Cold Temperature Operations

Airport Criteria:

• The CTA risk analysis is performed 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 with the corrected altitude when applying an altitude correction on any approach segment with the exception of 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

Examples for Calculating Altitude Corrections on CTAs:

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• All 14 CFR Part 97 IAPs must be corrected at an airport. The following example provides the steps for correcting the different segments of an approach and will be applied to all 14 CFR Part 97 IAPs:
  • Missoula Intl (KMSO). Reported Temperature -12°C: RNAV (GPS) Y RWY 12
    • All Segments Method: All segments corrected from IAF through MA holding altitude
      • Manual Calculation:
        • Cold Temperature Restricted Airport Temperature Limit: -12°C
        • Altitude at the Final Approach Fix (FAF) (SUPPY) = 6200 ft
        • Airport elevation = 3206 ft
        • Difference: 6200 ft. - 3206 ft. = 2994 ft
        • Use [Figure 2], ICAO Cold Temperature Error Table, a height above airport of 2994 ft. and -12°C ad interpolate:
          • -10°C demands 290 ft correction, -20° demands a 420 ft correction (420-290=130 per degree), from -10°, add 26ft (13*2°) or 30 for even math... 320ft
        • 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 = 9900 ft
          • CALIP (stepdown fix): 7000 + 320 = 7500 ft
          • SUPPY (FAF): 6200 + 320 = 6700 ft
        • Correct altitudes within the final segment altitude based on the minima used. LP MDA = 4520 ft
        • Difference: 4520 ft. - 3206 ft. = 1314 ft
        • [Figure 2]: 1314 ft. at -12°C is approximately 150ft. Use 150 ft. or round up to 200 ft
        • Add corrections to altitudes up to but not including the FAF:
          • BEGPE (stepdown fix): 4840 + 150 = 4990 ft
          • LNAV MDA: 4520 + 150 = 4670 ft
        • Correct JENKI/Missed Approach Holding Altitude: MA altitude is 12000:
          • JENKI: 12000 - 3206 = 8794 ft
        • [Figure 2]: 8794 ft. at -12°C. Enter table at -12°C and intersect the 5000 ft. height above airport column. The approximate value is 500 ft
        • Add correction to holding fix final altitude:
          • JENKI: 12000 + 500 = 12500 ft
  • Temperature compensating RNAV systems used to make altitude corrections will be set to the current airport temperature (-12°C) and activated prior to passing the IAF. A manual calculation of the cold temperature altitude correction is required for the MDA/DA
    • Individual Segments Method: Missoula requires correction in the intermediate and final segments. However, in this example, the missed approach is also shown
      • Manual Calculation: Use the appropriate steps in the All Segments Method above to apply a correction to the required segment
        • Intermediate. Use steps 7-3-6 a. 1. (a) (1) thru (6). Do not correct the IAF or IF when using individual segments method
        • Final. Use steps 7-3-6 a. 1. (a) (7) thru (10)
        • Missed Approach. Use steps 7-3-6 a, 1. (a) (11) thru (13)
      • Temperature Compensating System: Operators using a temperature compensating RNAV system to make altitude corrections will be set to the current airport temperature (-12°C) and activated at a point needed to correct the altitude for the segment. A manual calculation of the cold temperature altitude correction is required for the MDA/DA

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

• Non-standard temperatures can result in a change to effective vertical paths and actual descent rates when using aircraft Baro-VNAV equipment for vertical guidance on final approach segments
  • A lower than standard temperature will result in a shallower descent angle and reduced descent rate
  • Conversely, a higher than standard temperature will result in a steeper angle and increased descent rate
• Pilots should consider potential consequences of these effects on approach minima, power settings, sight picture, visual cues, etc., especially for 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 how they are used are independent of the temperature and procedures applied for a Cold Temperature Airport
    • The uncompensated Baro-VNAV chart note and temperature range on an RNAV (GPS) approach is applicable 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 applies to the entire procedure
      • For aircraft without a Baro-VNAV and temperature compensating system, the RNAV (RNP) approach is not authorized when the actual temperature is above or below 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 to be applied to procedure altitudes or VNAV paths outside of the final approach segment
  • Operators must advise ATC when making temperature corrections on RNP authorization required (AR) approaches while adhering to Baro-VNAV temperature note
  • Reporting altitude corrections is required when complying with CTAs in conjunction with the Baro-VNAV temperature note
    • The CTA altitude corrections will be reported in this situation
    • No altitude correction reporting is required 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 are reminded to 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, providing more response time in case the tires decide to slide on an icy patch

Purpose:

• Ensure you have a current airport diagram to reference prior to taxi as winter weather may obscure references
• Plan your route ahead of time, knowing where the runway safety areas are
• Runway safety happens on purpose because of your 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
  • Aircraft control can only be maintained if the main wheels are rolling
• Any braking should be applied gently and evenly using care not to lock up the wheels
• When the airplane slows down, control effectiveness from the rudder and ailerons are 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
• Be aware that you may be looking at a dominate runway, not the one that you were cleared 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

Equipment:

• Remove the airplane's wheel pants if equipped
  • Slush and ice can collect inside the wheel pant and freeze the brakes to the rotors making for an interesting landing with wheels that won't spin
  • Removal of the wheel pants will also allow you a clearer view to inspect tire condition and the possibility of leaking fluid
  • Check tire pressure as cold temperatures reduce pressure
• Use pre-heater to ease starting, prevent engine flooding, and reduce the risk of air filter fires
• Wear warming clothing and update survival gear as appropriate

Meteorological Considerations:

• Frost:

  • Frost is the formation of thin 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
  • Frost adds weight and disturbs smooth airflow over the aircraft and control surfaces
  • The closer dewpoint is to temperature, the increased risk of condensation, which when below freezing is 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
    • Frost/ice should again be checked after the aircraft has taxied to the runway
    • Thin surfaces (tail) tend to accumulate ice/frost the fastests
    • 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 for any preventative maintenance that may be required
• Change oil to a lower viscosity, if recommended by the manufacturer
  • Proper oil viscosity for the environment will help the aircraft during starting
• 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

Thrust:

• Propeller icing reduces thrust for the same aerodynamic reason that wings tend to lose lift and increase drag
• Propellers can be protected with anti-icing systems

Drag:

• The accumulation of ice affects the coefficient of drag of the airfoil
• [Figure 2-19] Note that the effect is significant even at very small angles of attack
• A significant reduction in CL-MAX and a reduction in the angle of attack where 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 airfoil stall, there can be changes in the pressure over the airfoil that may affect a control surface at the trailing edge
• Furthermore, on takeoff, approach, and landing, the wings of many aircraft are multi-element airfoils with three or more elements
  • Ice may affect the different elements in different ways
• Ice may also affect the way in which the air streams interact over the elements
• Ice can partially block or limit control surfaces, which limits or makes control movements ineffective
• Also, if the extra weight caused by ice accumulation is too great, the aircraft may not be able to become airborne and, if in flight, the aircraft may not be able to maintain altitude
• Therefore any accumulation of ice or frost should be removed before attempting flight
• Another hazard of structural icing is the possible un-commanded and uncontrolled roll phenomenon, referred to as roll upset, associated with 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 may be caused by airflow separation (aerodynamic stall), which induces self deflection of the ailerons and 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 tail-plane to counteract this moment by providing a downward force
• [Figure 2-21] The result of this configuration is that actions which 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 tail-plane, it may stall after full or partial deployment of flaps
• [Figure 2-22] Since the tail-plane is ordinarily thinner than the wing, it is a more efficient collector of ice
• On most aircraft the tail-plane is not visible to the pilot, who therefore cannot observe how well it has been cleared of ice by any deicing system
• Thus, it is important that the pilot be alert to the possibility of tail-plane stall, particularly on approach and landing

Weight:

• The more ice that accumulates, the more weight on the aircraft
• The actual weight of the ice on the airplane is insignificant however, when compared to the airflow disruption it causes

Flight Controls:

• As airfoils become less effective, so may flight control surfaces
• This means more deflection will be required until the point where the control surface is ineffective

Fuel Consumption:

• The more weight and drag increases, the more thrust is required
• Since thrust can also be degrading, the engine must work even harder, increasing fuel consumption

Communication & Navigation:

• Antennas are quick to accumulate ice and typically do not have protection, leading to navigation and communication problems or failures
• Avionics will perform slower 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:

• Find and follow manufacturer procedures, if available
• Clean the aircraft of any unncessary equipment, especially that which could freeze and explode (soda cans) inside of the aircraft
• Consider approved methods to prevent corrosion (moisture) and stabilize fuel
• Consider changing the oil (greater protection to internal parts) and filling the fuel tanks (to avoid moisture)
• Chocking the breaks avoids any damage to the brake system cauesed by long-term parking brake use
• Check on the aircraft over time to identify leaks caused by metal fittings contracting early
• Keep the aircraft in an enclosed environment (tent, hangar, etc.) when possible
  • A canopy cover should be applied when windy weather is anticipated, but not left on so as to avoid damage from it freezing and crazing the windows
• 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 if parked outside

• Conduct a thorough inspection, checking all cables, hoses, tubing, seals, etc. for cracks, hardening, distortion, and lumps
• Tighten any loose clamps or fittings
• Pay attention to the heater system or any Carbon Monoxide hazard
• Check for nests or any foreign objects