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twelve airplanes (17 percent) were de-stroyed in hard-landing accidents, and 47 airplanes (67 percent) were substan-tially damaged. Eleven airplanes received minor damage in hard landings during the period.
‘Hard Landing’ Not Well Defined
T
here appears to be no universal defini-tion of hard landing. The International Civil aviation organization (iCao) as-signs event code 263 for the reporting of hard landings by member states but has no formal definition of the term.4
Milton Wiley, an ICAO technical officer, said that the ICAO accident and incident database (adReP) includes hard land-ings in the category of events involving abnormal runway contact. 5
“There is no hard and fast rule for report-
ing a hard landing,” Wiley said “it really is in the eyes of the beholder.”
The Transportation Safety Board of CanadaandtheFrenchBureaud’Enquêtes et d’Analyses pour la Sécurité de L’Aviation Civile are among accident-investigation authorities that use the ICAO event code but have no formal definition of hard landing.6,7
In the United States, the National
transportation Safety Board (ntSB)
coding manual defines hard landing as “stalling onto or flying into a runway or other intended landing area with abnor-
mally high vertical speed.”8
Jacques Leborgne, senior director of structure engineering for Airbus, defined
a hard landing as one that exceeds the
limit landing loads specified in European
Joint airworthiness Requirements (JaRs)
and U.S. Federal Aviation Regulations (FaRs) transport category airplane cer-tification requirements.9

Landing Gear Absorbs the Shock
A
n airplane’s kinetic energy (vertical load, side load, back load, etc.) on touchdown is dissipated by the landing gear.10 The energy is dissipated primarily by the landing-gear struts. A strut typically is filled with oil that is forced at a controlled rate through an orifice as the strut is compressed on touchdown.

Under normal conditions, landing-gear load is
affected directly by the airplane’s gross weight.
As gross weight increases, the required approach speed increases. If the glide path is the same (e.g.,
an approach on a three-degree glideslope), the
higher approach speed results in a higher descent rate and, thus, a higher load on the landing gear. The load placed on the landing gear increases as the square of any increase in the vertical rate of
descent. For example, a 20 percent increase in vertical rate of descent (i.e., descent rate times 1.2) increases the landing load factor by 44 percent (1.2 squared = 1.44).11
Landing gear are either overdesigned to withstand landing loads greater than those required for cer-tification or incorporate fuse pins, which ensure that the landing gear breaks from the wing when
loads exceed the design limit. loads not dissipated
　
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