What is radar?
An object-detection system that uses radio waves to determine the range, angle, or velocity of objects.
What is the difference between primary and secondary radar?
- Primary radar: a radio pulse reflects off the skin of the aircraft
- Secondary radar: a transponder in the aircraft responds to the radio pulse by transmitting its own radio signal
What are the advantages of secondary radar over primary radar?
- A signal sent by a transponder is much stronger and easier to detect than a reflected radio pulse.
- The transponder's response can include a unique identifier so that ATC knows which aircraft the signal came from.
- The response can include other information, especially the aircraft's altitude.
What are the advantages of primary radar over secondary radar?
Secondary radar can only detect aircraft with functioning transponders. Primary radar can detect aircraft with no transponder, or with a malfunctioning transponder.
How many different squawk codes can you enter on a transponder?
4,096 - four digits, each of which can be 0 through 7, so 8 x 8 x 8 x 8 = 4,096.
What is a discrete transponder code?
- One that doesn't end in zero zero.
- The codes ATC assigns to specific aircraft so as to track them and provide radar services.
What are some examples of common non-discrete transponder codes?
- 1200 - VFR
- 7500 - Hijacking
- 7600 - Lost communications
- 7700 - Emergency
IFR traffic receives ATC radar services more or less automatically. How and where does VFR traffic receive radar services?
- In Class B and C airspace - ATC provides radar services to all VFR traffic, since they have to provide IFR/VFR traffic separation (and VFR/VFR, in Class B).
- In TRSAs - ATC provides radar services to VFR traffic unless the pilot specifically declines TRSA service.
- In other airspace - VFR traffic can request radar services, which ATC will provide on a workload-permitting basis.
If a VFR pilot is receiving radar traffic advisories from ATC, who is responsible for keeping the aircraft safely away from other traffic?
The pilot. VFR traffic advisories do not relieve the pilot of the responsibility to see and avoid other aircraft.
What information will ATC provide you when issuing a traffic advisory?
- Which direction the traffic is in (using the 12-hour clock).
- How far away the traffic is.
- Which direction the traffic is moving.
- Type of aircraft, if known.
- Altitude of the traffic, if known.
Example: "Traffic, 10 o'clock, 5 miles, eastbound, Cessna 152, 3,000 feet."
What are the proper responses to a traffic advisory?
- If you see the traffic - "Traffic in sight."
- If not - "Negative contact."
When receiving VFR flight following, do you choose your own altitude/heading, or do you follow instructions from ATC?
You choose your own. The AIM says you should advise ATC before changing VFR cruising altitudes, and advising them of major course changes would also be a good idea. ATC can suggest vectors, but it is up to the pilot to choose to accept them. The pilot can request vectors, but ATC will only provide them on a workload-permitting basis.
What is Mode C?
A transponder mode in which the transponder's reply includes the aircraft's pressure altitude, determined from a barometric altimeter called an altitude encoder.
Suppose your altimeter reads incorrectly because you have entered the wrong altimeter setting. Does ATC see the correct altitude on their scope?
Yes. The altitude encoder is calibrated to 29.92" Hg and is not affected by the altimeter setting entered in the Kollsman window. ATC converts your pressure altitude to your MSL altitude automatically, based on the altimeter setting in your area.
Suppose your altimeter reads incorrectly because your static port is blocked. Does ATC see the correct altitude on their scope?
No. The altitude encoder gets pressure information from the same static port that feeds your altimeter.
When should you operate your transponder in the ON mode (instead of ALT)?
If ATC tells you "stop altitude squawk," meaning they want you to turn off Mode C. (Your altimeter and altitude encoder are probably out of sync.)
When approaching an airport with approach radar services, how far out should VFR pilots contact ATC?
20 to 25 NM.
What do pilots need to consider re: VFR weather minima when receiving radar services?
Receiving radar services doesn't affect the pilot's responsibility to maintain basic VFR visibility and cloud clearance. However, ATC can't see clouds on radar, so it's up to the pilot to keep ATC informed and decline any guidance or clearances that would put the aircraft in IMC.
What is the difference between a traffic advisory and a safety alert?