朱鳴鳴

摘要：本文主要研究了歐洲民用運(yùn)輸類飛機(jī)25.729適航條款的要求，分析了中、歐兩個適航當(dāng)局的條款要求差異，并對差異內(nèi)容進(jìn)行了解讀，條款的差異對飛機(jī)起落架系統(tǒng)的設(shè)計(jì)進(jìn)行了分析。

關(guān)健詞：起落架系統(tǒng)；25.729條款要求；條款差異分析；EASA CS-25

引言

民用飛機(jī)起落架系統(tǒng)的研制，需要滿足25.729條款的要求。歐洲航空安全局（EASA）對該條款最近一次的修訂是在第18次修訂。本文對該條款的修訂背景及條款內(nèi)容以及中、歐條款差異進(jìn)行了研究和分析，差異部分對起落架系統(tǒng)的設(shè)計(jì)影響進(jìn)行了評估。

1 條款修訂歷史

25.729自CS 25部于首次發(fā)布以來，共經(jīng)歷了三次修訂。2007年，EASA第一次修訂25.729條，主要是刪除條款原文中的AMC參考索引，移到25.729條款標(biāo)題下面，并未改變條款的實(shí)質(zhì)要求[1]。2013年，EASA第二次修訂該條，主要移除25.729（f）款，將輪胎爆破相關(guān)的內(nèi)容單獨(dú)組成25.734條，而將機(jī)輪剎車的溫度影響要求移到25.735（l）款中[2]。2015年，EASA第三次修訂25.729條，主要是明確該條款適用于起落架的伸展和收回機(jī)構(gòu)，以避免歧義，并未改變條款實(shí)質(zhì)要求[3]。

2 中、歐條款要求原文

2.1 CAAC條款原文

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、歐條款要求差異分析

中國民用航空局（CAAC）于2011年發(fā)布了最新的第25部運(yùn)輸類飛機(jī)適航標(biāo)準(zhǔn)（R4版）[4]，CCAR25.729與CS25.729仍存在一定的差異，詳細(xì)差異比對如下：

a）標(biāo)題差異，CS25.729標(biāo)題特別增加了“extending”，用于表明該條款適用于伸展和收回機(jī)構(gòu)；

b）25.729（a）（1）（ii）中計(jì)算起落架收放機(jī)構(gòu)承受的載荷使用的空速要求不一樣。關(guān)于陀螺載荷，CAAC是參考1.3VS的機(jī)輪邊緣速度，EASA則用 1.23VSR；收放過程的載荷，CAAC要求是不超過1.6VS1速度下的載荷組合，EASA是要求直到1.5 VSR1的速度下的載荷組合；

c）25.729（a）（2）中EASA對收放機(jī)構(gòu)的翻譯采用extending and retracting，與CAAC采用的retracting不一樣；

d）25.729（b）中，關(guān)于起落架鎖的要求，CAAC只要求鎖能在空中和地面將起落架保持在放下位置，EASA除此之外還進(jìn)一步要求鎖在空中能將起落架和起落架艙門保持在收上位置，除非表面任何空速下放下起落架和艙門不會產(chǎn)生危害。

e）25.729（e）中，關(guān)于起落架位置指示的要求，EASA進(jìn)一步突出強(qiáng)調(diào)飛行員或相應(yīng)的機(jī)組成員容易看見該位置指示，明確指示起落架及相關(guān)艙門已鎖在收上位置或放下位置。

f）25.729（e）（5）中，關(guān)于減少不當(dāng)告警和虛假告警，CAAC要求的程度是“eliminate”，EASA則要“minimise”。

g）EASA多了一款25.729（e）（7），要求當(dāng)起落架位置與起落架控制桿不一致時飛機(jī)應(yīng)向機(jī)組發(fā)出告警，CAAC沒有該款。

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

4 中歐條款要求差異分析

上述規(guī)章差異主要集中在25.729（a）款、（b）款和（e）款，對飛機(jī)起落架的設(shè)計(jì)影響分析如下：

a）針對25.729（a），VS是飛機(jī)失速速度或最小定常飛行速度，在該速度下飛機(jī)是可控的。VS1是飛機(jī)在某個特定形態(tài)下得到的失速速度或最小定常飛行速度。VSR是參考失速速度，并且不得小于1-g失速速度。VSR1是飛機(jī)在某個特定形態(tài)下的參考失速速度。由于1-g失速速度比在失速機(jī)動中獲得的最小速度大，因此對參考VSR速度的系數(shù)進(jìn)行了適當(dāng)?shù)慕档?，?shí)際差異不會太大[5]。CAAC在修訂25部R4版本時，其他部分的條款已經(jīng)改為用VSR作為參考失速速度，但25.729條款中的參考速度遺漏而未改。起落架收放機(jī)構(gòu)的載荷計(jì)算，通過換算參考速度取兩個規(guī)章中的較大者就能同時滿足CAAC和EASA的要求。

b）針對25.729（b），雖EASA多了在鎖在空中保持起落架和艙門在收上位置的要求，一般在設(shè)計(jì)可收放起落架時，除了要能放下起落架，還要在飛機(jī)飛行時能使起落架及其艙門保持收上位置，同時也是飛機(jī)的設(shè)計(jì)需求之一，無需更改系統(tǒng)架構(gòu)也能滿足EASA的要求。

c）針對25.729（e），對設(shè)計(jì)的影響有限。首先，EASA多出來的條款要求，即使CAAC沒有要求，但從系統(tǒng)安全性分析出發(fā)，也會在系統(tǒng)架構(gòu)設(shè)計(jì)時要求起落架位置與操作桿不一致時發(fā)出告警，無需更改系統(tǒng)架構(gòu)也能滿足EASA的要求。

綜上分析，雖然中、歐在25.729條款上存在不少差異，但這些差異對設(shè)計(jì)的影響不大，不會引起系統(tǒng)實(shí)質(zhì)性的架構(gòu)更改，只是在表明對CS25.729條款的符合性時需要提供更多的證據(jù)。

5 總結(jié)

本文討論了EASA CS25.729條款的修訂歷史以及中、歐適航規(guī)章在該條上的差異，以及分析了差異對飛機(jī)起落架系統(tǒng)設(shè)計(jì)的影響，為飛機(jī)EASA型號取證工作提供參考。

參考文獻(xiàn)：

[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部運(yùn)輸類飛機(jī)適航標(biāo)準(zhǔn)