UK CAA CAP 168: Licensing of Aerodromes and PAPI Checks
What CAP 168 says about PAPI checks: daily and weekly checks, the six-monthly flight check, when a unit is unserviceable, its legal status and drones.
- 01 CAP 168 is published in support of the CAA's discretionary powers to grant an aerodrome licence. Its Introduction says should does not make compliance optional, and the CAA may accept an alternative means backed by a safety assurance.
- 02 Paragraph 6.565 says a PAPI shall be flight checked at least once every six months. Paragraph 6.483 asks for a vertical alignment check every week to a tolerance of one minute of arc.
- 03 Paragraph 6.491 counts a PAPI unit as unserviceable below half its originally specified minimum average intensity, with an elevation error beyond one minute of arc, or if its physical condition is in question.
- 04 The text sets no PAPI check that a drone could meet by itself. Flight checks are written for a pilot observing the signal, by persons holding appropriate flight crew qualifications.
- 05 The EASA acceptable means asks for a flight check of visual approach slope systems at least yearly, so CAP 168 is stricter for a PAPI than the EU baseline.
CAP 168 asks for a PAPI to be checked at three levels. Each day, check lamps, damage, red to white change, heaters and lens cleanliness (6.482). Each week, check each unit’s vertical alignment to one minute of arc (6.483). At least every six months, flight check the system (6.565).
A UK aerodrome operator who asks how often to check a PAPI ends up in CAP 168, the CAA’s licensing document, and specifically in the aeronautical ground lighting material of its Chapter 6. This page reads those paragraphs, says how binding the document is, and sets the PAPI checks beside the EU, ICAO and FAA texts.
What CAP 168 is, and how binding it is
CAP 168 is published by the UK Civil Aviation Authority. The CAA publication page describes it as setting out the standards required at UK national licensed aerodromes, covering management systems, operational procedures, physical characteristics, obstacles, visual aids, rescue and firefighting, and medical services. The page lists version 13, dated 2 December 2025, with status Current.
The document explains its own status in the Introduction. It is “published in support of the discretionary powers relating to the grant of an aerodrome licence contained in the Air Navigation Order (ANO)”. The CAA licence page confirms the link and names Article 212 of the Air Navigation Order 2016. Its stated purpose is guidance to applicants and licence holders, and it indicates the licensing requirements the CAA uses to assess an application. It “represents the minimum standards necessary to meet the licensing requirement.”
Three points from the Introduction matter for how to read the wording.
- Should is not optional. Some specifications use the word should so the CAA has room to deal with different aerodromes. The Introduction says this “does not mean that compliance is optional”. Where insurmountable difficulties exist, the CAA may accept an alternative means of compliance, provided the safety assurance shows the safety requirement is not reduced.
- The Chicago Convention sits behind it. The Civil Aviation Authority (Chicago Convention) Directions 2007 require the CAA to act consistently with the UK’s obligations under the Convention. The Introduction says not all ICAO Standards and Recommended Practices are implemented directly in the Order, so the CAA is expected to implement them through policy documents such as CAP 168. The same text says that where CAP 168 has no requirement, the relevant Annex 14 Volume I SARP will normally apply.
- Differences are published elsewhere. Where the UK has notified ICAO of a difference from Annex 14, the significant ones are published in the UK AIP at GEN 1.7.
Paragraph 1.2 adds the reason an operator needs a licence at all. Article 208 of the Order requires specified flights for public transport or for flying instruction to take place only at a licensed or government aerodrome.
Its status after the UK left the EU
CAP 168 was not written to carry Regulation (EU) No 139/2014, and it does not mention that Regulation. Its legal anchor is the Air Navigation Order and the Chicago Convention, as above.
The CAA also keeps a separate instrument. CAA Decision No. 0059, dated 20 January 2026 and in force from 31 January 2026, adopts acceptable means of compliance, guidance material and certification specifications for “UK Regulation (EU) No. 139/2014”. The Decision’s definitions treat that Regulation as assimilated law under the Retained EU Law (Revocation and Reform) Act 2023, and the CAA’s change-approval page calls it the UK Aerodromes Regulation. The sibling page on EASA CS-ADR-DSN covers the EU side.
So the UK has a licensing document and a separate assimilated regulation. The CAA pages read for this page do not map one to the other, so which applies to a given aerodrome is a question for the CAA and the aerodrome’s own licence or certificate.
CAP 168 at a glance
- Issuer
- UK Civil Aviation Authority. Edition 13, version date 2 December 2025, status Current on the CAA page.
- Status
- Published in support of the CAA's discretionary licensing powers under Article 212 of the Air Navigation Order 2016. Should does not make compliance optional (Introduction).
- PAPI daily
- Lamps serviceable and evenly lit, no damage, red to white change coincident across a unit, heaters working, lenses clean (6.482).
- PAPI weekly
- Vertical alignment of each unit checked to one minute of arc (6.483). Units inspected internally and cleaned, lenses polished (6.487).
- PAPI flight check
- Shall be flight checked at least once every six months (6.565). Alignment also verified by instrument and flight check at least twice a year (6.483).
- Unserviceable unit
- Below half its originally specified minimum average intensity, or elevation error over one minute of arc, or physical condition in question (6.491).
- Withdrawal
- A PAPI installation should be withdrawn from service if one unit is unserviceable, with exceptions in 6.76 and 6.77 (page 301).
- Records
- Maintenance and flight check records retained at least three years at the aerodrome (note 3 to 6.468).
Where the PAPI checks sit in Chapter 6
Chapter 6 covers aeronautical ground lighting . The PAPI has its own design paragraphs (6.65 to 6.77, with siting and setting angles from 6.85), and its checks sit in the maintenance part of the chapter, from paragraph 6.464.
Paragraph 6.464 says the maintenance procedures in that part “should be adopted as a minimum requirement”. Paragraph 6.466 says a competent engineer should assess the maintenance requirement and add to the minimum in scope and frequency where necessary. Paragraph 6.467 sets the baseline for all AGL, a daily visual inspection and a six-monthly alignment check of elevated lights, with series circuit currents, earth connections and insulation resistance checks. Paragraph 6.468 says photometric checks, if appropriate, should follow traffic density and AGL performance.
Why a PAPI gets extra care
Paragraph 6.481 gives the reason. Moisture or dirt on the lenses diffuses the beam and can send a white signal at every elevation angle. That is the hazard the extra measures address. Paragraph 6.68 separately says a PAPI installation should be equipped with a monitoring system that detects lamp failure, so that flight crew can be advised and the failure remedied without delay.
Daily and weekly checks
Daily, paragraph 6.482 asks for particular attention to five items. All lamps serviceable and evenly illuminated. No apparent damage to units. The change from red to white coincident for all elements of a unit. The heating facilities functioning. All lenses clean.
Weekly, paragraph 6.483 says the vertical alignment of each unit should be checked “once every week to a tolerance of ±1 minute of arc”, and should be verified by inspection with a suitable instrument and flight check at least twice every year. Paragraph 6.487 adds weekly internal inspection and cleaning, lens polishing and anti-misting fluid where appropriate.
The clinometer paragraphs need careful reading. Paragraph 6.484 says clinometers are for a quick check that the installation has not been disturbed and “should not be used for alignment adjustments”. Paragraph 6.485 then says small errors vary with the time of day and the weather and normally need no adjustment. Where a significant difference shows, probably on one unit, because a consistent error on all units usually means the clinometer is out of calibration, the unit may be adjusted with a clinometer. It must then be checked with a suitable instrument and flight checked as soon as possible. Paragraph 6.486 says clinometers should be calibrated annually, or as the manufacturer recommends, or when an error is suspected.
Paragraphs 6.488 to 6.490 deal with moisture. High intensity units without permanent lens heaters should run for 15 minutes at maximum intensity, or as the manufacturer recommends, to disperse moisture. Units with heaters should run them continuously if condensation is possible. Daily checks should cover the heater.
The flight check
Paragraph 6.565 is written with shall: an (A)PAPI system “shall be flight checked in accordance with the checking of (A) PAPI systems at least once every six months.” Paragraph 6.563 gives the same six months to all approach and runway AGL on an instrument runway, and 6.564 gives 12 months on other runways. Paragraphs 6.554 and 6.566 require commissioning flight checks of new AGL, including (A)PAPI, before operational use, and say the CAA may choose to participate in or conduct such checks. Paragraphs 6.557 and 6.569 say temporary runway lighting, including (A)PAPI, should be flight checked daily before night use.
Paragraph 6.567 says flight checks “shall be conducted by competent persons, holding appropriate flight crew qualifications”, and that the licence holder should ensure those persons are competent. Paragraph 6.568 says the licence holder should evaluate and action the results, which the CAA may audit.
The procedure on pages 411 and 412 has six checks. Effective range, where in daylight and good visibility red and white must be clearly distinguishable at a minimum of 7.5 km, checked at about 7.5 to 9 km and 1,500 ft QFE. Colour changes, from 7.5 km at 1,000 ft QFE, for even illumination and sharp transitions, with corresponding units coincident where there is a bar on both sides. An approach from about 5 km, descending until four reds are just visible, climbing to four whites and returning on slope, to confirm the colour changes track height. Intensity settings, called for progressively during an approach. Compatibility with an instrument glidepath where one exists. And an obstacle check, flown low from 7.5 km to just within the all-red indication to confirm clearance across the horizontal coverage of the beam.
When a unit is unserviceable
Paragraph 6.491 starts with the line that PAPI integrity “is of the utmost importance”. A unit should be considered unserviceable if it has less than half its originally specified minimum average luminous intensity, if its elevation setting error exceeds ±1 minute of arc, or if its physical condition on inspection is in question, for example a cracked filter glass.
Paragraph 6.75 says a PAPI or (A)PAPI installation should be withdrawn from service if one unit is found unserviceable. Paragraph 6.76 limits that to the affected side where there are installations on both sides of the runway. Paragraph 6.77 lets the two central units of a PAPI installed for Scale L3 or L4 serve temporarily as an (A)PAPI, without altering the setting angles, if either outside unit fails.
Records
Note 3 to paragraph 6.468 says all maintenance activities should be recorded in a suitable log, and that maintenance and flight check records should be retained for at least three years at the aerodrome. They are for maintenance staff and for examination during licensing inspections. For the series circuit current checks, paragraph 6.467 asks for the actual values and the type and serial number of the test instrument to be noted in the log. Note 4 asks for test equipment and alignment devices to be calibrated or checked at the manufacturer’s intervals, with results logged.
How it compares with the EU, ICAO and FAA texts
The European framework puts maintenance of visual aids in Regulation (EU) No 139/2014 at ADR.OPS.C.015, which requires a preventive and corrective maintenance programme for the serviceability of individual lights and lighting system reliability. The detail on PAPI is in AMC1 ADR.OPS.C.015(b) and (f), an acceptable means of compliance and not the rule itself. The ICAO and FAA columns are on the sibling pages for Annex 14 and AC 150/5340-26 .
PAPI checks compared across CAP 168, the EU, ICAO and the FAA
| Dimension | UK: CAP 168 | EU: ADR.OPS.C.015 and AMC1 | ICAO Annex 14 and FAA AC 150/5340-26C |
|---|---|---|---|
| Weight of the text | Policy document supporting the CAA's licensing discretion. Mixes shall and should. Should is not optional | A rule in the Regulation, with AMC as the default means of compliance and GM as explanation | Annex 14 10.5.2 is a Standard on preventive maintenance. The FAA circular is recommended guidance, mandatory for AIP and PFC funded projects |
| PAPI alignment check | Weekly, to ±1 minute of arc, with instrument and flight verification at least twice a year (6.483) | Alignment of visual approach slope systems checked at defined intervals. Errors over one minute of arc should be corrected | Annex 14 10.5 gives no PAPI interval. The FAA asks for a monthly alignment and aiming check with the PAPI aiming instrument (Table 5-9) |
| Flight check | PAPI at least every six months (6.565, shall). Approach and runway AGL every six months on an instrument runway, 12 months otherwise | Flight check of approach, runway and taxiway lighting, VASIS and beacon at least yearly (AMC1, should) | Annex 14 10.5 sets none. The FAA circular does not mention flight inspection |
| Unserviceable PAPI | Unit below half its specified minimum intensity, or ±1 minute of arc exceeded, or physical condition in question (6.491) | Unit with three or more lights and more than one out, or fewer than three lights and one out. A wrong or missing red filter extinguishes its lights | Annex 14 10.5.1 deems a light unserviceable below 50 per cent of the Appendix 2 value. The FAA says a PAPI may be unserviceable with more than one lamp out per box (3.0) |
The CAA’s six-month flight check for a PAPI is half the EASA acceptable means interval, and its weekly alignment check is tighter than the monthly FAA check. The tolerance of one minute of arc matches the figure in the EU acceptable means. These are different instruments, so a UK aerodrome follows CAP 168 and the CAA’s own decision for the regulation that applies to it, and not a table of other regimes. The EASA column cites the March 2026 Easy Access Rules. The Annex 14 column cites a hosted ninth edition consolidation that carries Amendment 18.
Where a drone survey fits
CAP 168 names no instrument platform for lighting checks. The one place the text mentions unmanned aircraft is the list of operational procedures an aerodrome manual should cover, on page 57, where the safe integration of other aviation activities includes unmanned aerial systems. That is about drones operating at the aerodrome, not about lighting checks.
What the text asks for is evidence of alignment, signal and serviceability at set intervals, plus a flight check carried out by qualified flight crew. A drone survey of a PAPI measures the transition angle of each unit from the approach. It supplies a number per unit where the flight check gives an observation.
What each CAP 168 PAPI check verifies, and what a drone survey can supply
| Check | What CAP 168 asks for | What a drone survey can supply | What stays with ground staff or the flight check |
|---|---|---|---|
| Daily lamp and lens check (6.482) | Lamps lit evenly, no damage, red to white coincident, heaters working, lenses clean | A record of lit or dark, relative output across the four units and colour against position, if flown | Cleaning, relamping, heater function and the daily cadence itself |
| Weekly vertical alignment (6.483) | Each unit checked to ±1 minute of arc once a week, and verified with a suitable instrument and flight check at least twice a year | Measured transition angle of each unit as seen from the approach | Clinometer or instrument adjustment of the unit, which 6.484 and 6.485 restrict |
| Flight check every six months (6.565) | Six checks flown by qualified flight crew, from effective range to obstacle clearance | Supporting angle and colour-transition evidence between checks | The flight check itself. 6.567 requires persons holding appropriate flight crew qualifications |
| Unserviceable unit (6.491) | Below half the specified minimum intensity, ±1 minute of arc exceeded, or damage | Elevation error per unit and relative output against the other units. Absolute intensity needs a calibrated anchor | Absolute intensity, filter and glass inspection, and the decision to withdraw the installation |
| Heaters and electrical (6.467, 6.487 to 6.490) | Lens heaters, moisture clearance, series circuit currents and insulation resistance | Nothing. These are not visible from the air | All of it, at the unit and in the vault |
TarmacView flies PAPI inspection by drone as part of its airfield lighting inspection . Each unit gets a measured transition angle, colour against position, output relative to its neighbours and to the commanded step, and an RTK-surveyed position. Flights run between movements in coordination with the tower, with no closure booked. Regulator output, insulation resistance and anything underground are not measured. The comparison with flight inspection sets out what each method covers, and the regulatory acceptance guide looks at how regulators treat a measured result.
Frequently Asked Questions
- Is CAP 168 law in the UK?
- It is not an Act or an Order. Its Introduction says it is published in support of the discretionary powers to grant an aerodrome licence in the Air Navigation Order. The CAA licence page says the CAA uses it in support of granting a licence under Article 212 of the Air Navigation Order 2016. The Introduction adds that should does not mean compliance is optional.
- What does CAP 168 say about PAPI checks?
- Chapter 6 gives four layers. Daily, check lamps, damage, red to white coincidence, heaters and lens cleanliness. Weekly, check the vertical alignment of each unit to one minute of arc and clean the units internally. At least twice a year, verify alignment by instrument and flight check. At least every six months, flight check the system under paragraph 6.565.
- How often must a PAPI be flight checked under CAP 168?
- Paragraph 6.565 says an APAPI or PAPI system shall be flight checked at least once every six months. That is the same interval as the approach and runway lights on an instrument runway in 6.563. Other runways get a flight check of approach and runway lights at least every 12 months. New installations are flight checked before operational use.
- When is a PAPI unit unserviceable?
- Paragraph 6.491 gives three tests. The unit has less than half its originally specified minimum average luminous intensity, or its elevation setting error exceeds one minute of arc, or its physical condition is in question, for example a cracked filter glass. Paragraph 6.75 adds that an installation should be withdrawn from service when one unit is unserviceable, with exceptions for two-sided installations and Scale L3 and L4 systems.
- Does CAP 168 allow drones for PAPI checks?
- CAP 168 does not mention drones in connection with lighting checks. Its flight check procedure for a PAPI is written for a pilot flying an approach and observing the signal. Paragraph 6.567 requires flight checks to be conducted by persons holding appropriate flight crew qualifications. Whether a drone measurement can stand in for any check is a question for the aerodrome and the CAA.
- How does CAP 168 compare with the EU, ICAO and FAA texts?
- CAP 168 sets the shortest PAPI intervals of the four texts. It sets a weekly alignment check and a six-month flight check. The EASA acceptable means asks for flight checks at least yearly and alignment checks at defined intervals. Annex 14 section 10.5 sets no PAPI intervals. The FAA circular sets a monthly aiming check and is silent on flight inspection.
- Which edition of CAP 168 is current?
- The CAA publication page lists version 13, dated 2 December 2025, with status Current. The document's own front matter calls it the Thirteenth Edition of July 2025, incorporating Amendment 15 and visual aids updates from ICAO State letter 25/23 and all-weather operations. The CAA page says Edition 13 was re-issued to correct formatting errors.
- How does CAP 168 deal with moisture and misting in a PAPI?
- Paragraph 6.481 explains that moisture or dirt on the lenses can send a white signal at every elevation angle. Units without permanent lens heaters should run for 15 minutes at maximum intensity, or as the manufacturer recommends, to disperse moisture. Units with heaters should run them continuously if condensation is possible, and the daily check covers the heater (6.488 to 6.490).
References
- caa-cap-168
- CAP 168, Licensing of Aerodromes, Edition 13 UK Civil Aviation Authority
- caa-apply-aerodrome-licence
- Apply for an aerodrome licence UK Civil Aviation Authority
- caa-decision-0059
- CAA Decision adopting AMC, GM and CS for UK Regulation (EU) No. 139/2014 (Aerodromes), Decision No. 0059 UK Civil Aviation Authority
- caa-changes-uk-certificated
- Changes to UK certificated aerodromes UK Civil Aviation Authority
- easa-ear-aerodromes
- Easy Access Rules for Aerodromes (Regulation (EU) No 139/2014) European Union Aviation Safety Agency
- icao-annex-14-vol-1
- Annex 14 to the Convention on International Civil Aviation, Volume I, Aerodrome Design and Operations International Civil Aviation Organization
- faa-ac-150-5340-26c
- AC 150/5340-26C, Maintenance of Airport Visual Aid Facilities Federal Aviation Administration