Instrument procedures
What counts as an instrument procedure
An instrument procedure is a published, obstacle-assessed sequence that takes an aircraft from one phase of flight to the next without the pilot needing visual reference to the ground. In the UK these are not home-grown: the AIP states that holding, approach and departure procedures are established in accordance with ICAO Doc 8168 (PANS-OPS), except for the differences listed at GEN 1.7 and in CAP 785B[1]. That single sentence is worth knowing, because it means the design rules behind a UK approach chart are ICAO rules, and the places where the UK genuinely diverges are enumerated in one findable list rather than scattered.
The procedures themselves fall into a small number of families:
- Departure procedures (SIDs), which take you from the runway to a defined en-route entry point on a protected track.
- Arrival procedures (STARs), which do the reverse, delivering you from the en-route structure to a point where an approach can begin.
- Approach procedures, which descend the aircraft toward a runway in segments, each with its own obstacle clearance, ending either in a landing or a missed approach.
- Course reversals, the procedure turns and racetracks that get you established on the final approach track when you arrive at the fix pointing the wrong way.
- Position fixing, which is less a procedure than a continuous obligation: knowing where you are from the aids available.
Holding sits alongside these as its own discipline and has its own pillar guide. The UK IR skill test treats it the same way, as a schedule item separate from the approach items[5].
Minimum levels change as the phase changes
The most common source of confusion across a whole IFR flight is that the number protecting you from terrain is not the same number throughout, and it is not always called the same thing.
En route, the rule is regulatory rather than charted. Under UK-retained SERA, an IFR flight must be flown at a level not below 2000 ft above the highest obstacle within 8 km of the estimated position of the aircraft over high terrain or in mountainous areas designated by the State, and 1000 ft above the highest such obstacle everywhere else[2].
On the charts, two different minimum altitudes appear, and they are not interchangeable. UK SID and STAR charts show an Area Minimum Altitude (AMA), not a Minimum Sector Altitude. This is a genuine UK difference, filed against ICAO Annex 4, on the grounds that the extent of an MSA does not sufficiently account for the complete route[3]. The approach chart, by contrast, does carry a Minimum Sector Altitude (MSA).
Above the transition altitude every level is flown on the standard pressure setting rather than QNH. UK altimeter setting procedures are in the AIP and the transition altitude varies by aerodrome; the planning side of this is covered in UK IFR flight planning.
Course reversals, and the choice the UK gives you
When you arrive at the fix on a heading that will not let you intercept the final approach track, a course reversal turns you round inside protected airspace. The two classical forms are the 45/180 procedure turn and the 80/260.
Which one you fly is usually up to you. The UK AIP states that except where an 80/260 procedure turn is specifically prescribed, procedure turns specified in instrument approach procedures may be flown as either the 45/180 or the 80/260 type, at the pilot's discretion[4]. The chart decides only when it explicitly prescribes the 80/260; otherwise habit does not, and neither does the examiner.
A racetrack procedure is the third form, shaped like a holding pattern and often flown in place of a procedure turn. The AIP recommends joining a racetrack from Sector 1 by joining the hold before entering the racetrack[4]; the entry geometry itself is holding-pattern geometry, covered in the holding guide.
The full flying mechanics of each reversal, including timing by aircraft category, belong to the procedure turn article in this cluster rather than here.
Position fixing
Everything above assumes you know where you are. Traditional fixing methods still form part of the skills test even where GNSS provides a continuous position:
- Cross-bearing fix: two or more VOR radials or NDB bearings intersecting at your position.
- Range fix: DME distance, which measures slant range to the station rather than distance across the ground.
- Combined fix: one bearing and one range from the same VOR/DME, the quickest single-aid fix available.
- Running fix: successive bearings from one aid, transferred over a known elapsed time.
How approaches are classified
Since the All Weather Operations package came into UK force on 30 October 2025, an approach operation is described by two independent questions rather than one. What guidance does it give: lateral only (a 2D operation) or lateral and vertical (3D)? And how low are the minima: a minimum at or above 250 ft is a Type A operation, below 250 ft a Type B, subdivided into CAT I, II and III[6]. The Type follows the minima, not the equipment, which is why the same procedure can be either.
The full mapping, including where non-precision, APV and precision approaches sit and why an LPV can be either Type, is in 2D, 3D, Type A and Type B approaches explained.
One UK policy point belongs here rather than there. The AIP states that continuous descent final approach is the preferred method for non-precision approaches in the UK where practicable[7], and the skill test expects steady, stable rates of descent flown to the published distance and altitude profile[5]. A dive-and-drive descent to minima is not what a UK examiner is looking for.
What the IR skill test actually examines
The CAA publishes the schedule and the tolerances, so this is not a matter of opinion. Standards Document 14(A) uses 3D operations (ILS or 3D RNP approach to DA/H) and 2D operations to MDA/H (or derived DA/H for CDFA) and MAP as literal schedule headings, which confirms the AWO language above is current examiner terminology and not merely regulatory prose[5].
| Item | Tolerance |
|---|---|
| Altitude, normal flight | ±100 ft |
| Starting a go-around at DA/H | +50 ft / −0 ft |
| MDA/H | +50 ft / −0 ft |
| "Not below" from FAF altitude to MDA/H | −0 ft (no allowance below) |
| Circling minima | +100 ft / −0 ft |
| Tracking | ±5° on a single-needle display; half-scale deflection on angular guidance |
| DME arc | ±1 NM |
| Heading, all engines | ±5° |
| Speed | ±5 kt |
Two further expectations catch candidates out. Where an overlay is used to assist situational awareness on an NDB or VOR final segment, continuous reference must still be made to the raw ADF or VOR data[5]; the substitution rules are covered in RNAV substitution on the IR skills test. And an RNP approach is not universally required: the UK has derogated from the Part-FCL requirement, so where RNP is unavailable two terrestrial-aid approaches are flown instead[5]. Raw-aid competence still earns its place in the syllabus.
Sources
- UK AIP, ENR 1.5 Holding, Approach and Departure Procedures, paragraph 1.1 (procedures established in accordance with ICAO Doc 8168 except the differences at GEN 1.7 and CAP 785B), paragraph 1.4 (CDFA preference), paragraphs 2.8.1 and 2.8.2 (procedure turns) and 2.9.1 (racetrack procedures). Published by NATS on behalf of the CAA; check the current AIRAC cycle. aurora.nats.co.uk/htmlAIP/Publications/
- UK-retained Standardised European Rules of the Air, Regulation (EU) No 923/2012, SERA.5015(b), minimum levels for IFR flight.
- UK AIP, GEN 1.7 Differences from ICAO Standards, Recommended Practices and Procedures, difference filed against ICAO Annex 4: Area Minimum Altitude shown in place of Minimum Sector Altitude on SID and STAR charts.
- Civil Aviation Authority, Standards Document 14(A), Version 10 (7 January 2026): skill test and proficiency check schedules for single-pilot aeroplanes, including the IR schedule and the Appendix 2 tolerance table. caa.co.uk/publication/download/12926
- Civil Aviation Authority, ORS9 Decision No. 47 (9 May 2025, in UK force 30 October 2025), amending AMC and GM to UK Regulation (EU) No 965/2012; GM36 and GM37 to Annex I define 2D/3D approach operations and the Type A / Type B split at 250 ft. caa.co.uk/our-work/publications/documents/content/ors9-no-0047/
- UK AIP, ENR 1.7 Altimeter Setting Procedures, transition altitude and pressure setting changeover.
Articles in this cluster
Frequently asked questions
What is a position fix?
A position fix is a determination of the aircraft's geographic location at a given moment from external references. Cross-bearing fixes use two or more VOR radials; range fixes use DME; combined fixes use one bearing and one range. Modern GNSS provides a continuous fix; traditional fixes form part of skills tests.
What is DME slant range?
DME measures the line-of-sight distance from the aircraft to the ground station, not the horizontal distance over the ground. At low altitude or large range, slant range and ground range are nearly equal; directly overhead at altitude, slant range equals altitude regardless of horizontal position.
What is a procedure turn?
A procedure turn is a charted course-reversal manoeuvre used during an instrument approach to align the aircraft with the final approach course. The two common types are the 45/180 (45° offset for a timed leg, then a 180° turn back) and the 80/260 (80° offset, then a 260° turn).
What is a DME arc?
A DME arc is a curved flight path flown at a constant DME distance from a ground station, used in some instrument approaches as a transition from the en-route structure to the final approach. The pilot intercepts the arc, then makes small heading changes to keep the DME constant as the bearing to the station rotates.