Possible Clues:

• Quantity with direction as well as magnitude
• Course to be taken by an aircraft
• Airplane course, for example
• What an arrow may represent
• Course taken by a plane or missile
• Course of an aircraft or missile
• Aircraft's required course from very small city on hill
• Covert manoeuvres to find carrier of disease
• Airplane's path
• Quantity having direction as well as magnitude — covert (anag)