overthewing asks
Originally Posted by overthewing
can anyone tell me what the FDR actually records?
Modern FDRs record a few hundred parameters. However, as Mad (Flt) Scientist points out, the parameters *required* to be recorded are comparatively few. In other words, you need to know the specific FDR installation to know what's on it.
Originally Posted by overthewing
if it records something that was commanded to happen, would it necessarily know that the 'something' didn't actually happen, if there was no failure signal?
One interpretation of the question: if the FDR records a command signal, does it necessarily record the reaction, if there is no equivalent sensor or other similar feedback?
The answer: obviously it doesn't.
Next interpretation: Are there command signals recorded, such that the reaction of the kit to that signal is not recorded?
Answer: Undoubtedly so.
Originally Posted by overthewing
... the fuel valves apparently tried to open to allow maximum fuel throughput. Would it be possible for the FDR to record the open-valve event, but have no knowledge of the valve's failure to do so?
Rephrase: is it possible for the FDR to record an open-valve command signal without recording the sensed position of the valve?
Answer: sure it's *possible*, but whether anything like that happened is something that I would think the AAIB knows already.
As FullWings notes, actual fuel flow is so fundamental a flight parameter that one assumes that both command and reaction are recorded. However, one does needs to know how something is sensed and what the failure modes of sensing are in order to judge whether record is a reliable indication of reality.
PBL