The plane! The plane!

From where I live in southwestern Connecticut, it seems that air traffic is everywhere.  Small planes loop about from uncontrolled (no tower) airports, commuter planes buzz overhead from larger controlled facilities, and  jumbo jets fly a regular path from southwest to northeast, heading to various destinations in Europe.

As a radio hobbyist, it's really easy to listen, since planes still use VHF AM to talk with controllers, just as they have since world War II.  The American air traffic control system - complex and laden with acronyms and jargon - is divided into 22 large sectors which direct planes before and after they talk to local airports.

Sector map for Boston ARTCC

The New England states, plus part of New York and eastern Pennsylvania, are part of the Boston Air Route Traffic Control Center (Boston Center) based in Nashua, New Hampshire. Since Boston Center covers so much territory - 165,000 square miles - it has remote radio sites all over the northeast, on Cape Cod and in two Connecticut towns, Shelton and Woodstock. View a complete list of frequencies here.

The busiest of these frequencies by far is 118.425 MHz, a high-altitude channel for flights entering and leaving Boston Center's western sector. It is so busy that 10 seconds rarely elapse without another plane signing on for altitude ("flight level") and radio frequency changes - depending on where they are headed.

Waterbury-Oxford (CT) Airport

Among major airports under Boston Center's control, I can hear Bradley International Airport tower on 120.3 MHz and Bradley approach and departure on 123.95 MHz. The largest of the New England airports, Logan Airport in Boston, (tower on 128.800) is too far away for me to hear directly - but it can be monitored through the online aviation service LiveATC.net.

I also have small controlled airports nearby, business-based Tweed-New Haven with a tower frequency of 124.8 MHz, unicom of 121.700, and Waterbury-Oxford Airport tower on 118.475 MHz, unicom of 122.95. The towers at these airports shut down at 10 p.m., so the unicom channels are used by aircraft to announce their intentions (landing, taking off, taxiing) during nighttime hours.

Closest to me at about 10 miles away is Meriden-Markham Airport, somewhat of a glorified airstrip. The airport has no tower and is popular with flight instructors and students. Its unicom frequency is 123.050 and, like the others, is busiest on weekends.

Unicom channels can provide hours of entertainment, as pilots chit-chat about their lives, loves and just about anything else. This is common on clear summer and autumn days, when hobby pilots take to the skies for sightseeing or a day trip to Martha's Vineyard or Nantucket. Try tuning to 123.07 122.700, 122.800, 122.900, 123.000 or 123.050, or a few other known "itinerant" aviation channels where anything goes: 123.300, 123.500, 123.025 (helicopter) and 122.750 (fixed wing). Supposedly 123.45 is the unofficial plane-to-plane frequency, but I almost never catch any chatter there.

Screen capture of air traffic over
Connecticut from Flightaware.net

Here's a fun fact - VHF radio can be heard over incredibly wide areas, based on this formula: Distance (miles) = 1.23 x (the square root of) altitude (feet). This means that an aircraft at 10,000 feet can be heard at a distance of 110.9 miles - which is slightly less than the distance from my house to Boston.

If listening isn't enough for you, there are websites that offer aircraft tracking in real time, complete with flight plans and information about the planes, with the simple click of a mouse. Of three similar sites, my favorite is www.adsbexchange.com because it plots both civilian and military aircraft based on commonly used ADS-B transponders and MLAT - a radar triangulation system for planes without ADS-B.

The other online flight trackers are Flightradar24.com and Flightaware.com, the second of which distributes self-contained ADS-B receivers to users who live where there is sparse transponder reception, provided the user streams the data back to the main site.

Aircraft also communicate over the open ocean, but at that distance, HF radio replaces VHF and Oceanic ATC stations handle all the communications. More on that in my next blog entry!