民用运输类飞机.适航条款要求研究
本文主要研究了歐洲民用运输类飞机25.729适航条款的要求，分析了中、欧两个适航当局的条款要求差异，并对差异内容进行了解读，条款的差异对飞机起落架系统的设计进行了分析。
关健词：起落架系统；25.729条款要求；条款差异分析；EASA CS-25
引言
民用飞机起落架系统的研制，需要满足25.729条款的要求。欧洲航空安全局（EASA）对该条款最近一次的修订是在第18次修订。本文对该条款的修订背景及条款内容以及中、欧条款差异进行了研究和分析，差异部分对起落架系统的设计影响进行了评估。
1 条款修订历史
25.729自CS 25部于首次发布以来，共经历了三次修订。2007年，EASA第一次修订25.729条，主要是删除条款原文中的AMC参考索引，移到25.729条款标题下面，并未改变条款的实
质要求[1]。2013年，EASA第二次修订该条，主要移除25.729（f）款，将轮胎爆破相关的内容单独组成25.734条，而将机轮刹车的温度影响要求移到25.735（l）款中[2]。2015年，EASA第三次修订25.729条，主要是明确该条款适用于起落架的伸展和收回机构，以避免歧义，并未改变条款实质要求[3]。
2 中、欧条款要求原文
2.1 CAAC条款原文
CCAR 25.729 Retracting mechanism
（a）General. For airplanes with retractable landing gear，the following apply：
（1）The landing gear retracting mechanism，wheel well doors，and supporting structure，must be designed for—
（i）The loads occurring in the flight conditions when the gear is in the retracted position，
（ii）The combination of friction loads，inertia loads，brake torque loads，air loads，and gyroscopic loads resulting from the wheels rotating at a peripheral speed equal to 1.3VS（with the flaps in takeoff position at design takeoff weight），occurring during retraction and extension at any airspeed up to1.6VS1（with the flaps in the approach position at design landing weight），and
（iii）Any load factor up to those specified in 25.345（a）for the flaps extended condition.
（2）Unless there are other means to decelerate the airplane in flight at this speed，the landing gear，the retracting mechanism，and the airplane structure（including wheel well doors）must be designed to withstand the flight loads occurring with the landing gear in the extended position at any speed up to 0.67 VC.
（3）Landing gear doors，their operating mechanism，and their supporting structures must be designed for the yawing maneuvers prescribed for the airplane in addition to the conditions of airspeed and load factor prescribed in paragraphs（a）（1）and（2）of thi
s section.
（b）Landing gear lock. There must be positive means to keep the landing gear extended，in flight and on the ground.
（c）Emergency operation. There must be an emergency means for extending the landing gear in the event of—
（1）Any reasonably probable failure in the normal retraction system；or
（2）The failure of any single source of hydraulic，electric，or equivalent energy supply.
（d）Operation test. The proper functioning of the retracting mechanism must be shown by operation tests.（e）Position indicator and warning device. If a retractable landing gear is used，there must be a landing gear position indicator（as well as necessary switches to actuate the indicator）or other means to inform the pilot that the gear is secured in the extended（or retracted）position. This means must be designed as follows：
（1）If switches are used，they must be located and coupled to the landing gear mechanical systems in a manner that prevents an erroneous indication of “down and locked” if the landing gear is not in a fully extended position，or of “up and locked” if the landing gear is not in the fully retracted position. The switches may be located where they are operated by the actual landing gear locking latch or device.
（2）The flightcrew must be given an aural warning that functions continuously，or is periodically repeated，if a landing is attempted when the landing gear is not locked down.
（3）The warning must be given in sufficient time to allow the landing gear to be locked down or a go around to be made.
（4）There must not be a manual shut-off means readily available to the flightcrew for the warning required by paragraph（e）（2）of this section such that it could be operated instinctively，inadvertently，or by habitual reflexive action.
（5）The system used to generate the aural warning must be designed to eliminate false or inappropriate alerts.
（6）Failures of systems used to inhibit the landing gear aural warning，that would prevent the warning system from operating，must be improbable.
（f）Protection of equipment in wheel wells. Equipment that is essential to safe operation of the airplane and that is located in wheel wells must be protected from the damaging effects of—
（1）A bursting tire，unless it is shown that a tire cannot burst from overheat；and
（2）A loose tire tread，unless it is shown that a loose tire tread cannot cause damage.
2.2 EASA款原文
CS 25.729 Extending and retracting mechanisms
（a）General. For aeroplanes with retractable landing gear，the following apply：
（1）The landing gear extending and retracting mechanisms，wheel well doors，and supporting structure，must be designed for：
（i）the loads occurring in the flight conditions when the gear is in the retracted position；
（ii）the combination of friction loads，inertia loads，brake torque loads，air loads，and gyroscopic loadsresulting from the wheels rotating at a peripheral speed equal to 1.23VSR（with the flaps in take-off position at design take-off weight），occurring during retraction and extension at any airspeed up to 1.5VSR1 with the wing-flaps in the approach position at design landing weight，and（iii）any load factor up to those specified in CS 25.345（a）for the wing-flaps extended condition.
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