LOW VISIBILITY PROCEDURES & AGL COMPLETE NOTES

WHAT IS LVP?

Low Visibility Procedures (LVP) maintain safe aircraft and vehicle movement when visibility and/or cloud is so poor that normal visual surface movement becomes unreliable. The "see and be seen" principle is impaired, so designated taxi routes, stop bars, runway guard lights and tighter vehicle control are used.

Low RVR / cloud → Safeguarding → Verify critical facilities → Configure AGL and ground-movement system
→ Restrict movement → LVP ENFORCED → Continuous monitoring → Termination on recovery

SAFEGUARDING AND ACTIVATION

Safeguarding protects the manoeuvring area before or during the move to low visibility, and often starts before full LVP. It is not the same as LVP. It also protects the ILS critical and sensitive areas, so vehicles and aircraft do not disturb the localizer and glide-path signals that CAT II/III operations depend on.

Typical actions: suspend works, remove people, machinery and material, secure sites, inspect critical facilities, confirm communications and taxi routes, report readiness to ATC. Perfect AGL does not make the airport LVP-ready if a crane is still near a taxiway: readiness = AGL + RVR + nav aids + SMGCS + ATC procedures + vehicle control + safeguarding + communications.

ATC or the designated airport authority declares and terminates LVP; the AGL engineer reports technical status and does not declare LVP. Termination needs improving RVR and ceiling, a favourable trend and facilities available, not just "the fog looks better". Status goes to ATIS, operations, apron, ARFF, Met and stakeholders.

AGL READINESS CHECKS

Critical hierarchy (airport-specific): very critical are RCL, TDZ, threshold, runway end and stop bars; high are runway edge, approach lights and taxiway centreline (but the inner 300 m of a CAT II/III approach carries the same 1 s switch-over requirement as the very critical group). Some airports also switch on lead-in lights for compatible stands after LVP declaration.

Intensity: low visibility does not automatically mean maximum brightness. The engineer maintains capability; ATC or the approved control function sets the operational state. Some airport procedures forbid intensity changes without tower permission. Too bright means glare and lost contrast.

During LVP the CCR room may need to stay attended, or the electrical engineer must be reachable by phone or radio. The AGL team is part of the operational chain. Physical checks: lens, cover, bolts, base, frangible parts, transformer, connector, cable; for in-pavement lights also rubber, water and sealing; for elevated lights tilt and alignment.

UPS, GENERATOR AND POWER

Critical aids may have very short permitted changeover (ICAO Annex 14 Vol. I Table 8-1, precision approach CAT II/III: 1 s for the inner 300 m of the approach lighting, threshold, RCL, TDZ, runway end and all stop bars; about 15 s for the rest of the approach lighting, runway edge and essential taxiway lights; runway edge also needs 1 s where the runway is used for take-off in RVR below 800 m. Check the current edition). A generator start plus ATS transfer alone may not meet 1 s.

Mains fails → UPS carries critical AGL immediately → DG starts → DG takes sustained load

Some airports use the generator as the primary source during LVO; follow the approved procedure.

STOP BARS, GUARD LIGHTS AND TAXI GUIDANCE

A stop bar is a row of red lights across the taxiway at a holding position. It belongs to a system: AGL + ATC control + interlocking + LVP + incursion prevention.

STOP BAR ON  → red, centreline beyond OFF (ICAO: at least 90 m)
ATC clearance → STOP BAR OFF, lead-on centreline ON → aircraft proceeds

When are they required? Annex 14 (§5.3.20, check current edition) calls for a stop bar at every runway-holding position serving a runway intended for use in RVR below 550 m, unless suitable aids and procedures prevent inadvertent runway incursions or traffic is limited to one aircraft at a time on the manoeuvring area with vehicles at the essential minimum. Where no stop bar is installed in those conditions, runway guard lights are required at the taxiway/runway intersection (§5.3.21).

Interlocking prevents RED STOP and PROCEED guidance together. Selective switching lights only the required route section, giving guidance and less clutter.

Stop-bar failure is an operational control question: is the stop indication still recognisable, is interlocking healthy, can ATC control the crossing, what does the LVP require? Never judge by lamp count alone.

Taxiway centreline lighting becomes the continuous route guide as markings and surroundings vanish. A-SMGCS adds surveillance, routing and control; AGL is its physical visual interface. Vehicle movement is restricted to essential vehicles on designated routes, and Follow-Me service may apply at set visibility limits. Follow-Me is a procedure, not a substitute for working AGL.

FAULT RESPONSE AND MAINTENANCE

1. Confirm the fault, facility and circuit; check adjacent failures.
2. Assess operational significance against the LVP criteria.
3. Inform ATC/operations; repair or isolate.
4. Retest, confirm control and monitoring, record, update status.

A critical fault may mean suspending an operation, changing runway or procedure, restricting movement or terminating LVP. Any NOTAM action is the operational authority's decision; you supply accurate technical status. Example: RVR 350 m, one RCL out: locate it, check neighbours and circuit, total serviceability and pattern, local LVP criteria, then tell ATC. Do not locate cable faults by random digging; use records and fault localisation.

No universal inspection interval exists: some airport procedures inspect runway lights about every two hours during LVP. Do not copy an interval from another airport. Routine photometry (intensity, beam, orientation, colour, trends) is not the LVP check (availability, state, power, control). A light can be on yet weak or mis-aimed. ICAO treats a light as unserviceable when its main-beam average intensity falls below 50% of the specified value, and Annex 14 Chapter 10 sets system serviceability objectives. For CAT II/III these are 95% for the inner 450 m of approach lighting, threshold, runway edge and RCL, 90% for TDZ, 85% for approach lights beyond 450 m and 75% for runway end lights, with no unserviceable light next to another (a barrette or crossbar may have two adjacent). FAA 70% is a maintenance target for in-pavement lights. None of these is a complete LVP acceptance criterion. Pattern matters more than count: adjacent or clustered failures hurt even at 95%. Interleaved circuits keep the pattern after a circuit loss. See Note 15.

Safety: low visibility does not relax isolation, lockout/tagout, verification of dead and discharge before touching series-circuit equipment. Control FOD and tools strictly. Do not carry out ordinary maintenance in the manoeuvring area during active LVP without authorisation and a work permit coordinated with ATC.

After LVP: restore normal mode, check stop-bar and taxiway modes and standby status, review alarms, log defects, then analyse repeats. If a transformer fails three times, find the cause (moisture, sealing, connector, overload, wrong type, waterlogged pit) rather than replacing it again. Keep an LVP fault log, trend data and a status report in the airport's prescribed format.

QUICK REVISION AND MISTAKES

LVP = SAFEGUARD + LIGHT + POWER + CONTROL + MONITOR

Airport approved AIP/LVP procedure and the regulatory/project specification take precedence over generic study-note values.

AIRFIELD LIGHTING DURING LOW VISIBILITY

Airfield lighting during low visibility must be complete, reliable and powered with short switch-over. Before LVP starts, the lighting is checked and critical circuits are confirmed serviceable. During LVP, faults are reported at once, because the pilots depend more on the lights. The exact requirements come from the aerodrome's approved procedures.

EXAM QUESTIONS

FINAL STUDY TAKEAWAY

LVP is an integrated airport operating system and AGL is one of its most critical physical systems: low visibility leads to a controlled airport, safeguarded movement area, and reliable AGL, power, control and monitoring.

ENGINEERING & EXPERT NOTES

REFERENCES & FURTHER READING

A study aid. Verify against current primary sources.

EXPLORE ALL AGL STUDY NOTES