民用运输类飞机.适航条款要求研究

朱鸣鸣

摘要：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 this 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條款原文

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.

（2）Unless there are other means to decelerate the aeroplane in flight at this speed，the landing gear，the extending and retracting mechanisms，and the aeroplane 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 manoeuvres prescribed for the aeroplane in addition to the conditions of airspeed and load factor prescribed in sub-paragraphs（a）（1）and（2）of this paragraph.

（b）Landing gear lock. There must be positive means to keep the landing gear extended in flight and on the ground. There must be positive means to keep the landing gear and doors in the correct retractedposition in flight，unless it can be shown that lowering of the landing gear or doors，or flight with the landing gear or doors extended，at any speed，is not hazardous.

（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 extension and retraction systems；or

（2）the failure of any single source of hydraulic，electric，or equivalent energy supply.

（d）Operation test. The proper functioning of the extending and retracting mechanisms 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 easily visible to the pilot or to the appropriate crew members（as well as necessary devices to actuate the indicator）to indicate without ambiguity that the retractable units and their associated doors are secured in the extended（or retracted）position. The 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 flight crew 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 flight crew for the warning required by subparagraph（e）（2）of this paragraph 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 minimise 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.

（7）A clear indication or warning must be provided whenever the landing gear position is not consistent with the landing gear selector lever position.

3 中、歐条款要求差异分析

中国民用航空局（CAAC）于2011年发布了最新的第25部运输类飞机适航标准（R4版）[4]，CCAR25.729与CS25.729仍存在一定的差异，详细差异比对如下：

a）标题差异，CS25.729标题特别增加了“extending”，用于表明该条款适用于伸展和收回机构；

b）25.729（a）（1）（ii）中计算起落架收放机构承受的载荷使用的空速要求不一样。关于陀螺载荷，CAAC是参考1.3VS的机轮边缘速度，EASA则用 1.23VSR；收放过程的载荷，CAAC要求是不超过1.6VS1速度下的载荷组合，EASA是要求直到1.5 VSR1的速度下的载荷组合；

c）25.729（a）（2）中EASA对收放机构的翻译采用extending and retracting，与CAAC采用的retracting不一样；

d）25.729（b）中，关于起落架锁的要求，CAAC只要求锁能在空中和地面将起落架保持在放下位置，EASA除此之外还进一步要求锁在空中能将起落架和起落架舱门保持在收上位置，除非表面任何空速下放下起落架和舱门不会产生危害。

e）25.729（e）中，关于起落架位置指示的要求，EASA进一步突出强调飞行员或相应的机组成员容易看见该位置指示，明确指示起落架及相关舱门已锁在收上位置或放下位置。

f）25.729（e）（5）中，关于减少不当告警和虚假告警，CAAC要求的程度是“eliminate”，EASA则要“minimise”。

g）EASA多了一款25.729（e）（7），要求当起落架位置与起落架控制杆不一致时飞机应向机组发出告警，CAAC没有该款。

h）CAAC仍保留25.729（f），EASA已在其它条款中另行要求（25.734和25.735）。

4 中欧条款要求差异分析

上述规章差异主要集中在25.729（a）款、（b）款和（e）款，对飞机起落架的设计影响分析如下：

a）针对25.729（a），VS是飞机失速速度或最小定常飞行速度，在该速度下飞机是可控的。VS1是飞机在某个特定形态下得到的失速速度或最小定常飞行速度。VSR是参考失速速度，并且不得小于1-g失速速度。VSR1是飞机在某个特定形态下的参考失速速度。由于1-g失速速度比在失速机动中获得的最小速度大，因此对参考VSR速度的系数进行了适当的降低，实际差异不会太大[5]。CAAC在修订25部R4版本时，其他部分的条款已经改为用VSR作为参考失速速度，但25.729条款中的参考速度遗漏而未改。起落架收放机构的载荷计算，通过换算参考速度取两个规章中的较大者就能同时满足CAAC和EASA的要求。

b）针对25.729（b），虽EASA多了在锁在空中保持起落架和舱门在收上位置的要求，一般在设计可收放起落架时，除了要能放下起落架，还要在飞机飞行时能使起落架及其舱门保持收上位置，同时也是飞机的设计需求之一，无需更改系统架构也能满足EASA的要求。

c）针对25.729（e），对设计的影响有限。首先，EASA多出来的条款要求，即使CAAC没有要求，但从系统安全性分析出发，也会在系统架构设计时要求起落架位置与操作杆不一致时发出告警，无需更改系统架构也能满足EASA的要求。

综上分析，虽然中、欧在25.729条款上存在不少差异，但这些差异对设计的影响不大，不会引起系统实质性的架构更改，只是在表明对CS25.729条款的符合性时需要提供更多的证据。

5 总结

本文讨论了EASA CS25.729条款的修订历史以及中、欧适航规章在该条上的差异，以及分析了差异对飞机起落架系统设计的影响，为飞机EASA型号取证工作提供参考。

参考文献：

[1]NPA 18/2006 CS-25 Amendment 4 Explanatory Note

[2]NPA 2013-02 Draft Decision of the Executive Director of the European Aviation Safety Agency

[3]NPA 2015-11 Regular Update of CS-25

[4]CCAR-25-R4 第25部运输类飞机适航标准