Preflight Strategies

Avoiding precipitation and icing in flight is a process that begins on the ground. It’s good to use several sources of weather information to develop an accurate picture of current and forecast conditions. Use airmets, sigmets, and PIREPS, together with graphical depictions of current and forecast icing conditions to determine icing potential along your route and altitude.

CIP and FIP

NOAA’s Current Icing Product (CIP) and Forecast Icing Product (FIP) tools show both icing probability and severity at a glance.

CIP—This supplementary weather product provides a graphical view of the current icing environment. Using forecast model data for temperature, relative humidity, and liquid water content and drop size, it also includes observational data from METARs, NEXRAD, satellite, lightning, and pilot weather reports. Updated hourly and available about 20 minutes past each hour, the CIP provides current—not forecast—information as of the top of the most recent hour via icing severity graphics and icing probability graphics. All graphics display icing severity in five categories: none, trace, light, moderate, and heavy. Keep in mind that these icing severity levels are not specific to a type of aircraft or flight condition—they depict general icing conditions for situational awareness.

FIP—This tool examines numerical weather prediction model output to calculate the probability of in-flight aircraft icing conditions.

Note: If your aircraft is not certified for flight into known or forecast icing conditions, be especially cautious of areas displaying any type if icing severity, regardless of the probability indicated on CIP graphics.

Always have at least two good alternative plans to get out of unwanted situations.

Weather Sources

• Flight Service 1800wxbrief
• AOPA Weather (members only)
• NOAA Aviation Weather Center (AWC)
  • Graphical Forecast for Aviation
  • Graphical Airmets
  • Sigmets
  • PIREPs
  • Icing
    • CIP and FIP Plots
  • Ceiling/Visibility
  • Low-Level Prog Charts
  • Winds/Temps Forecasts
  • TAFs

Personal Minimums

How to make the best go/no-go decisions? Develop personal minimums and write them down in advance of a flight, free of external pressure. Then consult your personal minimums before each flight to back up your go/no-go decision. This makes it easier to resist the temptation of “mentally negotiating” yourself into a tight spot during flight when influenced by emotion and hope of a successful outcome.

Personal minimums should cover minimum ceiling and visibility (day/night), maximum winds/crosswinds, minimum fuel reserves, pilot currency and proficiency, overall pilot wellness assessment, and aircraft/equipment limitations.

TIP: Update your personal minimums regularly to reflect current proficiency in the aircraft you fly.

Accident Case Study: Cross-Country Crisis

Personal Minimums Contract

Download the AOPA Air Safety Institute’s VFR and IFR personal minimums contracts to develop your minimums.

Have a Plan B and a Plan C

In addition to adhering to personal minimums, always have at least two good alternative plans to get out of unwanted situations. These plans must include being prepared to divert and NOT make it to your destination. Before loading the aircraft, inform your passengers that a weather-related diversion is always a possibility.

Ask ATC: Weather Deviating

An air traffic controller explains how you can communicate your concerns about the weather and work with ATC to deviate from your assigned heading and altitude.

Aircraft Clean?

In addition to a normal, thorough preflight inspection, there are a few extra items to pay special attention to before departing for a flight where clouds and/or precipitation are likely to occur.

Pitot Heat—Without actually touching it, test the pitot heat by turning it on and feeling its heat near the palm of your hand. Use caution; some pitot tubes get hot very fast.

Drain Holes—Some aircraft have one or more small drain holes in the bottom of the fuselage to drain rainwater. If the airplane has been parked outside in cold, wet weather, ensure there isn’t a block of ice inside the fuselage and wings.

Aircraft Contamination—Frost, snow, and ice can accumulate on wings, elevators, and other surfaces when an aircraft is parked outside. Remove all frost, snow, and ice from the aircraft before departure. Any unremoved contamination will disrupt airflow over the wings and substantially alter flight characteristics, such as increased stall speeds, longer takeoff rolls, or even an inability to fly at all.

Clean it Up!

 

In the highly regulated airline world, the rule is simple: An aircraft can depart only when it’s clean—no snow, frost, or ice on any part of the aircraft. GA pilots should use the same operating principle.

The easiest way to prevent contamination is to park the aircraft in a hangar. If that’s not an option and the aircraft is snow-covered, consider using soft bristle brooms or small snowbrushes. While effective, they can scratch paint, so use care. Clean towels or shop rags will also remove snow without scratching the paint.

Removing frost and ice is trickier but just as critical. Again, a heated hangar is a great tool. But make sure to remove all the moisture before flying so it won’t refreeze before takeoff. Alternatively, use approved deicing fluids—but do not use these on the windshield or windows:

• Glycol is the most expensive and generally only available at select FBOs.
• Polypropylene antifreeze is pink in color an available at RV, automotive, or marine stores. It works quite well used in a small garden sprayer. Composite aircraft owners should test it in an inconspicuous area first, as there have been reports of staining.
• Automotive windshield deicer in a spray can is inexpensive and can be purchased at gas stations and department stores. Do not use it on aircraft windshields or windows. It’s the easiest to carry with you.
• Rubbing alcohol, sold in relatively small quantities in drugstores and supermarkets, can work in a pinch using a spray bottle with a hand pump.

With the exception of Glycol, these products are inexpensive and should be used liberally. Remember, you want the aircraft to become airborne!

Use a clean towel or shop rag to clean off the windshield. Or, you can start the airplane and wait for the defroster to do the job, but this could take a while in cold weather at idle power.

Note: No scraping! Do not use ice scrapers and credit cards as they can cause damage to paint and windshields/windows.

Tip: Dress warm since do-it-yourself airframe decontamination takes a while, in cold, often windy conditions. A parka, boots, gloves, and hat will encourage you to give this critical job the time and attention it deserves.

A garden sprayer can be used to help remove frost.

“Hangar-in-a-can” products are small enough to fit in a flight bag.

Preflight Factors

Let’s review the preflight factors for a flight conducted under visual flight rules (VFR) and a flight conducted under instrument flight rules (IFR).

Tip: Remember to write down the freezing levels before flight. You can compare them to the outside air temperature while en route. In addition, improve your situational awareness of freezing levels and icing potential by monitoring onboard datalink weather information.  

Graphical Forecast

The text area forecast for the contiguous U. S. has been replaced with the Graphical Forecast for Aviation (GFA) tool. This tool provides an excellent overview of expected cloud tops/bases/coverage, ceiling/visibility, precipitation/weather type, icing levels, etc.

Note: Text area forecasts are still available for Alaska, Hawaii, and the Caribbean.

How to make the best go/no-go decisions? Develop personal minimums and write them down in advance of a flight, free of external pressure.

Fast Escape

 

As mentioned in Preflight Factors, fronts can bring temperature changes that create severe icing conditions. If you’re flying IFR and plan to cross a front, it’s best to cross it as quickly as possible.

Terrain Avoidance Plan

Obstacle altitude information is charted on VFR and IFR aeronautical charts—so use it! This is especially critical when you plan to fly at night or in low visibility.

• Stay above the charted maximum elevation figures
• Know your planned cruising altitudes
• Know your minimum safe cruising altitudes (for emergency planning)
• Have an exit strategy for unexpected weather/malfunctions

Rules of Thumb

Use these formulas for quick estimates.

• Cloud Bases
  Temp (F) - Dew Point (F) / 4.4 x 1000
  For example, if the temperature at the surface is 65 F and the dew point is 40 F, the cloud bases should be at about 5,600 feet agl (65 - 40 = 25/4.4 = 5.68 x 1,000 = 5,680).

  Or

  Temp (F) - Dew Point (F) x 2 and add two zeros
  For example, if the temperature at the surface is 59 F and the dew point is 57 F, the cloud bases should be at about 4,000 feet agl (59 - 57 = 2 x 2 = 4 and add two zeros = 400).

• Celsius to Fahrenheit
  Double the temperature and add 30.
  For example, 20 degrees Celsius is close to 79 degrees Fahrenheit (20 + 20 + 30 = 70).
  The most accurate formula requires more thought: (Celsius x 9/5) + 32 = Fahrenheit