From my field experience across multiple airport projects, even small installation mistakes can lead to major performance issues, non-compliance, and operational risks. This article highlights some of the most common AGL installation mistakes observed on site and their practical impact.
- 01 Incorrect Fitting Alignment
- 02 Poor Cable Jointing & Termination
- 03 Improper Sealing of Pits & Bases
- 04 Photometry Mismatch After Installation
- 05 Incorrect Series Circuit Practices
- 06 Lack of Testing Before Commissioning
- 07 Ignoring Manufacturer & ICAO Guidelines
- 08 Key Takeaways
- 09 Frequently Asked Questions
In my field experience, many site issues come from execution rather than design faults — misalignment, a weak joint, an incomplete seal, a skipped test. Each one directly impacts the safety, compliance, and long-term reliability of the system.
Incorrect Fitting Alignment
One of the most common issues on site is improper alignment of AGL fittings.
- Incorrect horizontal aiming of directional lights (for example centreline, touchdown zone and approach lights)
- Bi-directional fittings (red/green, red/white, yellow/white) installed facing the wrong way
- Wrong vertical tilt affecting beam projection
- Misalignment during base plate or shallow base installation
- Light beam does not reach the intended viewing angle
- Reduced visibility for pilots
- Non-compliance during photometric testing
Even a few degrees of misalignment can noticeably change how the light is perceived from the cockpit — aim and orient every fitting to the design and the manufacturer’s tolerance, and check bi-directional colour faces on a night inspection.
Poor Cable Jointing & Termination
Cable jointing is a critical part of AGL series circuits, but it is often not executed properly.
- Improper crimping of connectors
- Poorly made or loose terminations in L-823-type connectors
- Moisture ingress in joints
- Use of non-standard or incompatible materials
- Increased circuit resistance
- Intermittent or flickering lights
- An open circuit, or earth faults (a second earth fault in particular), that trip the CCR and take the whole circuit out
In a series circuit, one weak joint can affect the performance of the entire circuit. Primary-circuit work is carried out only de-energised, under permit-to-work and isolation/LOTO.
Improper Sealing of AGL Pits and Bases
AGL pits and bases are exposed to harsh environmental conditions, especially water ingress.
- Incomplete sealing of cable entries
- Damaged or improperly fitted gaskets
- Poor epoxy or compound application
- Open conduits allowing water entry
- Drainage provision in the design not built, or blocked after installation
- Water accumulation inside pits
- Corrosion of connectors and cables
- Insulation failure over time
Water ingress is one of the biggest long-term threats to AGL system reliability.
Photometry Mismatch After Installation
Even when fittings are compliant in the laboratory, site conditions can affect their actual performance.
- Improper installation depth of inset lights
- Surface-level mismatch with the runway
- Dirt, debris, or sealant blocking light output
- Misalignment after installation
- Reduced light intensity
- Distorted beam pattern
- Failure during site acceptance testing
Photometric performance must be maintained not just in design, but after installation under actual runway conditions.
Incorrect Series Circuit Practices
Most AGL systems operate on constant-current series circuits, requiring careful installation practices.
- Fittings or transformers connected into the wrong circuit, against the design (including circuit interleaving)
- Open or high-resistance points in the series loop
- Incorrect isolating transformer connections or ratings
- Mixing incompatible components (transformer ratings, lamp or LED loads, connector types) on one circuit
- Wrong current at the fittings or an overloaded CCR
- Flickering, dimming or failed lights
- Difficulty in fault detection
Proper circuit discipline is essential for stable AGL operation.
Lack of Proper Testing Before Commissioning
In many cases, systems are installed but not thoroughly tested before commissioning.
- Insulation Resistance (IR) testing
- Continuity testing
- Earth resistance and earth-fault checks
- CCR performance verification, including circuit current at each brightness step against the rating (for example 6.6 A at the top step)
- Visual inspection at different brightness steps
- Hidden faults remain undetected
- Failures occur during actual operation
- Delays during inspection and handover
Testing is not a formality — it is a critical step before commissioning any AGL system. Insulation tests are done only on an isolated, locked-out circuit with a correctly rated instrument, following the approved procedure and acceptance limits.
Ignoring Manufacturer and ICAO Guidelines
Another common issue is deviation from standard installation practices.
- Not following installation torque values
- Ignoring recommended sealing methods
- Using alternative materials without validation
- Reduced system life
- Warranty issues
- Non-compliance during audits
AGL systems must always be installed according to the manufacturer’s instructions, the approved design and the applicable standards — ICAO Annex 14 and the Aerodrome Design Manual (Doc 9157) Part 5, or FAA AC 150/5340-30 where FAA requirements apply — as adopted by the national regulator.
Key Takeaways
- A few degrees of fitting misalignment can change how a light is perceived from the cockpit and fail photometric testing
- A single weak cable joint can affect the performance of an entire series circuit
- Water ingress through poorly sealed pits is one of the biggest long-term threats to AGL reliability
- Laboratory-compliant fittings can still fail site acceptance testing due to installation depth, debris, or misalignment
- Series circuit discipline — correct circuit assignment, loop continuity and transformer connections and ratings — is essential for stable operation
- IR testing, continuity checks, and CCR verification before commissioning catch hidden faults before they become operational failures
- Deviating from manufacturer and ICAO guidelines reduces system life and creates compliance and warranty risk
Where Installation Mistakes Creep In
Physical Installation → Electrical Practices → Verification → Compliance
Conclusion
AGL installation is not just mechanical work. It requires precision, understanding of system behaviour, and strict adherence to standards.
In my experience, many site issues are not design faults but small mistakes during execution. These mistakes directly impact the safety, compliance, and long-term reliability of the system. From alignment to jointing, sealing to testing, every step matters in delivering a safe and compliant airfield lighting system.
In this article, I've shared real on-ground insights that highlight how proper installation practices can prevent failures and ensure reliable AGL performance.
In AGL systems, small installation mistakes can lead to big operational risks. Precision on site is as important as design on paper.
Frequently Asked Questions
What are the most common AGL installation mistakes?
Based on the author's field experience, they include incorrect fitting alignment, poor cable jointing and termination, improper sealing of pits and bases, photometry mismatch after installation, incorrect series circuit practices, lack of testing before commissioning, and ignoring manufacturer and ICAO guidelines. Many site issues come from execution rather than design faults.
What problems does incorrect fitting alignment cause?
Typical mistakes are wrong horizontal aiming of directional lights, bi-directional fittings installed facing the wrong way, wrong vertical tilt and misalignment during base plate or shallow base installation. The impact is that the beam does not reach the intended viewing angle, pilot visibility is reduced and photometric testing can fail. Even a few degrees can noticeably change how the light is perceived from the cockpit.
Why do poor cable joints matter in a series circuit?
In a series circuit, one weak joint can affect the performance of the entire circuit. Improper crimping, loose terminations in L-823-type connectors and moisture ingress can raise circuit resistance, cause flickering, or produce an open circuit or earth faults (a second earth fault in particular) that trip the CCR and take the whole circuit out. Primary-circuit work is carried out only de-energised, under permit-to-work and isolation/LOTO.
Why is sealing AGL pits and bases important?
Pits and bases are exposed to harsh conditions, especially water ingress. Incomplete cable entry sealing, damaged gaskets, poor epoxy or compound application, open conduits and drainage that was not built or is blocked lead to water accumulation, corrosion of connectors and cables, and insulation failure over time. Water ingress is described as one of the biggest long-term threats to AGL reliability.
Why can a laboratory-compliant fitting still fail on site?
Site conditions can affect actual performance. Common reasons are improper installation depth of inset lights, surface-level mismatch with the runway, dirt, debris or sealant blocking the light output, and misalignment after installation. The result can be reduced intensity, a distorted beam pattern and failure during site acceptance testing.
What series circuit mistakes does the article warn about?
Fittings or transformers connected into the wrong circuit against the design (including circuit interleaving), open or high-resistance points in the loop, incorrect isolating transformer connections or ratings, and mixing incompatible components such as transformer ratings, lamp or LED loads and connector types on one circuit. These can cause wrong current at the fittings, an overloaded CCR, flickering or dimming, and difficulty in fault detection.
What testing should be done before commissioning?
The missing checks listed are insulation resistance testing, continuity testing, earth resistance and earth-fault checks, CCR performance verification including circuit current at each brightness step against the rating (for example 6.6 A at the top step), and visual inspection at different brightness steps. Insulation tests are done only on an isolated, locked-out circuit with a correctly rated instrument, following the approved procedure and acceptance limits.
Which guidelines should installations follow?
Installations must follow the manufacturer's instructions, the approved design and the applicable standards: ICAO Annex 14 and the Aerodrome Design Manual (Doc 9157) Part 5, or FAA AC 150/5340-30 where FAA requirements apply, as adopted by the national regulator. Deviating, for example on torque values, sealing methods or unvalidated alternative materials, reduces system life and creates warranty and audit risk.