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by the landing gear typically are transferred to the landing-gear support structure, wing spars, fuselage structure and skin.
During the certification of transport cat-egory airplanes, the European Joint Aviation authorities (Jaa)12 and the U.S. Federal Aviation administration (Faa)13 require a test of “reserve energy absorption,” in which the landing gear must withstand touchdown at a descent rate of 12 feet
per second with the airplane at the design landing weight and with lift not greater than weight on
impact (i.e., with a vertical acceleration of 1.0 g [standard gravitational acceleration]).
JAA and FAA also require that the main land-
ing gear on transport category airplanes with 10
or more passenger seats be designed so that an overload failure is not likely to result in enough fuel spillage to create a fire hazard.

Is the Landing ‘Hard’ or Just ‘Firm’?
E
arly in their careers, pilots typically strive to conduct smooth touchdowns, in which the transition from flight to the landing roll is barely noticeable. A smooth touchdown typically is accomplished by extending the flare to allow airspeed to decrease to just above the point of a stall.14
The loss of airspeed during an extended flare,
however, can result in a sudden, rapid loss of altitude and a hard landing.15 A normal flare that results in a smooth touchdown in the runway touchdown zone generally is desirable when flying turbine-powered airplanes. Nevertheless, a firm touchdown might be appropriate in specific con-
ditions (e.g., crosswinds, a short runway and/or a
runway that is wet or contaminated with standing
water, snow, slush or ice).
The major advantage of a firm landing is the reduced risk of a runway overrun. Deliberately and positively landing the airplane in the runway touchdown zone not only precludes a “dropped-in
touchdown” but promptly gets the weight of the
airplane on the main wheels, thus improving the
effectiveness of wheel braking. a firm landing also
allows the pilot to fly the nosewheel onto the run-way, reducing angle-of-attack and lift, and further
improving the effectiveness of wheel braking.
As a report by a Boeing 737 captain to the U.S. National Aeronautics and Space Administration
(naSa) aviation Safety Reporting System (aSRS) indicates, however, the difference between a firm
landing and a hard landing might not be clearly discernable.16
The captain said that the visual approach and the landing flare appeared to be normal, but the airplane bounced high on touchdown. While air-borne, the airplane pitched nose-up, and both the captain and the first officer applied nose-down pitch control. The captain said that the second touchdown and
rollout were “without incident.”
“After securing the aircraft at the gate, I asked the [first officer] if I
should write up a hard landing,”
　
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