Flying in the winter brings a new set of challenges for pilots of all airplane types. The number of flyable days is reduced when the weather is IFR due to the increased probability of icing conditions in the clouds, and engine preheat is often required when the only option is to leave your airplane outside overnight in freezing temperatures before a morning flight.
Pilots flying larger airplanes with de-/anti-ice systems may be able to launch on more trips in the winter compared to the Cessna 172 pilot, but that’s not always a guarantee. The workload increases further when icing conditions exist at ground level at the departure airport, which requires the application of a surface fluid right before takeoff. Even if you’re not actively flying a turbine airplane in these conditions, you’ve likely been a participant in this application process as an airline passenger on an early morning flight.
As the surface fluid is applied before, pilots must calculate a holdover time (HOT) based on the fluid type applied, precipitation type and outside air temperature, and must be airborne before the HOT expires.
Every year, the FAA, EASA and Transport Canada publish holdover times for pilots to follow based on these variables, which are typically presented in a chart. Here’s an example of the FAA Holdover Time Guidelines when using Type 1 fluid:
For those interested in putting their iPad to work for this calculation, there’s an app called Winter Ops designed specifically for that mission. The main feature here is the Holdover time calculator, which requires the entry of the following variables:
- Precipitation type and intensity
- Wing surface material
- Flap configuration when fluid is applied
- Calculated rotation speed (Vr)
- Surface fluid type and mixture ratio
The app then calculates the holdover time and serves as a timer, actively showing you the countdown before you need to depart (or return for an additional surface fluid application):
The Winter Ops app also includes a few additional resources to assist with operations in surface icing conditions. First, you’ll find a comprehensive database of the popular brands of qualified fluids. Each includes technical details, dilution and valid temperature ranges. There’s also a SNOWTAM and Snow Visibility decoder feature:
Winter Ops is free to download but requires an annual subscription ranging from $3.49 to $9.49 per year.