本文轉載自【微信公眾號：我愛修飛機，ID:csnnng】經微信公眾號授權轉載，如需轉載與原文作者聯繫
前言：對於沒有明確標準的缺陷，損傷或者故障，通常根據對飛行安全有無影響來判斷標準，明顯影響安全或飛行操作的，認為飛機不能放行，比如少了一臺發動機。明顯對飛行安全沒有影響的，比如客艙一個座椅海綿墊破損，正常放行是沒有異議的。當然有些故障雖然不影響飛行安全，但考慮到舒服性，比如頭等艙座椅靠背無法向後調節，保留放行時需要公司決策。介於以上兩種情況的，如果對標準沒有把握，只能諮詢波音。
1
甚高頻天線掉漆和損傷標準
甚高頻天線掉漆或者有小缺口是常見的事 ，但對於這個缺陷的放行標準和維護標準疑問也是挺多的？AMM和SRM並沒有關於這個損傷的標準。
在日常檢查維護中，發現VHF通信天線外觀出現漆層脫落時，單個VHF天線單處漆層脫落範圍大於4CMx4CM或多處累計超過25平方釐米的，建議更換。如因時間、工具、航材等原因不能及時更換的，開非例行卡更換。如發現有缺口、裂紋、分層、劃傷、刻痕等明顯損傷，需要更換或開非例行卡儘快更換。
對於放行，如損傷已影響天線接收功能的，需要立即更換或按系統失效保留放行。損傷可能會導致導電汙染物的侵入，例如水進入到天線內部，汙染物會干擾信號的接收或傳輸，如發現此種情況，需要立即更換天線。如因時間、工具、航材等原因不能及時更換的，參考相關MEL進行保留。如不能保留的，例如1號VHF系統，由於天線無法修復，只能停場待件更換。而掉漆或者外表的一些劃傷明顯不會導致汙染物進去天線內部的，可以放行。
有了天線損傷標準判斷依據，但無法判斷什麼損傷影響到天線的接收功能，只能按個例諮詢波音。我們以上圖的小缺口損傷為例，對於距離VHF天線端部20至30毫米處存在小缺口的典型情況，根據波音SR4-4057043242，如未穿透到天線內部，允許放行，但建議開非例行卡儘快更換。
以上的損傷標準具體參考附件SR.
2
甚高頻天線件號互相性說明
查閱IPC23-12,甚高頻天線共有三個件號DMC50-17、DMC50-17-2和DMC50-17-3。尾號-2/-3的天線有紅色標記，有注意警示作用，避免被刮碰。常見的DMC50-17-3是帶紅色條紋的天線，DMC50-17是全白色的天線，如上文圖所示。DMC50-17-2沒見過實物，庫存也不多。不同件號的天線物理功能上是沒有區別的，使用時看公司對外觀顏色有無要求，互換性手冊描述如下。
3
附件SR
Service Request ID: 4-4057043242
GUN-GUN-18-0295-02B
DESCRIPTION:
China Southern experienced painting loss or erosion on VHF antenna as picture REF/A/ during routine inspections, and there was a nick on the antenna (20-30mm away antenna tip）.
China Southern can't get the VHF antenna serviceable limit from AMM and SRM.
ACTION:
Boeing please advise the VHF antenna damage replacement limit, assuming that the VHF system functions normal.
RESPONSE:
In general, antennas with lightly damaged finishes are satisfactory for flight. However, when attempting to determine whether an antenna should be replaced, the first consideration is whether it will still perform its intended function of being an antenna. The primary source of detuning antennas is the ingress of conductive contaminants, such as water, into the antenna. These contaminants can interfere with the reception or transmission of signals. Boeing's recommended guideline for the physical and visual inspection of an antenna is that if the protective finish is breached and the integrity of the antenna is compromised to the extent that water can ingress into the antenna, it should be immediately replaced.
GUN-GUN-18-0295-05B
Dear Terrence,Thanks for your reply. But I still wonder if the surface of antenna lose paint, or paint cracking or wind erosion can cause the ingress of conductive contaminants, such as water, into the antenna? And we often found there was a nick on the antenna (20-30mm away antenna tip as picture REF /B/ ）during routine inspections. We also wonder if this nick can cause the ingress of conductive contaminants?
If this nick can not cause the ingress of conductive contaminants. How can we repair? Replace it? Or filling resin adhesive into the nick, then painting?
Question 1. I still wonder if the surface of antenna lose paint, or paint cracking or wind erosion can cause the ingress of conductive contaminants, such as water, into the antenna?
Response 1. If cracks or erosion provide a path for water to ingress into the interior of the antenna, then the antenna must be replaced. The antenna elements are located in the interior, and water in the interior will interfere with reception and transmission.
Question 2. We often found there was a nick on the antenna (20-30mm away antenna tip as picture REF /B/ ）during routine inspections. We also wonder if this nick can cause the ingress of conductive contaminants?
Response 2. The nick shown in the Ref /B/ message photos does not appear to penetrate into the interior of the antenna. If this is indeed the case, the antenna is still serviceable.
Question 3. How can we repair? Replace it? Or filling resin adhesive into the nick, then painting?
Response 3. According to CMM 23-10-03, no repairs can be made on VHF antenna P/N DMC50-17.