An Introduction to En-Route Control

Overview

Welcome to En-Route (Center) Controlling.   This is where you will combine all the skills that you have mastered up to this point to oversee the entire ZJX airspace.  You have reached this level due to your prior commitment and dedication to ZJX and with the recommendation of your instructor and the Training Administrator.  Each of these has recognized that you have mastered the skills of being an accomplished Approach controller and that you represent the best that ZJX has to offer.  I would like to welcome you to the fast paced and exciting world of Center Controlling and wish you the best as you begin the final stages of your training.

Center Controllers are responsible for many thousands of square miles of airspace and for all the airports within that airspace.  At Center you will control IFR aircraft from the time that they enter ZJX airpace, depart the terminal area's airspace, or depart an uncontrolled airport; until they land, depart ZJX or enter a terminal area airspace.  You will be responsible for climbing the aircraft to their requested altitude while, at the same time, ensuring that the aircraft is properly separated from all other aircraft in the immediate area.  Your effort's are complicated by cross traffic, severe weather, military operations, and the overall traffic density.  The vast amount of airspace and multiple airports make working Center a challenge.  There will be times when you will find yourself busier than you ever thought possible as you control aircraft arriving and departing from airports hundreds of miles apart.  It may seem a bit daunting at first, but don't let that discourage you.  Keep at it and practice all the things you have learned.  Before you know it, you will be a proficient and professional Center controller.

Altimeter Settings and Lowest Usable Flight Level

As the Center controller, you must always issue the altimeter in the following situations:

• To en route aircraft below FL180 at least once while in your airspace or any time you issue descent below the lowest usable flight level.  Use the altimeter for the airport closest to the aircraft's position.
  
• To arrivals when 50 nm from their destination if there is no approach control.  In this case, use the destination airport altimeter.
   
  

 

Flight levels are based on a standard altimeter setting of 29.92.  If the local pressure falls below that there is no longer 1,000 feet separtation between normal altitudes and flight levels.  Some flight levels become unusable as the pressure drops.  Which ones depends on how far the pressure drops.  You may not assign these unusable flight levels to aircraft:

• If the local pressure is between 29.91 and 28.92, FL180 is unusable and may not be assigned.  Fl190 becomes the Lowest Useable Flight Level.
  
• If the local pressure is between 28.91 and 27.92, FL180 and FL190 are both unusable and may not be assigned.  FL200 becomes the Lowest Useable Flight Level.
  
• In the unlikely event the pressure drops below 27.92 you are probalbly in a hurricane.  FL210 then becomes the Lowest Useable Flight Level.

Finally, when issuing the altimeter setting at the Center position, always be sure to identify its source to the pilot.

Altitude Assignments

Remember from from your first introduction to altitude assignments that aircraft flying below FL290 on  a North and Eastbound (360-179) course are assigned ODD altitudes; South and Westbound (180-359) aircraft get EVEN altitudes.  And starting at FL290 only odd flight levels are used alternating eas and west bound.  Well from time to time traffic, weather, or aircraft performance limits prevent following these rules.  This allows you to assign any altitude so long as the aircraft remains within your airspace.  If it will enter another controller's airspace, the Wrong Altitude For Direction Of Flight (WAFDOF) must be coordinated with and approved by the receiving controller.  Regardless of the direction of flight, any altitude you assign must be at or above the Minimum Enroute Altitude for the airway being used or the Minimum Instrument Altitude for the area the aircraft is in.

 Another altitude you may assign if the pilot requests it is VFR-ON-TOP.  As the name implies, the aircraft is on an IFR flight plan but flying under Visual Flight Rules on Top of any clouds or other weather.  Do not use VFR-ON-TOP in Class A airspace.  When VFR-ON-TOP, the pilot flies at the appropriate altitude for direction of flight plus 500 feet.  The pilot is responsible for his own separation from the other traffic.  You only provide traffic advisories and safety alerts as necessary.

When you assign VFR-ON-TOP as an altitude there are four things you must do:

• Tell the pilot the height of the tops or that no tops report is available  ie:  "Climb to and report reaching VFR-ON-TOP, Tops reported 12,000" or "No Tops reported."
• Ensure separation from all other traffic until the aircraft reaches VFR-ON-TOP.
• Issue alternate instructions in case the aircraft can't reach VFR-ON-TOP,  ie:  "If not on Top at FL180, maintain FL180 and advise."
• Re-clear the aircraft when it reports reaching VFR-ON-TOP, ie:   "Maintain VFR-ON-TOP."

ARTCC Separation

Centers are responsible for much more airspace and use a different radar system than Approach Controllers.  Therefore, the separation standards they apply are slightly different as well.

Vertical separation standards at the Center level are as follows:

• Up to and including FL290 = 1,000 feet
  
• Above FL290 = 2,000 feet
  
• Above Fl600 between military aircraft = 5,000 feet
  
• In oceanic airspace, above FL450 between a supersonic and any other aircraft = 4,000 feet

Radar separation standards at the Center level are as follows:

• Below FL600 = 5 nm
  
• At or above FL6000 = 10 nm
  
• When accepting a handoff on a departure = 3 nm increasing to 5 nm if the aircraft are on diverging courses or the first aircraft is and will remain faster.

NOTE:  Centers may also use visual separation except in Class A airspace.

Descent Procedures

Once the aircraft is at its cruising altitude, the next thing to determine is when to start and aircraft on its descent.  The actual point can be affected by terrain, traffic, and adjacent airspace.  Here is a simple formula to give you a general idea of when to start a typical aircraft down.

• Subtract the destination airports elevation from the aircraft's current altitude, all rounded to the nearest thousand.
• Simplify by dropping the thousands
• Multipy the resulting number by
• The product is the number of flying miles from the destination where the aircraft should start its descent.

The following is an example:

• Airport elevation = 668 (rounded up to 1,000)
  
• Aircraft altitude = FL310 (31,000 feet)
  
• 31,000 - 1,000 = 30,000  (simplify to 30)
  
• 30 x 4 = 120

The aircraft inbound at FL310 should start its descent approximately 120 flying miles from the airport.

Another handy tool for determining when to start an aircraft's descent is to use the term "Descend at Pilot's Discretion."  You must still assign an appropriate IFR atltitude to maintain, "Descend at Pilot's Discretion, Maintain 8,000", but this shifts the burden of choosing the right descent start point from you over to the pilot.  If necessary to have the aircraft at a certain altitude by a certain point you may include a restriction, "Descend at Pilot's Discretion, Cross LEESE at and Maintain 12,000."  In this case the pilot can start whenever and descend at any rate he wants as long as he crosses LEESE at 12,000.

"Descend at Pilot's Discretion" does not relieve you of your responsiblity to assign an altitude which ensures separation from terrain, obstructions, or other traffic.  If an aircraft calls outside of your airspace requesting descent, inform the aircraft of the altitude to enter your airspace and advise the pilot, "Outside Controlled Airspace, Descend at Your Own Risk, Cross AMG at or above 17,000, Maintain 17,000."

Operations at Uncontrolled Facilities

When working a Center, there will be many times when you are controlling aircraft into airports without an approach control or tower.  Some of them don't have them full time or at all in real life;  others do but they aren't always staffed in VATUSA.  If it's the latter situation, you have the option to provide these tower and approach servies yourself.  However, you are not required to do so and there will often be times you may not be able to due to workload, experience, widely scattered operations, or many other factors.

If you issue an IFR departure clearance to an aircraft at an airport without a tower you have several options:

• Release the aircraft when you issue its IFR clearance.  This way the aircraft my depart any time it is ready.
  
• "Cleared to KVLD Airport as Filed, Maintain  14,000,  Taxi and Departure at pilot's discretion, contact me when airborne"
  
• Include the term "Hold for Release."  This way the aircraft has its clearance but may not depart until you call it back and issue a departure release.
  
• "Cleared to KVLD Airport as Filed, Maintain 14,000, Hold for Release."
  
• "Released for Departure, Contact me on this frequency when airborne."
  
•  Include a release time and time check with the clearance.  This way the aircraft may not depart until the release time.
  
• "Cleared to KVLD Airport as Filed, Maintain 14,000, Released for Departure at 1700, Time now 1642, Contact me on this frequency when airborne.:
  
•  Issue a clearance void time and a time check.  This way the aircraft may depart anytime up until the void time but not after it.
  
• "Cleared to KVLD Airport as Filed, Maintain 5,000.  Released for Departure, Clearance void if not off by 1345, Time now 1315, Contact me on this frequency when airborne."
  
• Arrivals may be vectored to final as in an approach control.  However, in a center you will often be controlling other aircraft some distance away.  This may make it impractical to zoom in enough to give accurate vectors.  Most arrivals to uncontrolled airports should be sent to the Initial Approach Fix and cleared for the complete approach.

NAVAID Use Limitations and GPS

• The typical range of an FS VOR above FL180 is 130 nm.  Below FL180 it can be as little as 40 nm depending on terrain and the aircraft's altitude. 
  
• The range of most NDBs is approximately 50 nm but this also varies with the terrain and altitude.
  
• Unless the aircraft is on an airway, you must constantly watch the aircraft on radar and provide course corrections as necessary.

Global Positioning Systems such as the SB/FSINN FMS are making direct routings more common.  Using GPS, you are no longer limited to only clearing an aircraft direct to VORs or NDBs.  You may now clear the aircraft direct to virtually any navaid, intersection, DME fix, or airport.

LOA's

Make sure that you are very familiar with all Letters of Agreement between ZJX and our nieghboring ARTCC's.  These agreements dictate altitude and crossing restrictions for arriving and departing aircraft.  Your neighboring CTR controllers depend on you to follow these agreements so that they can maintain safe separation inside thier airspace.

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