Air traffic controllers can separate aircraft using radar or non-radar rules. You will know you are in a radar environment when the air traffic controller informs you that you are “radar contact”. If the controller states, “radar contact lost”, it means you are no longer in radar contact.

When not in radar contact, the controller must issue you a large block of airspace, which is protected from other IFR traffic. The controller will follow the flight using pilot position reports in lieu of radar. This means you must report all compulsory reporting points along your route to the controller, as well as any other reporting points specifically assigned by air traffic control. For example, a controller might instruct you to “Report 25 miles south of Burlington VOR” or “Report reaching 4,000”.

If radar contact is established just after departure, the controller may simply say, “radar contact”. However, if radar contact is established elsewhere, the controller must verify the observed target is actually you before announcing radar contact has been established. The controller may have you change your squawk code or use the IDENT feature of your transponder. Under these circumstances, the controller will announce the position of the target which has been identified as you. This allows you the opportunity to speak up and say, “Hey, that’s not me”. For example, a center controller might inform you that you are “radar contact 37 miles southwest of Falmouth, verify at three thousand”. In this case, the controller also verified your Mode C.

Mode C Verification

The first controller at each facility must verify the accuracy of the Mode C altitude reported by your transponder. Out of habit and as a backup, it is common for every controller in the facility to check the Mode C readout for validity. Pilot’s are in the habit of providing this altitude verification upon check in to save the controller from asking for it. However, it is not technically required when transferring from one controller to another inside the same facility, since the same computer system is used for both sectors.

So, if you were talking to Orlando approach on 121.1 and you received the instruction to “maintain five thousand and contact Orlando approach on 119.4”, you could technically just check on by announcing yourself on frequency and omitting the altitude. The controller would not need to verify your Mode C readout, since you were transferred between two Orlando approach positions. However, it is expected and considered normal to verify the Mode C on every check in.

As part of the air traffic control system, the flight service stations also have the ability to contact facilities they serve directly. This allows them to provide services to controllers and pilots, such as air traffic control clearance relay.