Winter Ops
Winter Operations at Guwahati – A Proactive Guide for ATCOs
ATCOs – VEGT ACC / APP / TWR / GND Based on MATS / AWO CAR / LGBI RVO SOP
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Part 1 – The Guwahati Winter Challenge
Cold is not our enemy – unstable fog and contamination are.
ATCOs – ACC / APP / TWR / GND Use ← / → keys to move slides

Winter operations at Guwahati are about capacity, workload and risk – not just cold weather. As controllers, we are the system that keeps fog from becoming an incident.

What makes VEGT winter special?
  • Unstable radiation fog – visibility can swing from 1200 m to 200 m in minutes, especially around sunrise.
  • Local topography – river, low-lying areas and uneven cooling create pockets of dense fog on and around the runway.
  • Mixed fleet – different operator SOPs, minima and crew experience levels interacting with the same RVR values.
  • Single-runway constraints – every closure or inspection hits our capacity immediately.
Winter ops at VEGT are about anticipation and disciplined surface movement.
How a typical fog morning feels in TWR
  • Start of watch – surface is clear, but METAR hints at falling temperature / light winds.
  • By 05:00–06:00 local – RVR fluctuates, first banks of fog around RWY 02 side.
  • Traffic demand remains high – banks, rotations, cargo, diversions from other stations.
  • Every change in RVR / runway condition forces:
    • Recalculation of arrival / departure feasibility.
    • More coordination with ACC, AOCC, airlines, ARFF, MET.
    • Increased runway incursion risk at hotspots.
The aim of this session: give you a mental playbook for those mornings – what to look for, what to ask, when to say "No", and how to keep ground movements safe.

Before anything else, remember the most important constraint at Guwahati: we do not have LVP for Cat II / III operations.

The Critical Constraint: NO LVP / Local RVO
Guwahati (VEGT) does NOT have a classic CAT II / III Low Visibility Procedure (LVP) environment.

What the RVO SOP tells us:
  • No Runway Guard Lights (RGL) are provided at LGBI.
  • Therefore Low Visibility Take-off (LVTO) below 800 m visibility / 550 m RVR is NOT permitted.
  • Instead of CAT II / III LVP, LGBI uses a Reduced Visibility Operation (RVO) concept for visibilities at or above 800 m, focused on preventing runway incursions and surface movement incidents.
  • When conditions fall below these thresholds, arrivals and departures are restricted in line with AWO CAR and local minima, and ATCO workload and runway-incursion risk increase sharply.
Source: LGBI RVO SOP – Issue 01 / 26-12-2024 & AWO CAR
Our Specific Threat: 05:00–09:00 Fog
  • Type: Dense radiation fog – our "local personality".
  • Onset: Sudden and rapid deterioration, usually around sunrise.
  • Volatility: RVR can jump between 200 m and 1200 m minute to minute.
  • Location: Slant visibility often vanishes first at RWY 02 threshold (river side).
  • Ground risk: Fog pockets at hotspots and intersection holding points.
This is more than "morning fog". It is an operational threat profile that drives flow control, runway safety and surface movement risk.

The RVO SOP introduces a formal Safeguarding Procedure (SP) – a set of actions we trigger before visibility becomes critical.

When do we start Safeguarding?
  • Trigger SP when:
    • Visibility < 1200 m or forecast to deteriorate towards 800 m / 550 m or less, and/or
    • Cloud ceiling < 400 ft and forecast to fall to around 200 ft or less.
  • RVO band at LGBI:
    • RVO is intended for operations with visibility ≥ 800 m.
    • Below 800 m, LVTO is not permitted and operations are curtailed as per minima.
Numbers to remember: 1200 → 800 / 550 and ceiling 400 → 200 ft.
What does Safeguarding do on the ground?
  • One Crash Fire Tender (CFT) positioned on the fire access road.
  • Stop maintenance on the manoeuvring area:
    • All men and mobile equipment withdrawn from runway / taxiways.
  • Ensure secondary power for RWY edge & end lights:
    • Changeover to DG / UPS within 15 seconds.
  • Runway & lights inspection (Airside Ops + E&M):
    • Once in the hour before SP is implemented.
    • Then once every two hours while SP is in force.
  • Close access roads leading to runway:
    • Old Radar Road.
    • Fire Pit Road.
  • Follow-Me vehicle kept available on pilot request.
  • TSO / WSO maintains a dedicated log (Annexure-I) for SP / RVO.
As ATCOs, we may not drive the CFT or close the road ourselves – but we are the ones who know the triggers, initiate SP and follow-up till all actions are complete.

Once fog starts forming, your main tools are RVR, runway condition (RCR) and an awareness of the Approach Ban Policy in CAR 4.6. The policy is addressed to the PIC; our job is to provide the information that lets the crew apply it correctly.

RVR – what do you look at?
  • TDZ RVR – primary controlling value for most approaches.
  • Mid & stop-end RVR – controlling when reported and relevant: mid normally ≥ 125 m (or not less than TDZ requirement), stop-end ≥ 50 m.
  • Trend – improving, steady or rapidly deteriorating?
  • Compare with tower view – does slant visibility match the numbers?
  • Update frequently during critical phases (final, line-up, take-off roll).
Treat RVR as a time series, not a single number.
Approach Ban – what CAR 4.6 actually says
  • Who is addressed?
    • CAR 4.6 is written for the PIC – it tells the pilot when they may commence or continue an instrument approach based on RVR/visibility.
    • ATC does not declare “approach ban”; we provide RVR/visibility and runway information.
  • Commencement of approach (4.6.1)
    • PIC shall not commence an instrument approach if the reported RVR/visibility is below the applicable minimum for that approach.
  • Continuation after start (4.6.2)
    • If, after commencing the approach, reported RVR/visibility falls below minima, the approach shall not be continued:
    • – below 1000 ft above the aerodrome; or
    • – into the final approach segment (FAF–MAPt for NPA, from FAP for precision).
  • Below DA/MDA and use of CMV (4.6.3–4.6.4)
    • If deterioration occurs only after entering the final segment / below 1000 ft, the PIC may continue to DA/H or MDA/H, using reported RVR or converted visibility as applicable.
    • To go below DA/H or MDA/H and land, the required visual reference for the runway must be established at DA/MDA and maintained thereafter.
  • ATC angle
    • We must pass accurate, timely RVR/visibility and RCR, and highlight significant changes or trends.
    • Crews then apply CAR 4.6 and their own minima; ATC may still instruct a go-around or hold for other safety reasons (blockage, traffic conflict, equipment failure, etc.).
In winter, our job is to give the clearest possible RVR and runway picture. The PIC applies AWO CAR 4.6 to decide when to start, continue or discontinue the approach.

A good winter watch starts before you pick up the headset. Your pre-duty checklist should cover MET, equipment and local constraints.

Pre-duty checks for ATCOs
  • Read MET properly:
    • METAR / SPECI trend – any fog, mist, shallow fog, dew point spread behaviour?
    • TAF – is there TEMPO / BECMG for BR / FG around your watch time?
  • Check RVR / visibility equipment status with CNS / TMO.
  • Confirm runway lighting status (edge, end, PAPI, stop bars if any).
  • Review NOTAMs affecting winter ops – construction, closures, displaced thresholds etc.
Team briefing items
  • Agree on who watches what (RVR, strip bay, SMR if available, hotspots).
  • Clarify division of tasks between GND and TWR when traffic peaks.
  • Review hotspots, current work in progress, and any known vehicle issues.
  • Discuss “if we go below minima” scenario for that watch.
Pre-season / yearly preparation
  • Participate in pre-winter preparedness / sensitisation sessions organised by ATS & Aerodrome Operator.
  • Review latest SOPs / orders on winter operations, reduced visibility and runway inspections.
  • Ensure familiarity with local RVO SOP:
    • Trigger values.
    • Safeguarding steps.
    • Restrictions on LVTO / surface movements.
  • Revisit runway incursion prevention material – especially for winter.
The best winter defence is a well-briefed, well-rested controller.

Fog plus busy ground movement is a runway incursion trap. As controllers, we must treat every runway crossing or line-up as a high-value clearance.

Why incursion risk goes up in fog
  • Reduced visual surveillance – you cannot always see intersections or backtrack portions.
  • More conditional clearances – "behind landing aircraft", "after crossing traffic".
  • Increased R/T loading – more queries from crews, more coordination with vehicles.
  • Human shortcuts – pilots / drivers may “assume” clear runway when they cannot see traffic.
Incursions in fog are almost always fatal combinations of assumptions.
Hotspots & local watchpoints
  • Identify and mark VEGT hotspots on your mental map:
    • Runway entry points used in low visibility.
    • Intersections where vehicles cross the runway strip.
    • Backtrack entry/exit points.
  • Use explicit phraseology:
    • No mixed messages like “line up and wait for landing aircraft to vacate”.
    • Separate “line up” and “cleared for take-off” by time and scan.
In fog, do less with more attention. Fewer conditional clearances, more positive control, and a runway that is either in use or protected – never ambiguous.

Winter operations are full of “what if” situations. Thinking through them in advance reduces hesitation and confusion on position.

Scenario 1 – Sudden RVR drop on final
  • Aircraft established on approach, RVR 1000 m, then drops to 500 m:
  • As ATCO:
    • Pass updated RVR and trend immediately.
    • Expect crew to apply CAR 4.6 (continuation / discontinuation rules).
    • Prepare for possible go-around, holding or diversion.
Scenario 2 – Lining up in marginal RVR
  • Departure wants to “try” in marginal visibility:
  • Check:
    • Local restriction – No LVTO below 800 m at LGBI.
    • Runway lights, RVR, surface condition and safeguarding status.
  • Actions:
    • If LVTO requirements not met, do not line up or clear for take-off.
    • Explain clearly with reference to local SOP / minima.
Scenario thinking as a habit
  • Use quiet time to ask “what if RVR falls by half in the next 5 minutes?”.
  • Decide in advance:
    • At what RVR you will stop departures due LVTO rules.
    • How you will manage approaches when crews start discontinuing under CAR 4.6.
    • How you will brief the WSO / TSO and AOCC.
  • Plan ground movement strategies for further reduction:
    • Limit runway crossings, more Follow-Me use.
    • Preferential use of certain exits / entries.
Winter operations reward controllers who think 2–3 moves ahead.

Winter operations at Guwahati are a team sport. Our job is to be the calm, predictable centre of that team when visibility starts to vanish.

Key ATCO takeaways
  • Understand and respect local constraints – no LVP, no LVTO < 800 m, single-runway vulnerability.
  • Use RVR, RCR and MET trends to anticipate, not just react.
  • Treat every runway clearance as a high-consequence instruction, especially in fog.
  • Communicate early and clearly with ACC, AOCC, ARFF, CNS, MET and Aerodrome Operator.
  • Keep logs accurate – they are part of professional practice and safety assurance.
For the group discussion
  • What is the most stressful fog morning you have handled at VEGT?
  • Which decisions were hardest (approach ban, diversions, runway inspection timing)?
  • Where do you see runway incursion risk during winter mornings?
  • What small habits can we adopt (checklists, cross-checks, phraseology) to make winter ops safer?
Winter safety is built long before the first fog bank appears – in procedures, training and everyday discipline. This session is one step towards that discipline.