Critical DME
在FAA中,Critical DME的定義:
地址:http://www./air_traffic/flight_info/aeronav/criticaldme/
A critical Distance Measuring Equipment (DME) is a DME facility that, when notavailable, results in navigation service which is not sufficient forDME/DME/IRU operations along all or portions of a specific route or procedure.The required performance assumes an aircraft's RNAV system meets the minimumstandard (baseline) for DME/DME RNAV systems found in AC 90-100A, appendix 1,or the minimum standard for DME/DME/IRU systems found in AC90-100A, appendix 2.For example, terminal RNAV DPs and STARs may be published with only two (2)DMEs, in which case, both are critical.
If any critical DME facilities exist on an RNAV DP or STAR, they are identifiedon the relevant chart. NOTAMs should be checked to verify the operation ofcritical DMEs for navigation relying on DME. Pilots should assess theircapability to navigate (potentially to an alternate destination) in case offailure of critical DME while airborne. The critical DME list is updated ascharts are published. This list is searchable to determine which facilities arecritical for portions or all of a procedure and/or route.
在google里關(guān)于DME GAP的說(shuō)法:
DME Gap is the distance where you wonthave any signal coverage from the navaids the procedure is based upon. If youhave any other equipment onboard, i.e. GPS/GPS you can still fly the procedureaccurate.
Critical DME has to do with your RNAV Capabilities and availability for theSTAR/SID. Japan has not quite embraced pure GPS navagation so for RNAV aircraftyou must also have ground based navaids for backup position recognition. So. Toanswer your question Lets go though the chart. Lets take the Celes Rnav Arrivalto RWY 34.
In this case the box on the lower left hand corner (if using Jepps) shows theCritical DME. Let's take the Kajiki VOR for example. it has a DME Gap of 12.5NM, so basically if the KGE VOR is inop, somewhere in this arrival there wouldbe a 12.5nm gap in coverage of the ground based navaids to calculate DME/DMEfor your RNAV equipment. Obviously this is probably not a problem because mosttransport catagory aircraft use a FMS that has GPS/GPS or GPS/DME calculationsso you're navigation performance is not degraded significantly. Most operatorsin Japan have a DME Gap limit for each type of aircraft flown. My aircraft forexample has a max DME Gap of 14.0 nm, so if the KGE VOR (which is mostrestrictive) is INOP I am still ok to fly this arrival.
RNAV運(yùn)行不是一定需要借助GNSS系統(tǒng),它完全可以利用地基導(dǎo)航系統(tǒng)進(jìn)行定位并完成RNAV運(yùn)行。
所以在PBN運(yùn)行中,如果GNSS數(shù)據(jù)不可用,則飛機(jī)還可以依賴(lài)其他傳感器或?qū)Ш皆O(shè)備進(jìn)行定位,從而完成PBN運(yùn)行。在RNAV1和RNAV2中,飛機(jī)可以依賴(lài)DME/DME/IRU定位。此時(shí)機(jī)組必須確認(rèn)關(guān)鍵DME臺(tái)工作正常。RNAV1經(jīng)常用于進(jìn)離場(chǎng)程序,在杰普遜航圖中的進(jìn)離場(chǎng)圖中,會(huì)經(jīng)常用一個(gè)表格列出Critical DME和DME GAP。如下圖:(以下表格識(shí)讀方法為筆者推測(cè),準(zhǔn)確與否還有待考證)
![](http://image109.360doc.com/DownloadImg/2018/07/0922/138076586_2_20180709102027629.png)
ROUTE SEGMENT表示該Critical DME所處的位置和DME GAP影響的航段,而DME GAP表示該Critical DME信號(hào)無(wú)法覆蓋到的范圍。但還有下列一種表格:
![](http://image109.360doc.com/DownloadImg/2018/07/0922/138076586_3_20180709102027832.png)
這里的DME GAP所表示的意義僅為在該范圍內(nèi)沒(méi)有除了GNSS以外的任何導(dǎo)航設(shè)施的信號(hào)覆蓋。但是這并不代表在該范圍內(nèi)無(wú)法繼續(xù)執(zhí)行RNAV程序?qū)嵤┻M(jìn)近,因?yàn)橛蠫NSS可以繼續(xù)進(jìn)行定位導(dǎo)航。關(guān)于DME GAP的產(chǎn)生原理:根據(jù)《在航路和終端區(qū)實(shí)施RNAV1和RNAV2的運(yùn)行指南》里的“附件1 DME/DME RNAV系統(tǒng)的最低(基準(zhǔn))性能標(biāo)準(zhǔn)”里的規(guī)定:
![](http://image109.360doc.com/DownloadImg/2018/07/0922/138076586_4_201807091020284.png)
由此可知,只有滿(mǎn)足以上規(guī)定范圍的DME才被作為有效的DME。這也很好理解,因?yàn)镈ME所測(cè)距離為斜距,因此越靠近DME上方,由于航空器和DME的高度差的影響,其所測(cè)距離越不準(zhǔn)確。但要說(shuō)明另外一種情況,在進(jìn)近著陸的時(shí)候DME不可用的范圍要比上述規(guī)定的范圍要小很多,因?yàn)榧磳⒅懙暮娇掌髋cDME的高度差變得很小,所以其所提供的斜距仍具有較高的精確度。