Consultation expired without comments.
Details
Introduction of M-TS reference and clarification that the CS 25.571 applicability is a note and not a special condition (SC) itself. As per Management Board (MB) Decision 12-2007, the update is evaluated as "non-important" and is therefore not subject to a new public consultation.
Identification of issue
An automatic braking (autobrake) system is a pilot-selectable function that allows earlier braking at landing without pilot pedal input. When the autobrake system is armed before landing, it automatically commands braking at, or very shortly after, main wheels touchdown. Normal procedures remain unchanged and call for manual braking after nose wheel touchdown.
CS-25 does not contain adequate specifications to address the potentially higher structural loads that could result from this type of braking system.
CS 25.493 addresses braked roll loads, but does not contain a specific “pitchover” requirement addressing the loading on the nose gear, the nose gear surrounding structure and the forward fuselage. Moreover, CS 25.493 specifies aeroplane attitudes in accordance with CS-25 Appendix A figure 6, which are level landing attitudes. For aeroplanes with traditional braking systems, the current ground loads requirements are considered adequate for the design of the nose gear and airframe structure. However, an aeroplane autobrake system, which could apply braking at the main wheels with the aeroplane in a tail-down attitude, well before the nose touches down, will cause a high nose gear sink rate and potentially higher gear and airframe loads. Therefore, EASA has determined that additional airworthiness standards are needed for the certification of this unusual design feature.
The effects on fatigue covered by CS 25.571 also need to be considered.