landing inertia readout

[aeroguru]

anyone know how to view the landing g force at the flight deck of a B747-4?

[Blacksheep]

To view the actual instantaneous landing "G" force of any aircraft you would need a specially instrumented aircraft that monitored "G" continuously. The FDR records Vertical Acceleration only as a series of extremely short samples recorded eight times per second. In other words it plots a graph of vertical acceleration as a series of points on a time base of one eight of a second. The chances of one of the sample points actually coinciding with the instant of touchdown are very remote, the peak "G" is more likely to occur between samples. Boeing specifically stated, when we posed the question asked by our Flight Operations "What would be the DFDR reading for a 'Heavy Landing'", that it is not possible to tell. Quote "A heavy landing is one that is heavy in the opinion of the crew or after which signs of structural damage or overload are evident." Unquote.

In conclusion: Don't try to use aircraft instruments for purposes for which they were not designed nor overestimate their accuracy.

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Through difficulties to the cinema

[aeroguru]

Thanks Blacksheep for clarifying that one.
MM talks about 8 sample and 16 sample FDR's.
So do I conclude then that the write up "heavy landing" could never be cleared by answer "checked DFDR, readout was well below 1.7".Because I have seen this done.MM talks about 1.7G(incremental 0.7G)and I assume there would be an auto snapshot above this?

[CONES R US]

Just as an additon to your question, older military aircraft used to have G meters fitted to them (dunno about the newer stuff) where there was a meter for each axis and a pointer. How ever far along each scale the pointer had moved, showed the max G in that axis the aircraft had pulled. They were checked each day and reset. Just thought you might like to know that.

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NO FAULT FOUND