The sudden roar of low-flying aircraft riveted us to the spot.

低空飞行的飞机突然轰鸣，吓得我们呆在那里一动不动。

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During the past week the search was expanded several times, and by now more than 25 thousand square kilometers of rugged desert wilderness have been scanned by low-flying aircraft.

过去一个星期来，搜寻范围不断扩大。到目前为止，低空飞行的搜寻飞机已经覆盖了内华达州2万5千平方公里的荒山野漠。

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Capable of flying above 16, 000 feet, the unmanned aircraft provides low-altitude reconnaissance.

“扫描鹰”的最大飞行高度超过4880米(16000英尺)，可以提供低空侦察能力。

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Tall buildings pose an obvious danger to low-flying aircraft, but here too there are strict rules to minimise pilots' risk.

BBC: London helicopter crash: What are the rules for pilots?

Under safety regulations, tall buildings must have navigation lights on top to make them visible to low-flying aircraft, he said.

CNN: London helicopter crash prompts safety questions

As a massive security operation swung into operation, the Federal Aviation Administration barred low-flying aircraft from within 3.5 miles (5.6km) of the site.

BBC: Boston bombs: FBI probes deadly marathon 'terror' blasts