The 737 is capable of withstanding landings at a speed of 600 fpm, which must be reduced to 360 fpm at MLW before a hard landing inspection is necessary. The majority of pilots describe a hard landing when the sink rate surpasses 240 fpm. Due to their low sampling rates, proximity to the CofG, and potential underrepresentation of peak loads in other portions of the aircraft, on-board accelerometers are notoriously inaccurate indications of heavy landings. A hard landing may be felt at much lower vertical acceleration values if the acceleration values are recorded during a hard nose landing or accompanied by more than 2 degrees of a roll at the time of main landing gear impact.
For a number of reasons, accelerations recorded on flight data recorders are not regarded as sufficient evidence for harsh landings. Accelerometers only measure G forces where they are mounted. Due to the data sample rates, it is impossible to determine whether the forces are at a minimum, maximum, or some other number in between. During in-flight maneuvers where accelerations are constant or slowly variable, these devices can deliver accurate acceleration data.
Boeing flight experiments, though, have demonstrated that recorded acceleration data may be a wildly incorrect predictor of a hard landing. The system’s reaction during the brief period when the wheels are in touch with the runway is what causes this. The reported vertical acceleration component can become very inconsistent during this time. When data that appears to be accurate is legible, the peak value is typically not visible due to the data sampling rates or recording time intervals.
Additionally, a number of accelerometers dispersed throughout the aircraft have shown that structural dynamics, speed, external forces, and the weight of the aircraft all significantly affect the time and magnitude of G forces. Boeing has determined that a reliable technique is impractical due to the sheer volume of complicated parameters that must be analytically merged and connected to an equivalent G force component. If the acceptance criteria were to quote a G level low enough to ensure that the plane has exceeded the design sink speed, it would result in repeated and pointless inspections. Some high sink speed occurrences would go uninspected if the inspection threshold was set at a medium or high G level.
According to Boeing, the greatest sources of information for determining if a hard landing has taken place are pilot judgment and records detailing the landing. Ordinarily, pilots land the aircraft well within the permitted parameters and become used to the feeling. Translation of service experience reports reveals that when sink rates near 4 feet per second, airline flight and cabin crew frequently report a hard landing (240fpm). At the maximum designed landing weight and 6 feet per second (360 fpm) at the maximum designed takeoff weight, all Boeing model airplanes are designed to sink at a rate of 10 feet per second (600 fpm). These factors are taken into account when constructing the wing and fuselage support structure, as well as the main landing gear and nose landing gear assemblies.
Thank you for visiting our website! We hope you found soᴍᴇᴛʜing that sparked interest on our website.
Video resource: DutchPilotGirl
