Cold Temperature Operations

Airport Criteria:

• The FAA performs a CTA risk analysis on airports that have at least one runway of 2500 ft.
  • Pilots operating into an airport with a runway length less than 2500 ft may make a cold temperature altitude correction in cold temperature conditions, if desired.
    • Comply with operating and reporting procedures for CTAs.

ATC Reporting Requirements:

• Pilots must advise ATC of the corrected altitude when applying an altitude correction on any approach segment, except the final segment.

Methods to Apply Correction

• The FAA recommends operators/pilots use either the All Segments Method or the Individual Segments Method when making corrections at CTAs.

Applying Cold Temperature Altitude Corrections on an Approach:

• 

• Pilots must correct all 14 CFR Part 97 IAPs at an airport.
• Pilots determine corrections using the all-segments method and the individual-segments method.

• All Segments Method:

  • Pilots may correct all segment altitudes from the IAF altitude to the MA final holding altitude.
  • Pilots only need to use the published "snowflake" icon/CTA temperature limit on the approach chart for making corrections.
  • When the aircraft is not using a compensating system, manual corrections are necessary.
  • The ICAO Cold Temperature Error Table is used to calculate the correction needed for the approach segment(s). [Figure 16]
  • Supposing the RNAV (GPS) Y RWY 12 into Missoula, Montana: [Figure 15]

  • Manual Corrections Outside the FAF:

    • Cold temperature restricted airport temperature limit: -12°C.
    • Final Approach Fix (FAF) (SUPPY) Altitude = 6200 ft.
    • Airport elevation: 3206 ft.
    • Difference: 6200 - 3206 = 2994 ft.
    • Using the ICAO Cold Temperature Error Table:
      • Start with the 3,000 ft (2,994 ft rounded up) height above the airport and move down the chart to the reported temperature.
        • If the temperature is -10°C, a 290 ft correction is required.
        • If the temperature is -20°, a 420 ft correction is required.
        • 420 - 290 = 130 ft across 10°, which is 13 ft per °C.
      • The correction required is 290 + 26 ft, or 316 ft, which rounds up to 320 ft.
    • Add 320 ft. to the FAF and all procedure altitudes outside of the FAF up to and including IAF altitude(s):
      • LANNY (IAF), CHARL (IAF), and ODIRE (IAF Holding-in-Lieu): 9400 + 320 = 9720 ft.
      • CALIP (stepdown fix): 7000 + 320 = 7320 ft.
      • SUPPY (FAF): 6200 + 320 = 6520 ft.
  • To calculate manual corrections inside the FAF, use the same procedure as outside the FAF, but subtract the airport elevation from the MDA or DA instead of using the FAF value described above.

  • Manual Corrections Inside the FAF:

    • Cold temperature restricted airport temperature limit: -12°C.
    • LP MDA: 4,520 ft.
    • Difference: 4520 - 3206 = 1,314 ft.
    • Using the ICAO Cold Temperature Error Table:
      • While you can interpolate between the height above the airport and reported temperature fields, it is often best to round up (in this case, to 1,500 ft) for added safety and simplify the calculation.
        • If the temperature is -10°C, a 150 ft correction is required.
        • If the temperature is -20°C, a 210 ft correction is required.
        • 210 - 150 = 60 ft across 10°, which is 6 ft per °C.
      • The correction required is 150 + 12 ft, or 162 ft, which rounds up to 170 ft.
    • Add 170 ft. to the LP MDA, including any intermediate steps within the FAF as applicable.

  • Manual Corrections for Missed Approach Holding Altitude:

    • Follow the same steps as outside the FAF.

• 

• 

• Temperature-Compensating Systems:

  • If flying an aircraft equipped with a system capable of temperature compensation, follow the instructions for applying temperature compensation provided in the airplane flight manual (AFM), AFM supplement, or system operating manual. Ensure that the temperature compensation system is on and active before the IAF and remains active throughout the entire approach and missed approach.
    • Pilots who have a system that can calculate a temperature-corrected DA or MDA may use the system for this purpose.
    • Pilots who have a system unable to calculate a temperature-corrected DA or MDA will manually calculate an altitude correction for the MDA or DA.
    • Note: Some systems apply temperature compensation only to those altitudes associated with an instrument approach procedure loaded into the active flight plan, while other systems apply temperature compensation to all procedure altitudes or user-entered altitudes in the active flight plan, including altitudes associated with a Standard Terminal Arrival (STAR). For those systems that apply temperature compensation to all altitudes in the active flight plan, delay activating temperature compensation until the aircraft has passed the last altitude constraint associated with the active STAR.

Individual Segment(s) Method:

• Pilots are allowed to correct only the marked segment(s) indicated in the CTA list (https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/search/).
• Pilots using the Individual Segment(s) Method will reference the CTA list to determine which segment(s) need a correction. [Figure 2]
• When the aircraft is not using a compensating system, manual corrections are necessary.
• The ICAO Cold Temperature Error Table is used to calculate the correction needed for the approach segment(s). [Figure 16]

• Manual Correction for Initial Segment:

  • The initial segment is all altitudes from the intermediate fix (IF) altitude up to and including the IAF altitude.
  • Pilots calculate corrections by using the "Manual Corrections Outside the FAF" technique outlined above.

• Manual Correction for Intermediate Segment:

  • The intermediate segment encompasses all altitudes from the FAF/PFAF up to, but not including, the IF altitude.
  • Pilots calculate corrections by using the "Manual Corrections Outside the FAF" technique outlined above.

• Manual Correction for Final Segment:

  • The final segment corrects for the MDA or DA for the approach flown.
  • Pilots calculate corrections by using the "Manual Corrections Inside the FAF" technique outlined above.

• Manual Correction for the Missed Approach Segment:

  • The missed approach segment is all altitudes on the missed approach.
  • Pilots calculate corrections by using the "Manual Corrections for Missed Approach Holding Altitude" technique outlined above.

• Temperature-Compensating Systems:

  • Aircraft with temperature compensating system: If flying an aircraft equipped with a system capable of temperature compensation, follow the instructions for applying temperature compensation provided in the AFM, AFM supplement, or system operating manual. Turn on and activate the temperature compensation system before correcting the segment(s). Manually calculate an altimetry correction for the MDA or DA. Determine an altimetry correction from the ICAO table based on the reported airport temperature and the height difference between the MDA or DA, as applicable, and the airport elevation, or use the compensating system to calculate a temperature-corrected altitude for the published MDA or DA if able.

Effects of Cold Temperature on Baro-Vertical Navigation (VNAV) Vertical Guidance:

• Non-standard temperatures can lead to changes in effective vertical paths and actual descent rates when using aircraft Baro-VNAV equipment for vertical guidance on final approach segments.
  • A temperature lower than standard will result in a shallower descent angle and a reduced descent rate.
  • Conversely, a temperature higher than standard will result in a steeper angle and an increased descent rate.
• Pilots should consider the potential consequences of these effects on approach minima, power settings, sight picture, visual cues, and other factors, especially in high-altitude or terrain-challenged locations and during low-visibility conditions.

• Uncompensated Baro-VNAV note on 14 CFR Part 97 IAPs:

  • The area navigation (RNAV) global positioning system (GPS) and RNAV required navigation performance (RNP) notes, "For uncompensated Baro-VNAV systems, lateral navigation (LNAV)/VNAV NA below -XX°C (-XX°F) or above XX°C (XXX°F)" and "For uncompensated Baro-VNAV systems, procedure NA below -XX°C (-XX°F) or above XX°C (XXX°F)" apply to Baro-VNAV equipped aircraft.
    • These temperatures and their application are independent of the temperature and procedures used for a cold-temperature airport.
    • The uncompensated Baro-VNAV chart note and temperature range on an RNAV (GPS) approach applies to the LNAV/VNAV line of minima.
      • Baro-VNAV-equipped aircraft without a temperature-compensating system may not use the RNAV (GPS) approach LNAV/VNAV line of minima when the actual temperature is above or below the charted temperature range.
    • The uncompensated Baro-VNAV chart note and temperature range on an RNAV (RNP) approach apply to the entire procedure.
      • Aircraft without a Baro-VNAV and temperature compensating system may not conduct the RNAV (RNP) approach when the actual temperature is outside the charted uncompensated Baro-VNAV temperature range.

• Baro-VNAV temperature range versus CTA temperature:

  • The Baro-VNAV and CTA temperatures are independent and do not follow the same correction or reporting procedures.
    • However, there are times when both procedures, each according to its associated temperature, should be accomplished on the approach.

• Operating and ATC reporting procedures:

  • Do not use the CTA operating or reporting procedure found in this section, 7-3-4a. thru 7-3-5e. When complying with the Baro-VNAV temperature note on an RNAV (GPS) approach.
    • Correction is not required nor expected for procedure altitudes or VNAV paths outside of the final approach segment.
  • Operators must advise ATC when making temperature corrections on RNP authorization required (RNP AR) approaches, while adhering to the Baro-VNAV temperature note.
  • Reporting altitude corrections is required when complying with CTAs in conjunction with the Baro-VNAV temperature note.
    • Pilots do not need to report altitude corrections in the final segment.
  • Note: When executing an approach with vertical guidance at a CTA (i.e., ILS, localizer performance with vertical guidance (LPV), LNAV/VNAV), pilots must intersect the glideslope/glidepath at the corrected intermediate altitude (if applicable) and follow the published glideslope/glidepath to the corrected minima. The ILS glideslope and WAAS-generated glidepath are unaffected by cold temperatures and provide vertical guidance to the corrected DA. Begin descent on the ILS glideslope or WAAS-generated glidepath when directed by aircraft instrumentation. Temperature affects the precise final approach fix (PFAF) true altitude where a Baro-VNAV-generated glidepath begins. The PFAF altitude must be corrected when below the CTA temperature restriction for the intermediate segment or outside of the Baro-VNAV temperature restriction when using the LNAV/VNAV line of minima to the corrected DA.

Speed:

• When taxiing, keep it slow.
• Taxi slowly to avoid throwing up snow and slush into the wheel wells and onto aircraft surfaces.
• Taking it slow is also safer, as it provides more response time in case the tires decide to slide on an icy patch.

Purpose:

• Ensure you have a current airport diagram to reference before taxi, as winter weather may obscure references.
• Plan your route ahead of time, knowing where the runway safety areas are.
• Pilots achieve runway safety through planning and airmanship.

Aerodynamics:

• Since braking is not effective on a wet or icy runway, take advantage of aerodynamic braking by holding the nose up as long as possible.
  • Pilots can only maintain aircraft control if the main wheels are rolling..
• Braking should be applied gently and evenly, with care not to lock up the wheels.
• When the airplane slows down, the effectiveness of control from the rudder and ailerons is lost.
• The airplane does what comes naturally - it weather­vanes into the wind.
  • If there is ice, the amount of wind the airplane can tolerate drops dramatically.
  • Land into the wind on icy surfaces, or divert to a less contaminated runway or one with less of a crosswind.

Runway:

• Offset, parallel runways continue to challenge GA pilots.
• Pilots must be careful to look at the dominant runway, not the runway that air traffic control cleared them for.
• Snow-covered terrain may add to the difficulty.
• Understand your clearance and reference the airport diagram. If you're not 100% sure, go around and check.

Equipment:

• Remove the airplane's wheel pants if equipped.
  • Slush and ice can collect inside the wheel pant, freezing the brakes to the rotors and making for an interesting landing with wheels that won't spin.
  • Removing the wheel pants will also provide a clearer view to inspect the tire condition and check for any possible fluid leaks.
  • Check tire pressure as cold temperatures reduce pressure.
• Use pre-heaters to ease starting, prevent engine flooding, and reduce the risk of air filter fires.
• Wear warm clothing and update your survival gear as needed.

Meteorological Considerations:

• Frost:

  • Frost is the formation of a thin layer of ice crystals on the ground or other surfaces on solid objects below the freezing point of water.
    • It develops in Arctic coastal areas during spring, autumn, and winter.
    • Typically, frost occurs on clear nights with calm winds when both the air temperature and dew point are below freezing.
    • It may occur when descending from a zone of freezing temperatures into an area of high humidity.
  • Frost adds weight and disturbs smooth airflow over the aircraft and control surfaces.
  • The closer the dew point is to the temperature, the greater the risk of condensation, which, when the temperature is below freezing, results in frost.
  • Remove all accumulation on the aircraft, especially flight surfaces, as frost and ice may reduce lift by up to 30% and increase drag by up to 40%.
    • Use a broom or a deicing liquid, if available, to avoid scratching the paint.
    • Monitor for frost/ice as the aircraft taxis to the runway.
    • Thin surfaces (tail) tend to accumulate ice/frost the fastest.
    • Consider hand flying to maintain the tactile feel of ice accumulation.
  • Taxi slowly to avoid throwing anything from the surface onto the wings.
  • Avoid flying near cloud types as water droplets are concentrated most towards the top.

Maintenance:

• Review the Pilot Operating Handbook to identify any required preventative maintenance.
• Change oil to a lower viscosity, if recommended by the manufacturer.
  • Proper oil viscosity for the environment will help the aircraft during start-up.
• Replace or add carbon monoxide detectors, especially if your engine heats air over the exhaust shroud.
• Add fuel additives, if recommended by the manufacturer.

Technique:

• Be more gentle with power changes that may abruptly change engine temperatures, such as adding takeoff power to avoid shocking the engine.

Lift:

• We know from our principles of flight that lift is generated primarily on the first 25% of our wingtip, which is the exact location where ice will tend to build.
• Ice alters the shape of an airfoil, reducing the maximum coefficient of lift and angle of attack at which the aircraft stalls.
• Note that at very low angles of attack, there may be little or no effect of the ice on the coefficient of lift.

Thrust:

• Propeller icing reduces thrust for the same aerodynamic reason that wings tend to lose lift and increase drag.
• Anti-icing systems protect propellers.

Drag:

• The accumulation of ice affects the coefficient of drag of the airfoil.
• [Figure 2-19] Note that the effect is significant even at tiny angles of attack.
• A significant reduction in CL-MAX and a decrease in the angle of attack at which stall occurs can result from a relatively small ice accretion.
• A reduction of CL-MAX by 30% is not unusual, and a large horn ice accretion can result in reductions of 40% to 50%.
• Drag tends to increase steadily as ice accretes.
• An airfoil drag increase of 100% is not unusual, and for large horn ice accretions, the increase can be 200% or even higher.
• Ice on an airfoil can have other effects not depicted in these curves.
• Even before an airfoil stalls, changes in pressure over the airfoil can occur, potentially affecting a control surface at the trailing edge.
• Furthermore, during takeoff, approach, and landing, the wings of many aircraft are equipped with multi-element airfoils, featuring three or more elements.
  • Ice may affect the different elements in different ways.
• Ice may also affect how the air streams interact over the elements.
• Ice can partially block or limit control surfaces, rendering them ineffective for control movements.
• Additionally, the extra weight caused by ice accumulation is too great.
  • In that case, the aircraft may be unable to become airborne, and if in flight, it may be unable to maintain altitude.
• Therefore, remove ice or frost accumulation before attempting to take off the item.
• Another hazard of structural icing is the potential for an uncommanded and uncontrolled roll phenomenon, commonly referred to as roll upset, which can occur during severe in-flight icing.
• Pilots flying aircraft certificated for flight in known icing conditions should be aware that severe icing is a condition outside of the aircraft's certification icing envelope.
• Roll upset occurs with airflow separation (aerodynamic stall), which induces self-deflection of the ailerons and results in a loss of or degraded roll handling characteristics [Figure 2-20].
• These phenomena can result from severe icing conditions without the usual symptoms of ice accumulation or a perceived aerodynamic stall.
• Most aircraft have a nose-down pitching moment from the wings because the CG is ahead of the CP.
• It is the role of the aircraft's tail to counteract this moment by providing a downward force.
• [Figure 2-21] The result of this configuration is that actions that move the wing away from stall, such as deployment of flaps or increasing speed, may increase the negative angle of attack of the tail.
• With ice on the aircraft's tail, it may stall after full or partial deployment of flaps.
• Since the aircraft's tail is ordinarily thinner than the wing, it is a more efficient collector of ice.
• On most aircraft, the tail is not visible to the pilot, who therefore cannot observe how well it has been cleared of ice by any deicing system.
• Thus, the pilot must be alert to the possibility of tail-plane stall, particularly on approach and landing.

Weight:

• The more ice that accumulates, the more weight the aircraft carries.
• The actual weight of the ice on the airplane is insignificant; however, it significantly disrupts the airflow.

Flight Controls:

• As weight and drag increase, the powerplant must generate more thrust to maintain lift.
• More deflection will be required until the control surface becomes ineffective.

Fuel Consumption:

• As weight and drag increase, more thrust is required.
• Since thrust effectiveness can also degrade, the engine must work even harder, resulting in increased fuel consumption.

Induction Icing:

• Engine icing occurs when ice forms on the induction or compressor sections of an engine, reducing performance.
• Ice in the induction system can reduce the amount of air available for combustion, resulting in reduced engine performance.
• The most common example of reciprocating engine induction icing is carburetor ice.
• Most pilots are familiar with this phenomenon, which occurs when moist air passes through a carburetor venturi and is cooled.
  • As a result of this process, ice may form on the venturi walls and throttle plate, restricting airflow to the engine.
  • Temperatures between 20°F (-7°C) and 70°F (21°C) result in the greatest chances of icing.
  • Applying carburetor heat, which uses the engine's exhaust as a heat source, melts the ice or prevents its formation.
• On the other hand, fuel-injected aircraft engines are usually less vulnerable to icing but still can be affected if the engine's air source becomes blocked with ice.
• Manufacturers provide an alternate air source for use in case the normal system malfunctions.
• In turbojet aircraft, air ingested into the engines creates an area of reduced pressure at the inlet, which lowers the temperature below that of the surrounding air.
• In marginal icing conditions (i.e., conditions where icing is possible), this reduction in temperature may be sufficient to cause ice to form on the engine inlet, disrupting the airflow into the engine.
• Another hazard arises when ice breaks off the aircraft’s surface and enters a running engine, potentially damaging fan blades or causing a compressor stall or combustor flameout.
• When using anti-icing systems, run-back water can refreeze on unprotected surfaces of the inlet. If excessive, it can reduce airflow into the engine or distort the airflow pattern, causing compressor or fan blades to vibrate and possibly damage the engine.
• Another problem in turbine engines is the icing of engine probes used to set power levels (for example, engine inlet temperature or Engine Pressure Ratio (EPR) probes), which can lead to erroneous readings of engine instrumentation, operational difficulties, or total power loss.

Communication & Navigation:

• Antennas are prone to accumulating ice and often lack protection, which can lead to navigation and communication problems or failures.
• Avionics will perform more slowly until warmed up.

Flight Instruments:

• Flight instruments rely on data from external sources such as the Pitot tube, static ports, and stall warnings.
• Interruptions to external sources due to icing can result in instrument failures.

Flight Control Systems:

• Cold weather causes components, even flight controls and cables, to contract.
  • Components contracting can cause previously unexperienced binding or tension.

Preparing for Cold/Winter Storage:

• Follow the manufacturer's procedures, if available.
• Clean the aircraft of any unnecessary equipment, especially that which could freeze and potentially explode (such as soda cans) inside.
• Consider approved methods to prevent corrosion (such as moisture) and stabilize the fuel.
• Consider changing the oil (for greater protection of internal parts) and filling the fuel tanks (to avoid moisture).
• Chocking the brakes prevents damage to the brake system that can occur from prolonged use of the parking brake.
• Regularly check the aircraft to identify leaks caused by metal fittings contracting early.
• Keep the aircraft in an enclosed environment (tent, hangar, etc.) when possible.
  • Apply a canopy cover for windy weather, but be sure to remove it to avoid damage from freezing, which can cause the windows to craze.
• Orient the propeller spinner vertically to avoid contamination buildup.
• When storing in a hangar, lay antimal traps and still cover all appropriate ports and vents to avoid foreign intrusion.
• Consider moving the aircraft periodically to protect tires and shocks from becoming lodged in place or damaged.
• Consider supervised adjustment of control cables to compensate for cold contraction.
• Keep batteries (engine, ELT, etc.) charged or remove them if parked outside.

• Conduct a thorough inspection, checking all cables, hoses, tubing, seals, and other components for cracks, hardening, distortion, and any other abnormalities.
• Tighten any loose clamps or fittings.
• Pay attention to the heater system and any potential carbon monoxide hazards.
• Check for nests or any foreign objects.