Japanese investigators are advising improvements to the longitudinal stability system on the Boeing MD-11 to reduce the risk of hard landing, in the wake of the fatal FedEx roll-over at Tokyo.
The inquiry is also recommending studies to determine whether a visual display of landing-gear touchdown status, and an aural warning system, would aid recovery from a bounced landing and enable the crew to judge whether a go around is necessary.
Both pilots were killed when the freighter landed heavily on Narita's runway 34L and bounced, the impact fracturing its left wing and causing the aircraft to roll inverted and veer off the runway. It caught fire and the blaze destroyed the aircraft.
In its final analysis of the March 2009 accident the Japan Transport Safety Board found the aircraft's approach, in gusting winds, was unstable and the MD-11F flared late, at only 20ft. The late flare did not arrest the descent rate, and the jet bounced, while a large nose-down pitch input initiated a porpoising effect.
It bounced again and the heavy third impact - more than 3g vertically and some 6.8 times the ultimate load for certification - snapped the wing. The MD-11 is susceptible to wing fracture during hard landings which result in vertical overload of the airframe structure, and this has led Boeing to develop flight-control systems to lessening such loads.
These include a longitudinal stability augmentation system which assists in protecting pitch attitude. The inquiry says the functions of this system should be improved, possibly to incorporate a limit on large nose-down elevator inputs during touchdown.
FedEx, which also operated the MD-11F involved in a similar accident at Newark in 1997, has since taken measures to prevent a recurrence.
It raised the height for initiating flare to 40-30ft, revising operating manuals to reflect the change as well as removing references which allow nose-down elevator input on landing.
FedEx introduced additional simulator training sessions to underline the need to control descent rates with thrust, particularly below 50ft. Its manual revisions also included directives to execute a go-around in the event of a bounced landing.
The JTSB says the carrier has "aggressively reinforced" the go-around as a safety strategy. "As a result, [operational safety] data indicate that go-arounds in response to bounces have increased," it adds.
FedEx has also installed head-up displays in cockpits to improve pilot awareness during the landing phase.