Air Traffic Control
There are 21 Air Traffic Control Centers in the US employing 300-700 controllers each. The Air Traffic Control System Command Center (ATCSCC) is located in Herndon, VA.
When flying under Instrument Flight Rules in controlled airspace, you must always have a clearance. As an instrument pilot flying in Class G airspace, you may do do without a clearance, but suffice to say natural selection is not your friend.
As such, you will need an ATC assigned clearance for the following phases of flight:
- Takeoff and Departure
- Enroute
- Arrival
- Approach
Takeoff and Departure
Upon requesting your clearance, clearance delivery with deliver a rapidfire clearance with the following elements. Make it standard practice to write out the acronym CRAFT and copy each of its elements as they are read to you so you can effect a proper readback.
CRAFT:
- C - Clearance limit
- R - Route
- A - Altitude
- F - Frequency (departure)
- T - Transponder code
Two types of departure procedures:
1. Obstacle Departure Procedures (ODP) - developed to assist pilots in obstruction avoidance
2. Standard Instrument Departure (SID) - developed to communicate ATC clearances
Obstacle Departure Procedures
An ODP must be developed when obstructions penetrate 40:1 departure OCS. Textual ODPs only issued by ATC controllers when required for traffic. If they are not issued by ATC, text ODPs are at pilot's option to fly or not fly.
Pilot should enter "will depart [airport] [runway] via textual ODP" in remarks of flight plan. All newly developed area nav ODPs are issued in graphic form.
All ODP procedures listed in front of NACO approach chart booklets under heading Takeoff Minimums and Obstacle Departure Procs. They are listed in alphabetical order by city and state. Pilots do not need an ATC clearance to use an ODP and they are responsible for determining if the deptarture airport has this type of procedure.
It is worth noting that, based on the performce of the aircraft and the requirements of the ODP, the pilot may have to depart at higher climb rate or in opposite direction. Fuel burn should also be a consideration.
Standard Instrument Departure
SIDs are an ATC requested and developed departure route. Their primary goal is to reduce ATC/pilot workload while providing seamless transitions to the en route structure.
If you cannot comply with a SID, or if you do not have the charts or text descriptions, state "NO SIDs" in remarks section. ATC will instead will clear you via filed route to the extent possible or via a Preferential Departure Route (PDR). While you are not required to depart using SID, it may be more difficult to receive "as filed" clearance when departing busy airports. But let's face it, you're not getting what you filed anyway so what the heck... :)
SIDs are always charted graphically and are located in the TPP after the last approach chart for an airport. Charted transition routes allow pilots to transition from the end of the basic SID to a location in the en route structure. Typically transition routes fan out in various directions from end of SID. ATC will include both departure name and transition, eg Joe Pool Nine Departure, College Station Transition.
ATC can assign SIDs or radar vectors as necessary for traffic management and convenience. You can also request a SID in your initial flight plan or from ATC. To fly a SID, you must receive a clearance that includes a SID, and you must have at least text description of the SID in your possession. It is your responsibility as PIC to accept or reject SID based on:
1. Ability to comply with the required performance
2. Possession of at least text description
3. Personal understanding of SID in its entirety
If you cannot comply with climb gradient in SID, you should not accept clearance for that SID.
If you cannot maintain standard climb gradient specified in ODP you must wait until you can depart under VMC.
Enroute
The enroute phase is defined as the segment of flight from the termination point of a departure procedure to the origination point of an arrival procedure. Part 91.181 is the basis for the course to be flown. Pilots must either fly along the centerline when on federal airways or on routes other than airways along a direct course between navaids or fixes defining the route.
Altitudes:
0-179 - odd thousand altitude (no 500 unlike VFR)
180-359 - even thousand altitude
Controller can give you arbitrary altitudes though.
Note, if you reach a clearance limit before receiving a further clearance from ATC, a hold is required.
Preferred Routes
Preferred Routes are published in the AFD. Preferred IFR routes beginning or ending with a fix indicate that pilots may be routed to or from these fixes via a standard instrument deptarture (SID) or standard terminal arrival route (STAR).
Tower Enroute Control (TEC) allows flight planning between city pairs while remaining within approach control airspace. Also called "tower-to-tower" Use coded identifiers, ie BURL1, VTUL4, etc used in lieu of route of flight on flight plan.
Obstacle Clearance and Altitudes
Primary obstacle clearance of 8 nm with 4 nm on each side of centerline. 1000 ft clear normally, 2000 mountains. Secondary area extends along line 2nm on each side of primary. 500 ft above obstacles tapering to 0. When VHF airway or route terminates at NAVAID, primary area extends beyond that termination point. Pilots expected to adhere to airway and route protected airspace by leading turns early before a fix.
MEA - Minimum Enroute Altitude - Lowest published altitude between radio fixes that assures acceptable navigational signal and obstacle clearance. Pilots may operate an aircraft below MEA down to, but not below, the MOCA, only when within 22nm of the VOR.
MOCA - Minimum Obstruction Clearance Altitude - lowest published altitude between fixes that meets obstacle clearance for entire route of segment. Assures acceptable navigational signal only within 22 nm of VOR.
MVA - Minimum Vectoring Altitudes - established for use by ATC when radar ATC is exercised. MVA provides 1000/2000 ft clearance. (mountains).
MRA - Minimum Reception Altitude - minimum altitude at which navigational signals can be received for a route
MCA - Minimum Crossing Altitude - lowest altitude at certain fixes at or above which the aircraft must cross when proceeding in the direction of a higher MEA.
MAA - Maximum Authorized Altitude - published altitude representing maximum usable altitude or flight level for an airspace structure or route segment.
OROCA - Off-route Obstruction Clearance Altitude - off-route altitude that provides obstruction clearance with 1000/2000ft buffer. Not subject to same scrutiny as MEAs, MVAs, MOCAs and other min IFR alts.
Arrival
Term "cruise" may be used instead of "maintain" to assign a block of airspace to an aircraft. The block extends from the minimum IFR altitude up to and including the altitude that is specified in the cruise clearance. You are allowed to climb or descend within the block at your own discretion. However, once you start a descent and verbally report leaving an altitude in the block to ATC, you may not return to that altitude w/o additional clearance.
ATC may ask you to descend and maintain a specific altitude. Descend at optimum rate for your aircraft until 1000 feett above assigned altitude, then descend at a rate between 500-1500 fpm. Second type of clearance allows you to descend "at pilot's discretion" - you may begin when you choose at any rate you choose.
Arriving aircraft usually are vectored to intercept the final approach at least 2nm outside the approach gate unless:
1. Reported ceiling at least 500 feet above MVA and visibility at least 3nm - aircraft may be vectored to intercept final approach course closer than 2nm outside gate but no closer than the gate
2. If requested by pilot, ATC may vector aircraft to intercept final approach inside approach gate but no closer than FAF
Standard Terminal Arrival Routes (STARs)
Principal difference between SIDS or departure procedures (DPs) and STARs is that departure procedures start at the airport pavement and connect to the en route structure. STARs on the other hand, start at the en route structure but don't make it down to the pavement; they end at a fix or NAVAID designated by ATC because STARs serve multiple airports.
STARs provide transition from en route structure to an approach gate, outer fix, instrument approach fix, or arrival waypoint in the terminal area and they usually terminate with an instrument or visual approach procedure. STARs are included at the front of each Terminal Procedures Publication regional booklet.
Interpreting the Star
STAR clearances generally much shorter: "Cessna 32G cleared to Seattle/Tacoma Intl Airport as filed, then CHINS FOUR ARRIVAL, Ephrata Transition, Maintain 10000 feet."
STARS usually named according to point at which procedures begins. Usually the same as the last fix on the en route transitions where they come together to begin the basic STAR procedures. When a significant portion of arrival is revised, such as altitude, route, or data concerning a NAVAID, the number of the arrival changes. Example: "CHINS ONE ARRIVAL" becomes "CHINS FOUR ARRIVAL" due to modifications in the procedures.
You may accept a STAR within a clearance or you may file for one in your flight plan. ATC can assign a STAR even if you have not requested one. You must have at least a text description of the procedure in your possession. If you don't want to use a STAR, write "No STAR" in remarks. You can also refuse a STAR given verbally by ATC.
MEAs printed on STARs are not valid unless stated within an ATC clearance or in cases of lost communications. ATC either clears you to a specific altitude, or they give you a "descend via" clearance that instructs you to follow the altitudes published on the STAR. You are NOT authorized to leave the last assigned altitude unless *specifically* cleared to do so!
"Cessna 20350, cleared via JANESVILLE FOUR ARRIVAL" - gives you only routing clearance, not a descent clearance
Approach
Only when you are cleared for an approach, and established on a published portion of the approach procedure, may you descend from the last assigned arrival altitude.
Alternate Minimums
Exceptions to 600-2 and 800-2 alternate minimums are listed in front of NACO TPP and are indicated by reverse triangle "A" symbol on approach charts. This does not preclude flight crews from initiating instrument approaches at alternate airports when weather conditions are below these minimums. The 600-2 and 800-2 and exceptions only apply to flight planning purposes, while published landing mins apply to the actual approach at the alternate.
Approach Categories
Aircraft approach categories are based on 1.3 times Vso.
| Category | Speed |
|---|---|
| A | 90 KIAS |
| B | 91-120 KIAS |
| C | 121-140 KIAS |
| D | 141-165 KIAS |
| E | > 166 KIAS |
Although a faster approach may requir higher category minimums to be used, an airplane cannot be flown to the minimums of a slower approach category. Pilots are responsible for determining if a higher approach category applies. Circling approaches conducted at faster-than-normal straight-in approach speeds also requir a pilot to consider the larger circling approach area.
Circling Approaches
When two or more straight-in approaches with the same type of guidance exist for a runway, a letter suffix is added to title of app. Letters Z-A.
Circling only procedures designed for one of two reason:
1. Final approach course alignment with runway centerline exeeds 30°
2. Descent gradient is greater than 400 fpnm.
MSA - Minimum Safe Altitude - Published for emergency use on IAP charts. Normally based on primary omnidirectional facility on which IAP is predicated. MSAs provide 1000 feet clearance but not necessarily navigational signal coverage.
ATIS will provide info on what IAPs in use. If more than one, make an educated guess as to which approach will be issued to them based on weather, direction of arrival, and NOTAMs. If going into an airport without a tower, a flight crew will occasionally be given the choice of any available IAP at field. In this case, you must choose an appropriate approach based on weather, aircraft performance, direction of arrival, etc.
Missed Approach
There are many reasons to execute a missed approached. The primary reason is that required flight visibility in IAP being used does not exist or required visual references for runway cannot be seen on arrival. Landing on the intended runway must be able to be made at normal rate of descent using normal maneuvers, and for part 121 or 135, allow a touchdown to occur within the touchdown zone.
When a missed approach is executed prior to reaching the MAP, pilot required to continue along final approach course at altitude above DA, DH, or MDA until reaching MAP before making turns, otherwise obstacle clearance not guaranteed. It is appropriate after passing the FAF, and recommended, where there aren't any climb restrictions to begin a climb to missed approach altitude w/o waiting to arrive at MAP.
The Missed approach course begins at the MAP and continues until aircraft has reached designated fix and a holding pattern has been entered. The deptarture controller will issue further instructions before the aircraft reaches the final fix of missed approach course.
Missed approaches depicted by the end of solid course line and the beginning of dotted missed approach course line. For precision approaches, the MAP is the point at which the aircraft reaches DA or DH while on the glide slope. On some non-precision approaches, the MAP is given as fixed distance with associated time from the FAF. Pilots must determine the approximate groundspeed and time based on approach speed and true airspeed of aircraft and current winds along the final approach course.
Course Reversals
During a procedure turn, the maximum speed is 200 KIAS. When holding pattern published in place of a procedure turn, pilots must make a standard entry and follow the depicted pattern.
When "No PT" depicted, a procedure turn is prohibited. If pilot is uncertain whether ATC intends for a procedure turn to be flown, request clarification. A minimum of 1,000 ft obstacle clearance provided in procecure turn primary area. Secondary area, 500 ft.
If visual contact with ground made before the approach is completed, the entire approach procedure will be followed unless pilot receives approval for a contact approach, is cleared for a visual approach, or cancels the IFR flightplan.
ATC may clear pilots for a visual approach in lieu of a published approach procedure if flight conditions permit. Requesting a contact approach may be advantageous since it requires less time than the published IAP and provides separation from IFR and SVFR traffic.
Visual Approach
Pilot or controller can initiate a visual approach. Controller must verify that pilots have the airport or preceding aircraft that they are to follow in sight. Pilot assumes responsibility for their own separation and wake turbulence avoidance. A visual approach is NOT an instrument approach procedure. Also, there is no missed approach segment, and pilots must remain clear of clouds at all times.
When radar service is provided, it is automatically terminated when the controller advises pilots to change to the tower or advisory frequency.
Contact Approach
A contact approach can NOT be initiated by ATC. Reported ground visibility must be at least 1 sm, and pilots must be able to remain clear of clouds. Contact approaches allow pilots to retain an IFR clearance, and provide separation from IFR and SVFR traffic. Obstruction clearances and VFR traffic avoidance is pilot's responsibility.
Main differences:
1. Pilot must request a contact approach, while a visual can be assigned by ATC or requested by pilot
2. Contact approach may be approved if airport has weather reporting and current report is 1 mi visibility or more. A visual requires pilot to have airport or proceeding aircraft in sight and ceiling must be greater than or equal to 1000 feet
3. For a contact approach, the pilot does not need to be able to see the airport, but must have ground features in sight that he/she knows will lead to the airport. Alternately, the pilot may report preceding traffic to the same airport in sight, and follow that aircraft until the airport is in sight.
Advantages to contact approaches:
1. The pilot may short-cut the instrument approach to land sooner when conditions are not good enough to permit ATC to offer a visual approach.
2. The pilot may maneuver as needed to lose altitude or slow down.
3. The pilot may descend lower than IFR procedures permit when crossing terrain near the airport, reducing the need to dive toward a close-in airport.