WEBVTT NOTE Monitoring the Aircraft Band 1 00:00:00.000 --> 00:00:10.320 The band. 118.000 to 136.975 MHz, AM voice, 25 kHz channels (8.33 kHz in much of Europe). 2 00:00:10.320 --> 00:00:30.033 Immediately above the 2 metre amateur band, and receivable on almost any scanner or SDR, including the RTL-SDR from the lab track, which needs no modification to hear it. 3 00:00:30.033 --> 00:00:55.079 The assignments come from the section 87.173(b) frequency table, which is worth reading once rather than trusting a forum post: Range, 108.000 to 117.950; Use, VOR navigation; 108.100 to 111.950 is the ILS localizer. 4 00:00:55.079 --> 00:01:15.719 Range, 118.000 to 121.400; Use, ATC, tower, approach, departure. Range, 121.500; Use, emergency and distress, the guard frequency. Range, 121.600 to 121.925; Use, ground control. 5 00:01:15.719 --> 00:01:34.156 Range, 122.000; Use, enroute flight advisory service (Flight Watch). Range, 122.700 to 123.075; Use, UNICOM at airports with no control tower, CTAF lives here. 6 00:01:34.156 --> 00:01:56.072 Range, 122.950; Use, UNICOM at airports with a control tower. Range, 123.600 to 128.800; Use, ATC operations. Range, 128.825 to 132.000; Use, domestic VHF, airline company traffic, not ATC. 7 00:01:56.072 --> 00:02:20.886 Range, 132.025 to 135.975; Use, ATC operations. Range, 136.000 to 136.975; Use, ATC, then domestic and international VHF to the top of the band. Everything is on 25 kHz channel spacing (8.33 kHz in much of Europe). 8 00:02:20.886 --> 00:02:38.860 Two easy mistakes the table settles. 128.825 to 132.000 is not centre, it is company and dispatch traffic, and tuning there expecting ATC will confuse you. 9 00:02:38.860 --> 00:02:52.542 And UNICOM splits on whether the field has a tower: 122.950 is the towered one, the rest of 122.700 to 123.075 is not. 10 00:02:52.542 --> 00:03:09.240 The frequency you care about most as a drone operator is the CTAF, Common Traffic Advisory Frequency, at any non-towered airport near your site. 11 00:03:09.240 --> 00:03:23.043 Why aviation is still AM. Every other VHF service moved to FM decades ago. Aviation did not, and the reason is directly relevant to the signals module. The capture effect. 12 00:03:23.043 --> 00:03:39.995 An FM receiver locks onto the strongest signal and suppresses everything else entirely. Two aircraft transmitting at once on FM would mean the weaker one vanishes, nobody hears it, and nobody knows it happened. 13 00:03:39.995 --> 00:03:53.960 On AM, two simultaneous transmissions produce a heterodyne, an audible squeal, and both voices remain partly intelligible. Everyone immediately knows two people transmitted. 14 00:03:53.960 --> 00:04:11.719 That failure mode is loud rather than silent, and in aviation a loud failure is much better than a silent one. Two consequences follow: AM is less efficient and noisier than FM. Aviation accepted that trade deliberately. 15 00:04:11.719 --> 00:04:25.280 You must set your receiver to AM. An NFM-demodulated aircraft transmission is a distorted mess, which is the usual reason a new scanner user concludes the band is dead. 16 00:04:25.280 --> 00:04:35.816 What you may legally receive. Receiving is not regulated the way transmitting is. You may listen to the aircraft band with any receiver. 17 00:04:35.816 --> 00:04:49.916 Two limits worth knowing, and neither is an FAA rule: The Communications Act (47 U.S.C. 605) prohibits divulging or benefiting from the content of certain intercepted communications. 18 00:04:49.916 --> 00:05:06.185 Listening is fine; using what you hear against someone's interest is not. A few US states restrict scanners in motor vehicles. Aircraft-band monitoring is rarely the target, but the statutes are worded broadly. 19 00:05:06.185 --> 00:05:22.686 You may not transmit on the aircraft band without an FCC aircraft station licence and the appropriate operator authorisation. An amateur licence does not convey this, and a Part 107 certificate certainly does not. 20 00:05:22.686 --> 00:05:25.320 This band is receive-only for you. 21 00:05:25.320 --> 00:05:34.503 Using it as a drone operator. At a non-towered field, monitoring CTAF is the single highest-value radio thing you can do. 22 00:05:34.503 --> 00:05:48.618 You hear aircraft announcing position and intentions, "five miles north, inbound, runway two seven", which tells you where manned traffic will be several minutes before you could see it. 23 00:05:48.618 --> 00:06:06.073 Add ATIS or AWOS for the field: continuously broadcast weather, including the ceiling and visibility figures that decide whether your flight meets section 107.51's 3 statute miles and 500 below / 2,000 horizontal cloud clearances. 24 00:06:06.073 --> 00:06:15.863 That is an authoritative source rather than a phone app's estimate. This is situational awareness, not a substitute for anything. 25 00:06:15.863 --> 00:06:25.273 section 107.43 requires you not to interfere with airport operations, and section 107.37 gives manned aircraft right of way. 26 00:06:25.273 --> 00:06:34.228 Monitoring helps you comply with both; it does not replace the visual line-of-sight obligation, and you cannot answer. 27 00:06:34.228 --> 00:06:50.483 The two transmitters you may not carry. section 107.52, Unless otherwise authorized by the Administrator, no person may operate a small unmanned aircraft system under this part with a transponder on. 28 00:06:50.483 --> 00:07:05.105 section 107.53, Unless otherwise authorized by the Administrator, no person may operate a small unmanned aircraft system under this part with ADS-B Out equipment in transmit mode. 29 00:07:05.105 --> 00:07:18.910 These surprise people, because both sound like safety equipment. The reasoning is system capacity: ATC surveillance and the ADS-B network were sized for manned aircraft. 30 00:07:18.910 --> 00:07:35.165 Tens of thousands of drones squawking would saturate the infrastructure and degrade it for the aircraft that depend on it, the classic case of individually sensible behaviour that fails collectively. 31 00:07:35.165 --> 00:07:47.418 Note the asymmetry, which is the point: ADS-B In (receiving) is fine, and useful, it shows you nearby traffic. ADS-B Out (transmitting) is prohibited. 32 00:07:47.418 --> 00:08:02.203 Remote ID is the drone-scale answer, broadcasting locally over Bluetooth or Wi-Fi instead of into the aviation surveillance network. That is the next lesson but one. Check yourself. 33 00:08:02.203 --> 00:08:18.948 You tune 122.8 MHz and hear only noise, though the waterfall shows a signal. What is wrong? Why does aviation use AM when FM has better noise performance? Your aircraft has an ADS-B module. May you use it? 34 00:08:24.948 --> 00:08:35.937 Wrong demodulator. The aircraft band is AM; NFM produces unintelligible audio from an AM signal. The capture effect. 35 00:08:35.937 --> 00:08:52.611 On FM a simultaneous transmission is silently lost; on AM it produces an audible heterodyne with both voices partly readable, so nobody is unknowingly blocked. In receive only. 36 00:08:52.611 --> 00:09:02.748 section 107.53 prohibits ADS-B Out in transmit mode; receiving traffic information is permitted and useful.