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  3. Is using a cell phone aboard an airplane really dangerous? More and more airline companies are expanding in-flight Wi-Fi Interne

Is using a cell phone aboard an airplane really dangerous? More and more airline companies are expanding in-flight Wi-Fi Interne

admin2015-02-12  32
问题     Is using a cell phone aboard an airplane really dangerous? More and more airline companies are expanding in-flight Wi-Fi Internet service to their entire fleet. In-flight calls, however, are still prohibited. If one can surf the Web, why can’t he use the cell?
    It operates on a totally different frequency. Cell phones transmit signals at roughly the same frequencies as aircraft communications—pilot radios and radar range from below 100 to 2,000 MHz, and many phones operate at 850 MHz or 1,900 MHz. Your cell could therefore—at least theoretically—interfere with navigation. Wi-Fi, on the other hand, signals at a higher frequency— anywhere from 2,500 to 5,000 MHz—and thus won’t get mixed up with the plane’s transmissions.
    In-flight Wi-Fi works like a moving Starbucks hot spot. The plane is rigged with three antennae— two on its belly and one on top—that receive signals from towers across the country. The frequency of those transmissions, 849 MHz, is within the range of airline communications. But they don’t interfere with the plane’s navigation, since 849 MHz is a dedicated frequency that was auctioned off and bought in 2006 by Aircell, which services American, Delta, and Virgin.
    But are cell phones on planes really that dangerous, anyway? Studies analyzing the dangers of inflight cell-phone use suggest the risks are small but real. In 2003, a study by IEEE Spectrum concluded that "continued use of portable RF-emitting devices such as cell phones will, in all likelihood, someday cause an accident by interfering with critical cockpit instruments such as GPS receivers." A study produced by the Radio Technical Commission for Aeronautics in 2006 found that portable electronic devices can interfere with airplane communications and laid out testing guidelines for airlines to figure out which devices should be permitted.
    The rationale for switching off other portable electronic devices is slightly different. Even if a device doesn’t transmit a signal—think iPods, Game Boys, "anything with an on-off switch"—it still emits energy at a frequency that could, possibly, interfere with the plane’s electronics. The Federal Aviation Administration requires all such devices to be off during takeoff and landings, but you’re allowed to turn them on once you reach a cruising altitude—presumably because any interference would be minimal and temporary. There are exceptions, though, for necessary devices like hearing aids and pacemakers.
All of the following is prohibited during takeoff and landings except______.
选项 A、electronic book
B、MP5
C、tablet computer
D、brain pacemaker
答案D
解析 属事实细节题。文章第五段中提到所有带开关的设备都不允许在飞机起飞和降落时使用，但最后一句说那些必须的设备可以不受此约束，因此可知选项D(脑起搏器)符合题意。选项A(电子书)、选项B(MP5)、选项C(平板电脑)都属于被禁止使用的物品，故不符合题意。
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