UK CAA IFR flight planning: rules and weather minima
By Rory Bennett (ATPL, FI: CPL, IR, ME, UPRT) · Published 4 June 2026 · Updated 5 June 2026
Direct answer
Under UK CAA regulations you plan an IFR flight by choosing a route and minimum levels that satisfy SERA, then confirming the forecast weather meets the minima for your operation - departure, take-off alternate, two options of safe landing. Commercial flights apply Part-CAT (CAT.OP.MPA.182); non-commercial flights in other-than-complex aircraft apply Part-NCO (NCO.OP.140 and NCO.OP.143). Each sets when a destination alternate is required and the minima you must plan against[3][1][2].
What are the instrument flight rules?
The instrument flight rules (IFR) are the rules for flying by reference to your instruments rather than by visual reference. In UK airspace they sit within the Standardised Rules of the Air (SERA), retained in UK law, which set the minimum levels for IFR flight, the cruising levels you fly outside controlled airspace, and the separation and clearances inside it[3]. Planning IFR differs from VFR in several places:
- You plan to defined minimum levels ("MSA").
- There is a cruising level semicircular rule above 3000 ft AMSL.
- There are set, objective criteria with regard to selection of aerodromes and weather minima.
Where are the instrument flight rules?
The instrument flight rules are currently not easy to find or interpret from one definitive source. The basic regulation is in SERA.5015, 5020 and 5025. However, the UK has issued several exemptions to these inherited EASA rules, found in ORS4 (Official Record Series 4, miscellaneous). The relevant ORS4 at the time of writing are:
- ORS4 No.1578 for the UK exemption to the cruising-level requirements[5].
- ORS4 No.1496 for the exceptions to the minimum-height requirements (practising approaches, checking navigation aids, or flying a CAA-notified procedure)[4].
When must you fly IFR in the UK?
Two things drive a flight onto the instrument flight rules: the airspace, and the weather.
Airspace. Class A airspace is IFR only: VFR flights are not permitted (SERA.6001(a)(1)), so any flight in Class A is conducted under IFR[3]. In the UK, Class A is the airways, the upper parts of the TMAs and the upper airspace.
Weather. You may only fly in accordance with the Visual Flight Rules when you can meet the VMC minima in SERA.5001 and comply with the visual flight rules in SERA.5005[3]. The VMC minima are:
| Height band | Class B to E | Class F or G |
|---|---|---|
| At or above FL 100 (10,000 ft AMSL) | 8 km flight visibility; 1500 m horizontally and 1000 ft vertically from cloud | 8 km flight visibility; 1500 m horizontally and 1000 ft vertically from cloud |
| Above 3000 ft AMSL, below FL 100 | 5 km; 1500 m horizontally and 1000 ft vertically from cloud | 5 km; 1500 m horizontally and 1000 ft vertically from cloud |
| At or below 3000 ft AMSL | 5 km; 1500 m horizontally and 1000 ft vertically from cloud | 5 km; clear of cloud and with the surface in sight |
At or below 3000 ft AMSL in Class F or G, by day, an aeroplane at 140 kt IAS or less may reduce flight visibility to 1500 m (SERA.5001 Table S5-1 note). VFR is not permitted in Class A, so the figures there are for guidance only[3].
When the forecast or actual conditions are below these minima you cannot fly VFR, so you plan IFR (or, within a control zone, consider a Special VFR clearance).
What equipment is required?
SERA.5015 states (at time of writing): "Aircraft shall be equipped with suitable instruments and with navigation equipment appropriate to the route to be flown and in accordance with the applicable air operations legislation."
The applicable air ops regulation includes:
- NCO.OP.116, NCO.IDE.A.125, NCO.IDE.A.195
- CAT.OP.MPA.126, CAT.IDE.A.100, CAT.IDE.A.130, CAT.IDE.A.135, CAT.IDE.A.345
Importantly in this day and age, the consideration largely sits around sufficient RNP or RNAV specification for the route intended to be flown. ATS routes can be found in UK AIP ENR 3.1, 3.2, 3.3 and include the minimum RNAV specification to use them.
The next consideration is equipment for the approaches intended to be flown, with an "interesting" and altogether rather sensible consideration for PBN approaches. NCO.OP.142 states that the pilot-in-command of an aircraft must only select an aerodrome as a destination alternate aerodrome if either:
- An IAP that does not rely on GNSS is available either at the destination aerodrome or at a destination alternate aerodrome; or
- all of the following conditions are met:
- the onboard GNSS equipment is SBAS capable;
- the destination aerodrome, any destination alternate aerodrome, and the route between them are within the SBAS service area;
- ABAS is predicted to be available in the event of the unexpected unavailability of SBAS;
- an IAP is selected (either at the destination or destination alternate aerodrome) that does not rely on the availability of SBAS;
- an appropriate contingency action allows the flight to be completed safely in the event of the unavailability of GNSS.
So, effectively, if we are planning a PBN approach, we must either have SBAS or the capability of flying a terrestrial approach at the destination or alternate.
Something similar exists for Part-CAT, now under AMC1 CAT.OP.MPA.182(f) Fuel or energy scheme - aerodrome selection policy - aeroplanes, after the confusing and incredibly frustrating move of regulation regarding alternates and minima into the fuel-planning AMCs. I digress:
"BASIC FUEL SCHEME – DESTINATION AERODROMES – PBN OPERATIONS. To comply with point CAT.OP.MPA.182(f), when the operator intends to use PBN, the operator should select an aerodrome as destination alternate aerodrome only if an instrument approach procedure that does not rely on a GNSS is available either at that aerodrome or at the destination aerodrome."
Good luck finding this one.
What air traffic control services apply outside controlled airspace?
Most of the UK below the airways is Class G(uncontrolled) airspace, and you may fly IFR in it. Outside controlled airspace (OCAS) ATC does not by default separate you from other traffic or issue the clearances it does inside controlled airspace; instead you may request one of the four UK Flight Information Services set out in CAP 774. It is not mandatory to receive a service in Class G, and whatever service you take, you remain ultimately responsible for collision avoidance and terrain clearance[8].
| Service | What the controller provides | Surveillance? | Available to |
|---|---|---|---|
| Basic Service | Advice and information useful for the safe conduct of the flight. Avoiding other traffic rests with the pilot alone, and the controller is not required to monitor the flight. | Not required | IFR or VFR |
| Procedural Service | A Basic Service plus restrictions, instructions and approach clearances that achieve deconfliction minima against other aircraft participating in the Procedural Service. No traffic information or deconfliction advice is given on unknown traffic. | Not required | IFR only |
| Traffic Service | A Basic Service plus surveillance-derived traffic information to help the pilot avoid other traffic. Headings or levels may be given for positioning or sequencing, but the controller is not required to achieve deconfliction minima. | Required | IFR or VFR |
| Deconfliction Service | A Basic Service plus surveillance-derived traffic information and headings or levels aimed at achieving deconfliction minima. Expect headings or levels that may require flight in IMC. | Required | IFR only |
Deconfliction and Procedural Services are available only to IFR flights outside controlled airspace; Basic and Traffic Services are available to both IFR and VFR flights[8]. A surveillance-based Traffic or Deconfliction Service in the lower airspace is commonly obtained through the Lower Airspace Radar Service (LARS), available from participating units, workload permitting, as described in UK AIP ENR 1.6[9]. Controllers apply these services under MATS Part 1[10].
The planning point is simple: outside controlled airspace you cannot rely on guaranteed separation. For an IFR flight in IMC in Class G, a Deconfliction Service gives the most protection where radar is available, and a Procedural Service where it is not, but neither removes your own responsibility for collision avoidance and terrain clearance[8]. That duty for terrain is exactly why the minimum-level and MSA calculation below still matters even when you are working a radar unit.
What are the IFR minimum levels?
You will likely be familiar with the phrase "MSA" or "Minimum Safe Altitude" - this is largely a colloquialism, a figure calculated by pilots to comply with the minimum level requirements of the IFR.
Under SERA.5015(b), except for take-off and landing or where specifically authorised, an IFR flight must be flown at or above the minimum flight altitude set by the State, or where none is established, at least[3]:
- 2000 ft above the highest obstacle within 8 km of the estimated position, over high terrain or in mountainous areas; or
- 1000 ft above the highest obstacle within 8 km of the estimated position, elsewhere.
SERA.3105 adds the congested-area rule: you must not fly so low that, in an emergency, you could not land without undue hazard to people or property on the surface[3].
How to calculate a minimum safe altitude (MSA)
SERA.5015(b) sets the legal requirement in flight, but you still have to decide what altitude to actually plan and fly in order to comply with this. The usual technique is to compute a Minimum Safe Altitude (MSA) for each leg. The catch is that the charted obstacles are not the whole story: the UK AIP only notifies and charts the Area 1 obstacle dataset for obstacles that are 100 m (328 ft) AGL and above[7], so a smaller, uncharted obstacle, up to roughly 328 ft tall, could sit anywhere you have not surveyed. Prudent planning allows for it.
A standard instrument-flying method builds the MSA in three steps:
- Take the highest charted obstacle or terrain in the corridor around your track. SERA.5015(b) defines the legal area as within 8 km (about 5 nm) of the estimated position, and its guidance material says you must widen that to allow for the navigation accuracy actually achievable on the segment[3]. In practice planners assess a corridor of about 10 nm either side of track to allow for navigation error.
- Add 328 ft (100 m) to the highest terrain for the tallest obstacle that could be uncharted, taking the AIP charting threshold as the worst case[7].
- Add the SERA.5015(b) obstacle clearance: 1000 ft, or 2000 ft over high terrain or in mountainous areas[3] to the highest of the highest charted obstacle, or highest terrain elevation + 328 ft. Round the result up to a sensible level.
Worked example (MSA)
Leg: the highest charted spot elevation in the corridor either side of and around the track is a hill at 800 ft AMSL, with no charted obstacle above it. The terrain is not mountainous.
Uncharted-obstacle allowance: 800 ft + 328 ft = 1128 ft. This guards against an obstacle below the 100 m charting threshold standing on that hill.
Obstacle clearance (SERA.5015(b), non-mountainous): 1128 ft + 1000 ft = 2128 ft, rounded up to a planned MSA of 2200 ft (and a semicircular cruising level at or above it where one applies). Over high terrain you would add 2000 ft instead, giving 3128 ft, rounded to 3200 ft.
Consequence: in the latter case over mountainous terrain, you would now have to comply with the semicircular rule for this leg.
What are the IFR cruising levels (the semicircular rule)?
An IFR flight in level cruise outside controlled airspace must be flown at a cruising level appropriate to its magnetic track, taken from the table of cruising levels in SERA Appendix 3 (the semicircular rule)[3]:
| Magnetic track | IFR cruising levels |
|---|---|
| 000° to 179° | Odd thousands of feet: FL 50, 70, 90, 110 and up (4000 ft intervals above FL 410) |
| 180° to 359° | Even thousands of feet: FL 40, 60, 80, 100, 120 and up (4000 ft intervals above FL 430) |
SERA.5025(a) lifts this requirement at or below 3000 ft AMSL, and UK CAA ORS4 No.1578 confirms the alleviation: at or below 3000 ft AMSL an IFR flight outside controlled airspace need not hold a semicircular level, and above 3000 ft AMSL it may fly a different level only when ATC has allocated one or it is flying a CAA-notified instrument approach procedure[3][5].
What are the altimeter setting procedures?
Cruising levels only make sense alongside the UK altimeter setting procedures. At or below the transition altitude you express your vertical position as an altitude on QNH; at or above the transition level you express it as a flight level on the standard pressure setting (1013.2 hPa)[6]. So the semicircular table applies to the flight levels you fly above the transition level, on the standard setting.
- Transition altitude. In the UK this is variable, not a single common value. It is generally 3000 ft, but a higher value (commonly 5000 ft or 6000 ft) applies in, or beneath, certain controlled airspace such as a TMA (AIP ENR 1.7 expresses it as 3000 ft "except in, or beneath" the airspace it lists). The beneath is the catch: underneath the London TMA, for example, your transition altitude is 6000 ft even down at low level, so you keep flying altitudes on QNH up to 6000 ft before you change to flight levels. The value for a given aerodrome is published in the AIP (AD 2.17) and on its approach charts[6].
- QNH and the Regional Pressure Setting. Below the transition altitude you fly altitudes on QNH. Where an aerodrome QNH is not available, the UK is divided into Altimeter Setting Regions, each with a Regional Pressure Setting: the lowest forecast QNH for the hour, used for terrain clearance in the cruise. Because it is the lowest forecast value the altimeter normally underreads, so it is conservative for terrain but not valid for airspace bases defined as altitudes[6].
- Transition layer. The airspace between the transition altitude and the transition level. Aircraft do not normally cruise in it[6].
How to plan an IFR flight
With those rules in place, here is the planning sequence:
- Plot the route and select minimum levels (SERA.5015) and cruising levels (SERA.5025), flown on the correct altimeter setting.[3][6].
- Check for hazards or obstacles to navigation: HIRTA, SUA, gliding sites, parachute dropzones, etc.
- Consider whether these levels will be altitudes or flight levels.
- Consider ATSOCAS (Air Traffic Services outside controlled airspace) and LARS availability.
- Confirm suitable equipment for the route to be flown.
- Check the forecast for departure minima.
- Nominate a suitable take-off alternate.
- Check the destination forecast against the planning minima for your operation (Part-CAT or Part-NCO).
- Decide whether a destination alternate is required, and if so select one (or two) that meets the alternate planning minima.
- Compute fuel for the route, the alternate (if any), and the final reserve.
What are the Part-CAT planning minima?
Planning minima apply to the destination and destination alternate aerodromes.
For commercial air transport (Part-CAT), the planning minima live in CAT.OP.MPA.182, the fuel/energy scheme aerodrome-selection policy that took over the old CAT.OP.MPA.185 planning minima when the All-Weather Operations changes came into UK force on 30 October 2025[1].
The new rules are all based on one idea (for a non-isolated aerodrome): having two options of safe landing at destination:
- Destination with weather at or above actual minima + 1 alternate with planning minima (ETA +/- 1 h).
- 2 destination alternates, both with planning minima (ETA +/- 1 h).
- For flights less than 6 hours: 2 separate runways at destination, with the greater of 2000 ft or circling + 500 ft cloud base, and 5 km visibility (ETA +/- 1 h).
A destination alternate (and the fuel en-route alternate and isolated-destination cases) is planned against raised planning minima, added to the approach minima, in AMC6 CAT.OP.MPA.182 Table 2[1]. Meaning the weather has to be better than the approach minima by a set amount:
| Approach at the alternate | Ceiling | RVR / visibility |
|---|---|---|
| Type B (DH below 250 ft) | DA/H + 200 ft | RVR or VIS + 800 m |
| Type A (DH or MDH 250 ft or more) | DA/H or MDA/H + 400 ft | RVR or VIS + 1500 m |
| Circling | MDA/H + 400 ft | VIS + 1500 m |
Aerodrome selection sits in CAT.OP.MPA.182 (renumbered from the former .180 when the fuel/energy scheme came into UK force on 30 October 2025), which requires two safe-landing options on reaching the destination. In practice a destination alternate is not required only when the destination is isolated or both: the planned flight time does not exceed 6 hours, and two separate usable runways are available with the forecast for ETA plus or minus 1 hour giving a ceiling of at least 2000 ft (or circling height plus 500 ft, whichever is greater) and ground visibility of at least 5 km. Two destination alternates are required when the forecast is below planning minima, or no meteorological information is available[1].
What are the Part-NCO planning minima?
Most general-aviation IFR flights are Part-NCO (non-commercial, in other-than-complex motor-powered aircraft). Part-NCO does not use the Part-CAT increment table; it gives you fixed figures instead. Watch one trap: NCO.OP.135 is "Flight preparation" (the duty to study the forecasts and plan an alternative course of action for every IFR flight), not the planning minima[2]. The minima themselves are in NCO.OP.140 and NCO.OP.143.
You must nominate a destination alternate for an IFR flight under NCO.OP.140 unless the current forecast for the hour either side of ETA (or from departure to an hour after ETA, whichever is shorter) shows a ceiling at least 1000 ft above the DH or MDH of an available instrument approach, and a visibility of at least 5000 m[2]. When you do need an alternate, you can only use one whose forecast for that window meets NCO.OP.143[2]:
| Approach at the alternate | Ceiling | Visibility |
|---|---|---|
| DH below 250 ft | At least DH/MDH + 200 ft | At least 1500 m |
| DH or MDH 250 ft or more | At least DH/MDH + 400 ft | At least 3000 m |
| No instrument approach | At least the higher of 2000 ft and the minimum safe IFR height | At least 5000 m |
NCO.OP.142 adds the GNSS-resilience rule: you may only select an aerodrome as a destination alternate where an instrument approach not relying on GNSS is available at the destination or the alternate, or the defined SBAS conditions are all met[2].
Worked example (Part-NCO)
Flight: IFR, non-complex aeroplane, to an aerodrome of 100 ft elevation whose only approach is RNP to LNAV minima with an MDH of 520 ft. Arrival forecast BKN012, 6000 m.
Alternate required? (NCO.OP.140) No alternate is needed only if the forecast shows a ceiling at least 1000 ft above the MDH, that is at or above 1520 ft, and visibility at least 5000 m. The forecast ceiling is 1200 ft, below 1520 ft, so a destination alternate must be nominated.
Choosing the alternate (NCO.OP.143). Your chosen alternate has an ILS with a DH of 200 ft (the "below 250 ft" band), so its forecast for the window must show a ceiling at least DH plus 200 ft (at or above 400 ft) and visibility at least 1500 m.
When choosing the alternate, it will have to have a terrestrial approach available unless SBAS criteria are met.
Worked example (Part-CAT)
Flight: IFR to an aerodrome of 100 ft elevation whose only approach is an RNP to LNAV with an MDH of 520 ft. Arrival forecast BKN012, 6000 m.
Alternate required? Yes, at least one destination alternate is required with planning minima (ETA +/- 1 h) and it must have a terrestrial approach unless SBAS criteria are met.
When is an alternate required?
The alternate-required test differs by operation:
| Part-CAT | Part-NCO | |
|---|---|---|
| Rule | CAT.OP.MPA.182 | NCO.OP.140 |
| Default | At least one destination alternate for every IFR flight | At least one destination alternate for every IFR flight |
| No alternate needed when | Destination isolated or "two safe-landing options" exist: flight under 6 h, two usable runways, and forecast (ETA plus or minus 1 h) ceiling at least 2000 ft (or circling height + 500 ft) and ground visibility at least 5 km | Forecast (ETA plus or minus 1 h, or shorter) ceiling at least 1000 ft above the DH/MDH of an available approach, and visibility at least 5000 m |
| Two alternates when | Forecast below planning minima (AMC5/AMC6 CAT.OP.MPA.182), or no meteorological information | Not applicable |
How do Part-CAT and Part-NCO compare?
The two regimes plan the same flight to different numbers. At a glance[1][2]:
| Item | Part-CAT (commercial) | Part-NCO (non-complex, private) |
|---|---|---|
| Annex and rules | Annex IV: CAT.OP.MPA.110, .181, .182 | Annex VII: NCO.OP.110, .140, .143 |
| Destination planning | Forecast at or above operating minima (RVR/VIS; ceiling at or above MDH for Type A/circling), or two alternates | Governed through the alternate test (NCO.OP.140) |
| Alternate planning minima | AMC6 CAT.OP.MPA.182 Table 2: Type B +200 ft / +800 m; Type A +400 ft / +1500 m; circling +400 ft / +1500 m | NCO.OP.143 fixed values (DH<250 ft: +200 ft / 1500 m; DH>=250 ft: +400 ft / 3000 m; no IAP: 2000 ft / 5000 m) |
| Final reserve (IFR) | 45 min piston / 30 min turbine at 1500 ft (AMC) | 45 min at 1500 ft (AMC default) |
| Take-off minima | Aerodrome operating minima; lowest standard RVR/VIS 400 m (still defined as LVTO <550m under new definitions), LVTO to 125 m with SPA approval | PIC selects and uses aerodrome operating minima; no RVR table |
What are the take-off minima?
For Part-CAT the take-off minima are aerodrome operating minima under CAT.OP.MPA.110, expressed as RVR or visibility. The lowest standard value, with no low-visibility approval, is 400 m, or 500 m with nil facilities by day. Anything below 400 m RVR is a low-visibility take-off (LVTO) and requires a specific approval under SPA.LVO. Strangely, Annex 1 (Definitions) describes any take-off with an RVR below 550m as a "LVTO." Though the LVO rules still use 400m as the minimum without approval.[1]:
| Facilities | Minimum RVR or VIS |
|---|---|
| Day, nil facilities | 500 m |
| Runway edge lights and/or centreline lights or markings | 400 m |
Part-NCO sets no take-off RVR table. You select and use aerodrome operating minima for the departure aerodrome (NCO.OP.110), and before take-off you must be satisfied that the weather and runway state would not prevent a safe take-off and departure, and that the applicable minima will be met (NCO.OP.175)[2].
How much fuel must you plan to carry?
For Part-CAT, the fuel/energy scheme (CAT.OP.MPA.181, in UK force since 30 October 2025) builds the pre-flight fuel from taxi, trip, contingency (AMC default 5% of trip, reducible to 3% with a fuel en-route alternate), destination alternate (or, with no alternate, a minimum 15 minutes holding at 1500 ft), final reserve, and any additional, extra and discretionary fuel. Final reserve is holding speed at 1500 ft above the aerodrome, and at least 45 minutes for piston aeroplanes or 30 minutes for turbine aeroplanes[1].
For Part-NCO, NCO.OP.125 (also amended on 30 October 2025) is now performance-based: carry fuel to the intended aerodrome plus, where a destination alternate is required, on to that alternate, plus a final reserve. The AMC default final reserve for IFR (and VFR by night) is 45 minutes at holding speed at 1500 ft[2].
Related
See the IFR flight planning overview. Further planning articles will link here as the cluster grows.
Common mistakes
- Comparing a forecast cloud base to the decision altitude instead of the decision height. Planning minima are stated against decision HEIGHT (DH) or minimum descent HEIGHT (MDH). A reported cloud base is a height above the aerodrome, so compare it to the DH/MDH, not to the DA/MDA (a height above mean sea level). Mixing them overstates the margin by roughly the aerodrome elevation.
- Applying US/FAA planning rules to a UK flight. Much online IFR planning content is FAA-based, but UK flights are planned under SERA and Part-CAT or Part-NCO. Use NCO.OP.140 and NCO.OP.143, or CAT.OP.MPA.182, and the UK alternate-required test, rather than carrying across FAA values.
- Treating NCO.OP.135 as the planning minima. In Part-NCO, NCO.OP.135 is "Flight preparation" (study the forecasts and plan an alternative course of action). The planning minima themselves are in NCO.OP.140 (whether an alternate is needed) and NCO.OP.143 (the alternate minima).
- Forgetting that the semicircular cruising-level rule is lifted at or below 3000 ft AMSL. SERA.5025(a) and UK CAA ORS4 No.1578 lift the cruising-level requirement at or below 3000 ft AMSL. Above 3000 ft you must hold a semicircular level unless ATC allocates one or you are flying a CAA-notified instrument approach.
- Not adding a buffer to the 8 km assessed region for minimum level calculation. When planning, allow up to 10 NM either side of, and around, your planned track for "MSA" to ensure safe terrain clearance, taking into account navigational accuracy.
- Using grid MEF figures as an MSA "MEF" figures, the big blue numbers on VFR charts, represent the highest terrain, obstacle, or possible obstacle in a grid. They are not an MSA figure. They can be useful for a "quick number" in flight, but are not fine-grained enough for pre-flight planning.
- Not accounting for uncharted obstacles in calculating MSA Remember that uncharted obstacles can exist up to 328 ft, this should be added to the highest terrain when calculating minimum level or "MSA."
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Frequently asked questions
What are the instrument flight rules (IFR) in the UK?
IFR are the rules for flying by reference to your instruments rather than by visual reference to the surface. In UK airspace they form part of the Standardised European Rules of the Air (SERA), retained in UK law, which set the IFR minimum levels (SERA.5015), the cruising levels you fly outside controlled airspace (SERA.5025), and the separation and clearances inside it.
When must a flight be flown under IFR in the UK?
Whenever the conditions are below the SERA.5001 VMC minima you cannot use the visual flight rules, so you plan IFR. The separate requirement to hold an instrument rating to fly IFR comes from the UK Aircrew regulations.
What are the IFR minimum levels?
Under SERA.5015(b), you must be at or above the minimum flight altitude set by the State, or where none exists, at least 2000 ft above the highest obstacle within 8 km of your estimated position over high terrain or mountainous areas, and at least 1000 ft elsewhere.
How do you calculate a minimum safe altitude (MSA) for an IFR leg?
A common planning method has three steps: take the highest charted obstacle or terrain in the corridor around track, add 328 ft (100 m) for the tallest obstacle that could be uncharted, then add the SERA.5015(b) clearance of 1000 ft (2000 ft over high terrain or mountainous areas), and round up. The 328 ft allowance reflects the UK AIP ENR 5.4 charting threshold: Area 1 obstacles are notified and charted only at 100 m (328 ft) AGL and above, so a smaller obstacle may not appear on the chart. This MSA method is a planning convention; the only legal minimum is SERA.5015(b), measured within 8 km of the estimated position.
How high can an uncharted obstacle be in the UK?
Up to about 100 m (328 ft) above ground level. The UK AIP (ENR 5.4, corroborated by GEN 3.1) notifies and charts the Area 1 obstacle dataset only for obstacles 100 m (328 ft) AGL and above, so a smaller obstacle need not appear on charts or in the obstacle data. That is why a prudent minimum safe altitude calculation adds 328 ft to the highest charted obstacle before applying the SERA.5015(b) obstacle clearance.
What air traffic control service do you get outside controlled airspace in the UK?
Outside controlled airspace (class G), ATC does not separate you or issue clearances as it does inside controlled airspace. Instead you may request one of the four UK Flight Information Services in CAP 774: a Basic Service (advice and information, you avoid traffic yourself), a Traffic Service (surveillance-based traffic information, but no separation guaranteed), a Deconfliction Service (IFR only, headings and levels aimed at deconfliction minima), or a Procedural Service (IFR only, no surveillance, deconfliction against other participating traffic only). A service is not mandatory, and whatever you take you remain responsible for collision avoidance and terrain clearance.
Does a Traffic Service provide separation?
No. Under a Traffic Service the controller passes surveillance-derived traffic information and may give headings or levels for positioning or sequencing, but is not required to achieve deconfliction minima, and the pilot remains responsible for collision avoidance (CAP 774). Only a Deconfliction Service (with surveillance) or a Procedural Service (without it) applies deconfliction minima, and even then avoiding other traffic is ultimately the pilot’s responsibility.
How are IFR cruising levels chosen in the UK?
By magnetic track, from the SERA Appendix 3 semicircular table (mirrored in UK AIP ENR 1.7 para 6.1): tracks 000 to 179 degrees fly odd flight levels (FL 10, 30, 50, ...), tracks 180 to 359 degrees fly even flight levels (FL 20, 40, 60, ...). SERA.5025(a) and ORS4 No.1578 lift this at or below 3000 ft AMSL. The old UK quadrantal rule no longer applies.
When do I need a destination alternate for an IFR flight?
Part-CAT (CAT.OP.MPA.182): at least one for every IFR flight, unless the destination is isolated or the flight is under 6 hours with two usable runways and a forecast of at least 2000 ft and 5 km; two alternates if the forecast is below planning minima. Part-NCO (NCO.OP.140): one alternate, unless the forecast (1 hour either side of ETA) gives a ceiling at least 1000 ft above the DH or MDH of an available approach and at least 5000 m visibility.
What are the Part-NCO destination alternate planning minima?
NCO.OP.143: for an approach with a DH below 250 ft, the alternate forecast must show a ceiling at least DH/MDH + 200 ft and visibility at least 1500 m; for a DH or MDH of 250 ft or more, at least DH/MDH + 400 ft and 3000 m; with no instrument approach, at least the higher of 2000 ft and the minimum safe IFR height, and 5000 m.
How much fuel must I plan for a UK IFR flight?
Fuel to the destination, on to the alternate where one is required, plus a final reserve. For Part-CAT the fuel/energy scheme (CAT.OP.MPA.181) adds taxi, trip, contingency, alternate, final reserve and any additional or extra fuel; final reserve is at least 45 minutes (piston) or 30 minutes (turbine) at holding speed at 1500 ft. For Part-NCO (NCO.OP.125) the rule is performance-based, with a 45-minute IFR final reserve as the AMC default.
What are the take-off minima for an IFR departure?
For commercial (Part-CAT) operations the take-off minima are aerodrome operating minima (CAT.OP.MPA.110), expressed as RVR or visibility. The lowest standard value is 400 m, or 500 m with nil facilities by day; below 400 m RVR a low-visibility take-off approval (SPA.LVO) is required, down to RVR 125 m with full runway lighting (not below the AFM minimum, or 75 m if none is stated). Part-NCO sets no take-off RVR table: you select and use aerodrome operating minima (NCO.OP.110) and must be satisfied that a safe take-off and departure is possible (NCO.OP.175).
Is the take-off alternate planned to the same minima as a destination alternate?
No. A take-off alternate is planned against the actual landing (aerodrome operating) minima for that aerodrome: AMC5 CAT.OP.MPA.182 refers straight to CAT.OP.MPA.110. The raised increment table in AMC6 CAT.OP.MPA.182 Table 2 applies only to destination alternates, fuel en-route alternates and isolated aerodromes, not to the take-off alternate.
Sources
- UK Regulation (EU) No 965/2012 (Air Operations), Annex IV (Part-CAT): CAT.OP.MPA.110, CAT.OP.MPA.180 to 185, and SPA.LVO.100, via the UK CAA Regulatory Library. The fuel/energy scheme and All-Weather Operations changes came into UK force on 30 October 2025 (CAA ORS9 Decision 47). regulatorylibrary.caa.co.uk/965-2012
- UK Regulation (EU) No 965/2012 (Air Operations), Annex VII (Part-NCO): NCO.OP.110, 125, 135, 140, 142, 143 and 175, via the UK CAA Regulatory Library (All-Weather Operations and fuel-planning amendments in UK force 30 October 2025). regulatorylibrary.caa.co.uk/965-2012
- UK Regulation (EU) No 923/2012, Standardised European Rules of the Air (SERA): SERA.5001, SERA.5015, SERA.5025, SERA.6001 and Appendix 3, via the UK CAA Regulatory Library. regulatorylibrary.caa.co.uk/923-2012
- UK Civil Aviation Authority, Official Record Series 4 (ORS4) No.1496, (UK) Standardised European Rules of the Air, Exceptions to the Minimum Height Requirements. caa.co.uk/.../ors4-no1496
- UK Civil Aviation Authority, Official Record Series 4 (ORS4) No.1578, Standardised European Rules of the Air, Compliance with Cruising Level Requirements. caa.co.uk/.../ors4-no1578
- UK Aeronautical Information Publication (AIP), ENR 1.7, Altimeter Setting Procedures, AIRAC cycle 2026-05-14. NATS Aeronautical Information Service. aurora.nats.co.uk/.../EG-ENR-1.7
- UK Aeronautical Information Publication (AIP), ENR 5.4, Air Navigation Obstacles, AIRAC cycle 2026-05-14. NATS Aeronautical Information Service. Area 1 obstacles are notified and charted at 100 m (328 ft) AGL and above (corroborated by AIP GEN 3.1). aurora.nats.co.uk/.../EG-ENR-5.4
- UK Civil Aviation Authority, CAP 774, UK Flight Information Services, Fourth Edition (15 December 2021). The Basic, Traffic, Deconfliction and Procedural Services, and the principle that the pilot is ultimately responsible for collision avoidance and terrain clearance (paras 1.2, 1.4, 2.1, 3.1, 4.1, 5.1). caa.co.uk/cap774
- UK Civil Aviation Authority, CAP 413, Radiotelephony Manual, Edition 24 (effective 1 July 2026): the Lower Airspace Radar Service (LARS) is available from participating ATS units, as described in UK AIP ENR 1.6. caa.co.uk/cap413
- UK Civil Aviation Authority, CAP 493, Manual of Air Traffic Services (MATS) Part 1, Twelfth Edition (31 October 2025): controllers apply the UK Flight Information Services in accordance with MATS Part 1. caa.co.uk/cap493
This article does not constitute flight instruction. Always defer to the guidance of your qualified flight instructor and to current charts and procedures or regulations published by your country's aviation authority.
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