Cruising levels

The previous chapter covered who has authority over which airspace. This chapter covers what actually puts that authority into practice: how a flight — VFR or IFR — chooses its level, which visibility minima apply at each altitude, and what changes when a VFR flight cannot operate within them.

Art. 22 of ICA 100-12 states that the cruising levels at which a flight, or part of it, is to be conducted "shall be expressed as: I - flight levels, for flights conducted at or above the lowest usable flight level or, where applicable, for flights conducted above the transition altitude; or II - altitudes, for flights conducted below the lowest usable flight level or, where applicable, for flights conducted at or below the transition altitude"². In practice: above the transition altitude, a flight's vertical position is a flight level (FL); at or below the transition altitude, it is an altitude.

That is the cruising level rule. The moment the altimeter actually changes reference, however, is not the same in both directions: when climbing, the boundary is the transition altitude; when descending, it is the transition level. The Transition altitude and level section, further on, details this asymmetry — one of the most common mistakes among those who learned only half the rule.

The choice of level within this reference is not free — it depends on the magnetic track of the route. Annex IV of ICA 100-12 contains, in Table 7, the correlation between magnetic track, type of flight (IFR or VFR) and cruising level². This is what aviation usually calls the semicircular (or hemispheric) rule — a name that does not appear in the text of ICA 100-12, but that describes the effect well: tracks from 000° to 179° use one family of levels; tracks from 180° to 359° use another, interleaved with the first. The first rows of the table illustrate the pattern:

Table 7 of Annex IV of ICA 100-12, first rows, reproduced as an example². The pattern: in each track range, the IFR level ends in a "round" thousand and the corresponding VFR level is 500 ft above it; the 000°–179° range and the 180°–359° range never share the same level. The complete table extends up to the highest levels used en route — for the level of a specific route, consult Annex IV of ICA 100-12 or the AIP-Brasil.

RVSM airspace

In RVSM airspace, cruising levels do not follow Table 7 — they follow Table 8 of the same Annex IV of ICA 100-12²:

Between FL 290 and FL 410, Table 8 spaces the levels every 2,000 ft, alternating between the two track ranges — the 1,000 ft of minimum vertical separation between adjacent levels that gives RVSM (Reduced Vertical Separation Minimum) its name².

When RVSM procedures are suspended, item 3 of Annex IV requires Table 9 to be applied in that same airspace²:

The grid becomes sparser: without reduced vertical separation, fewer levels are available in the same altitude band.

VFR levels

Art. 123 of ICA 100-12 sets the general rule: except when authorized by the ATC unit, VFR flights in level cruising flight, when conducted more than 900 m (3,000 ft) above the ground or water, shall be conducted "at a level appropriate to the route, in accordance with the table of cruising levels, as a function of magnetic track, contained in Annex IV"² — the same Table 7 from the previous section.

Art. 124 of ICA 100-12 adds: the VFR flight level so selected shall be maintained while the aircraft can meet the conditions of Art. 107 and Art. 108, subsection I, of the same ICA 100-12² — maintaining flight visibility and distance from cloud at the Table 1 minima (Art. 107)², and maintaining reference with the ground or water such that meteorological formations do not obstruct more than half of the pilot's field of view (Art. 108, I)². If these conditions are no longer met, the aircraft must change level and/or heading until it meets them again, subject to Art. 88 of ICA 100-12 on the deterioration of weather conditions below VMC².

Also under Art. 108, subsection II, of ICA 100-12, VFR flights shall be conducted below FL 150² — unlike Art. 107, Art. 108 does not repeat the exception for Special VFR flights, covered in the section below.

IFR levels in controlled airspace

Within controlled airspace, Art. 142 of ICA 100-12 requires the cruising levels of IFR flights to be selected "in accordance with the table of cruising levels shown in Annex IV of this publication, except when another correlation of levels and route is indicated in aeronautical information publications or in air traffic control clearances"². The exception is broad in practice: the AIP-Brasil or the ATC clearance may assign a level different from the one in the table, and that assignment prevails².

Transition altitude and level

Two references divide a flight's vertical position. At or below the transition altitude, the altimeter uses QNH — the altimeter setting that makes the instrument indicate altitude², and this is how subsection II of Art. 22 of ICA 100-12 already classified this band: flights "conducted at or below the transition altitude" are expressed in altitudes². Above the transition altitude, QNE is used, the standard setting of 1013.2 hPa, and the flight's position is expressed as a flight level².

But when one setting is changed for the other depends on the direction of flight, and ICA 100-37 covers the two cases in separate subsections.

When climbing, the boundary is the transition altitude. Art. 482 of ICA 100-37 is explicit about the scope: "the vertical position of an aircraft during climb shall be expressed in terms of altitude until reaching the transition altitude, above which the vertical position shall be expressed in terms of flight level"¹. And Art. 481 of ICA 100-37 requires the altimeter to be set to 1013.2 hPa (QNE) "during climb, when passing the transition altitude of the departure location"¹. Before that, Art. 480 of ICA 100-37 requires the QNH to be passed to the aircraft in the taxi clearance¹.

When descending, the boundary is the transition level. Art. 486 of ICA 100-37 covers the aerodrome without a control unit: "aircraft descending to the procedure initial altitude, at a location not served by an air traffic control unit, shall have their altimeters set to the QNH setting when passing the transition level"¹. Art. 487 of ICA 100-37 says the same for aircraft under conventional control — QNH "when passing the transition level or when so instructed or authorized by the air traffic control unit"¹ — and the sole paragraph adds that the unit "shall instruct or authorize the introduction of the QNH setting above the transition level whenever the descent is expected to be continuous, without long segments of level flight"¹. There are also two particular cases in the same subsection: Art. 484 requires setting QNH when starting the descent on the penetration track, when the descent procedure includes it in its chart; and Art. 485 leaves the moment up to the unit for descending aircraft under radar control being vectored to intercept the final segment of the procedure or for a visual approach¹. Before all of this, Art. 483 requires the QNH to be passed to arriving aircraft "as soon as communications are established"¹.

The transition altitude is not a fixed national number — it is published per aerodrome. Art. 477 of ICA 100-37 states that "the transition altitude of each aerodrome is the one shown on the Instrument Approach Charts – IAC and/or the Standard Instrument Departure Charts – SID"¹. The transition level, in turn, is not fixed even per aerodrome: Art. 479 of ICA 100-37 requires the air traffic control unit — or the pilot, when the unit only provides the Flight Information Service — to determine it at any given moment, crossing the aerodrome's transition altitude with the current QNH in Table 7 of that article¹; the lower the QNH, the higher the resulting transition level (Art. 479 § 3)¹.

Neither of these two values — the transition altitude of a specific aerodrome, or the current transition level — is fixed in this manual: both vary by aerodrome and by weather condition. For the current value, consult the AIP-Brasil, the aerodrome's IAC or SID chart and the portal's Operational Manuals section.

It is the same boundary that the VFR Phraseology Manual uses to decide how to read it on the radio: below the transition level, the designator is feet; above it, flight level.

VMC minima

Art. 104 of ICA 100-12 states that "the visibility and distance from cloud minima in VMC are contained in Table 1"². Art. 107 ties these minima to VFR flight: except when operating as a Special VFR flight — covered in the next section — every VFR flight shall be conducted maintaining flight visibility and distance from cloud equal to or greater than those in Table 1². The table below reproduces Table 1 of Art. 104 of ICA 100-12²:

Class A does not appear in this table. Art. 21, subsection I, letter "a" of ICA 100-37 states that in Class A "only IFR flights are permitted"¹ — there is no VFR flight in Class A, so there is no VMC minimum to meet there.

Art. 104 § 1 of ICA 100-12 resolves the reference for the first band when the aerodrome's transition altitude is lower than the 3,050 m (10,000 ft) AMSL used as the reference in Table 1: "when the height of the transition altitude is lower than 3,050 m (10,000 ft) AMSL, FL100 shall be used in place of 10,000 ft"² — the same rule, with the same wording, that the sole paragraph of Art. 127 of ICA 100-12 already sets for VFR speed limits (see Airspace Classes, Speed limits for VFR flight).

§§ 2 to 4 of the same article cover how the pilot should assess flight visibility: using their best judgment, supported by general flying experience, knowledge of local conditions and procedures and visible reference points, and always equipped with the latest weather observations and forecasts².

Special VFR

Section VIII of Chapter V of ICA 100-12, Art. 128 to 135, covers Special VFR flight — the clearance that allows a VFR flight to operate below the Table 1 minima².

Art. 128 requires that, under a Special VFR clearance, the pilot comply with ATC instructions and always remain in flight conditions that allow them to determine their flight path and keep clear of obstacles; the sole paragraph of the same article is stricter still: upon receiving the clearance, the aircraft must remain clear of cloud and in sight of the surface². Art. 129 recalls that this clearance does not exempt from the minimum height restrictions of Art. 21 of ICA 100-12 itself — which prohibits flying over cities, towns and open-air assemblies of people at a height lower than that which would allow a safe emergency landing, and refers to Art. 110 (minimum heights for VFR flight) and Art. 137 (minimum levels for IFR flight)². This is a different provision from Art. 21 of ICA 100-37, which classifies airspace and has already been covered in the Airspace Classes chapter — same number, different regulations.

Art. 130 and 131 set the speed limit: 140 kt IAS, the value considered the maximum acceptable to maintain the ability to "see and avoid" when flight visibility is 1,500 m or greater²; the sole paragraph of Art. 131 requires a lower speed depending on local conditions, the number and experience of the pilots, or flight visibility below 1,500 m — the case, among others, of helicopters².

Art. 132 limits the period of operation: an aircraft may only operate as a Special VFR flight between sunrise and sunset². Art. 133 limits the airspace: only in a CTR or ATZ of a controlled aerodrome, and only with clearance from the relevant ATC unit² — this is where the applicability of Special VFR flight in CTRs and ATZs comes from.

Art. 134 sets the aerodrome operating minima below which an ATC unit shall not issue a Special VFR clearance for an aircraft to take off from, or land at, an aerodrome within a CTR/ATZ, or to enter the traffic circuit: a ceiling of 300 m (1,000 ft) — or the restriction published by DECEA for fixed-wing aircraft at that aerodrome, whichever is higher; and visibility of 3,000 m, or the value shown on the SID, whichever is higher². Art. 135 closes the section with an important caveat: these minima do not constitute a "Special VFR aerodrome operation", nor a general authorization for several aircraft to operate as Special VFR flights at a given aerodrome — they serve only to guide the issuance of clearances by the ATC unit, case by case, also taking into account other factors established in ICA 100-37².

The rules in this chapter — especially the VMC minima and the correlation between track and level — are the basis of the Quick Checklist, the final chapter of this manual.