| 21. | Aeronautical communications and navigational aids were minimal and at some airports relatively primitive.
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| 22. | The following navigational aids are installed for non precision instrument approaches at this airport.
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| 23. | The tracking system is frequently used as a navigational aid.
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| 24. | The light is still in use as a navigational aid.
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| 25. | The lighthouse is currently in use as a navigational aid.
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| 26. | Thus maps and compasses are the only acceptable navigational aids.
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| 27. | McMurdo staff were preparing for the unexpected flight and were activating electronic navigational aids.
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| 28. | The current beacon tower is the second navigational aid located on the Keskiniemi promontory.
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| 29. | As of 2001, both the light and radio beacon served as active navigational aids.
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| 30. | He worked in the marine industry where amongst other things he developed navigational aids.
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