Standard Terminal Arrival Routes (STARs)

A standard arrival route (STAR) is the arriving counterpart of a SID: a published, coded IFR route that takes an aircraft from the en-route structure to the start of an instrument approach. ICAO calls it a standard instrument arrival and the FAA a standard terminal arrival, but the abbreviation and the purpose are the same. A STAR fixes the lateral path, the levels and speeds at which traffic reaches the terminal area, and often the holding patterns used when it cannot land at once.

For the crew a STAR is a sequence of constraints to plan and fly, and a clearance whose meaning depends on the words used. The FAA's "descend via" phraseology, the distinction between restrictions and "expect" altitudes, and speed limits that apply whether or not they are charted are all common sources of exam questions and of real level busts.

Purpose of a STAR

A STAR joins a significant point, usually on an ATS route, to the point from which the instrument approach begins, normally an initial approach fix (IAF) (see instrument approach procedures). It simplifies clearance delivery, since one designator replaces a long list of fixes and levels, separates arrival flows from departures and neighbouring aerodromes, and keeps traffic clear of noise-sensitive areas. The FAA describes STARs as ATC coded arrival routes that simplify clearances and ease the transition from en-route flight to the approach.

ICAO designators follow the same pattern as SIDs: a basic indicator, here the name of the significant point where the STAR begins, a validity number and a route letter. At Toulouse-Blagnac the LMB 8S runs from LMB via TADAN to SURAS, an IAF with FL080 underlined, "at or above". At Bordeaux the MIRBA 2L ends at LIBRU, which is labelled with the distance to go (DTG) to each threshold, 27.8 NM to runway 23: the figure crews use to plan the descent. The FAA names its STARs in words, such as the Eagul Five arrival, with named transitions.

STAR charts also show holding patterns at the arrival fixes, with their own limits. The SURAS hold is flown inbound on 076° with right turns, 1-minute outbound legs and a maximum of 220 kt between FL080 and FL140 (see holding patterns). They also show minimum obstacle clearance altitudes along legs, printed in a dark box on French charts, such as 6,100 ft on the Lyon MEZIN 9S.

Many STARs are now RNAV STARs, designed to RNAV 1 or RNP 1: total system error within 1 NM for 95% of the flight time. The chart box states the positioning sources allowed: the Lyon STARs accept GNSS or DME/DME with an inertial reference unit, while a box reading "GNSS only" excludes an aircraft updating by DME/DME alone. At Toulouse a pilot who loses RNAV capability reports "NON RNAV" at once, and approach provides radar vectors if necessary. In the United States, pilots must hold at least the approved chart, RNAV STARs must be retrievable by name from the database, and a pilot who does not want STARs writes "NO STAR" in the flight plan remarks.

Altitude constraints

An altitude constraint is a level to be respected at a fix. Charts use a common convention:

At IZPIQ the upper figure becomes FL150 when restricted area LF-R 322 is active, so the chart notes must be read with the constraint.

The FAA's expect altitudes and speeds are published only for planning. They are not STAR crossing restrictions unless ATC issues them verbally, and they may not be used after a communications failure unless ATC has told the pilot to expect them as part of a further clearance. Minimum en-route altitudes printed on a STAR are not restrictions either, but the aircraft must stay above them unless ATC instructs otherwise.

Speed constraints

A speed constraint is a maximum, minimum or mandatory speed at a fix; IZPIQ carries "MAX IAS 250 kt". Under the FAA's rules published STAR speed restrictions are independent of altitude restrictions and mandatory unless ATC modifies them. The pilot plans to cross the fix at the published speed and does not exceed it after the fix unless authorised. ATC expects the speed change to begin only the minimum distance before the fix. A chart note may give a transition from Mach number to IAS: the crew hold the cruise Mach until reaching that speed, then keep it until the next restriction or the regulatory speed limit.

Speed limits apply even when not charted. In classes D, E, F and G ICAO applies 250 kt IAS below 10,000 ft to all traffic, and in class C to VFR flights. In France, IFR flights below 10,000 ft AMSL on an ATS route, a SID, a STAR or under radar vectors must not exceed 250 kt IAS unless cleared otherwise, with FL100 used where the transition altitude is lower. An aircraft that cannot fly slowly enough for technical reasons may exceed the limit with ATC approval. The FAA's 14 CFR 91.117 sets 250 kt below 10,000 ft MSL, 200 kt at or below 2,500 ft above the surface within 4 NM of the primary airport of Class C or D airspace, and 200 kt beneath Class B or in a VFR corridor through it. Jeppesen charts mark speed limiting points, where a maximum IAS begins.

When both an altitude and a speed are issued or charted at a fix, the AIM says ATC expects the pilot to descend to the crossing altitude first and then slow down.

Crossing restrictions

A crossing restriction requires the aircraft to pass a fix at, above or below a stated level, and sometimes at a stated speed or time. ICAO phraseology is "CROSS (significant point) AT (or ABOVE, or BELOW) (level)"; the FAA adds restrictions to a descend via clearance with "except", as in "descend via the Eagul Five arrival, except cross Vnnom at or above one two thousand".

Meeting a restriction is a descent planning problem (see climb and descent planning). A 3° descent path loses about 318 ft per NM, so the rule of thumb is three times the height to lose in thousands of feet: from FL350 to cross a fix at FL100, start about 75 NM before it, plus distance to slow down. The rate of descent for a 3° path is about five times the groundspeed. A tailwind moves the top of descent further out and a headwind brings it closer. For a slower aeroplane, the same logic uses time: descending 8,000 ft at 500 ft/min takes 16 minutes, 32 NM at 120 kt. The FAA's fuel efficient descents use a gradient of 250 to 350 ft per NM.

Descend via clearances

Under FAA rules, when a cleared route includes a STAR, the pilot keeps the last assigned altitude until authorised to descend so as to comply with the published restrictions. The clearance can take three forms:

• Routing only, "cleared Tyler One arrival": fly the lateral path and meet the published speed restrictions, with no descent authorised.
• Routing with an altitude, "descend and maintain flight level two four zero": descend as directed, meet the speed restrictions and hold FL240 until cleared further.
• Descend via, "descend via the Eagul Five arrival": descend at the pilot's discretion, navigate the lateral path and meet every published or assigned altitude and speed restriction down to the bottom altitude. "Except" clauses change a restriction or the bottom altitude.

Under a descend via clearance, a pilot cleared direct to a waypoint on the STAR may descend at discretion to the altitude depicted there; where none is depicted, ATC assigns a crossing altitude. On each new frequency the pilot reports the level leaving, "descending via" the procedure, the runway transition or landing direction and any restriction not published on the chart. If ATC vectors the aircraft off the STAR, the STAR and its published restrictions are cancelled, ATC gives an altitude and, if needed, a speed, and says where to expect to rejoin. The departure equivalent is climb via (see instrument departures); together they are known as the descend via / climb via clearance.

Optimised profile descents

An idle-thrust descent from the top of descent is the most fuel-efficient way down, because the aircraft trades its height for distance instead of flying level at low altitude on thrust. A continuous descent keeps the aircraft descending with minimum thrust and as little level flight as the procedures and ATC allow, to cut noise, fuel burn and emissions. The FAA calls arrivals built for it optimised profile descents (OPD): RNAV STARs whose constraints are placed to allow a near-idle descent while keeping traffic spaced, which works only if crews fly the published speeds. European AIPs speak of continuous descent operations (CDO); Toulouse-Blagnac publishes RNAV initial approaches "developed under the CDO concept".

ATC may still shorten the route. At Toulouse a published CDO may be joined after the IAF by radar vectors or by a direct routing to one of its points, and the level and speed constraints then apply at the corresponding distances to go; a crew that cannot comply must tell ATC. The same aerodrome asks for the glide path to be intercepted at 3,000 ft AMSL or above and recommends a 5.2% slope in the initial approach, the same gradient as a 3° final. The flight management system builds the descent backwards: the A320's FMGS, for example, computes the top of descent from a point at 1,000 ft on final at approach speed, taking the descent constraints into account, so a shortcut or a new constraint changes the energy picture at once. Crews compare altitude with distance to go throughout and use drag early rather than arriving high at the final approach fix.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.