Los Angeles is a helicopter town, and Advisory Circular LA lets you know what’s up with that helicopter circling overhead.

One of the first things any newcomer to Los Angeles notices almost immediately is the relentless sound of helicopters flying overhead. With an urban metropolis as sprawling as L.A. (500 square miles, give or take) that’s full of clogged traffic arteries, much of the policing (and news reporting) is done from the air.

However, after spending a little time living in Los Angeles, you become inured to the sound of helicopters and low-flying planes passing overhead. But every once in a while, you’ll realize that helicopter has been hovering over you for much longer than normal. You’re left wondering, “What is going on?”

That’s where Advisory Circular LA (on Twitter as @SkyCirclesLA) comes in.

Advisory Circular LA Knows What’s Going On

Advisory Circular LA is a Twitter bot, created by John Wiseman, that does just one thing — send out tweets reporting on aircraft circling over greater Los Angeles. Here’s an example:

Okay, so now you know what helicopter is circling over your house. What do you do with that information?

In every tweet, SkyCircles includes a link to the global ADS-B Exchange (short for Automatic Dependent Surveillance–Broadcast), which bills itself as the world’s largest source of unfiltered flight data. For instance, following the ADS-B Exchange link the above tweet, you get some details about the aircraft, including its current location, speed, altitude, and a bunch of other aviation-related information.

When possible, the Advisory Circular LA tweets include the aircraft’s registration number (also known as the tail number, N-number, or callsign). Again, using the above tweet, we know this helicopter’s registration number is N358TV. With this data, you can visit FlightAware or the FAA’s Aircraft Inquiry to get more information about that aircraft.

For instance, we know that N358TV is a 2004 Eurocopter with six seats owned by Tiny Bubbles Aviation and flying out of Whiteman Airport in Pacoima. FlightAware also has three photos of this copter emblazoned with the NBC LA logo treatment, so we know this is a news helicopter (the TV in the callsign kind of gives it away).

Squawking?

Advisory Circular LA also includes squawking information in most of the tweets. This refers to a numerical code that the aircraft’s transponder emits to a radar inquiry.

A squawk code is always four digits from 0 to 7 (that is 0000 to 7777) allowing for 4096 different combinations. Wikipedia has a full list of what these transponder codes mean. Most of the time, the aircraft over Los Angeles seem to be squawking 1200, which means they’re operating under visual flight rules — or flying by sight and not necessarily relying on instrumentation.

Advisory Circular LA isn’t just limited to helicopters that are circling somewhere in the greater Los Angeles area. It also tweets about small planes, like this 1977 Cessna (a 44 year-old aircraft):

So next time some aircraft has been circling overhead long enough for you to notice it, head over to @SkyCirclesLA to learn what’s up. Better yet, give them a follow to keep tabs on all the circling aircraft in Los Angeles County. We do.

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Advisory Circular LA

• @SkyCirclesLA on Twitter

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