non-directional radio beacon

Japanese: non-directional radio beacon（英語表記）nondirectionalradiobeacon

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[History of Air Traffic Control]
The need for an organization to regulate traffic is clear for air routes, terminal airspace, and airports where many fast-flying aircraft converge, but the first control tower was built to give instructions to departing and landing aircraft in 1930 at Cleveland Airport in the United States. At the time, pilots flying to their destinations were free to choose their course and altitude while visually checking landmarks on the ground, but in response to the coming of use of radio communication and the development of instrument systems, air routes linked by NDBs (non-directional radio beacons) were established in the United States in 1933.

From [Air Safety Radio Facility]

…[Hidemaro Nagano]. …

*Some of the terminology that refers to "non-directional radio beacon" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

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［航空交通管制の歴史］
　高速で飛行する多くの航空機が集約される航空路，ターミナル空域ならびに空港などで，交通を規制する組織の必要性は明らかだが，初めて管制塔がつくられて離発着する航空機に指示を与えるようになったのは，1930年，アメリカのクリーブランド空港においてである。当時は，目的地に飛行するパイロットは地上物標を目視しながら自由にコースと高度を選んでいたが，無線通信が使われるようになり，計器システムが発達するのに対応して，33年，アメリカでNDB(non‐directional radio beaconの略。無指向性無線標識)を結んだ航空路が設置された。…