Relatives of passengers onboard the downed Malaysia Airlines flight MH 17 arrive at Kuala Lumpur International Airport in Sepang July 18, 2014. [Photo/Agencies]

　　The explosion captured in a video likely didn't happen until the Boeing 777 aircraft crashed into the ground, Timothy Holt, a professor at Embry-Riddle Aeronautical University told ABC News。

　　"In this case, it looks like most of the aircraft disintegrated upon impact [with the ground]," he said。

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　　飞机被导弹击中，究竟会发生什么？美国广播公司(ABC)就此采访专家后指出，马航MH17航班遭此横祸时，机上的人们不知道导弹来袭，即使知道也无力阻止惨剧发生。

　　当地时间7月17日，马来西亚航空公司一架波音777客机在靠近俄罗斯边界的乌克兰东部地区坠毁，机上298人全部遇难。

　　What happened to the aircraft depends on where the missile struck, he explained, saying that if it pierced the wings -- where the fuel is located -- the plane might have exploded mid-air。

　　乌克兰内政部长顾问安东•杰拉申科宣称，客机在1万米的高空飞行时被一枚导弹击中，而这枚导弹是由巴克(Buk)导弹发射器发射。美政府官员也表示，是一枚地对空导弹导致了这场灾难，但尚无法确定导弹是来自乌克兰还是俄罗斯境内，以及导弹的发射方。

　　But with this explosion, "it looks like most of the gas was still contained," Holt said。

　　"You don't see a fireball in the sky ... you see the flame when it hits, you see the black clouds coming out."

　　Commercial planes like the one that was taken down today in eastern Ukraine carrying 295 people don't have the equipment that lets crews know if a missile is tracking the aircraft. The only way a pilot might know is if he saw the missile fired from the ground。

　　"If you had some warning in a commercial aircraft, if you see a visual, the best you could hope for is maybe doing a quick descent, taking it into a turn," said Holt, who flew surveillance aircraft in the U.S. Navy for about 15 years. "But we're not talking a high-performance jet that's going to try to out-maneuver a missile. I don't see a way pilots really could have avoided it at that point. And commercial pilots aren't trained for missile strikes."

　　It's not yet clear if passengers, whose remains are scattered in Hrabove in eastern Ukraine, died immediately when the missile struck or possibly minutes later, when the plane crashed to the ground。

　　美国安博瑞德航空航天大学教授蒂莫西•霍尔特表示，从事发视频中可以看到，这架波音777客机是撞向地面时才发生了爆炸，“在这种情况下，像是飞机受地面撞击的影响而解体”。

　　霍尔特进一步解释称，至于飞机究竟遭到何种损坏，则取决于其被导弹击中的具体位置。“如果导弹穿过装有燃油箱的机翼，飞机会在半空中爆炸。但在视频里，马航客机没有在空中变成一个火球，而是待其坠至地面时，才看见火焰和浓烟。”

　　霍尔特还表示，受机载设备局限，驾驶波音777之类商用客机的飞行员无法知晓是否有导弹正在追踪飞机，假如他知道了，唯一的解释就是他透过窗户玻璃看到了导弹。

　　“即使收到了预警、发现了导弹，飞行员能够采取的最佳避险措施可能只是操纵飞机快速下降、急转弯……”霍尔特曾在美国海军服役，担任侦察机飞行员长达15年，“但民用客机不是高性能喷气式飞机，它无法应对导弹。我认为，在当时的情境下，马航飞行员根本无法避开导弹，毕竟他们也没有接受过导弹袭击相关培训。”

　　"A lot depends on missile type and where the missile impacts," Holt said。

　　A U.S. official told ABC News that a surface-to-air missile struck the Boeing 777 that went down today in Ukraine near Russia's border. It is unclear whether the missile was fired from inside Ukrainian or Russian territory and who fired it, the official added. Debris and remains are spread across 10 miles in the area。

　　The flight, carrying 280 passengers and 15 crew members, was traveling from Amsterdam to Kuala Lumpur。

　　目前，还不清楚遇难人员是在客机被导弹击中后立即丧生还是死于几分钟后的地面撞击。“诸如此类的许多细节问题，要由导弹类型、击中位置等事故要素来决定，”霍尔特说。