Separation Standards
Some ATC calls are courtesy calls, some are ‘point outs’, some are advisories, and some are mandatory advisories. The pilot must learn to listen to the tonal variations of the controller to separate one from the other since there is no other obvious distinction.

ATC contract..."provide separation". If standards are violated a "deal" occurs which causes economic and training problems for controller. To protect themselves from the minimums controllers maintain greater than minimum required separation. Separation can be both horizontal or vertical and need not be both. a ‘snitch patch’ in the computer tells if separation is less than standard. Makes a ‘deal’ for the controller

Standard separation is determined by aircraft type, altitude, type of ATC facility, stage of flight (departure, cruise, approach) weather, and antenna distance. If visual separation exists by pilots or by ATC the separation may be much closer than 5 miles. If aircraft are separated by altitude the separation may be as little as 2.5 miles.

A limiting separation factor is the distance of the aircraft from the antenna, class of airspace and size of aircraft (heavy). Minimum is miles within 40 nm of antenna; 5 miles beyond 40 nm. Center (ARTCC) uses 5 nm standard separation and 1000’ below FL290 regardless. Terminal areas most likely 3 nm and 1000’ with visual separation allowed. Vertical rules are same everywhere. There are no standards of separation for VFR aircraft. Only in Classed B and C is IFR separation mandatory. Class B separation of IFR/VFR is 500’ and 1500’. Class C separation is 500’ and ‘green between. In Class C there are no mandatory advisories. VFR advisories are given as load allows.

IFR aircraft fly in a cylinder 10 nm (ARTCC) to 6 nm (terminal) diameter. The cylinder extends 1000' above and below the aircraft, ATC normally allows much more space.

Your encoding altimeter must be within 300' because the "snitch patch" of center's radar is set to alarm if altitudes encroach on 700' separation. An encoder off by 300' could set off the alarm. If you should wander more than 300' off IFR assigned altitude and ATC questions, delay your response until altitude is within 300'. Better yet, advise "unreadable" while making the correction. "Snitch" is found (1993) only in ARTCC radars.

A radar target may not be in ATC contact so the altitude is only ‘indicated’ not confirmed. Traffic advisories are a part of flight following which includes weather advisories, terrain, obstruction, and low altitude alerts. asking for flight following and being given flight following leaves out the rest of radar flight services. You can even request that traffic advisories be omitted from flight following.

An IFR flight with visual contact on VFR aircraft is allowed to maneuver to avoid without regard to an ATC clearance. The radar controller is required to advise you if your target merges with another on the screen. The advisory may just to indicate how far above or below you the altimeter reading indicates. Giving ATC your indication of visual contact relieves them of responsibility. ‘Mode-C intruders’ are aircraft that have encoders but are not in communication contact with ATC. Many radars can give you two-three minute warnings if such an aircraft is in conflict with your route.

Center Facilities
Radar is a multifaceted term. The antenna of a center is known as a sensor. Several sensors have their radar returns made into a mosaic the presents a single picture via digital computers for each controller’s sector.

Each antenna either an ARSR-3 or -4 has two parts, the search antenna and the transponder interrogator. Some -3s cannot get primary targets at all.

Center antenna turn slowly and search in slightly over 10-degree arcs at a time. At a distance the 10-degree arc covers so much distance that a target blip can be a mile long at the 100-mile range setting. At five turns a minute the antenna a target can move several hundred feet between return updates.

Updates are processed to allow the best antenna data to the controller. This data can be used to forecast future positions and to give direct route vectors with a couple of clicks. Projections allow conflict alerts and Minimum Safe altitude Warnings (MSAW) warnings. None of these work within 25 miles of your destination. Carry a sectional.

Center can help with weather because of the multiple antenna used. One antenna can show the front of a weather condition while another antenna will show the back side. Light precipitation is shown as slashes. Where two antenna (sensors) have overlapping slashes there will be areas of Hs. Pilots should be told by ATC to avoid areas of such Hs.

Radar Help
Center radar is not good enough to safely call step down fixes. TRACON can call fixes that are on their screens. There is no way to know extent of radar coverage to secondary airports unless you get some idea of the minimum vectoring altitude from the SVFR clearances given. SVFR clearances usually give an altitude that in poor conditions indicates the letter-of-agreement separation altitude of a Class D and TRACON. You might just ask ATC what it is.

All radar facilities have differing capabilities. Center antenna rotate slower than TRACONs and has a more limited vectoring precision. Center is a mosaic of a number of long range radars and a given controller has a limited sector scan for working aircraft in a specific area. Within 40 miles of the antenna separation is 3-miles; beyond that it is 5-miles.

I have, on occasion, had ATC indicate that I am drifting off an airway centerline. This is even though my CDI is centered. The solution is to indicate that you would like a vector to intercept his center line. It is the pilots responsibility to know where both high and low terrain lies. This information is best obtained from a sectional.

The NEXRAD is a set known as WSR-88D which has both a clear air mode and a precipitation mode. In the precipitation mode the size of droplets can be determined.

Radar Altitudes
–Radar contact means nothing relating to altitude safety.
--Minimum Vector Altitude (MVA) TRACON chart may take you lower than you like. Query
–Minimum Instrument Altitude (MIA) used by ATC Center
--Minimum Safe Altitude (MSAW) Warns ATC without regard to other terrain.
--Minimum En route Altitude (MEA) is arc around navaid.
--Emergency Safe Altitude (ESA) is used by military.
--Minimum Off-Route Altitude (MORA) by Jeppesen grids.
--Off-Route Obstacle Clearance Altitude (OROCA) Government charts.

IFR Separation from IFR
--VFR-on-Top and visual climb/descents responsibility: A VFR on top clearance is all right below a cloud deck or between layers as long as you can remain VFR and meet cloud clearance-criteria.
ARTCC 5 miles/1000' Relieves ATC only during altitude change.
Class B 3 miles/1000' Other aircraft need not be visible.
Class C 3 miles/1000' Use when possible.

IFR Separation from VFR
ARTCC nothing When IFR pilot agrees to keep visual separation, ATC is relieved of responsibility.
Class B 1.5 miles/500'
Class C conflict/500' Pilot may climb, descend or get closer than ATC minimums.
TRSA 1.5 miles/500'

VFR Separation from VFR
ARTCC nothing
Class B 1,5 miles No requirement but you may get traffic advisories and safety alerts.
Class C nothing Be careful in Class C.
TRSA 1.5 miles

Visual Separation
ARTCC limited Must report aircraft in sight to ARTCC
Class B allowed then must report passing clear. Seldom used.
Class C allowed ATC controller uses his visual contact of allowed aircraft involved to expedite
TRSA When a pilot acknowledges visual contact he relieves ATC of responsibility for
separation.

Note: There is no time duration limit on this exchange of separation responsibility. A pilot can hand back this responsibility to ATC by advising that visual contact cannot be maintained or is lost.

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