Managing the challenges of winter helicopter flying
By Simon Sparkes | November 8, 2023
Estimated reading time 12 minutes, 5 seconds.
The approach of winter, signified by shorter, darker days and the inexorable changes in the weather, should tell us that we need to start increasing our focus on the weather when we look at threat and error management of flight operations.
While these clues are unchanging year to year, I must admit it is always a little surprising when I suddenly have to think about looking at the icing forecast or, as was the case in the last few weeks, consider the effects of freezing rain.
Increases in the amount of rain or low visibility days are often easier to deal with, but life in the more extreme latitudes does lead you to think about more than just how deep the snow might be.
Helicopter operations in cold conditions present a formidable challenge for pilots, operators, and maintenance crews. Helicopters, more so than any other aircraft, are uniquely vulnerable to these threats, and we need to understand the dangers posed by ice and snow accumulation.
If you are a light single-engine helicopter pilot, it’s about deciding whether you can fly or not. But for those using more complex aircraft, where achievement of the task requires almost all-weather capability, understanding the limitations of both you and your platform must be second nature.
Icing conditions occur when the temperature is at or below freezing and the moisture in the atmosphere transforms into ice on contact with the aircraft. This presents the pilot with significant challenges to continued flight, such as ice accumulation on critical components, including rotor blades, engine inlets and sensors, leading to a myriad of other problems — from decreased lift and increased drag to altered aerodynamics and engine inefficiency.
But of course, its not just about temperature. In fact, when you get below approximately -20 degrees Celsius (-4 degrees Fahrenheit), the ice effectively stops sticking to the aircraft as the thermodynamic interaction between water droplet and helicopter changes. This doesn’t mean there will not be any icing at all, but it does change the context and the things we, as pilots, must think about.
So it is in that band — between 0 C and -20 C — where icing conditions can really happen, and this depends on a range of factors.
1.Temperature and moisture: The two primary factors contributing to ice formation are temperature and moisture, with freezing temperatures and the presence of moisture in the air creating a fertile environment for ice formation. The moisture can take various forms, including freezing rain, sleet, or supercooled water droplets, each of which creates its own type of ice on the aircraft.
2.Rotor downwash: The rotor downwash generated by your helicopter’s main rotor system can exacerbate ice accumulation by directing moisture and ice particles into critical areas, such as the engine and sensors.
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3.Atmospheric conditions: Localized atmospheric conditions, such as freezing fog, freezing drizzle, and freezing rain, can lead to rapid and severe ice accumulation on helicopter surfaces. These are the ones you need to know about. If they are in the forecast, you must avoid them. I can’t think of a helicopter operation that is allowed to fly if they are present.
We must use our threat and error management skills to implement comprehensive safety measures and procedures to minimize the risks of such weather. Some of these skills are generic but others demand that you, as the pilot, know your icing systems, how they work, and what you need to do if they don’t. Here are a few thoughts:
1.Preflight planning: Before each flight, pilots must conduct a thorough weather analysis to identify where potential icing conditions exist along the intended route, how severe they might be, and what escape routes exist if the aircraft systems don’t work. This involves utilizing various resources, including meteorological aerodrome reports (METARs), terminal area forecasts (TAFs), and other weather data such as icing forecasts, hazard reports (HAZREPS) and other reports. To make an informed decision about whether to proceed with a flight, think about other tools that might help you, such as helicopter landing sight webcams or live weather reports.
2.De-icing and anti-icing systems: To get airborne in icing conditions, you’re going to be in a helicopter approved to operate with a variety of de-icing and anti-icing systems, which can prevent or mitigate ice accumulation. These systems can include heated rotor blades, windscreens, engine inlet anti-icing mechanisms and even hoist heaters, but be sure to do the preflight functional checks, which are normally long and not easy to remember. You don’t want to find out the systems don’t work when they are really needed.
3.Pilot training: If you have a helicopter with complex de-ice and anti-ice systems, how often do you train in their use? Does your simulator have the fidelity to mirror individual system failures and the effects of icing on the aircraft or de/anti-icing system if they don’t work? The problem with such systems is its almost impossible to train their use and various failure modes on a real flight.In addition, the training should also cover how you would escape from icing conditions if things have gone wrong and that is the only option. Do you climb into an area of clear air away from the moisture? Do you descend to try to escape the cold temperatures? How do you use other systems like the radar to help you?
4. Avoidance and diversion: If icing conditions are unexpectedly encountered during a flight, what action should you take immediately to avoid or exit the icy environment if your systems are not working correctly? If they are working, how long do they take to warm up and become effective?
5.Clear communication: Effective communication between pilots and air traffic control is of paramount importance when the weather gets cold and conditions are not on your side. Pilots must promptly convey concerns about icing conditions, and air traffic control should attempt to provide information and assistance. They may have previous reports or radar indications of better conditions.
But what happens if all the above threat management and avoidance activities happen? What might be the consequences of inadvertent entry or system failure? Here are some of the main issues to think about:
1.Reduced lift: Ice accumulation on rotor blades decreases the lift, typically leading to increasing torque requirements. If you are in this condition, reduce speed to the minimum power speed and keep maneuvers gentle as you conduct your escape.
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2.Increased drag and weight: Buildup of ice on the aircraft will increase parasite drag and weight across the aircraft. This will add to the problems of the first point.
3.Altered aerodynamics: Ice accumulation on the rotor blades and other aerodynamic surfaces will lead to unpredictable behavior, including vibration, and pitch and roll changes.
4.Engine inefficiency: Ice buildup around engine inlets can disrupt the engine’s airflow, leading to power loss and potential engine stall.
5.Visibility impairment: Icy conditions can also result in poor visibility due to ice accumulation on the windshield and sensor systems. That ice may take a long time to disappear if your windshield heaters are not working.
6.Increased workload: Above all, managing the effects of unexpected ice accumulation will raise whole crew workload, diverting focus from other essential aspects of flight, such as navigation and communication.
The problem for all helicopters is that they really don’t like icing conditions. Outside of knowing the seasons are changing, predicting exactly when and where they are going to occur is not an exact science.
As a result, helicopter operations in icing conditions demand the utmost vigilance, preparedness, and training. Understanding the hazards associated with ice accumulation requires regular refresher reading.
As we come into another Northern Hemisphere winter season, take a look at the training notes and flight manual, and get in the simulator to make sure you are ready to manage the threats that cold weather will bring. Also, think about previous errors you might have made in planning a winter flight, and above all, expect the unexpected.
Simon Sparkes is a test pilot for the Norwegian Defense Materiel Agency who started his flying career with the Royal Navy at the end of the 1980s. With over 50 aircraft types in his logbook, his experience has ranged from anti-submarine warfare operations on the Sea King, to basic helicopter instruction on the Gazelle, to commercial light twin operations in both the EC135 and AS355. Previously the commanding officer of the Empire Test Pilots’ School, he currently works on a variety of projects with the AW101 SAR Queen in the challenging Norwegian environment.