SID and STAR on aviation radio: standard departure and arrival routes explained

You are sitting at the fence with a scanner or stream, and out of the speaker comes: “… cleared to Palma via ABMUX Three Kilo departure, climb flight level seven zero, squawk four two one five.” To beginners that sounds like a jumble of numbers. In fact, this one sentence contains the aircraft’s complete departure route – and with it the answer to whether it will pass over your spot after takeoff or turn away in the other direction. This article explains how SID and STAR on aviation radio show up, what the fixed phrases mean and how you can use what you hear as a spotter.

SID and STAR in one sentence

A SID (Standard Instrument Departure) is a published departure route for flights under instrument flight rules. It leads from the end of the runway over defined waypoints to a point in the route network. A STAR (Standard Terminal Arrival Route), officially called Standard Instrument Arrival by ICAO, is the counterpart: it picks the flight up from the route network and brings it to where the actual landing approach begins – such as an ILS approach.

The clever part for radio communication: each of these routes has a name. Instead of giving a crew ten individual instructions (“after takeoff straight ahead to 2,000 feet, then left to heading …”), the controller just says the name. The route is in the aircraft’s navigation database, the crew loads it into the flight management system, and both sides know exactly what is meant. That saves radio time and avoids misunderstandings on crowded frequencies.

What a SID or STAR name sounds like on the radio

In Europe the names usually consist of three parts: the name of a waypoint, a version digit and an identifying letter. For a SID the waypoint is the point where the route ends, for a STAR the point where it begins. On the radio, digit and letter are pronounced using the ICAO phonetic alphabet. A (here freely invented) SID “ABMUX 3K” thus becomes “ABMUX Three Kilo”.

Waypoint names are usually five letters long and chosen so that they can be pronounced. Some sound like real words, others like made-up names. Procedures named after a radio beacon carry its name or shorter identifier. After a while at the scanner you will recognize the waypoints of your home airport – and that is exactly the key to reading directions from the radio.

The departure clearance: where the SID comes up first

Before a scheduled flight starts its engines or is pushed back, the crew gets the route clearance. At large airports there is a separate frequency for this, often called “Delivery” or “Clearance Delivery”. Which radio stations exist and how they work together is explained in the guide Understanding aviation radio frequencies.

According to ICAO requirements, a departure clearance typically contains the following building blocks:

Building block	Example on the radio	What it means
Callsign	“Lufthansa four kilo x-ray”	who is meant, see Callsign and flight number
Clearance limit	“cleared to Palma”	usually the destination airport
SID	“via ABMUX Three Kilo departure”	the route after takeoff
Cleared altitude	“climb flight level seven zero”	how high the aircraft may initially climb
Transponder code	“squawk four two one five”	the code for the radar, more at Transponder modes A, C and S
Further details	frequency, departure time notes	what else the crew needs to know

Important: the SID name alone does not yet allow flying the route’s altitude profile all the way to the top. That also requires a cleared altitude. Depending on the country, this can be stated in the clearance or appear on the SID chart as an initial altitude.

The crew reads the clearance back. Route clearances, runways, altitudes, headings, speeds and transponder codes are among the instructions that must be repeated in full. For you as a listener that is handy: if you didn’t understand the controller, you get the SID a second time in the readback. How such standard phrases are constructed in general is explained in the article on radio phraseology.

“Climb via SID” and “descend via STAR”

Since Amendment 7 to ICAO Document 4444 (PANS-ATM), effective November 10, 2016, there are two fixed phrases: CLIMB VIA SID TO (altitude) and DESCEND VIA STAR TO (altitude). Each of them means the same package:

• The crew climbs or descends to the stated altitude.
• It follows the lateral path of the procedure.
• It complies with the published altitude restrictions at the waypoints.
• It observes published speed restrictions or those issued by the controller.

Before, it was often unclear whether a simple climb clearance cancels the altitude constraints on the chart or not. The new phrases make that unambiguous. In addition, the controller can selectively delete individual parts, for example with “cancel speed restriction” or “cancel level restrictions at …”. Everything he does not explicitly name continues to apply, and the lateral path remains in effect in any case.

The world is not entirely uniform on this. When it was introduced in 2016, several countries announced they would not adopt the new phrases for the time being, including Australia and Switzerland. The US uses its own variant: there, “climb via SID” can also be used without an altitude if the final altitude is already published on the chart. If you listen to streams from different countries, you will therefore encounter different variants – one more reason not to transfer every phrase literally to other airports. On the question of language in German airspace, the article English or German on aviation radio is worth a look.

From the holding point into the air: what happens after the clearance

After the clearance, the crew switches to ground control and later to the tower. The SID normally doesn’t come up there anymore – unless something changes. You should know three situations:

Runway change: If the wind shifts and the runway direction in use changes, or a flight is rescheduled to a different runway, it gets a new SID. On the radio you then hear a changed clearance with a different letter or an entirely different name. For you that means: careful, departures are now turning away elsewhere.

Direct clearance after takeoff: Shortly after liftoff, the flight moves to the departure or radar frequency. If the airspace is clear, you often hear “proceed direct …” to a later waypoint. This shortens the route, and the altitude and speed constraints at the skipped points no longer apply. The initial part of the SID with the first turn is usually still flown as published, though.

Radar vectors: With “turn left heading …” the controller guides the aircraft by heading instead of letting it follow the SID. The restrictions of the route are then canceled as well. With “rejoin SID” he sends it back to the procedure; from the rejoin point on, its constraints apply again.

STAR on the radio: how an approach announces itself

On arrival it works the other way around. The STAR is usually already part of flight planning and is assigned or confirmed to the crew via en-route control. According to ICAO requirements, an approach clearance contains the STAR, the landing runway (if it is not already in the STAR’s name) and the cleared altitude. Something like “descend via STAR to flight level one two zero” is typical, or simply a descent clearance with the STAR name.

Before the approach, the crew also listens to the ATIS, the automatic airport information with weather and runways in use. If you listen to the ATIS as well, you know which runway is active – and with it, which STAR variants and approaches come into question.

After that the radio traffic gets denser. On the approach frequency, descent clearances, speed instructions and, with heavy traffic, the heading instructions onto final follow. Many approaches are guided by radar vectors in the last part to set the spacing precisely. When things get tight, the controller sends aircraft into holding at a holding point of the STAR. What these ovals look like on the radar is shown in the guide Recognizing holding patterns on the flight tracker. At the end comes the approach clearance, for example for the ILS approach, and the handover to the tower.

Why controllers work with SID and STAR

From the air traffic control point of view, the procedures are a tool for safely organizing a lot of traffic with little radio. Departures and arrivals are guided so that they cross as little as possible. Altitude constraints separate the flows vertically, speed constraints keep the spacing stable. At the same time, the routes are designed so that obstacles are cleared safely and, where possible, densely populated areas are avoided.

In Germany, the DFS German Air Navigation Services designs the procedures, and they are established by the Bundesaufsichtsamt für Flugsicherung (the Federal Supervisory Authority for Air Navigation Services). In Austria and Switzerland, Austro Control and Skyguide are responsible. How controllers’ work has changed over the decades is described in the history of air traffic control; if you want to get on the microphone yourself, you will find information under Becoming an air traffic controller.

For controllers there is another advantage: a frequency carries only one voice at a time. The shorter each clearance, the more aircraft fit through. If you listen in at a hub during rush hour, you notice how valuable every saved second is.

How to use the knowledge at the spot

Anyone standing at the fence wants to know one thing above all: is the next aircraft coming by here, and when? SID and STAR on the radio help you with that on several levels.

• Pre-sorting departures: If you hear on delivery that a rare visitor gets a SID toward your spot, it is worth having the camera ready. If it gets the other direction, you might switch sides.
• Announcing arrivals early: The STAR name tells you which compass direction a flight is coming from. Combined with the flight tracker, you know on which side it goes onto downwind and when it will appear on final.
• Noticing runway changes: New SIDs, a changed ATIS or controllers who suddenly name different runways are often the first signs. That way you get to the other end of the airport faster.
• Recognizing holdings: If the controller sends several flights into holding, landings are delayed. Time for a coffee or a change of spot.

An example is Frankfurt Airport: Runway 18 West is only used for takeoffs to the south, so departures from there head in a different direction than those from the parallel runways. Anyone standing at the Zeppelinheim viewing platform and hearing on the radio which runway a flight is assigned can better judge where they will get to see it. At Munich Airport, the runway direction in use determines from which direction aircraft pass the visitors’ hill. You will find more on the spots at both hubs in the guides Plane spotting in Frankfurt and Plane spotting in Munich; how runway numbers come about is explained in the article on runway designations.

Technically you need either a scanner or SDR receiver or an online stream. What suits getting started is shown in the guides Buying an aviation radio scanner, Receiving aviation radio with an SDR stick and Listening to aviation radio online. Before you start, be sure to clarify the legal situation for listening to aviation radio – it differs considerably from country to country, and passing on or publishing radio traffic is often regulated more strictly than listening itself.

Common misunderstandings

• “The SID applies all the way to the destination.” No. It ends at a waypoint in the route network, after which the flight follows its planned route.
• “The STAR ends on the runway.” Not that either. It ends where the approach procedure begins, or the controller takes over earlier with vectors.
• “Anyone with a SID may climb the whole altitude profile.” Only the cleared altitude determines how far up it goes initially.
• “The chart shows where the aircraft flies.” It shows the procedure. Direct clearances and vectors mean the real tracks often deviate – especially in the later departure and on approach.
• “If I don’t hear the clearance, the flight has no SID.” Often it simply came by datalink.

Conclusion

SID and STAR are the shorthand of aviation radio. With one name, the controller conveys a complete route, and fixed phrases like “climb via SID” and “descend via STAR” govern which altitude and speed constraints apply. For you as a spotter, the radio is thus an early warning system: the SID on delivery tells you the departure direction, the STAR the origin of an approach, and runway changes and holdings announce themselves before you see them. Combined with the chart, ATIS and flight tracker, you know where the next aircraft will show up.