Although it seems like summer was just here, Christmas has come and gone, and the snow is falling here in the Northwest. With the thick of winter quickly approaching, we should focus on cold weather operations with the goal of awareness and flying as safely as possible.
The manufacturer of the business jet that I operate releases a Cold Weather Operations Guide each autumn. The OEM feels that although professional pilots operate these capable jets, the risks involved with cold weather and icing operations are so significant that they must reinforce proper cold weather procedures every year. I don’t have a photographic memory, so this valuable refresher gives me the confidence I need when heading off to work. In that spirit, let’s review cold weather operations, the hazards involved and the tradecraft used when flying in less-than-ideal conditions.
Let’s start with some icing basics. High-performance business jets perform optimally with smooth, uninterrupted airflow over their wings, tail and control surfaces. Introduce some disturbance to the airflow, and that optimization quickly erodes. Studies have shown that icing only as thick and rough as sandpaper can reduce lift by up to 30% and increase drag even more – as much as 100%. That eye-watering fact should make any aviator understand that icing is serious business, regardless of the aircraft flown.
As with most risk management, the best way to minimize negative consequences is to identify and mitigate the most significant dangers. This risk mitigation is essential for cold weather operations. In a perfect world, we would operate in calm, clear conditions and preferably to a destination near fine sand, warm water and delicious foods grilled on a stick. The reality is that we must attend meetings, visit loved ones or deliver goods to places that don’t fit my description of a perfect world – and we will be flying into icing conditions. Heck, your perfect world may be fine powdered snow while gliding down the ski slopes. Anyone operating in an icing environment must do their homework and master many things, including recognizing the conditions conducive to icing, deicing/anti-icing systems of their aircraft and the procedures each manufacturer recommends.
Detailed knowledge of meteorology beyond the basics is essential. A thorough understanding of frontal characteristics, temperature inversions, types of icing, and accumulation rates is critical – not optional. Knowing what goes into Icing Forecasts, AIRMETS, SIGMETS, field condition and braking action reports will give a disciplined pilot the information needed to make safe operational decisions.
FAA Advisory Circular 91-74B, titled Pilot Guide: Flight In Icing Conditions, is an invaluable resource that concisely (in 63 pages no less) covers everything any pilot should consider before attempting to operate in cold weather conditions. If one adopts a practice of periodic review, AC 91-74B is a valuable document to put on the list.
One of this AC’s many topics is explaining certification requirements and how they have changed over time. Before 1973, Part 23 aircraft were certified for light icing and flight into moderate icing for a limited time only. Those pre-’73 ice protection systems can only be considered a means of escaping an icing condition. It’s vital for anyone flying one of these aircraft to understand and respect this limitation. There are too many cases of overconfident pilots flying into icing conditions with the false impression that their aircraft could handle these conditions, often to their peril.
As time passed, certification included testing for flight into known icing (FIKI). Just because your aircraft may be certified FIKI, this is no magic bullet that allows you to disregard proper planning and decision-making.
Unless pilots exercise sound airmanship, they and their FIKI aircraft can become an accident statistic, too.
Enough of the doom and gloom – now is our opportunity to discuss best practices and tradecraft to avoid being the accident statistic. Weather is the hardest to predict and the most variable factor in every flight. Make every effort to obtain the most current PIREPS, AIRMETS, SIGMETS and freezing level forecasts before each flight into conditions that can produce icing. Remember that a lack of PIREPs does not mean there aren’t hazardous conditions present. Sometimes, pilots fail to give icing reports or simply no one flying along your flight route.
If your preflight weather planning points toward possible icing, your aircraft preflight will become even more critical. Aircraft equipped with leading-edge boots require a thorough inspection of all areas of the boots to find tears or cracks that could inhibit proper inflation when needed. The same holds for propeller heating elements. Ground testing of pitot heat, windshield heat or hot plate operation can prevent an accident before the aircraft leaves the ramp.
Should your departure airport be contaminated with snow, slush, or ice, care must be taken during taxiing to minimize splashing contaminants into wheel wells, flaps, and control surfaces where it can freeze. If flaps are used for takeoff, delaying flap deployment until taking the runway will eliminate frozen contaminants obstructing retraction mechanisms. After takeoff, delaying gear and flap retraction and allowing contaminants to blow away is a useful best practice.
Once airborne, listen up on frequency to hear what controllers and other pilots are saying about the conditions. Base and top reports are the best way to understand the weather in your sector and, along with your OAT gauge, will indicate when icing could occur. Take the initiative to ask ATC; if no reports are available, be responsible and give them accurate reports of what you are experiencing. The next pilot through that airspace will surely appreciate it. You should activate propeller heat, windshield heat, hot plates, etc., before entering any potential icing environment and always by the POH or AFM.
Icing will adhere to small protuberances before larger ones, so pay close visual attention to those areas of your airframe. The windshield wipers would be my first indication of icing in the Navajos, Cheyennes and King Airs I once flew. A high-intensity flashlight will help you see these unlit areas in darkness and is a great backup in case wing inspection lights fail.
A pilot exercising sound risk management will give himself three outs when icing conditions occur – vertically, either up or down, and if that fails, the ability to reverse course out of the icing event. In general, icing layers are relatively thin – only a few thousand feet thick and in most cases, climbing through or descending to a lower altitude will do the trick.
Beware if trying to climb through an icing layer, though. As ice accumulates on any airframe, the significant increase in drag can deteriorate the aircraft’s ability to climb. Depending on the accumulation intensity, expect higher than normal climb power settings. Aircraft sometimes run out of climb performance and, in some cases, the ability to maintain level flight. In this situation, if there isn’t enough terrain clearance to descend, the only out is to reverse course and exit the icing area from where you first encountered it. Do so calmly and carefully as the lift further deteriorates in turns, raising stall speed. When descending through icing layers, try to do so expeditiously and at as high an airspeed as practical, as ice accumulates less as airspeed increases.
Once entering the terminal area, the combination of being close to the ground while flying at slower airspeeds increases the risk in icing conditions, making it the most dangerous phase of flight. If you expect icing, activate all heated surfaces before beginning an approach, especially before entering this high-workload environment. If leading-edge boots have been activated, another cycle on and off is a good habit to adopt. Should you be required to enter a holding pattern in potential icing conditions, do so at a higher airspeed and refrain from extending flaps until they are required for landing.
During the approach and landing phase, tailplane icing becomes a significant factor to consider and manage safely. Tailplanes will collect ice earlier than wings because of their thinner profile. Compounding that problem is that most tailplanes are not visible to the pilot, so precautions must be taken. On most aircraft, tailplane ice accumulation can cause a nose-down moment as the center of lift (CL) moves aft of the center of gravity (CG). If using your autopilot, be aware that the trim may be trying to counter this moment and be prepared for a possible pitch down when you disconnect. The key is not to get startled when the workload is already high.
AC 91-74B also advises that if tailplane ice is suspected, approach speed should be increased 25% above non-icing speed, and with this airspeed additive, expect your landing distance to increase 20% for each 10% airspeed increase. If possible, a partial flap landing is preferable. Generally, flap settings up to half give the best lift performance, while the last half creates the most drag and can aggravate a pitch-down event. Of course, these are ballpark numbers, and POH, AFM, and runway requirements must always take precedence. Have a suitable alternate with a longer runway in your back pocket should your landing performance become critical.
I’ll end with a war story to reinforce my cold weather perspective. While flying an Aerostar during my check-hauling days, I flew the NDB approach into Hartford, CT (KHFD) to minimums one evening. It was particularly challenging with a rain-to-snow mix, and I was already busy trying to time my approach and drag the NDB tail to stay on the approach course. Undoubtedly, I had picked up ice on the arrival, as scary 4-inch-long icicles had formed on the propeller spinners. I delayed flap retraction and selected half flaps while adding about 20 knots to my approach speed. Although I was exercising all the tradecraft in my bag of tricks, when I went into the landing flare, about two feet over the runway, the aircraft stopped flying, and I landed hard.
My knees nearly buckled when I got to the ramp and post-flighted the tail. It looked like a scene from Shackleton’s expedition, with maybe an inch of ice covering the entire surface. I can only imagine how full my hands would have been if I hadn’t planned ahead and taken flap and speed precautions. These are the types of events that burn into your brain. This event alone is why I prefer destinations with sand, warm water and food on a stick!
When faced with cold weather operations, knowledge and planning will help mitigate some of the inherent risks, while sound judgment and understanding of both your aircraft and personal limitations will stack the deck in your favor. We should all strive to describe each of our flights as uneventful!
Y’all be careful out there.
