Clearances

<NAME> and <RWY> are the procedure as it is published and the runway it serves, written the way the chart writes them: clr star ROKI1B rwy 26L. A procedure the current AIRAC cycle does not publish for that runway is refused, and the reply lists what is available, so a wrong runway never quietly clears a different procedure.

clr <NAME> clears any of the three by naming it, and works out the rest for you. You do not say whether it is a departure, an arrival or a transition: a name belongs to exactly one of them, so clr ALG2E is the departure and clr ROKI1B the arrival. Short, it is c<NAME>, with the runway after a comma where one is needed: cALG2E, cROK26,26L. The examples below are written short, which is how most people type it.

Whether you also name the runway depends on the procedure. Departures and arrivals here carry it in the name, so you leave it out. Approach transitions serve both parallel runways and fly a different last leg to each, so they always need it. Where a name serves several runways the reply lists them, so you never have to remember which is which:

cALG2E            cleared the ALG2E departure, runway 08R
cROKI1B           cleared the ROKI1B arrival
cROK26            ROK26 serves runways 26L, 26R. Name one, e.g. cROK26,26L.
cROK26,26L        cleared the ROK26 transition to 26L

Both spellings of a name work. Navigation data shortens a name that does not fit its field, so the arrival published as ROKIL 1B is filed as ROKI1B and the LANDU 2B as LAND2B. Type either: cROKIL1B and cROKI1B are the same arrival. Transitions work the same way, except that what follows the waypoint is the runway rather than a revision, so the long spelling is cROKIL26 and the short one cROK26. The waypoint alone is not a name and does not resolve.

The reply always names the procedure the way the data files it, so you can see which one you got. That matters more than it sounds: what you type and what is flown need not be the same string, and the readback is where you check it.

via <FIX> on an arrival picks which enroute transition of that arrival to fly. Leave it out and the aircraft takes the first one alphabetically, which is a fallback rather than a choice, so name the fix whenever the arrival has more than one. A fix that is not a transition of that arrival is refused with the available ones listed.

clr sid exists and flies a published departure, but nothing takes off here: it is only useful on an aircraft you have put in the air yourself with spawn.

Approach transitions fly the published feeder route from the fix you name up to the point where the procedure hands over to radar vectoring, then hold that heading and wait. The via fix chooses where to join: an entry fix takes the whole transition, a fix part-way through skips what came before. An ambiguous fix is refused, with the available entry fixes listed.

Two-stage approaches. clr loc gives the aircraft the centreline while leaving it on your last assigned altitude, so you can keep stepping it down. clr ils for the same runway then adds the glideslope and keeps the existing capture.

Telling an aircraft which runway to expect is a note rather than a clearance:

DLH123, expect 26L
DLH123, e26L
DLH123, #26L

Nothing is armed, the aircraft keeps flying the heading and altitude you gave it, and it will not turn onto the approach. What it buys you is the clearance afterwards: clr ils or a bare i then needs no runway, and clears onto the noted one. l does the same for the localiser alone.

If the runway changes, name the new one; a second note replaces the first. There is no command to take a note back, and none is needed, because clearing an approach uses it up and a go-around drops it.

The aircraft does not yet fly any differently for having been told, which is a limitation rather than the intent. Planning the approach off a note is built and held back: an aircraft that is level and has not been descended yet reads as too high for the runway, and reaches for the speedbrake forty miles or more out. That is true of an approach clearance at the same place as well, so it is the plan that needs correcting rather than the note, and the note stays a note until it is.

A hold takes three optional values after the fix, in that order: the inbound course as three digits (270, never 27), the turn direction as l or r, and the leg as either a time or a distance (1min, 8nm). hold MIQ alone is a complete instruction.

What you leave out, it fills in: right turns, one-minute legs below FL140 and one and a half above, and an inbound course taken from the aircraft's bearing to the fix at the moment you issue it. Where the navigation data publishes a hold for that fix, that one is used instead. The ICAO holding speed for the altitude band is a cap rather than a target, so an aircraft already slower stays where it is.

Capturing an approach

Laterally, an intercept of 30° or less captures cleanly. Between 30° and 35° it still captures, with a note on frequency that stability is not assured. Past 35° it will not capture until you vector it inside that angle. The clearance stays armed either way, so there is nothing to re-issue.

What ends an approach clearance

Only you do. A clearance stands until cancel app, go around, a new approach clearance, a new route (clr star, clr trans, clr sid, route or hold, each of which replaces it, with "Approach cancelled" in the readback), or the landing. A heading, a direct, present heading or an orbit does not touch it, which is how it works on the frequency: cancelling an approach clearance is a transmission of its own.

That has three consequences worth knowing before you rely on them:

• An aircraft that is cleared and not yet on the localiser flies your heading with the clearance armed, and joins the localiser wherever it meets it at a usable angle. A correction on the intercept, a wider base, a re-intercept after it flew through: all of them are just headings, and none of them needs a second clr ils.
• That includes a heading across the final. A cleared aircraft that is vectored through the localiser turns inbound if it meets it at 35° or less. Say cancel app first when you want to take one across, exactly as you would warn a real crew to expect vectors across final.
• An aircraft already established follows your heading off the localiser, and the readback tells you so: "Leaving the localiser; the approach clearance stands." The clearance is still armed, but the aircraft will not rejoin on its own: your next heading is what re-arms it, and it captures once that heading brings it back at a usable angle. Losing the localiser through wind or a bad intercept works the same way: the aircraft coasts on its present heading, tells you the localiser is lost, and waits for a new intercept vector rather than for a new clearance.

An aircraft broken off final accelerates the way it does after cancel app rather than carrying its final-approach speed round the downwind. It holds the altitude it had when you turned it unless you give it one. It also cleans up. The flaps come in one position at a time as it gains speed, and the gear comes up with the first of them, or as soon as it climbs. The same happens after cancel app and after a go-around. Flaps or gear you set yourself with flaps or gear after the approach has ended are left where you put them. The speedbrake is not part of this yet. Boards still out when the approach ends stay out until you give speedbrake none or clear the aircraft for another approach.

Vertically, an aircraft below the glideslope holds its assigned altitude until the beam comes down to it, rather than starting down early. An aircraft up to one dot above the path joins it from above on its own, with nothing further from you.

Higher than one dot, the clearance still arms for as long as there is track left to shed the excess by 1000 ft above the airport, but the aircraft will not come down on its own: it holds the altitude you last gave it until you descend it, and then either crosses into the band or reaches the beam from below and captures normally.

Higher again, the approach is refused: either there is no usable signal to arm against, or too little track is left to lose the height by 1000 ft above the airport. The message tells you which, and the approach has to be set up again.

What an arrival does by itself

Once it is cleared for an approach, an aircraft plans its own energy. It works backwards from being stabilised at 1000 ft above the airport and asks whether the track it has left is enough to get there against the drag it will have. That plan is what decides how early it starts slowing down.

Having started, it flies the plan rather than the landing speed. It holds each speed until the track left makes the next reduction necessary, so it passes an ordinary 10 nm final somewhere near 190 knots and reaches its approach speed at the stabilisation point, not before. An aircraft that reaches approach speed with miles still to run is a bug, and used to be the normal case.

The plan assumes the aircraft slows down the way it actually does while descending. It keeps a comfortable rate of slowing and descends as steeply as it can without losing that rate, never steeper than its usual idle descent. Where its drag cannot give even that rate, it stays level. It does not assume the straight line down to the runway. A clean jet barely loses speed on a three degree descent, so a plan that assumed it had to would call every far-out arrival late and start slowing it in the cruise. That was the case until September 2026: an aircraft cleared for the approach 40 nm out would be told to slow down at once and take flap a long way from the runway. It now keeps its own speed until it is much closer in, somewhere between about 13 and 25 nm depending on the type and the arrival, and slows from there. A jet cleared for the approach high and fast, say on the 3 degree line at 300 knots, is genuinely high on energy and will use its speedbrake. With the boards out it descends noticeably steeper for a few miles, then stows them again. That holds for the 737, 757, 767, 777 and 787 families and for the A320, where published figures say how much steeper the boards make a descent. Other types, the A320neo, A319 and A321 among them, still use their boards, but on them the boards never take the descent past the type's usual rate. The exception is the final approach itself. Once the aircraft is at the point where the procedure's platform altitude meets the glidepath it is established and flies the gradient it is given, and the plan stops assuming it can level off. Where that point is comes from the procedure, not from a fixed distance: at Munich it is about 11 nm out, at most airports nearer 6.

It is not the only thing setting its speed. The type's own descent schedule and the 250-knot limit below FL100 apply alongside it, and a speed published on the procedure is flown as published, so a published figure can be higher than the plan's own. The plan is also held to the type's own certificated maximum speed, so a high-speed clearance issued a long way out does not make it wait any longer before it starts slowing down. What there is not is a table of fixed speeds at fixed distances. Two rules follow:

• It can only slow itself down. The plan never speeds an aircraft up, and never gives back a reduction it has made.
• Your instruction wins, with one exception. A hard speed overrides the plan and cancel speed hands it back. Below 1500 ft above the threshold on a captured localiser, a speed far above what the aircraft needs to be stabilised is overridden, because the alternative is an approach nobody would fly. The plan also counts on the speed you gave. An aircraft you keep fast is planned with the drag of that speed rather than as if it had already slowed down.

Flaps come out as the aircraft slows, one setting at a time. While it is slowing for an approach it takes each setting as soon as its speed permits, so it configures earlier and more deeply than a crew would. That is a known difference rather than the intended behaviour.

The landing gear goes down at about 2000 ft above the airport, and only at or below the speed its type may operate the gear at. That limit is lower than most people expect: several business jets are at 190 knots and the ATR family between 160 and 170. An aircraft you have held fast will not get its gear, will not have the drag to slow down, and will visibly miss the profile.