Snow

Large snowstorms

• Often easier to plan for as ATC/Airport Authority/airline dispatchers share common concerns on the impact. 
• Continuous snow removal will reduce the number of RWYs available, thereby reducing airport throughput. 
• De-icing will cause departure delays (see below) and arrival and departure demand must be balanced to avoid airport gridlock. 
• Arrival rates will be determined by threshold crossing speed, ROT, and spacing requirements between aircraft. The more contaminated runways become, the harder it is for aircraft to use the closest high-speed exits from their touchdown point. This increases their ROT and in turn the spacing required for inbound aircraft, which results in a lower arrival rate.
• Information from the Airport Authority will include whether they plan to pre-treat RWYs with chemicals, RWY temperatures, snow removal plans, and de-icing capabilities.

This information can then be used to assess how the forecast will impact operations by analyzing expected demand versus capacity, which helps determine start and end times, and best/worst case scenarios. 

• Major snowstorms require GDPs to manage the number of flights arriving per hour. The scope of the GDP will typically include aircraft from all over North America and will often result in hundreds of cancelled flights.

Benefits of major snowstorms is their predictability. There is usually good consensus to the timing and duration of the event, and strategic plans can be made by Operations Duty Managers for proper GDP implementation in a CDM effort with the NTMU, airport authorities, and major airlines.

High uncertainty or highly variable events are often most difficult to plan for given the complexity of snow removal operations and determining capacity constraints.

• It is where there is most often difficulty to gain a consensus during the CDM process and where unforeseen TMI can lead to significant and lengthy delays.
• Understanding a CMAC forecaster’s level of uncertainty here goes a long way in helping assess risk and make a plan for that period’s operations. Hearing a forecaster say “I am not sure and here is why” is far more valuable in cases that warrant it, and preferable over a “best guess”.
• In these cases, getting a best and worst case scenario from CMAC forecasters for timing, duration, and accumulation helps bracket what Operations Duty Managers have to work with and decisions that have to be made.

PROB30 Events

• Requires risk analysis to the operation. 
• Information required from the CMAC forecaster includes: onset, duration, accumulation, snow/rain ratio, triggers (lake effect, snow squalls, etc), and level of confidence. Wind direction is also critical in determining RWY configuration and potential for a configuration change to uncleared runways for airports that have them. (see airport authority impacts). 
• Operations Duty Managers with meteorological knowledge will occasionally ask which model is performing better so that they can monitor changes. This understanding allows for supplemental questions to be asked to maintain stronger situational awareness and better risk management for operational constraints.
• Higher risk is accepted during periods of low volume, but TMIs will be considered/implemented when the impact to the operation is significant, even though the risk is low. APREQs, airborne holding, GS, GS into a GDP, or a high-rate GDP are all possible options.

De-icing impacts departure volume especially during peak times. GTAA will institute a departure TMI (D-TMI) to stage aircraft (issued departure slot times) to minimize queuing.

Under certain conditions departures require ice-shedding run ups and if this is done on the RWY it increases the time required for departure and reduces the # of aircraft movements per hour.

Forecaster notes in HubWx are crucial to planning. Operations Duty Managers use CoSPA (winter precipitation mode), upstream stations, satellite imagery, real-time obs, and model data, to name a few, to monitor snow events. Usage varies based on an Operations Duty Manager’s knowledge and experience.

Questions that come up:

• Will there be accumulation and will it affect visibility and ceiling heights (IFR vs VFR)? If there is no accumulation then this is the same as a rain event.
• If there is accumulation, how many cm in each hour? When will it start and when will it stop? This will allow us to plan for a snow plowing operation and predict how fast braking action will deteriorate.

The GTAA will plan a snow removal and de-icing plan along with a departure rate which may need to be considered. If it is low, the NTMU will have to consider rates of snow fall and turn around to ensure the arrival rate will not cause gridlock. At this point they will predict a true arrival rate and should demand exceed capacity, determine a GDP rate.

There is a very big difference between TEMPO and PROB30/40: it’s where predicting the potential GDP rate and its impact on the true arrival rate become crucial, especially as these two numbers may not necessarily be the same.

• To determine a path forward, the NTMU participates in collaborative decision making with customers, and there has to be agreement on what we think is going to happen in reality.

It’s important to underscore the importance of understanding a CMAC forecaster’s confidence. It impacts how confident we and the users are in the forecaster.

• Snow events that are in a TEMPO are the hardest to work with, it is similar to thunderstorms as you cannot plan on the timings, they pop up randomly, so it is impossible to plan each hour.
• Snow events that are longer and consistent allow consistent rates and are easier to plan for and predict plow frequency and runway occupancy times.

Often when the events are temporary and sporadic a GDP will be planned at a higher rate than we can manage when it is actually snowing, as the hourly rates will hopefully even out as the evening progresses between low rates during the snow and higher rates when it is clear.

• This however creates additional concerns as now we have to ensure we have staff in enroute specialties to ensure we can handle the holding when the rate is lower during the times it is snowing (much like thunderstorms) so that we can catch up when it’s not snowing.

The more uncertain the forecast the more difficult the planning process is, as safety must be ensured while trying to achieve system efficiency and addressing users concerns. The users will usually push for more efficiency knowing that we will always ensure the system is safe.

Ideally a forecast would be as detailed as possible indicating what the CMAC forecaster believes is most likely to happen, if they are unsure, the second best scenario is they will provide a best case scenario and the worst case scenario. In these cases we will be as optimistic as we can be, but ensure we can ensure safety if the worst case scenario occurs.

Enroute

• Enroute ATC sub-units will be considered as mentioned when demand exceeds capacity as the overflow will be held here. The staffing and ability to hold will be considered when determining rates for major airports.
• Often holding will back up from low level to high level, so abilities to hold for high levels must also be taken into consideration.
• During highly unpredictable events, extreme events, or erroneous forecasts, these specialties become even more vulnerable as unexpected volumes of holding may occur when low level sectors get overwhelmed. This may also impact the volume of CAN Routes aircraft that can be handled.

Regional Airports

• At regional airports snow usually has little effect from an NTMU point of view as demand doesn’t typically exceed capacity unless the snow significantly impacts or closes the airport then consideration must be made for the aircraft workload in the enroute sectors. Managing diversions to alternate airports and not overwhelming them becomes a concern during severe weather events.

ATC (Major Tower)

Snow affects all tower operations.

• Use of alternating runways, taxiing depending on taxiway conditions.
• Snow type (dry vs wet) affects snow removal speed/efficiency.

When there is snow, aircraft go to de-icing and the vast majority of those going to de-icing need an engine clearing and a run-up before take-off on the threshold, which significantly increases runway occupancy time.

• For some years some airlines have started asking for fixed points when they are waiting on the ground even if they have not yet de-iced.
• Use of the de-icing bays also reduces the airport’s ground capacity, which is critical from an arrival and departure rate. Care must be taken to balance throughput on both sides to avoid gridlock and potential ground stops.
• Each aircraft has a HOT that cannot be exceeded, and the clock starts with de-icing. An aircraft that exceeds its HOT is required to return for a second de-icing.
• Depending on airport configuration, this may require using the runway as a taxiway as is the case in CYUL. This significantly impacts ROT and upstream workload as arrivals must be held until the aircraft is clear of the runway.
• The day after a snow event, airport crews will do a thorough clean up around lights and beyond, which can still lead to delays.
• ILS Localizer antenna and glide path (G/P) pad need to cleared of snow. The localizer antenna is within the runway protection area, therefore the runway needs to be released. The G/P needs to be shut off to clear the G/P pad. (Tower supervisors check with NAV CANADA’s technical ops team to confirm maximum snow accumulation on G/P pad).

The fact that snow is measured in terms of obstruction to visibility rather than the amount of precipitation per hour for our operation can be most misleading from a planning perspective.

Even once the precipitation is over, crews must return to the runways/taxiways to push the snow away from the edge so as to prevent additional contamination with the next storm. This will result in a reduced rate even after snow ends to allow for all runway and taxiway clearance to be completed.

Most often the maneuvering areas are clearer of snow than the aprons because the immediate need is to displace the snow on those areas whereas it needs to be completely cleared on the apron. This is done with trucks, which complicates and prolongs the operation and can lead to airport congestion. 

For CYUL:

• With only 2 parallels, the impact of the winds is less than when the 28 was used. Crosswinds do have a higher impact as only 06/24 are available and under contaminated runway surface conditions can significantly impact aircraft operations as each type has their thresholds in such operations.
• The ground control position is separated in two separate roles to account for increased workload.
• Regardless of a PROB30 or +SN, upstaffing will be attempted as this requires additional controllers on shift.

ATC (Regional Tower)

As a regional tower controller we are typically operating “in the moment” and forecasted snow isn’t considered until we are at work and running the operation for the day. During snow operations, however, there are some additional considerations as follows as an example of CYAM operations:

• Airport determines its own snow removal plan. They tell us what runways they’re planning to keep clear and how and when. Occasionally we’ll suggest they clear the alternate first due TAF forecast favouring other runway.
• If limited taxi surfaces are available i.e. it’s snowing so heavily that the maintenance staff can’t keep up and we only have one exit available, we’d work with Toronto ACC (enroute) for additional spacing between arrivals as required to allow for long backtracks etc.
• Snow squalls are the most significant weather event here at CYAM because we’ll often have aircraft holding, waiting for gaps in the squalls to shoot the approach into the airport. NW winds here = lake effect snow squalls and zero vis. Situations. Lake Effect weather is difficult to predict and we’ve found TAF less reliable in this regard.

Snow is a critical safety factor in winter operations, as removal of surface contamination is essential to safe airport operations. The effect of this phenomenon on FSS operations cannot be overstated – the extra effort and attention required for winter operations is demonstrated by the annual Winter Ops Refresher Staff Memos that are posted at Flight Service Stations and FICs across the nation in September, every year. These memos often refer to Interunit Agreements and Memoranda of Understanding with external agencies, reminding Specialists that our Unit may have advisory agreements with Airport Operations at aerodromes, to warn local operators of impending snow events.

Specialists at both Advisory Sites and FICs are responsible for Weather Observation, so snow events involve increased vigilance to detect when weather conditions meet local special criteria, multiple trips outside to monitor the Ice Accretion Indicator, and trips the Synoptic yard to measure snow depth and check the snow gauge for snow fall amounts.

FIC

At Flight Information Centres, the Area of Responsibility covers a vast geographical area, demanding a more strategic view of the weather. An FIC may have agreements with various airports within our AOR for snow event alerting, but most of the unit workload increase will be issuing CRFI. At Winnipeg FIC, it was standard operating procedures to issue well over 100 CRFI per day in Winter, with double or even triple that number on a heavy snowfall day. This workload is in addition to Weather Briefing and Flight Planning for the AOR. 

AAS

At FSS units providing Airport Advisory Service and Vehicle Control Service, snow events increase the workload for the Duty Specialist, depending on the intensity of snowfall, time of day and traffic flow at our Aerodrome. The mental demand for heightened situational awareness is a significant human factor, as the combination of increased vehicle access to runways under reduced visibility conditions puts additional stress on the specialist. Monitoring the speed and position of sweepers and plows by the FSS is essential, as vehicle operators must maintain vigilance on the radio while operating heavy, loud equipment under reduced visibility conditions. Extra coordination with the relevant ACC Sector is imperative, so that the Controller knows that destination runways are contaminated and occupied by slow moving vehicles – the consequences of a late handoff to FSS of an IFR Inbound can be costly (in the event of a “Go Around” because of insufficient time to evacuate vehicles from the landing runway), or even disastrous (this situation was a major factor in the PWA314 crash at Cranbrook, BC, 11 Feb 1978. This incident led directly to FSS being given Ground Control authority over vehicles on Airport Manoeuvring Areas in Canada.) 

Snow requires significant coordination between controllers along with complex and critical timing, and a steep rise in additional information to give to pilots. It also has a major impact on airport capacity and therefore, in the case of a major airport, on the entire upstream system. This can have a significant impact on a terminal controller’s workload since whatever affects the airport directly affects them almost immediately. An airport’s capacity may be significantly reduced for the following reasons, among others:

• Runway availability: probability of “losing” a runway, i.e. of not being able to maintain it in a usable state due to rapid accumulation of contaminants; ability to predict these probabilities; impact on approaches from wind and limited visibility; likely missed approaches increasing total traffic load.
• Hourly accumulation is critical throughout the event in addition to the forecast for the event as a whole, as it helps us better understand how airport operations will be impacted and the number of aircraft we will be able to land in any given 15 minute period.
• Significant impacts on in-flight visibility that may impact approaches and the ability of crews to establish visual contact with the runway. Higher probability of missed approaches.
• Missed approaches may also be conducted as a result of crosswinds coupled with a contaminated runway surface.

CYUL Example

There are 2 parallel runways, so when it’s snowing the snow removal teams will alternate runway sweeps. Impact:

• Snow removal, or SRIP as we call it (snow removal in progress) directly affects our work immensely.
• Instead of running our regular parallel runway operations, we alternate between the two parallels and run a single runway operation.
• On a very snowy day, this will go on during the entire day, for example as soon as 24R is cleaned up, the snow removal team will move on the 24L and vice versa.

What impacts the arrival rate?

In regular parallel runway operations, we will have one runway being primarily used for departures, and one runway primarily used for arrivals.

• In this situation, the tower can clear aircraft for departures as soon as the last departure is far enough away (with their norms and rules), and we can put aircraft on the approach as close as we’re allowed (usually 3 miles in trail).
• However, in single runway operations, we need to double the spacing to at least 6 miles in trail, because the tower will now need to depart an aircraft between each of our arrivals.

Often, snowstorms mean low visibility and reduced braking action, resulting in aircraft taking more time to taxi off the runway and a higher ROT.

Cold weather also often results in aircraft needing to do a short run-up before taking off. If this occurs on the runway, it will increase the amount of time (and resultant spacing) needed between planes. See Barrel Icing under the Commercial Pilot tab.

Final Result

• Instead of the usual 3 MIT given to arrivals, the spacing in snow often requires 6 MIT and in heavier accumulations likely 7 or even 8. This added spacing results in more time between arrivals and results in at least a 50% reduction in capacity. When these conditions coincide with peak traffic times, TMIs are required.

Uncertainty

SRIP – ATC must try to optimally “time” arrivals with the snow removal team to maximize the number of aircraft that can be landed safely and deliver optimal service. This requires multiple variables to be a viable option:

• The aircraft has to be properly positioned, the pilots have to be ready for a specific approach (for a specific runway), and then the final vectors-to-final and approach will take a good 7-10 mins to fly.
• If TCU controllers wait for the Airport Authority SRIP team to be completely off the runway before beginning to bring aircraft back, that’s a waste of 7-10 mins where the runway is fully available and fully clean. These precious minutes add up and can lead to a large impact to customers as each of those time frames could have landed aircraft.

Tools Terminal Controllers have

Controllers and the ACC Operations Duty Manager have an indicator controlled and filled in by the tower using information provided by the airport authority that gives two times:

• A SRIP time (which is when the snow removal trucks think they will be done) and
• FAT, which is “first arrival time”, usually 5 mins after the trucks plan clearing the runway, to give a little buffer.
• These numbers are estimates and are often revised as the snow removal trucks do their work. However, this gauge allows for terminal controllers to plan for what specific aircraft will be the “first arrival” on the newly cleared runway. An aircraft that is brought in too late is not efficient. An aircraft brought in too early may result in an overshoot as snow removal trucks would not have cleared the runway. It’s a tough balance to strike.

In either case, big airport or small, snow and winter weather mean a higher workload for controllers. Information to pass along includes:

• When the SRIP is over.
• Braking action reports.
• Runway surface condition reports.
• This means that every aircraft we have on our frequency "takes up more of our time".

Regional Airports

Most regional airports, for example CYHU, there is only one “main” runway (there are others but they are shorter and rarely used for our IFR traffic), snow removal requires a temporary closure of the airport.

• If controllers are on frequency with an arrival while snow is being removed, they have to hold them or give them additional delays, which increases controller workload.
• If the aircraft is already low on fuel, controllers will attempt to negotiate with the airport to see if the snow removal team can take a short break to accommodate the aircraft.

In either case, big airport or small, snow and winter weather mean a higher workload for controllers and a greater impact on the system as a whole. Information to pass along includes:

• Braking action reports.
• Runway surface condition reports.
• This means every aircraft we have on our frequency "takes up more of our time".

Overall, instead of having an initial contact that lasts 5 seconds, it might last 20 seconds. Snow means lots of coordination between controllers, timing, and loads of additional information to give to pilots.

Snowfall for low-level IFR ATC can have a major impact.

If there is too much, the airport can close for an undetermined amount of time. More commonly, at airports like CYUL, one runway will close at a time for snow removal, leading to delays for landing aircraft. Regional airports tend to close for an undetermined amount of time when there is heavy snowfall. NOTAMs are published but as enroute controllers, we must be certain that the pilots are aware of the closures as the NOTAM could have been published after the aircraft was already in flight.

• As controllers we must keep the aircraft informed at what time they can expect to land, provide them with delay vectors or holding patterns, and provide any available information on runway surface conditions and braking action.
• Depending on aircraft type and sometimes the operator, some can land in more marginal conditions than others, which adds to the complexity as we have to clear them from the traffic that has to be delayed.
• Above FL280, it is important to keep jet traffic in the picture about possible delays due to snowfall. If they must hold due to airport closures or delays, then they can stay at high altitudes to use less fuel and avoid having to land at an alternate airport.

Snow doesn’t directly impact the high-level in most cases.

• One caveat: Controllers working sectors in the far north of Canada (such as Iqaluit, NU (CYFB)) are required to give the latest METAR to all landing aircraft before or shortly after the clearance to descent; snowfall may cause changes to aircraft flight plans.
• This can lead to a slight increase in workload, though missed approaches/holding for these airports will be done with low-level controllers.

Two indirect impacts during major storms or unexpected heavy snowfall are:

• Holding aircraft in our sector when lower levels are saturated while ground crews clear the runway.
• Providing more spacing between airplanes for the same reason.
• These impacts are more ad-hoc, which can complicate planning and staffing adequately for days like this.

Three main threats with snow:

• Take-off performance
• De-icing operations
• Barrel icing

Pilots will start making their plan of action once in cruise.

• With the TAF, METAR and current RSC, a best guess for expected conditions on arrival will be made.
• The landing performance is assessed in the 15-30 minutes prior to descent.
• Similar to pre-flight with takeoff performance, it’s common practice to ask for a more conservative landing performance with worsening conditions. If the destination conditions are marginal, most pilots will reassess the alternate to make sure that it is still a solid and sure choice.

Pilots use visibility to assess snowfall intensity. We can look at the radar to check if a shower is approaching, but the visibility is how we judge snowfall intensity. With that in mind, let’s talk about threats to the operation during a snowstorm and how we mitigate those threats.

In a Forecast (a TAF)

Use of Prob/Tempo regarding snow/ceiling/vis changes how much fuel is loaded for additional attempts to land.

Ceiling and visibilities in snow tend to be better than reported while on approach.

• Example: 200 ½ in fog generally means that 100% of the time you will only see the lights at mins. 200 ½ in snow generally lets you see the lights at 300 ¾ (day) and 400 1 (night) – This is a big generalization but there are stark differences between different weather phenomena and what pilots see.

The temperature of the runway is key to determining the runway condition which is rarely available to flight crew.

• Example: 2 degrees and wet snow in October (ground warm) runway will stay wet. 2 degrees and wet snow in March (ground frozen) and the runway is a sheet of ice.

Takeoff performance

• The takeoff performance calculation will be accomplished at the gate during the pre-flight preparation. We will use the RSC report available at that moment. We are now using information that is based on Takeoff and Landing Performance Assessment (TALPA) methods to better qualify braking performance (see RCAM table image). For snow covered runways, this method reduces takeoff calculation to two scenarios:
• Runways that have trace amounts of contaminants (little to no impact).
• Runways that have contaminants with depth can be moderately to highly impactful.
• By referencing the latest RSC reports along with a flight crew's observations and pilot reports, a take off performance calculation will be completed. Pilots will also actively listen to communications on frequency for braking action reports from other aircraft on the runway.

De-Icing Operations

De-icing an aircraft is done in two steps:

• Using Type I de-icing fluid to clean the critical surfaces, and sometimes the whole body of the aircraft.
• Using Type IV anti-icing fluid to protect the critical surfaces of the aircraft from de-ice to takeoff roll. There is a time-limit to this protection which is called HOT.

Rate of snow is considered to use the snowfall intensity chart correctly for de-icing operations. The Day/Night changes are very important to recognize as at night visibility appears to be improved and you can underestimate the snowfall rate if not careful.

At most of our major airports, we now have a “Liquid Water Equivalent System” (LWES). It is an automated weather measurement system that determines the Liquid Water Equivalent (LWE) rate in conditions of frozen or freezing precipitation.

• We request a transaction through the aircraft’s ACARS which will interrogate the LWES to calculate a single HOT. This HOT will start at the beginning of the Type IV application.
• If we see that the conditions are worsening as we taxi from the de-icing bay to the runway, it could be a good idea to request a new HOT and if the time is less, a new HOT will take precedence.
• The LWES system performs an actual analysis of water content is completely independent of visibility- therefore a heavy snowfall condition is determined with more accuracy. This helps companies safely assess required HOT without unnecessarily penalizing crews and passengers with restricted operations.

If we are at an airport where there are no LWES or the LWES is U/S, we must use the METAR to determine the HOT, which can be more restrictive.

• One characteristic of using the METAR is the heavy snow condition which may prevent some aircraft types from taking off or requires additional precautions to be done before taking off.  This heavy snow condition will be determined with the METAR visibility (see visibility table).
• Under this heavy snow condition, some aircrafts cannot depart and will have to go for de-icing again after the heavy snow stops. Some aircrafts will be authorized to takeoff in heavy snow with a smaller time-limit (which is not a holdover time in this case), one pilot will need to conduct a visual inspection of the wing, which could mean some delays close to the hold short line.

Side note to de-icing or anti-icing fluid can infiltrate in the bleed air source of the aircraft might lead to a fume or smoke event in the aircraft. It has happened after takeoff, during the taxi-in as well. We don’t have a choice to take this threat seriously, if it happens, it could trigger an emergency.

• Pilots have a de-icing checklist with mitigations to minimize risk.

Barrel Icing

The main reason why we conduct an engine runup before takeoff. The A319/A320/A321 are more prone to this type of icing.

Prolonged taxiing in significant snow events can lower the heat efficiency of the engine anti-ice system. The engine anti-ice system is meant to be evaporative. Due to that reduced efficiency, the water doesn’t evaporate, but instead melts, moves aft into the unprotected nacelle liner, and eventually refreezes.

Over time, an ice plate forms in the engine nacelle inlet. The ice plate can detach and be ingested in the core of the engine. Also, the fan blades flex forward with takeoff thrust, and by moving forward, it can start to scrape that ice plate, damaging the fan blade tips.

•  Consequences of both possibilities would be engine damage or vibration, which might require a shutdown or might fail the engine, in flight or during the takeoff.

Overall

• For assessing how severely we will be affected by all the listed departure threats above, pilots use the METAR, the TAF, and the radar to guess if intensity will increase or decrease within the next hour or two from our departure, using mostly the visibility.
• If we expect FZRA to start soon, it will be a factor to consider.
• As far as planning goes, from a pilot’s perspective, we will discuss with our dispatch to board adequate fuel for a lengthy outbound taxi. Once we leave the gate, we will slowly make our way to de-icing and takeoff, and hopefully we have boarded enough fuel to not have to go back to the gate because we burnt too much before takeoff.
• Thinking about temperature of the ground (runway), air temp (water content in the snow which is driven by temperature). Example: -2C snow is heavy and sticky turning to ice quickly, -20C Snow is dry and blows away/doesn’t stick. How that will impact the type of contamination likely to form on the runway with lots of traffic packing that snow in/on to the runway between snow clearing events and the effectiveness of those snow clearing events.

Looking at streamers on RADAR off the great lakes to determine the best time to go to the de-ice bay.

• At the end of a streamer, get de-iced and depart during the quiet period. This can be difficult to do at a busy airport, particularly if there are ATC departure times that must be respected.

During snowfall, icing tends to not be a factor for jets. Turbo Props will get stuck with a little bit of leading edge impact ice that may not be removed via de-ice boots generally.

• Abnormal situations yielding moderate to severe icing can arise in cases of heavy snowfall. This can occur if there is rigorous convection (TCUs) and has led to urgent PIREPs on medium/heavy aircraft. Knowledge here is key with the issuance of SIGMETs in conditions that are optimal for heavy snowfall in prime icing conditions.

Snow combined with a crosswind/quartering headwind on final approach and landing can cause some pretty good illusions just prior to and during touchdown. Pilots will often choose to leave the landing lights off during landings of this type to see the runway rather than the snow, which may be disorienting - this is pilot preference but similar to a driver avoiding using high beams in heavy snowfall while on the road.

Rate of snow is considered to use the snowfall intensity chart correctly for de-icing operations. The Day/Night changes are very important to recognize as at night visibility appears to be improved and you can underestimate the snowfall rate if not careful.

Caution and extra time (fuel) is loaded to account for intermittent delays due to snow clearing of the runway, traffic backup possible diversions due to runway condition.

Regional Airports

• If airports have snow clearing capabilities, they are usually able to conduct continuous sweeps as the demand is far less than at major airports like Toronto or Montreal.
• Regional airports don’t have LWES system. Thus, pilots must use METAR visibility to assess the intensity of the snowfall (reference the visibility table).
• There is a difference for the required visibility in Restricted Visibility Operations (RVOP) at uncontrolled airport. It is possible to be legal to conduct the approach but being restricted from taking off.

For departure at uncontrolled airports, the controlling visibility is the lowest of the ground visibility (METAR), any reported RVR, or pilot visibility. We are regulated by all the available visibilities. Here’s two examples where we could land but can’t takeoff unless there is an improvement:

• RVR could be above limit for arrival, but the METAR visibility will be lower.
• If the fog is very localized, the METAR visibility could be above limit for an approach to a runway, but a fog bank at one end of an inactive runway will prevent any departure because that RVR is below limits.

At major airports, runways are typically long enough that the landing distance will not be an issue during the landing performance calculation.

Crosswinds

One likely main issue is a strong crosswind condition, when observed.

• The crosswind limitation will be more limited with a snow-covered runway.
• Crosswinds tend to create drifting snow over the runway and at runway exits.
• This further deteriorates the RSC; a deterioration that is quite often reported by pilots thru braking action that may lead to impromptu runway closure for clearing.

The greatest threat with a crosswind on a slippery runway is losing the directional control of the aircraft.

• The crosswind will weathercock the aircraft. If the tires start to get a grip while the aircraft is drifting, the aircraft would head towards the side of the runway.
• Also, thrust reversers are commonly used when landing on contaminated runways. If the aircraft starts to weathercock, thrust reversers will tend to push the aircraft off the runway as well.
• If an aircraft starts to drift, pilots must reduce the reverse thrust. This reduction sacrifices the deceleration of the aircraft in order to maintain directional control and results in a longer ROT.

Holding

Typically jets can exit airborne icing situation by climbing, descending, or accelerating. This includes flying through supercooled large water droplets and short-lived flight through freezing precipitation.

• Significant and rapid accumulation can occur in stronger convection such as TCus when conditions are prime for rapid ice crystal growth and aggregation, leading to urgent PIREPS. This can pose a hazard on take-off or landing as aircraft surfaces and resultant movements are impacted while the aircraft is close to the ground and flying at relatively low speeds.
• The most hazardous situation for jets would be to hold in significant icing conditions. If pilots descend to an altitude for a hold and notice that the aircraft is starting to pick up icing quite rapidly, they will need to change the altitude promptly.

Icing strongly depends on atmospheric conditions. On the prairies in winter anecdotally this hasn’t been an issue.

If you are near a large body of water and the water hasn’t frozen over yet, falling snow can be a hint of how severe the icing in the tops of the low-level clouds will be.

• Example: over the Cabot Straight in November/December, with stratus toping at 3-4000’ with snow underneath, pilots can expect severe icing in the top 500’ of the cloud. Towards the bottom of the cloud where the snow has fully formed, it’s likely not as much of a problem. The same can happen over the Great Lakes. It is all about moisture content and Outdoor Air Temperature (OAT) for the altitude being flown.

METAR and TAF reports can be hard to interpret and make it challenging for VFR pilots to predict how the snow will affect them. Interpretive weather briefings from FIC specialists can add clarity to flight planning through a snow event.

A forecast of light snow will often include a visibility greater than VFR, but still lower than the comfort level of many GA pilots. Snowflake size, amount, volume and frequency can change rapidly and can quickly affect the visibility in flight.

• For this reason, GA pilots are recommended to build in a safety margin of visibility when flying in conditions where light snow is predicted and additionally, to look at the bigger picture of weather (GFA, radar, etc) before making a decision.
• For example, if flying in controlled airspace, with a required visibility of 3SM, it would be wise for the pilot to require a minimum of 6SM in the forecast before departing for the flight. If this is the case on the TAF, it could be decided that the flight will be safe, however the GFA may show something different and must be taken into account.

At major airports, snow removal is efficient, but priority is given to commercial and IFR aircraft, so significant delays are to be expected for VFR aircraft.

Conditions of heavy snow will prevent VFR flights, so this is only an issue during light snow that requires continual clearing or shortly after a heavy storm has occurred – VFR GA anticipate long delays immediately following storm.

• This is especially apparent when using a single runway. As with commercial operators, delays occur and these trickle down to VFR/GA who have a lower priority. A smart GA pilot will plan a flight around these delays.

Snow at regional airports as well as uncontrolled aerodromes can have varying degrees of ground operations impact. In all cases, delays are to be expected and a certain element of risk is present. Snow creates many challenges for GA pilots, especially at less busy airports and they must consider all of the variables and scenarios presented when making a decision on how to operate their flight.

Moderate to heavy snowfall have the greatest impacts on the following:

De-icing

• For small GA aircraft, de-icing capabilities will vary.
• Application of anti-icing solutions or technology is not common for VFR GA operators and pilots because they typically will not be departing in conditions that can cause icing.
• Most operators will manually remove snow from the surfaces of their aircraft. Some will bring an aircraft inside for the snow to melt off.
• Some will apply a simple de-icing solution to the surfaces that removes snow and ice and evaporates before freezing.
• While the methods all vary, there is undoubtedly an extra delay created.
• Some operators will mitigate this by covering some surfaces of the aircraft, but this is not a perfect solution.
• Commercial de-icing is not cost-effective or even necessary for most GA operators.

Contaminated runway and taxiways

Many small GA aircraft can operate safely with some snow on the taxiway and runway surfaces. However it is often not recommended because there are many factors to take into account.

With light snow on surfaces, wind will create blowing snow which can greatly reduce visibility during taxi, takeoff and landing. Snow can also blow sideways across surfaces, creating an illusion to pilots that the ground is moving, even while the aircraft is stationary.

The depth of snow on the ground is an important factor.

• If the height of snow is less than half the diameter (height) of the wheel, safe operation is possible, however, the surface condition beneath the snow must also be taken into consideration, which can be difficult in some cases.
• A wet snow is often considered to be thicker and will therefore create more resistance and could increase the difficulty and decrease the safety margins when operating with snow on the ground.

Snow clearing operations

Snow removal operations vary greatly at regional airports and uncontrolled aerodromes.

• Some airports plainly indicate that they do not offer winter maintenance.
• Some do offer it even when indicated otherwise, but this is very much at the operators discretion.
• Some airports do have regular winter maintenance and services, but their efficiency varies and must be planned ahead.

When planning a flight, or in flight, pilots can’t rely on a runway to be cleared for them.

• If a pilot needs to divert to a different destination, they must know in advance where they will be able to land with a cleared runway surface. To that point, the quality of snow removal also varies greatly and is related to the previous explanation of why some pilots may elect to take off or land with a contaminated surface.

Some snow removal operations will just plow the current snow and leave a layer of compact snow on the runway.

• In some conditions or freezing and thawing cycles, this could result in the surface having combinations of snow or ice.

Some operators only remove snow from certain taxiways or runways, leaving the others untouched. Some will clear the runway during light snow while others will wait until no more snow falls and none is in the forecast.

Specific to low wing GA airplanes, snow removal operations at regional airports often leave snow banks on the edges of runways and taxiways, creating an extra hazard for these aircraft. In extreme cases, this can even affect high wing GA aircraft.

Snow presents an icing risk in flight, however visibility is the main factor to consider for VFR GA pilots.

The level of snow required to create a meaningful icing risk usually coincides with the visibility being below VFR conditions making the risk for moderate to severe icing relatively low as pilots shouldn’t be flying in those conditions in the first place.

However, when light snow is present with a high moisture content, in temperatures close to freezing (+5 to -5 degrees), there is a risk of light icing.

• Icing caused by light snow will not only affect the critical surfaces of the airplane, but also the windshield and will reduce forward visibility.

Pilots are cautioned against the risks associated with flying through snow in these conditions. All snow comes with a risk of reduced visibility. A pilot’s experience must back up the decision to fly with confidence in a potential visibility of 3-6SM. Pilots must be prepared for conditions to be worse than forecasted and if outside of their comfort zone, or legal limits, they must have a backup plan and execute it promptly.