Winter Readiness: The Pilot's Guide to Cold Weather Ops
Winter flying offers some of the smoothest air and best performance of the year, but it punishes unpreparedness. From the new SNOWTAM formats to the silent threat of airframe icing, winter demands a shift in mindset.
Whether you are flying a Cessna 172 or an ATR-72, this guide covers the essential knowledge updates you need for the season, including the Global Reporting Format (GRF) matrix.
1. The "New" Runway Codes (GRF)
Gone are the days of vague "Patchy Ice" reports. The Global Reporting Format (GRF) is now the standard. It assesses runway conditions on a scale of 0 to 6.
You will see these numbers in SNOWTAMs (e.g., "5/5/5" means Good/Good/Good across all three thirds of the runway). Memorise this matrix:
| Code | Condition Description | Braking Action |
|---|---|---|
| 6 | Dry | Good |
| 5 | Wet, Frost, or Dry Snow (<3mm) | Good |
| 4 | Compacted Snow | Good to Medium |
| 3 | Wet Snow or Dry Snow (>3mm) | Medium |
| 2 | Slush or Standing Water | Medium to Poor |
| 1 | Ice | Poor |
| 0 | Wet Ice / Water over Compacted Snow | NIL (Do Not Land) |
2. Decoding the SNOWTAM
The new SNOWTAM format can look intimidating. It is essentially a long string of data that breaks the runway down into thirds (Touchdown, Midpoint, Stop End).
Here is an example of the critical Runway Condition Report (RCR) section you will see on your iPad:
RWY 27 5/2/2 100/100/100 NR/03/03 WET/SLUSH/SLUSH
Runway Designator
Runway Condition Codes (RWYCC) for each third.
Touchdown is Good (5). Mid/End are Med-Poor (2).
% Coverage in each third.
Depth of deposit in mm.
NR = Not Reported (usually for Wet).
Condition Description.
This confirms WHY the codes are 5 and 2. Touchdown is just wet. The rest is slush.
3. De-Icing vs. Anti-Icing
There is a critical difference between getting ice off and keeping it off.
- De-Icing (Type I): Usually an orange/pink fluid. It is hot and designed to melt existing deposits. It has a very short "Holdover Time" (HOT). It offers almost no protection against new ice once you taxi.
- Anti-Icing (Type II/IV): Usually green. It is thick and jelly-like. It sticks to the wing to absorb new snow/ice while you taxi. It shears off during the takeoff roll.
The GA Warning:
Most light aircraft (Cessna/Piper) cannot use Type II/IV fluids because their rotation speeds are too slow to shear the thick fluid off. If you use it, you might stall on takeoff. Stick to Type I (or a heated hangar) and takeoff immediately.
4. Aircraft Health Check
Your aircraft feels the cold more than you do.
- Carbon Monoxide: We use cabin heaters constantly in winter. Most GA heaters use a shroud around the exhaust. A single crack can pump lethal CO into the cabin. Carry an active detector.
- The Battery: Cold batteries lose cranking amps. If your aircraft lives outside, take the battery home or invest in a trickle charger.
- Pitot Covers: Essential to stop insects, but in winter, they stop water ingress which can freeze at altitude. Ensure they are on whenever parked.
Essential Reading
The UK CAA Safety Sense Leaflet 03 is the bible for winter flying. Review it every November.
Download CAA Leaflet 03 (PDF)Final Thought
Winter flying is rewarding, but it removes the margin for error. If the runway code is 2 (Slush), and you haven't calculated the performance penalty, stay in the clubhouse. There is always another day.