lomapaseo;
I couldn't tell from my read if the G reading was before or after it hit he ground. It does make a difference.
In flight data analysis, 'g' is usually sampled at pretty high rates. The 320 LFL (logical frame layout - the software "frame", something like a spreadsheet, into which data is recorded) records 'g' at 8x per second. The DFDR (crash recorder) on the 777 records 'g' at the same rate but our LFL for the 777 records it at 10x per second.
UDRI, the
University of Dayton Research Institute with whom I and others have collectively worked in the past, does a very wide-ranging loads analysis program on different airframes including the 777. They wrote a
paper a while back discussing the reliability of the 'g' parameter on the Boeing 777 because of the sensors' location in the cockpit area, (IRS's), instead of near/at the center of gravity of the airplane*. We concur with that finding, (no formal communications with UDRI - it's a known issue for the Boeing).
The reading and interpretation of flight data requires considerable "time in". What can appear a "holy cow", can in fact be a non-event. The reverse can also be true.
The Airbus 'g' parameter is 99% reliable in my experience although, like any data, it can in rare occasions exhibit a spike or two. The way to read the parameter, (which is obvious if one thinks about it), is to see what the readings before and after the highest reading are doing.
A "3.5g" reading does not occur in one-eighth of a second - it will have a "ramp up", "ramp down" of readings in the previous and post samples even if it occurs over a half-second, (four readings).
I have seen such readings and before apprising anyone we ensure that such readings are valid, using this and other techniques such as interpreting the IVSI parameter. Anything over 6fps (about 340fpm) usually results in a hard landing. We also look at the rate of change of the radio altimeter which is also sampled at between four and eight times per second, (the 777 has 3 radio altimeters and parameters).
Interestingly, the 777 AMM states very clearly that the pilot must first report a hard landing (or any other aircraft limitation exceedance) before maintenance action will take place. Once reported, the 777 has the usual limits which are then examined in the DFDR or QAR to determine what kind of hard landing check is required. In other words, if it is not reported by the pilot, it didn't happen. The Airbus philosophy is substantially different, where data is an integral part of the operation. I do not know why these differences obtain and do not wish to spark an AB "discussion". The one difficulty inherent in waiting until a pilot reports an airframe exceedance however is, such an exceedance is always available and known through the daily flight data analysis by the safety department personnel but, because of the way the 777 AMM is written, even though there may be significant exceedance indicated in the data, the operator is not required to do anything about it. For many including myself, there are inherent ethical, legal and technical issues outstanding in this approach now that data analysis is becoming not only routine but mandated under SMS.
Also, there is in place, a mistaken impression, principally from operations and maintenance personnel, probably not intentional of course, that views "QAR" data as somehow "inferior" to DFDR data and so can be safely dismissed when/if commercially inconvenient, as "advisory" only. QAR data is the same kind of peripheral as the DFDR and receives exactly the same digital data from the ARINC 429, 617 etc databusses that the DFDR does. If the data is bad for the QAR, then it is likely bad for the DFDR in which case there could be a pending legal issue. The prevalence of this view (that QAR data is "not valid"), is a regulatory matter and not merely an airline SMS issue. Anyway, enough thread drift - the 'g' readings on this 320 are almost certainly accurate, having seen them and analyzed them in other cases. If I recall, a "3.5" g reading exceeds 320 airframe certification limits by at least 1g if not 1.5g's.
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* From the Abstract:
The B-777 airplane sensors, which measure vertical, lateral, and longitudinal acceleration, are located in the cockpit area. The estimates of the center of gravity (c.g.) accelerations are computed in the Air Data Inertial Reference Unit, which converts the measured crew station accelerations to accelerations at the c.g. For some dynamic and ground load conditions, inaccuracies could exist in these filtered c.g. time history measurements. Operators and inspectors who use the recorded B-777 acceleration values as maintenance action triggers or Flight Operational Quality Assurance events should recognize the possibility of recorded Digital Flight Data Recorder acceleration inaccuracies.