Trip to Grandmother's House And Aircraft Icing
With the fall and winter months approaching, it’s time again to think about icing aloft. Airfoil and airframe icing in flight is a dangerous phenomenon, and must be dealt with quickly and properly. Taking off with ice anywhere on the A/C is unforgivable, as you will find if you decide to try that!
Types of Ice
Let me explain the two most prevalent types of aircraft icing. You visit your grandmother for Thanksgiving and ask her if you can get her anything, and she replies ‘can you make me a martini on the rocks?’ So going to her refrigerator you open the freezer and find these old ice cube trays covered with ice. The color of the ice is white (or opaque) which is known as RIME ICE. It has air in it, which is indicated by the opaque color and can be easily broken loose, with some prying. So now you need to get the cubes out of the trays. You’re fighting with these ice cube trays, and the cubes DO NOT want to come loose. Finally, you beat them with a hammer and as they pop out you’re thinking ‘this is some tough ice!’ Yes, because it’s CLEAR ICE, and it’s tough. It has no air inside it and is hard to break.
We want to avoid clear ice on your A/C and to do this you need knowledge of the weather patterns and the FREEZING LEVELS that you will be encountering on your flight. Your Pre-Flight briefing from the FSS is always a good start! And while
En-route, PIREPS will help. Don’t take these reports lightly!
What causes these types of ice?
RIME ICE: This is formed on the wings and surfaces of the A/C by the rapid freezing of supercooled droplets of water, resulting in air being trapped within it which makes it brittle. It’s porous structure makes it relatively easy to break-off with wing and tail boots (deicing system). It is not smooth, and conforms to the leading edge of the airfoils; but it gives the pilot time to develop a plan-of-action.
CLEAR ICE (Glaze Ice); This is formed by supercooled water droplets striking the surfaces; but not freezing on contact. It is mostly smooth in appearance but can have air pockets in its structure. The ice formations are usually but not always smooth. Clear ice will accumulate at a faster rate than Rime ice. It is more difficult to combat with wing and tail boots, and the pilot must act quickly to continue to a safe landing.
Both ice types hinder the aircraft in several manners:
Airfoil shape changes, and the airflow is disturbed across the leading edges causing an increase in the normal stall speed.
As the weight of the ice on the A/C increases, it can quickly approach the max gross weight and structural limits.
An increase in fuel burn to keep the aircraft airborne, due to loss of lift, increased angle of attack, propeller icing, and total weight of the A/C.
What is the best plan of action? Get your tail on the ground! This is where your pre-flight planning comes into fruition. Know ahead of time that icing conditions could be present for your flight. Check for AIRMETS, SIGMETS, and PIREPS; know your En-Route airfields and EMERGENCY Airports!
Anti-Icing vs. De-Icing equipment:
Anti-Icing: is preventative, with such systems as: pitot tube heat, windshield heat, engine anti-ice heat, and spraying the A/C before flight.
De-Icing: is active, wait for the ice to form and use your systems to break the ice away; but you have to stay alert and watch the buildup and watch the elimination.
Be prepared for a heavier A/C while maneuvering and on approach, and the possibility that the windshield may freeze over. KEEP ‘ER FLYING!
My Will-ism for Icing is: if you are flying a single engine or light twin without anti-ice protection and hear airline or corporate pilots state “we are in MODERATE Ice”, or hear it on an AWOS, get on the ground, FAST!
FLY SAFE. FILE FLIGHT PLAN. CHECK WEATHER. WHAT IS THE FREEZING LEVEL? DO NOT DELAY ASKING FOR HELP!
Until Next Month…..Will Rondeau
References:
Aeronautical Information Manual: 7-1-21.AOPA: Safe Pilots. Safe Skies: (www.asf.org)