With regard to Flight Data Recorder Systems, what exactly does wps imply? I have noticed this abbreviation in our FDR documentation and in conversations several times:
wps = words per second. A word (12-bits in length) contains binary data which represents a specific parameter value. Please see figure 1 below. Your FDR records in frames (4 second intervals) and each frame contains 4 sub frames (one sub frame = 1 second). With each second that goes by a specific quantity of words are recorded into memory. If you operate a 64 wps FDR system, you will record 64 12-bit words in one second. The higher the word capacity the more information you can record.
|One Frame is equal to four (4) seconds|
|Subframe 1||Subframe 2||Subframe 3||Subframe 4|
|Word 1 = Sync Word|
|Word 2 = Vertical Acceleration||101101011101|
|Word 3 = Pitch|
|Word 64 = EGT|
How can I determine the speed of my Flight Data Recording system in words per second (wps)?
There are basically 4 ways to determine your speed, with the 4th being a bit more involved. First, the speed should be listed or documented in chapter 31 of your aircraft Maintenance Manual and/or Wiring Diagram Manual. However there are times when for some reason, the required information cannot be found. If this is the case, as a second method, you may reference the CMM or technical specification for your Flight Data Acquisition Unit (FDAU). If you are still unable to find this information, you may contact the aircraft manufacturer for the wps or review your previous FDR download analysis reports. Please keep in mind, the OEM will only know the as-delivered configuration of your aircraft. If there were modifications to your aircraft post-delivery - manufacturer unaware of the changes - youll need to contact us for an analysis of your raw data. Using our software we can determine the wps of your system.
Can you tell me the difference between the words Readout, Analysis, and Download with regards to FDR maintenance?
Readout = Download + Analysis. Historically, the FDR was removed from the aircraft and sent to an experienced FDR shop for download (data extraction) and analysis of the data. This entire process was known as an FDR Readout. Today the process of download and analysis are often separate, with the airline accomplishing the download and the shop accomplishing the analysis of the data. As such, Download simply means using a FDR downloader to extract the flight data into a file. The file can then be sent out for Analysis.
How can I determine the amount of hours recorded by my FDR?
For the simple case, recorded hours are dependent on a combination of your FDAU wps output and FDR maximum allowable recording speed. If there is a one to one relationship between the two units, i.e. - 64 wps FDAU with a 64 wps FDR, you will record the last 25 hours of flight data. This also applies to the case when the FDAU and FDR are both 128wps, 256wps, or even higher. If there is a mismatch between the FDAU and FDR speed, a small and simple calculation can be made to determine actual flight hour recording capacity. See figure 2 below for the various possibilities:
|FDR @ 64 wps||FDR @ 128 wps||FDR @ 256 wps|
|FDAU @ 64 wps||25 hours||50 hours||100 hours|
|FDAU @ 128 wps||25 hours||50 hours|
|FDAU @ 256 wps||25 hours|