text: Air Traffic Control
  3-9. The controller always starts a clearance (instruction) intended for a specific aircraft by identifying
  that aircraft. If he thinks that using the shortened identification could cause or is causing confusion, he can
  go back to using the full identification.
  Example: SIERRA TWO SIX, WIND CALM, CLEAR TO LAND, OVER.
  3-10. The controller can omit "THIS IS" from the reply.
  Example: SIERRA TWO SIX, DELTA THREE SIX, OVER.
  3-11. The controller can omit the facility identification.
  Example: SIERRA TWO SIX, TURN TO HEADING ZERO FOUR FIVE, OVER.
  3-12. Right after call-up, without waiting for the aircraft to reply, the controller can send a short
  message that he expects the aircraft to receive.
  Example: SIERRA TWO SIX, EXTEND DOWNWIND, OVER.
  3-13. If the message obviously requires a reply, he can omit "OVER."
  Example: SIERRA TWO SIX, WHAT IS YOUR LOCATION?
  3-14. To distinguish between similar aircraft identifications, he might emphasize appropriate numbers,
  letters, or words. The controller never transmits to an aircraft during the final approach, touchdown,
  landing roll (touchdown), takeoff (liftoff), initial climb, or turnaway from the field. At these times, the pilot
  must concentrate on flying the aircraft. However, he transmits at once any condition or information that
  could affect the safety of the aircraft. Under no circumstances does the controller withhold from the pilot of
  an approaching aircraft any information about hazardous runways, fields, weather, or traffic conditions.
  NUMBERS
  3-15. A pathfinder controller transmits numbers by units or digits (Table 3-1).
  To Transmit Say
  CEILING HEIGHTS "CEILING FIVE HUNDRED" (one unit) or "CEILING FIVE-ZERO-ZERO" (digits for emphasis).
  and FLIGHT
  "ALTITUDE ONE THOUSAND THREE HUNDRED" (two units) or "ALTITUDE
  ALTITUDES
  ONE-THREE-ZERO-ZERO" (in digits).
  TIME Use the word TIME followed by the number. For example, "0115 HOURS TIME,
  ZERO-ONE-ONE-FIVE" or "1315 HOURS TIME, ONE-THREE-ONE-FIVE."
  ELEVATION Use the words FIELD ELEVATION and the number. For example, for a 17-foot elevation, say,
  NUMBERS "FIELD ELEVATION SEVENTEEN." For a 50-foot elevation, say, "FIELD ELEVATION FIFTY."
  WIND SPEED Use the word WIND followed by compass direction and velocity (knots). For example, "WIND
  TWO-SEVEN-ZERO AT FIVE."
  HEADING Use the word HEADING followed by compass numbers (degrees); omit the word DEGREES.
  For example, "HEADING ONE TWO ZERO," "HEADING ZERO-ZERO-FIVE," or "HEADING
  THREE-SIX-ZERO." (The latter indicates a North [direction] heading.)
  Table 3-1. Numbers transmitted by units or digits.