Aviation Safety Newsletter - Volume 1, No. 2

Submitted by on Wed, 01.10.2003 - 00:00

Winter Operations

The following article presents some key points outlined in a recent RFC-sponsored Transport Canada seminar by Michel Treskin, Civil Aviation Safety Inspector, on operating aircraft during the winter (as well as some extra points from various sources).

Winter flying is safe, but as we all should know, ‘safe’ does not mean ‘risk-free.’ Learn to manage the extra risks of winter flying to fly safely all year round.

New to winter ops? Get a “winter operations” briefing at the RFC and consider going up with an instructor, and always consult your A.I.P. Canada publication

Before Winter Sets In

  • Start thinking about practicing soft-field take-offs and landings (which are standard procedure in the winter on the Rockcliffe runway) well before winter conditions arrive…if in doubt or you feel you’re rusty, take up an instructor for a few soft-field circuits
  • Winter daylight hours are in shorter supply than during the summer; know when the sun goes down and take extra precautions (get your night rating, check your on-board flashlights, and have you landed at night recently?)
  • CRFI is not a radio station; learn the Canadian Runway Friction Index system and be aware of the CRFI numbers at both your origin and destination airports
    • CRFI scales from 0 (no braking) to 1 (excellent braking)
    • Braking on dry pavement rings in on the scale at around 0.8 and above
    • An ice-covered runway could be rated between 0 and 0.2, depending on temperatures and if the ice is wet, and up to 0.4 if sanded
    • Slippery runways mean the crosswinds will affect you more than usual
    • Refer to your A.I.P. Canada pub to see how the CRFI number affects the calculation of the amount of runway length you’ll require to stop
  • While this article is a good primer, consider your A.I.P. Canada publication as a prime source of winter ops information:
    • A.I.P. Canada, section MET-2.4, “Airframe Icing”
    • A.I.P. Canada, section AIR-1.6, “Canadian Runway Friction Index”
    • A.I.P. Canada, section AIR-2.3, “Carburetor Icing”
    • A.I.P. Canada, section AIR-2.12, “Flight Operations in Winter”

Pre-flight

  • Rockcliffe Flying Club minimum temperatures for flights with club aircraft (these minimums also take human factors into account):
    • Cessna 150: –20°C
    • Cessna 172: –25°C
  • Don’t fly without winter survival gear on board
    • Even a local flight around Ottawa can become serious in the event of a forced landing in cold weather
    • Think about wearing warm boots, packing a warm parka, extra clothes, food, etc. and tossing it in the back of the aircraft (do a W&B check -- you may have overpacked!)
  • Get a weather briefing and understand it
    • Know the position of fronts, inversions, and the like –  knowing where above-freezing temperatures exist may give you an ‘out’ if you encounter icing conditions – and know where they are forecasted to be as your flight progresses
  • Know the weather and forecasted weather at your destination too – active runway, crosswind component, runway CRFI numbers, etc.
  • Have a lot of ‘outs’ en route to your destination like alternative airports, ability to say “we’re turning around,” etc.
  • Don’t fly if the forecast includes –
    • Freezing rain
    • Freezing drizzle
    • Ice pellets
  • Is it snowing? You may be surprised to see how much snow you’ll pick up during your taxiing & run-up
  • Consult the carburetor icing probability chart available in your A.I.P. Canada publication, section AIR-2.3, and be aware of that day’s carb ice risk
  • There should be no reason for you to have to fly during icing conditions, nor even to do a take-off run on a slushy runway (brakes may freeze, take-off run will be longer, you may have to land on it on the way back, etc.)

Walkaround

  • Dress warmly – winter walkarounds take more time
  • Beware of frozen hinges – make sure all control surfaces freely move during the walkaround
  • Make sure your wing surfaces and brakes are free and clear of snow, ice and frost
  • When you press the fuel sample cup’s needle into the valve under the wings to extract a sample, the valve can stick and continue to leak fuel if it has become iced; the only solution besides plugging the valve with chewing gum is getting a warm rag soaked in hot water and wrapping the valve with it until the jammed ice melts
  • Don’t use ice-scrapers on the windshields of club aircraft

Engine Start

  • If your club aircraft has had overnight heating, prime twice as during summer operations
  • If your club aircraft starts up but then dies twice, it’s time for pre-heating – don’t keep trying to turn over the engine as you’ll damage the engine, damage the starter, kill the battery, and incur the wrath of your formerly-friendly AME
  • Don’t even think of hand-cranking the propeller – but if your aircraft has no starter, make sure you are not standing on slippery snow or ice

Taxiing

  • Don’t ride your brakes – they will heat up and melt any snow you forgot to clean off the brakes, which will turn into water, and as soon as you get up to altitude the water will freeze and you’ll have lost your brakes

Run-up Checks

Whenever I made a roast, I always started off by cutting off the ends, just like I'd seen my grandmother do. Someone once asked me why I did it, and I realized I had no idea. It had never occurred to me to wonder. It was just the way it was done. Eventually I remembered to ask my grandmother. "Why do you always cut off the ends of a roast?" She answered, "Because my pan is small, and otherwise the roasts would not fit." -- anonymous

  • At 1700 RPM, the carb heat on check (you’re looking for a drop in RPMs) is not just to verify that the carb heat control works, but also to determine whether you’ve been building up carb ice during taxiing
    • See if your engine runs rough when pulling carb heat on; if so, you are in serious carb icing conditions and it’s pilot-decision-making time

Take-off Run

  • The Cessna POH recommends carb heat cold during taxiing & the take-off run on C150s and C172s, but if your run-up carb heat test showed symptoms of icing, you have some pilot-decision-making to do…remember, the recommendation is to make sure you have full power on take-off and to prevent sucking debris into the engine when the filter is bypassed
  • …and if you left it as carb heat cold during the take-off run, don’t then put carb heat on just after rotation – you will lose enough RPMs to possibly adversely affect your takeoff climb – wait until you’re at least 500’ up

Flight

  • Include the carbon monoxide (CO) detector in your ‘cockpit instrument scans’ during flight
  • Starting to feel funny? Sudden headache? Open the vents and check the CO detector

Flight into Inadvertent Icing Conditions

  • Types of ice
    • Rime ice – looks milky white, like the inside of your freezer needing a defrost
    • Clear ice – looks clear and accumulates rapidly
    • Mixed – a mix of rime & clear ice
  • Stay out of clouds – they have all that extra moisture just waiting to condense as ice on your propeller, wings, windshield, empennage, etc.
  • Accumulating ice…
    • …and you absolutely need to go lower into warmer air but ATC can’t clear you just yet? Declare an emergency – “Mayday mayday mayday” – and you’ll have top priority
    • Ice appearing on the leading edges of your wings? The situation on your empennage will be worse – start taking action to get out of the icing conditions (From the Ground Up states that tail section is two to three times more efficient at accumulating ice in icing conditions than the wings – and tail plane stalls from icing can be unrecoverable)
    • Speed up – icing rate on your airframe will decrease and you’ll be that much further away from a possibly-increasing stall speed, and the increased RPMs will minimize ice build-up on the propeller blades (think about leaning the mixture to maximize RPMs)
    • Turn pitot heat on if so equipped
    • If you came from a region where conditions weren’t icing, turn around and head back
    • Depending on weather conditions, getting into warmer air could mean climbing or descending or turning around
    • Shut off the auto-pilot so you can feel any changes in the way the aircraft is handling – these could be your first warning signs of icing
    • Don’t change the configuration of your aircraft – don’t add flaps, etc.
    • Starting planning to land at the nearest airport
  • Flying into freezing rain? Turn around, or possibly climb to get to warmer air – you need to know where above-freezing temperatures are to be found to get out icing conditions
  • Accumulating ice is changing your wings’ characteristics – stall speed will increase, for one thing, so be aware of your angle of attack and watch for “slow-flight / approaching stall” warning signs:
    • airframe buffeting
    • decrease in the effectiveness of control surfaces
    • loss of height, despite pulling back on the yoke (and stop doing that)
    • you probably won’t hear the stall warning horn so don’t expect it
  • Accumulating ice is making your aircraft heavier – were you close to the maximum weight on take-off? If so, you may be becoming overweight which may affect your stability

 

Carburetor Icing

 

  • Temperature in the carburetor can drop by well over 20 degrees C, causing any humidity in the airflow to condense as ice in your carburetor, thus restricting the airflow to the engine
  • Pull carb heat on occasionally during your flight; if the engine starts to run rough, leave it on to clear out the ice (more on this shortly)
    • Your A.I.P. Canada pub states in section AIR-2.3 that most carb ice accidents occur during normal cruise, perhaps because pilots may not be aware that carburetors might ice up during high power settings and not just during lower-powered descents
  • Be on the look-out for these clues –
    • Subtle drops in RPM (resist the temptation to simply increase the power to compensate – this will hide this crucial clue of carb icing)
    • Sublte drops in manifold pressure
    • Engine starts to run rough or sputters
  • If you suspect icing –
    • Pull carb heat on (all the way; never set the carb heat control partially in or out)
    • If the engine runs really rough & sputters when you pull carb heat on, resist the temptation to push carb heat cold! A rougher engine proves you have carburetor icing. As the ice melts and passes through the engine, it will run even rougher and you may feel it will even quit, but you’re on your way to solving your crisis. Your A.I.P. Canada pub states in section AIR-2.3 that this time may be in the range of 60 seconds or so, which I am sure will seem like an eternity on board as you sit there and hear and feel the engine sputter, but if you put back carb heat cold, you may guarantee yourself an engine failure moments or minutes later.
    • An EGT (Exhaust Gas Temperature) gauge can be used to assist in eliminating carb ice by leaning the engine to the point where more heat is being generated by the engine and therefore more heat can be directed to the carb

White-outs

  • White-out conditions can happen at RFC when the runway is snow-covered; pilots may have difficultly judging where the runway ends and snowbanks begin on either side, and this also makes judging when to flare very difficult
  • Beware of low sunsets on Runway 27; glare from the sun will reflect off the snow and through the propeller which may result in producing flicker vertigo – increase RPMs to remove the illusion

Post-Flight

  • After landing, consider filling up the fuel tanks to prevent water condensation inside the tanks, even if you flew for half an hour…

Further Reading

  • Various A.I.P. Canada sections outlined above
  • From the Ground Up, Millennium Edition, pages 65 – 68, “Carburetor Icing”
  • From the Ground Up, Millennium Edition, pages 152 – 155, “Icing”
  • From the Ground Up, Millennium Edition, pages 261 – 264, “Winter Operations”

Safe flying this winter!