data-bus is ARINC standard 429- which employs unidirectional transmission of 32 bit words over two-wire twisted pairs. Messages are transmitted at a bit rate of either 12.5 or 100 kilobits per second to other system elements- which are monitoring the bus messages. For many years the ARINC 563 serial binary data standard allowed for a bit-rate of 768 bits/second. This is equal to 64 words/second.

ARINC system standards have increased to 128 words/second and beyond. Effectively the rule of thumb here is: the higher the ARINC number- the faster the system. ARINC specifications include 419- 561- 573- 582- 615 and 717. Instead of two-wire systems- the higher the speed- the more twisted pairs are needed (naturally adding weight).

WHAT DATA IS RECORDED?
A Type 1 DFDR records all of the parameters required to determine accurately the aircraft’s flight path- speed- attitude- engine power- configuration and operation. The Type II and IIA DFDRs shall record the parameters required to determine accurately the aircraft flight path- speed- attitude- engine power and configuration of lift and drag devices.

Every data input signal sent through a wire channel for a specific monitored system component or condition- is called a parameter. The accepted standard of DFDR parameters that are now monitored by the latest DFDR equipment includes 91+ channels of data.

FOQA PROGRAM
ARINC is also the inventor and developer of the Aircraft Communications Addressing and Reporting System (ACARS)- along with the concept of reliability analysis as it relates to Mean Times Between Failure (MTBF) for avionics systems components.

This concept of monitoring and applying statistical analysis to equipment failures dovetails into the ability to interface reliability and fault recording platforms that are effectively piggy-backed off many of the parameter sensors that were installed to feed their data to the DFDR system.

The Flight Operations Quality Assurance (FOQA) program now installed under mandate by the FAA- is based upon the periodic download of DFDR information that is sent to a central database of gathered information for analysis. This system of in-flight- operational data analysis effectively allows a potential “accident waiting to happen” to be identified and dealt with before a real accident actually takes place.

What is wonderful about the FOQA program? Now corporate flight departments can take the downloaded data- and through the help of either a consulting firm- or their own software system- create their own in-house risk assessment graphs pertinent to specific flights made.

The same can be achieved with maintenance and reliability data to create a Maintenance Operations Quality Assurance audit- as well as create a 3-demensional in-flight animation of specific flights of interest.

FAA DFDR INSTALLATION AND USE MANDATES
There are approximately 29-000 words in the FAA’s Code of Federal Regulations that specify the requirements for the installation of a Flight Data Recorder in a U.S. Registered Aircraft.

Unfortunately the actual regulations are incredibly convoluted as specific manufacture- certification and target dates all testify to evolution of the FDR as it became capable of recording more and more parameters of data. In an attempt to simplify the criteria specified in the FARs- I have simplified it as follows:

PART 23 - AIRWORTHINESS STANDARDS:
Normal- Utility- Acrobatic and Commuter Category Airplanes- specified by cfr 14- Part 23.1459.

Primary Mandate is for a FDR that records three parameters (airspeed- altitude and directional data).

PART 25 - AIRWORTHINESS STANDARDS:
Transport Category Airplanes- specified by cfr 14- Part 23.1459.

Primary Mandate as per Part 23- but the time of all sent- and received conversations with air traffic control must be recorded.

PART 27 - AIRWORTHINESS STANDARDS:
Normal Category Rotorcraft- Mandated by cfr 14- Part 27.1459- has the same mandates as Fixed Wing Aircraft.

Primary Mandate is the same as it is for Part 23- but the time of all sent- and received conversations with air traffic control must be recorded.

PART 29 - AIRWORTHINESS STANDARDS:
Transport Category Rotorcraft- specified by cfr 14- Part 27.1459 has the same mandates as Fixed Wing Aircraft.

Primary Mandate is the same as it is for Part 23- but the time of all sent- and received conversations with air traffic control must be recorded.

PART 91 - GENERAL OPERATING AND FLIGHT RULES:
Specified by cfr 14- Part 91.609- and applicable to multi-engine turbine powered airplanes and rotorcraft with 10-or-more passenger seats.

Required- without exception- on all aircraft that were built after October 11- 2010. All other aircraft built before April 7th- 2010- must meet the equipment requirements specified by 23.1459 or 25.1459 by April 7- 2012. All other aircraft and rotorcraft built after April 7- 2010 must meet 23.1459- or 25.1459- or 27.1459- or 29.1459 respectively- and then have a system that is capable of retaining the last 25 hours of data.

PART 135 - OPERATING REQUIREMENTS:
Commuter and On-Demand Operations and rules governing persons on board such aircraft- specified by cfr 14- Part 135.152. Applicable to multi-engine turbine powered airplanes and rotorcraft with 10 or more passenger seats.

Required without exception- on all aircraft that were built after October 11- 2010. All other aircraft built before April 7- 2010- must meet the equipment requirements specified by 23.1459 or 25.1459 by April 7- 2012. All other aircraft and rotorcraft built after April 7- 2010 must meet 23.1459- or 25.1459- or 27.1459- or 29.1459 respectively- and then have a system that is capable of retaining the last 25 hours of data.

EASA
EASA has not finalized its requirements for Digital Flight Data Recorder requirements for business aircraft. The proposed requirements contained within the JAR-Ops 4 that is in-work are all frozen until this document is issued - therefore guidance must be sought from JAR-Ops 1- which applies to Aircraft used in Commercial Air Transportation Operations.

JAR-Ops 1 is published by the Joint Airworthiness Authorities’ (JAA) Joint Airworthiness Requirements (JAR) Operations Regulations. The standard specified by this regulatory document requires Digital Flight Data Recorders that record 17 parameters of data for all aircraft. For aircraft that are above 59-000 lbs maximum weight- the required parameters go up to 32- with 10 additional parameters added for EFIS equipped aircraft.

ICAO AND IS-BAO
ICAO on the other hand- has been a strong advocate for the installation of DFDR in all turbine powered aircraft. Its controversial International Standard of Business Aviation Operations (IS-BAO) finally adds some teeth to this advocacy program.

IS-BAO 8.14.1 states that: All aircraft for which the individual certificate of airworthiness was first issued on or after January 1- 1989 and that have a maximum certificated take-off mass over 59-525 lbs shall be equipped with a Type I flight data recorder. Then IS-BAO tightens up its requirements to encompass virtually all aircraft by requiring that any aircraft for which the individual certificate of airworthiness was first issued on or after January 1- 2005 and that have a maximum certificated take-off mass of over 12-567 lbs shall be equipped with a Type IA flight data recorder.

Further- IS-BAO 8.14.3 recommends - but does not mandate - that all aircraft for which the individual certificate of airworthiness was first issued on or after January 1- 1989 and that have a maximum certificated take-off mass over 12-567 lbs should be equipped with a Type II flight data recorder.

PAST DFDR PROBLEMS
Over the years- I have personally been faced with the sometimes complicated issue of “does it- or does it not require the installation of a DFDR”. Some examples follow:

• A Gulfstream GII and GIII re-entering the US Register were outside of the certification dates where a DFDR is required. However any aircraft that has left the country (and flown on a foreign registration and airworthiness certificate) upon re-entering the U.S. Register with the re-issuance of a new Certificate of Airworthiness- are required to have a DFDR installed.
• A Hawker 700 was being sold to a European country. It did not have a DFDR required under U.S. rules- but since it was being placed onto an Air Transport Certificate of Airworthiness abroad- it was required to have a Type I DFDR installed.
• Many years ago- a Basic Fanjet Falcon 20 was moving to Ecuador. Unfortunately there was no bi-lateral agreement between the FAA and Ecuador- even though the authorities in that country were effectively mirroring the FAA’s FARs. We installed a Type I DFDR under ICAO recommended rulings.
• The first Falcon 2000 series aircraft came out before the current Type II DFDR requirements were in effect- which required an 88+ parameter monitoring set. They left the factory with 25 parameter systems instead. To place an older Falcon 2000 on a 135 certificate here in the U.S. it would be necessary to upgrade the existing 25 parameter system to an 88+ system.

CONCLUSION
All aircraft operators that are going for IS-BAO SMS Program approval for an aircraft that weighs above 59-525 lbs- and was certificated after January 1- 1989- must have a Type I DFDR installed to meet the requirements of IS-BAO.

All aircraft operators that are going for IS-BAO SMS Program approval for an aircraft that weighs above 12-567 lbs- and was certificated after January 1- 2005- must have a Type IA DFDR installed to meet the requirements of IS-BAO.

All Multi-engine turbine powered airplanes and rotorcraft with 10 or more passenger seats must have a Type I- DFDR installed by the April 7- 2012 to meet the requirements of Part 91.

Jeremy Cox draws on a wealth of experience as a pilot- an aircraft engineer/ mechanic and an aviation writer. He currently serves as Vice President at JetBrokers- Inc - a professional aircraft sales company. More information from jcox@jetbrokers.com