Here some factual Engineering Dept based guidance regarding the assessment of hard landings (
from the Boeing AMM for the B737-600/700/800/900, though other types will undoubtedly be similar):
B) Hard Landing
1) The hard landing procedure is for hard landings at any weight.
(a) If the landing is also overweight, the Overweight Landing Conditional Inspection, plus the Hard Landing Conditional Inspection, must be done as defined in the respective procedures. If damage is found in the Phase I Conditional Inspection of either procedure, then both Hard landing and Overweight Landing Conditional Inspection Phase II inspections must be done.
NOTE: for a hard landing that is overweight, the peak recorded vertical acceleration can be significantly less that the G-level thresholds provided for landings at or below the designed landing weight.
NOTE: When both the Hard Landing Conditional Inspection, and the Overweight Landing Conditional Inspection, as defined above, must be done, it is not necessary to do duplicative tasks twice, such as: Landing gear, nacelle struts, fuselage, wing LE fairings, horizontal stab, cargo area, engine inspection, flight controls, etc.
2) The pilot must make a decision if a structural examination is necessary.
(a) If a structural examination is necessary, do the procedure “Phase I Inspection” in this section.
(b) For a landing at or below the maximum design landing weight on airplanes with flight data recording systems capable of at least eight (8) samples per second, the following can be used: An indication of a hard landing on the main landing gear is a peak recorded vertical acceleration that exceeds 2.1 G (incremental 1.1 G). This vertical accelerometer data must be measured by the flight data recorded accelerometer at a data sampling rate of at least eight (8) samples per second. This vertical acceleration G-level threshold is valid for a conventional landing with impact with no more than two (2) degrees of roll, main landing gear touchdown first and normal rotation onto the nose gear. For a hard landing that is a hard nose landing or is accompanied by more than two (2) degrees of roll at the time of main landing gear impact, the recorded peak acceleration can be significantly less than the 2.1. G, but a hard landing inspection may still be necessary.
(c) For a landing at or below maximum design landing weight on airplanes with flight data recording systems capable of at least sixteen (16) samples per second, the following can be used: An indication of a hard landing on the main landing gear is a peak recorded vertical acceleration that exceeds 2.2 G (incremental 1.2 G). This vertical accelerometer data must be measured by the flight data recorded accelerometer at a data sampling rate of at least sixteen (16) samples per second. This vertical acceleration G-level threshold is valid for a conventional landing with impact with no more than two (2) degrees of roll, main landing gear touchdown first and normal rotation onto the nose gear. For a hard landing that is a hard nose landing or is accompanied by more than two (2) degrees of roll at the time of main landing gear impact, the recorded peak acceleration can be significantly less than the 2.1. G, but a hard landing inspection may still be necessary.
Reference should be made to the AMM, the most notable point of which is that IT IS THE CAPTAINS DECISION as to whether a hard landing inspection is required, regardless of the peak “G” figure. This is because due consideration needs to be given to aircraft weight, wind, which wheel touched down first, and several other ‘feel’ aspects.
It is possible to get the touch-down 'G' from out of the FMC, albeit that very few pilots are taught how to do this, and also that accessing this (ACMS) data is much dependent upon which FMC is installed (
e.g. Teledyne or Honeywell).