Research on Flight Test Method for High Speed Characteristic — Dive to VDF/MDF in Civil Aircraft

Abstract

This paper investigates the flight test method for the high speed characteristic – dive to VDF/MDF on civil transport category aircraft equipped with high-speed protection functions. The existing CCAR 25.335(b)(1) does not address the influence of high-speed protection, which may prevent the aircraft from maintaining the required dive flight path angle or cause recovery load factor exceeding the value required by the provision. Taking a specific twin-engine civil mainline airliner as a reference case, a special condition referring to EASA CS 25.335(b)(1)(ii) is established as part of its certification basis. The typical design architecture of a high-speed protection control law is introduced, followed by detailed flight test procedures for both 7.5° and 15° flight path angles. Flight test data from the certification campaign of this aircraft are presented to illustrate aircraft responses and key maneuvering points, including practical recommendations such as decelerating before dive, timing based on speed or over-speed warning, and releasing the stick for recovery to avoid excessive load factor. The results demonstrate that the proposed test methods are feasible and effective, providing a practical reference for the certification process of similar aircraft types, particularly in establishing the certification basis (special condition) and flight test methods for high speed characteristic testing.