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Freezing Rain

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Legend

METAR Code

FZRA

Weather Symbol

HAZARDS

  • Can cause severe clear in-flight icing from the surface to the base of the above freezing level. Moderate mixed icing will generally also exist above the above freezing level for a few thousand feet.
  • Ice accretion at the surface requires de-icing prior to departures.

Example of in-flight icing caused by freezing rain.

About

Definition

Rain that falls in liquid form but freezes upon contact with the ground or other surfaces. It occurs when a near or above freezing level exists in the atmosphere allowing ice at altitude to melt to rain and then freeze on contact with the surface. These near and above freezing layers generally exist within the vicinity of warm fronts and trowals, though freezing rain can also occur locally in valleys where cold air is channeled.

Associated terms coming soon:

Cold air damming, inversion, low-pressure system, and wind channeling are all terms associated with freezing rain that will be coming soon to the Aviation Meteorology Reference.

Associated Terms

5

Freezing Rain

Visualization

Freezing rain poses a forecasting challenge in diagnosing the relative thicknesses of the warm, melting layer, and the cold, re-freezing layer. If the warm layer is thick, and the cold layer shallow, freezing rain is almost guaranteed. However, if both layers are thick, freezing rain, ice pellets, or a combination of the two, are possible. In cases of a shallow warm layer, only partial melting of the snow would lead to ice pellets possibly mixed with unmelted snow. This challenge in diagnosing the relative thickness of the above-and-below freezing layers is why you often see TAFs whose main or TEMPO condition is PL, with FZRA in a PROB. In this scenario, the forecaster has assessed that the relative depths of the layers are more conducive to ice pellets, but if the warm layer is slightly thicker, or the cold layer shallower, precipitation might fall as FZRA. Tools such as model soundings, radiosondes, and radar imagery can help forecasters determine the relative depths of these two essential layers. 

Freezing rain is generally well predicted by numerical models, except in areas where local effects cause models to inaccurately predict surface temperatures. The most notable exception is in valleys, where cold air remains trapped in the valley even after the warm front has passed. In this case, forecasters will use their knowledge of local effects and climatological data to predict the end of a freezing rain event. 

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MAIN CONCERNS

Tends to be more severe than freezing drizzle but same general impacts. Loss of lift due to ice accretion on critical surfaces, higher runway occupancy time, reduced braking action capability and potentially slippery surfaces due to accumulation on the ground.

Service Providers

Freezing rain events tend to be an unusual weather event at West Coast airports (like CYVR), but are more common at CYYZ and CYUL. 

  • Weather forecasts are critical for ensuring adequate staff are present for freezing rain events so a mix of public and aviation weather forecasts are used to prepare for events. Some airports secure 3rd party (WSI (CYVR/CYYZ) or WPRED(CYUL)) weather forecasting services.
  • Freezing rain events generally require increased levels of staffing to coordinate and conduct operations. Additional staffing may be required to clear runways, taxiways and apron areas, as well as to operate central de-ice facilities and large airports tend to activate operations centers to coordinate all of these operations. Snow and ice clearing crews are generally part of the general staffing but for large events, additional crews may be required on a call out basis. With the increase in staffing required, taxiways, gates and the runways may be closed for brief or extended periods of times. Equipment checks will be completed as well as ensuring there is enough stock of supplies (chemicals, glycol, sand) available.
  • Lead time to coordinate additional staffing is critical.
  • Runway condition reports become critical and require frequent updates.
  • Runway anti-icing treatments tend to be required and yield additional costs.
  • The band of freezing precipitation can sometimes be narrow and a few kilometers can determine whether or not it will be snow, freezing rain, or straight rain. If this is the case, we monitor other aerodrome METARs where the system is coming from to plan on how to deal with it. Normally, pre-treating the runways and other surfaces is the best way to prevent or slow ice formation; however, if it comes down as rain or snow first, putting chemical down is a waste as it will either wash or be swept away. Freezing rain falling on snow is ideal as it forms a crust on the snow that is easier to sweep.

Outside of the impact to aircraft/aviation, ice accretion will also have significant impact to the airport in other ways:

  • Ground operations will slow down due to vehicles slipping. Tow bars can be easily broken on pushback or towing an aircraft.
  • There is a higher risk of slips and falls as well as motor vehicle collisions. Ice formation on trees can cause them to break and impede vehicular traffic.
  • Employees may find it difficult to get to work; there is historically a much higher number of sick calls during significant weather events.
  • Municipal electrical transformers start blowing causing blackouts.

Other impacts:

  • If there is an extended period of freezing rain overnight, airlines would be requested to park as many aircraft in hangars as possible to reduce the amount and length of deicing required.
  • At some large airports, D-TMI may be implemented due to the reduction of throughput through the deicing facility as aircraft will take longer to deice.
  • HOT may be reduced, so reducing the number of departing flights will prevent congestion and aircraft needing to return to be deiced, refuel, or some flights may be cancelled altogether. To prevent gridlock, the AAR must not be more than the D-TMI rate.
  • There may be some airlines whose policy is not to take off during various degrees of active freezing precipitation. This may require either holding on the airfield or at the gate or cancelling the flight outright.
  • There will be an increased number of diversions away from the airport, and recovery of the flights may cause issues if not coordinated properly to ensure there are gates available at the time they are looking to arrive. For example: CYYZ is also an alternate for many airlines enroute to other large airports, especially the New York City area, so freezing rain events at those locations will see an increase in diversion of wide-body aircraft to CYYZ. If we are already experiencing irregular operations and the risk of incoming diversions is high, we would issue a NOTAM effectively only allowing non-scheduled flights to CYYZ if it was an emergency, or with prior permission. CYUL and Ottawa (CYOW) are also diversion airports for CYYZ. Coordination is often needed as alternate airports can only take so many diversions among their own arrivals and require a crew on the ground at the arrival airport.
  • Extended or successive freezing rain events will deplete deicing fluids quickly, so there may be plans to have tankers of fluids on site or nearby to be able to quickly replenish stock.
  • Accurate forecasting will help in determining which route to take.
  • There is a higher risk of aircraft becoming stuck on the ramp or the airfield due to lack of traction. Depending on accumulation or accretion rates, it may be safer and effective to identify one or two runways as active along with a dedicated taxi route. This ensures the focus is on clearing those surfaces of ice or treating them, but can increase delays depending on demand.
  • Communication to the airport community and traveling public is important during extreme weather conditions. Advisories will be sent out prior to the forecast event to ensure all are prepared, and conference calls to brief the community will take place to ensure any changes to the plan or forecast are communicated. Information to the public will be disseminated through social media as well as traditional media outlets.
  • Although the responsibility is on the airlines to comply with the passenger bill of rights, the Airport Authority will also monitor this and reach out to the affected airline to assist and facilitate as much as possible, such as prioritizing the flight for the next available stand or through hardstand busing operations.

Operations Duty Managers

A good knowledge of expected icing is important. The TAF is carefully reviewed to determine intensity, time frame, accumulation anticipated, forecaster confidence level.

  • Start and end times are critical. If there is uncertainty, hearing the CMAC forecaster speak to that, provide reasoning for the uncertainty and the triggers they’re looking for, and provide a best/worst case scenario is what helps us best assess possible TMI options.
  • Forecaster notes are critical in getting additional information beyond the TAF. Likewise for the Visual TAF, especially for hourly forecast accumulations.
  • Other weather models may be reviewed to assess forecast consensus with further investigations being required with CMAC forecasters if models are not consistent and to gain a better understanding of the event focusing on the discussion points above. 

Information is gathered on what the Airport Authority plan is for treating runways that are active and ones that may be activated to keep operations flexible, time frames and arrival spikes to prepare for, staff limitations, D-TMI details.

  • Deicing capabilities are critical, including the type of fluid to be used and the number of pads available.
  • Understanding shift change timing is also important in timing treatment plans and staffing levels.

Operations Duty Managers will take all information provided in a forecast, from Airport Authorities, from the NTMU, and from the Airlines to discuss the operational plan in-depth with their tower, terminal, and en-route ATC supervisors.

  • The goal is to have every sector on-board and aware of the game-plan, to allow for discussions of concerns/constraints, and to develop mitigation strategies.

Some additional considerations taken by an Operations Duty Manager planning during a freezing rain event:

  • Assess where the arrival and departure spikes in the operations are in relation to the freezing rain time frame. Is anticipated traffic in the evening periods expected to shift around as airlines deal with delays/rearrange their schedule?
  • Can additional ATC staff be brought in for anticipated holding in sectors that are clear of icing?
  • When considering a formal TMI- what runways are favourable and what spacing can be anticipated during the event and during RWY treatment? How do hold over times for flights constrain/prioritize the airport's departures over arrivals? Due to the severity of freezing rain and the impact on flight, aircraft have a short timeframe to be airborne after they have been de-iced. ATC will prioritize departures as best as possible to prevent departures from needing to de-ice a second time while also ensuring that airborne flights are safe and able to land. This is also critical at airports without much room to maneuver aircraft. For example - if an aircraft has to return to the deicing bay in CYUL, it will have to taxi back down along the active runway, significantly impacting both arrivals and departures.
  • Do adjacent Flight Information Regions have constraints that may be ongoing that may slow traffic down and make it challenging to anticipate traffic flow?
  • When considering a TAF: TEMPO or PROB groups in a timeframe that doesn’t have a lot of traffic might drive a plan to remain tactical and reactive with with holding, APREQ, and/or GS. TEMPO or MAIN groups in a timeframe that has a lot of traffic impacting operations might drive a formal TMI such as a GDP or a GS into GDP.
  • Increased staff for enroute to aid in the ability to hold and accommodate reroute, diversions, and alt changes to avoid icing.

Operators generally have a good knowledge of expected icing conditions and are prepared and flight planned to avoid the worst areas of icing- ATC intervention is often not required.

Freezing rain is considered to be a rare event in the Canadian Prairies (ZEG FIR).

  • Freezing rain can be a very challenging weather event for operations as predicting it tends to be difficult and the impacts are significant. The NTMU relies on weather briefings to better anticipate upcoming weather in addition to the TAF to gain a better understanding of what is to come.
  • Real time monitoring of approaching weather is done through radar or calling airports (towers/FSS/FAA facilities) upstream of the weather to better gauge what impacts could be in store for airports ahead of the system. At major airports, ground operations are the main focus ensuring that arrival rates (challenged by runway conditions) and departure rates (challenged by deicing) are balanced.
  • When considering an upcoming forecast the NTMU will often evaluate a best and worst case scenario and will plan an operation somewhere in the middle, meaning they will plan the most optimum operation possible, that will allow a recovery should the worst case scenario occur which could be a complete disruption to the arrivals.
  • In a TAF a PROB30 or TEMPO won’t make much difference to a NTMU controller, both will spark questions for more detailed information and request for expert opinions. This is where gauging the best and worst case outcomes from the CMAC forecaster is critical so that the NTMU can formulate the most efficient plan while maintaining safety.
  • In addition to consultations with CMAC forecasters, detailed conversations with the airport authority takes place to determine the plan for runway clearing for the entire event up to and including the end of the event (which often involves runway changes) as well as deicing rates so that airport gridlock does not occur.
  • Ideally extra staff would be brought in for enroute sectors, so that the highest possible rate could be run and accommodate airborne holding safely if the rate at the airport drops to zero for runway cleaning.
  • Runway temperatures at a major airport will be closely monitored along with the runway foreman’s confidence in what can be done to prepare the runway before the event and what they can do after the event. There have been occasions where lack of runway preparation overnight has led to disastrous situations where the runways have been lost for hours or even days because freezing rain preparation was not completed.
  • Due to the unpredictability of freezing rain and its high impact, collaborative decision making and sharing of information and concerns is very important. Ensuring everyone is aware of the possible events and possible outcome so that there are no surprises regardless of what happens is of the utmost importance.
  • Regional airports are less of a concern because they just don’t have the volume, however diversions from these airports could lead to further issues at major airports if they are choosing to divert there.
  • Freezing rain enroute tends to be more of a concern for the airlines rather than for the NTMU unless aircraft are required to hold in these conditions which can lead to a higher likelihood of diversions.

Usually freezing rain is not isolated and happens over large areas, affecting more than one major airport in Canada or the FAA, this can lead to multiple delays as airlines get off schedule and struggle to keep the system updated meaning volume information is not very accurate.

ATC (Major Tower)

The TAF, public forecasts, watches, and warnings are all reviewed when planning and preparing for an event.

ADM personnel monitor the arrival of the freezing rain to accurately time runway treatment prior to onset. So much so that when they ask to extend the product, it has to be done right away, otherwise it won't work.

Additional ATC staff will be called in as workload during freezing rain events can be complex.

  • Longer communications with airline crews, and a heightened risk of additional unforeseen requests (runups, HOT misses and need to return to deicing bay, stuck aircraft on a taxiway or runway needing a tow, etc.).
  • Runway Occupancy Time fluctuates significantly as it is directly tied to braking action. In freezing rain events aircraft will be more likely to spend more time on the runway, complete runups in position at departure, which can increase communications with Terminal ATC when coordinating arrivals and departures in high demand periods.
  • Additional positions will be opened in the tower so there can be dedicated communications with Airport Authority crews responsible for runway treatment.
  • Long events or events leading up to TMI may also spread demand later into the night, meaning more aircraft will be taking off or landing than normal, which may require more staff.

Extensive communications are required throughout a freezing rain event with the Airport Authority, Terminal ATC, and NAV CANADA’s Operations Duty Manager, and NTMU.

  • These communications include planned runway treatments, configuration changes, operational updates, and tactical adjustments.

During a severe precipitation episode, the delays at the deicing center are extremely long.

ATC (Regional Tower)

Airport authority will be working hard to ensure the runway friction index is suitable for the airlines. Regional tower ATC facilitates passing on that information in a timely manner.

  • Vehicles will likely be on the runway(s) throughout the day to maintain RSCs.
  • Additional staffing is not likely - poor conditions lead to little or no VFR aircraft which decreases the workload.
  • If the braking action is NIL, an aircraft will likely fly a missed approach and ask for a hold until RWY treatment/clearing can take place and a new RSC issued. Tower ATC contact airport maintenance for RWY treatment/clearing.
  • Aircraft holding will do so with the enroute IFR controller until a new RSC is issued and another attempt at landing can be made.
  • All attempts will be made to keep the RWY(s) active and the airport open, but extreme conditions can sometimes lead to closures depending on the airport, the available equipment, and the duration of the event.

Freezing rain is definitely a greater threat to aviation safety than snow, as it adheres to all surfaces on an aircraft in flight, adding weight while degrading aerodynamic performance. Additionally, it is significantly more difficult to operate on an ice-covered manoeuvring area than one that only has snow on it, while ice clearing operations are slow and expensive due to more chemicals being needed to melt the ice. The best way for Airport Maintenance Personnel to deal with freezing rain events is to get ahead of the game and get chemicals down to stop the ice from sticking in the first place. As freezing rain may follow a period of rain, timing the chemical application so it’s not washed away before the freezing rain starts is crucial.

FSS, whether operating at an airport or in a FIC, pay very close attention to any potential freezing rain event, due to the threat to safety and the resulting degradation of operational efficiency – longer Runway Occupancy Times, reduced speed on taxiways and aprons, and impaired efficiency of ramp operations translate directly to delays for all airport customers. 

FIC

Right at the start of any Pilot Briefing, any serious threat to safety will be mentioned first – as this information may cause the pilot to delay or cancel the flight due to an unacceptable level of risk, and they may even pause the briefing to advise Dispatch or the Customer directly. Freezing rain is definitely in that category of threat.

The Briefing Specialist will communicate observed and/or forecast freezing rain as it relates to the pilot’s flight plan including start times, end times, and extent of spatial coverage and emphasize the level of risk inherent in conducting Flight Operations under such hazardous conditions. A critical aspect of a specialist’s role is to communicate such hazardous conditions, with weather briefings meant to strengthen a pilot’s situational awareness and decision-making by providing context, local knowledge, and the latest weather information. Safety remains at the core of every briefing we provide.

AAS

Advisory specialists monitor possible freezing rain conditions primarily with the ice accretion indicator, but also monitoring precipitation rates and temperature. We must account for de-icing and holdover times when working with IFR controllers for arrival/departure sequencing and keeping maintenance vehicles on the manoeuvring area for as long as possible before a departure or arrival.

Freezing rain affects terminal ATC similar to snow, but far worse, especially on the arrivals side.

  • Alternating runways in snow is normal operations but in freezing rain is harder to do efficiently.
  • The team on the ground will chemically treat the runway, but if the freezing rain is falling rapidly, it really doesn’t take long until the runway is 100% ice again.
  • Braking action reports deteriorate quickly, and it doesn’t take long to have several “poor braking” reports.
  • As soon as a “nil” report is received, ATC workload goes up considerably. All aircraft on the frequency will want to either wait until the braking conditions improve (hold), or divert to their alternate. In both cases, ATC coordinate with the sectors around them to let them know, because at that point letting other aircraft into the terminal airspace to hold is difficult if not impossible (unless some specific pilots want to try the landing). Terminal ATC also have to ask every aircraft on frequency of their intentions, either to try the approach now (unlikely), wait for the conditions to improve, or divert to their alternate. Aircraft that decide to hold will advise of how long they can wait based on their remaining fuel. Terminal ATC take note of the time and call them back once it’s reached to advise if conditions have improved or not, in which case they’d likely choose to divert.
  • During the event most coordination is with the tower and getting information from the ground team on surface observations, RSCs, and treatment timing.
  • As soon as a runway is treated, a new RSC is issued and the first aircraft that choose(s) to land provide(s) a braking action report. Subsequent aircraft will then decide if they want to attempt to land as well, which in some cases can mean a lot of landings in short periods of time - all with aircraft running low on fuel. This takes terminal ATC from a high workload of “giving lots of information to pilots” to a high workload of “vectoring and controlling”. We’ll land as many aircraft as we can while the conditions remain good, but if the freezing rain is still falling, it usually won’t take long before we start getting poor or nil braking action reports, and then the whole cycle repeats itself.

Icing on final approach

When pilots get severe icing, they want to stay in it for as little time as possible.

  • In freezing rain, severe icing is in the “final approach” altitudes, so in this case for terminal this is anything below 3000 feet, there isn’t much that can be done.
  • If it’s really just at the “top of the approach”, for example 2500 feet and above, ATC can break noise abatement procedures and descend aircraft as low as possible as per MVAs, which vary greatly depending on where you are.
  • The aircraft will often keep a good rate of descent until they reach the lowest altitude we can give them, in this case.
  • However if the icing is at 1000 feet, there is nothing ATC can do, the aircraft will have to slowly descend on the glideslope and “slowly” pass through the icing.
  • Loss of ability to hold or maneuver at different altitudes due to severe icing can negatively impact aircraft throughput every hour, with suboptimal conditions meaning fewer aircraft can be supported over the same period of time.
  • Freezing rain impacts en-route ATC significantly.
  • If the freezing rain is manageable, runways can be treated with product, and delays can be held to a minimum, especially in large airports with multiple runways that can be treated one at a time.
  • If the freezing rain falls too rapidly, the airport can be forced to close for extended periods of time, causing long delays and possible diversions for incoming aircraft. If the major airport has a diminished capacity or is closed due to the weather, en-route ATC will be forced to give delays (usually in holds) to incoming aircraft. If the delays are too significant, aircraft will have to be re-routed to alternate destinations. This greatly increases the intensity of the work, as each aircraft gives and receives lots of information, creating frequency congestion.
  • Smaller airports can close for long periods of time (sometimes multiple days) if a lot of freezing rain falls and they do not have the equipment to deal with it. ATC will provide the information to pilots who departed for the destination before the weather occurred and will reroute them to their alternate destination (usually a major airport that has properly treated the runway).

Freezing rain will only impact high level ATC indirectly.

The TAF is not used by high-level ATC for planning local flights heading to regional airports.

In high-level sectors such as the North High in Montreal's FIR, the impact of freezing rain for the high level involves a few more steps in the analysis of ATC tasks.

  • ATC controls regions over the far north, such as Iqaluit (CYFB), with the regulations Manual of Air Traffic Services stating that the METAR be given to all aircraft landing, before or shortly after the clearance to descent this precipitation can cause changes to the aircraft flight plan.
  • Pilots get more curious about the METARs in effect when the conditions are poor.
  • This could turn into a missed approach with low level ATC/site and return to an alternate airport or request a holding pattern for as long as possible if the crew feel they have time for conditions to improve and the track to be cleaned. For the high level, this leads above all to a slight increase in the level of the tasks, but since the aircraft will wait more often at low altitude, this is a rarer situation.

Users

Freezing rain events are some of the most challenging weather conditions an airline will operate in and a heightened level of safety consciousness is required:

  • Freezing rain can degrade airport movement areas quickly, to the point that operations must be suspended or are slowed to an impractical level. Prolonged periods of freezing rain tend to lead to significant delays and/or major cancellations.
  • Deice HOT is reduced (as compared to snow for example) and Type 3 or 4 anti-ice fluid is required. Freezing rain mixed with other precipitation can further reduce the HOT.
  • Deice fluids are an additional cost.
  • Deice fluids reduce take off performance and may require reductions in take off weights leading to less passengers/revenue being carried.
  • Flights operating in/out of an airport carry additional fuel (increased cost) for delays. Freezing rain events are often widespread over a region and safe alternates tend to be further distances away from their destination. These increased fuel carriages often lead to a point where passengers and their bags are not able to be carried.
  • Deicing at a major airport tends to have more resources/services while at regional airports, resources can be reduced (only 1 deice truck instead of multiple, limited deice fluid types).
  • Regional airports have less aircraft movements and may tend to treat airports with chemicals less often as this can be a cost consideration.
  • Keeping active runways in operational condition is difficult in freezing rain conditions. Regular runway condition reports are important as conditions change quickly but are sometimes difficult to get as airport operations can become overloaded.
  • Runway braking action reports are therefore critical- often control towers and FSS solicit braking action reports and relay to other crews.
  • Freezing rain in crosswind conditions requires good runway conditions.
  • Freezing rain conditions almost always lead to delays and cancellations so a good understanding of timing, severity and confidence is critical to planning an operational day. In order to do this, a 24 hour lead time of the weather event is important.
  • TAFs with PROBS rather than TEMPOS of freezing rain tend to be interpreted as showing a lower confidence of a weather event occurring and may lead to increased scrutiny of a forecast.
  • Adjusting an airline schedule is best done prior to an event so adjustments can be made as seamlessly as possible.
  • In all cases, the consequences of freezing rain (particularly at a major airport) are significant. A consensus of weather forecasts is sought prior to any schedule adjustments are made from independent sources whether that is by comparing weather models (not just Canadian) to TAFs, the public weather forecast along with using a dispatcher’s intuition.
  • Intuition, experience levels and familiarity with weather models and decision making can vary significantly amongst dispatchers/operators.
  • Operations in freezing rain leads to SIGMETS for severe icing further constraining operations.
  • SIGMETS for severe icing are often issued based solely on the presence of freezing rain being reported rather than actual reports (that can contradict reports on the ground). Depending on the airline, there is the possibility that operations will be restricted or forbidden even in a forecast SIGMET. Other companies may only restrict operations in areas of reported severe turbulence or icing, with specific restrictions placed on the required distance from a given PIREP. This could allow for an aircraft to transit through a SIGMET, though dispatchers first prioritize confirming the safety of transiting flights across all phases in consultations with the crew.
  • Severe icing associated with freezing rain tends to not be a concern in cruise. During descent however, delays can be encountered. Holding at mid/lower levels can be hazardous and are avoided.

Weather products used:

  • TAFs for major airports are >12 hrs in duration and freezing rain can be identified ahead of time. Forecaster notes for major airports are very useful giving the background to weather events, explanations and confidence levels.
  • TAFs for regional airports are of shorter duration and are not useful for strategic planning. Public weather forecasts are used but adverse weather is generally only identified if a special weather statement or warning has been activated.
  • Weather models are used by some dispatchers but familiarity and use of this is widespread leading to wide ranges in use/expertise.
  • CMAC forecasters are often consulted to assess forecast confidence, variability, and trend.
  • Graphical Forecast Areas (GFAs) are consulted along with Aviation Weather Centre (AWC) icing forecast chartsOpen a new window for the enroute portion of flying.

Freezing Rain has a significant impact on flight operations. The impact on pilots is similar at regional airports to major airports. For major airports:

  • Gate availability
  • Taxi / de-ice delays
  • Guest connections / interruptions
  • Cancellations

Freezing rain is associated with severe icing conditions. Aircraft are not certified for flight in severe icing and severe icing conditions can overwhelm the aircraft de-icing and anti-icing systems. Ice can form on the aircraft increasing the aircraft weight and modifying the shape of the aircraft’s aerodynamics. Ice can build on the aircraft propellers and jet engine fan blades leading to severe vibration. Pilots will not knowingly enter severe icing conditions and if severe icing is encountered, procedure is to exit the conditions as quickly as possible.

  • When the possibility of freezing rain exists at an airport increased fuel carriage is generally planned as extended holding and/or the increased possibility of diversions to alternate airports.
  • PIREPS from preceding aircraft are carefully monitored to determine the extent of icing at an airport.
  • Forward visibility can be impaired if the rate of accretion is more than the de-ice system can handle.
  • Public forecasts are monitored for possible freezing rain as well as TAFS and METARs. The degree (light, moderate, heavy) and associated severity of icing forecasts determines whether it is possible to operate in freezing rain. PIREPS, RSCs, ground temperatures and the weather trend are also important to watch.

Ground Operations

  • Runway and Taxiway Conditions. Freezing rain can lead to runway conditions that are very slippery which may or may not allow for continued flight operations. Crosswind limitations can be exceeded as well as insufficient runway lengths for both takeoff and landing due to the low friction values on the runway associated with freezing rain. Airport operations slow down as aircraft must come almost to a stop prior to exiting the runway. Runway exits and taxiway conditions are often much worse than the runway condition.
  • Aircraft de-icing - De-icing and anti-ice fluids are often unable to keep up with freezing rain conditions which results in a suspension of departures until conditions improve. Propellers become coated in ice requiring the propellers to be de-iced at the departure gate prior to taxiing to the de-ice facilities.
  • Taxiways and Aprons can become covered in ice, becoming so slippery it is dangerous to taxi the aircraft. Dash 8 aircraft have been known to lurch forward when feathering the propellers which can be dangerous for ground crew and pose a risk if colliding with ground support equipment.

If freezing rain is present or predicted on any weather products, GA (General Aviation) Visual Flight Rules flights will not occur. Some small and medium GA aircraft are equipped for anti-icing, but these systems are commonly not approved for flight into known icing conditions. They typically exist as a back up if unpredicted icing occurs in flight.

  • Seeing a TEMPO for a properly cautious pilot would mean a canceled flight, a PROB30 in the TAF might also be a cancellation but may not be enough information to make a good decision.
  • Decision making for GA pilots is often based on the GFA information because it gives a broader overview of what to expect. Consultation with FIC specialists provides detail specific to the intended flight path and associated forecast conditions. Special consideration should be made on a relatively warmer day with the presence of rain, because temperatures aloft will be cooler and so freezing precipitation may occur, that was not present at lower altitudes.

For GA VFR pilots, if icing is encountered in freezing rain, their best bet is to climb out of it and into warmer temperatures. However, should the accumulation on the critical surfaces make it difficult to achieve the performance necessary to climb, the next best option is to immediately reverse course to return to non-icing conditions. Once out of icing conditions it would be advisable to descend to warmer temperatures, if possible, to attempt to melt any accumulated ice. The critical notion here for a GA pilot is their need to be spatially aware of where they are in reference to the occurring freezing rain and associated weather systems. This is because there is a chance, with the temperature inversion in the area, that temperatures may actually be colder below them! It is in cases like this where proper flight planning and analysis of weather maps can make a difference in the safe execution of a GA flight.

For GA pilots operating IFR, there are some systems approved for flight in known icing conditions, especially in multi-engine or turbine powered GA aircraft, but it is not always recommended to plan a flight into known icing because the capability of these systems will vary depending on the severity of the icing.

Anything beyond light icing can surpass the limits of smaller aircraft anti-icing systems, so pilots should use extreme caution if they choose to operate in these conditions, keeping in mind that a known presence of icing can quickly change severity.