Cold Temperature Operations

Introduction:

  • Pilots should begin planning for operating into airports with cold temperatures during the preflight planning phase

Pre-Flight Planning for Cold Temperature Altimeter Errors:

  • Flight planning into a CTA may be accomplished prior to flight. Use the predicted coldest temperature for plus or minus 1 hour of the estimated time of arrival and compare against the CTA published temperature. If the predicted temperature is at or below CTA temperature, calculate an altitude correction using [Figure 1]
  • This correction may be used at the CTA if the actual arrival temperature is the same as the temperature used to calculate the altitude correction during preflight planning
  • Example Cold Temperature Restricted Airport List - Required Segments
    Example Cold Temperature Restricted Airport List - Required Segments

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

Cold Temperature Airports (CTA):

  • The FAA has determined that operating in cold temperatures has placed some 14 CFR Part 97 instrument approach procedures in the United States National Airspace System at risk for loss of required obstacle clearance (ROC)
    • An airport that is determined to be at risk will have an ICON and temperature published on the instrument approach procedure (IAP) in the terminal procedures publication (TPP)
  • CTA identification in TPP: A CTA is identified by a "snowflake" icon and temperature limit, in Celsius, on U.S. Government approach charts
  • For a complete list, see the "Cold Temperature Airports" link under the Additional Resources heading at the bottom of the following page: https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/search/
    • Airports are listed by ICAO code, Airport Name, Temperature in Celsius, and affected segment(s)
  • 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

Cold Temperature Airport Procedures:

  • PILOTS MUST NOT MAKE AN ALTIMETER CHANGE to accomplish an altitude correction
    • Pilots must ensure that the altimeter is set to the current altimeter setting provided by ATC in accordance with 14 CFR 91.121
  • Actions on when and where to make corrections: Pilots will make an altitude correction to the published, "at", "at or above", and "at or below" altitudes on all designated segment(s) to all runways for all published instrument approach procedures when the reported airport temperature is at or below the published CTA temperature on the approach plate
    • A pilot may request an altitude correction (if desired) on any approach at any United States airport when extreme cold temperature is encountered
    • Pilots making a correction must comply with ATC reporting requirements
  • Correctable altitudes: ATC does not apply a cold temperature correction to their Minimum Vectoring Altitude (MVA) or Minimum IFR Altitude (MIA) charts
    • Pilots must request approval from ATC to apply a cold temperature correction to any ATC assigned altitude. Pilots must not correct altitudes published on Standard Instrument Departures (SIDs), Obstacle Departure Procedures (ODPs), and Standard Terminal Arrivals (STARs)
  • Use of corrected MDA/DA: Pilots will use the corrected MDA or DA as the minimum altitude for an approach
    • Pilots must meet the requirements in 14 CFR Part 91.175 in order to operate below the corrected MDA or DA
    • Pilots must see and avoid obstacles when descending below the minimum altitude on the approach
    • Note: The corrected DA or MDA does not affect the visibility minima published for the approach. With the application of a cold temperature correction to the DA or MDA, the airplane should be in a position on the glideslope/glidepath or at the published missed approach point to identify the runway environment
  • How to apply Cold Temperature Altitude Corrections on an Approach:
    • All Segments Method: Pilots may correct all segment altitudes from the initial approach fix (IAF) altitude to the missed approach (MA) final holding altitude. Pilots familiar with the information in this section and the procedures for accomplishing the all segments method, only need to use the published "snowflake" icon, /CTA temperature limit on the approach chart for making corrections. Pilots are not required to reference the CTA list. The altitude correction is calculated as follows:
      • Manual correction: Pilots will make a manual correction when the aircraft is not equipped with a temperature compensating system or when a compensating system is not used to make the correction. Use the ICAO Cold Temperature Error Table to calculate the correction needed for the approach segment(s) [Figure 1]
        • Correct all altitudes from the final approach fix (FAF)/PFAF up to and including the IAF altitude: Calculate the correction by taking the FAF/PFAF altitude and subtracting the airport elevation. Use this number to enter the height above airport column in [Figure 1] until reaching the reported temperature from the "Reported Temperature" row. Round this number as applicable and then add to all altitudes from the FAF altitude through the IAF altitude
        • Correct all altitudes in the final segment: Calculate the correction by taking the MDA or DA for the approach being flown and subtract the airport elevation. Use this number to enter the height above airport column in [Figure 1] until reaching the reported temperature from the "Reported Temperature" row. Use this number or round up to next nearest 100. Add this number to MDA or DA, as applicable, and any applicable step-down fixes in the final segment. (3) Correct final holding altitude in the MA Segment: Calculate the correction by taking the final missed approach (MA) holding altitude and subtract the airport elevation. Use this number to enter the height above airport column in [Figure 1] until reaching the reported temperature from the "Reported Temperature" row. Round this number as applicable and then add to the final MA altitude only
      • Aircraft with 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 temperature compensation system is on and active prior to the IAF and remains active throughout the entire approach and missed approach
        • Pilots that have a system that is able to calculate a temperature-corrected DA or MDA may use the system for this purpose
          • Pilots that 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 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. See FIG 7-3-1
          • Manual Correction: Pilots will make a manual correction when the aircraft is not equipped with a temperature compensating system or when a compensating system is not used to make the correction. Use [Figure 1], ICAO Cold Temperature Error Table, to calculate the correction needed for the approach segment(s)
            • Intermediate Segment: All altitudes from the FAF/PFAF up to but not including the intermediate fix (IF) altitude. Calculate the correction by taking FAF/PFAF altitude and subtracting the airport elevation. Use this number to enter the height above airport column in [Figure 1] until reaching the reported temperature from the "Reported Temperature" row. Round this number as applicable and then add to FAF altitude and all step-down altitudes within the intermediate segment (inside of the waypoint labeled "(IF)")
            • Final segment: Calculate correction by taking the MDA or DA for the approach flown and subtract the airport elevation. Use this number to enter the height above airport column in [Figure 1] until reaching the reported temperature from the "Reported Temperature" row. Use this number or round up to next nearest 100. Add this number to MDA or DA, as applicable, and any applicable step-down fixes in the final segment
            • Missed Approach Segment: Calculate the correction by taking the final MA holding altitude and subtract the airport elevation. Use this number to enter the height above airport column in [Figure 1] until reaching the reported temperature from the "Reported Temperature" row. Round this number as applicable and then add to the final MA altitude only
          • 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. Ensure the temperature compensation system is on and active prior to the segment(s) being corrected. 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
  • Acceptable Use of Table for manual CTA altitude correction: [Figure 1]
    • Pilots may calculate a correction with a visual interpolation of the chart when using reported temperature and height above airport. This calculated altitude correction may then be rounded to the nearest whole hundred or rounded up. For example, a correction of 130 ft. from the chart may be rounded to 100 ft. or 200 ft. A correction of 280 ft. will be rounded up to 300 ft. This rounded correction will be added to the appropriate altitudes for the "Individual" or "All" segment method. The correction calculated from the table for the MDA or DA may be used as is or rounded up, but never rounded down. This number will be added to the MDA, DA, and all step-down fixes inside of the FAF as applicable
      • No extrapolation above the 5000 ft. column is required. Pilots may use the 5000 ft. "height above airport in feet" column for calculating corrections when the calculated altitude is greater than 5000 ft. above reporting station elevation. Pilots must add the correction(s) from the table to the affected segment altitude(s) and fly at the new corrected altitude. Do not round down when using the 5000 ft. column for calculated height above airport values greater than 5000 ft. Pilots may extrapolate above the 5000 ft. column to apply a correction if desired
      • These techniques have been adopted to minimize pilot distraction by limiting the number of entries into the table when making corrections. Although not all altitudes on the approach will be corrected back to standard day values, a safe distance above the terrain/obstacle will be maintained on the corrected approach segment(s). Pilots may calculate a correction for each fix based on the fix altitude if desired
      • Note: Pilots may use Real Time Mesoscale Analysis (RTMA): Alternate Report of Surface Temperature, for computing altitude corrections, when airport temperatures are not available via normal reporting. The RTMA website is http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtma/prod/airport_temps/
  • Communication: Pilots must request approval from ATC whenever applying a cold temperature altitude correction. Pilots do not need to inform ATC of the final approach segment correction (i.e., new MDA or DA). This request should be made on initial radio contact with the ATC facility issuing the approach clearance. ATC requires this information in order to ensure appropriate vertical separation between known traffic. Pilots should query ATC when vectored altitudes to a segment are lower than the requested corrected altitude. Pilots are encouraged to self-announce corrected altitude when flying into a non-towered airfield
    • The following are examples of appropriate pilot-to-ATC communication when applying cold-temperature altitude corrections
      • On initial check-in with ATC providing approach clearance: Missoula, MT (example below)
        • Vectors to final approach course: Outside of IAFs: "Request 9700 ft. for cold temperature operations"
        • Vectors to final approach course: Inside of ODIRE: "Request 7300 ft. for cold temperature operations"
        • Missed Approach segment: "Require final holding altitude, 12500 ft. on missed approach for cold temperature operations"
      • Pilots cleared by ATC for an instrument approach procedure; "Cleared the RNAV (GPS) Y RWY 12 approach (from any IAF)". Missoula, MT (example below)
        • IAF: "Request 9700 ft. for cold temperature operations at LANNY, CHARL, or ODIRE"

Instrument Approach Cold Temperature Operations:

  • Instrument approach charts will contain a snowflake symbol and a temperature when cold temperature correction must be applied
    • Pilots operating into airports requiring cold temperature corrections should request the lowest forecast temperature at the airport for departure and arrival times
    • If the temperature is forecast to be at or below any published cold temperature restriction, calculate an altitude correction for the appropriate segment(s) and/or review procedures for operating automatic cold temperature compensating systems, as applicable
  • The pilot is responsible to calculate and apply the corrections to the affected segment(s) when the actual reported temperature is at or below any published cold temperature restriction, or pilots with automatic cold temperature compensating systems must ensure the system is on and operating on each designated segment
  • Advise ATC when intending to apply cold temperature correction and of the amount of correction required on initial contact (or as soon as possible) for the intermediate segment and/or the published missed approach
    • This information is required for ATC to provide aircraft appropriate vertical separation between known traffic
  • Examples for Calculating Altitude Corrections on CTAs:

    • Cold Temperature Error Table
      Cold Temperature Error Table
    • Missoula IAP Example
      Missoula IAP Example
    • 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 + 180 = 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 System: Operators using a temperature compensating RNAV system 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

Cold Weather Safety:

  • For cold weather safety, The FAA Safety Team recommends following the below tips may "SPARE" you from dangerous runway incursions
  • 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 wheelpants 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 wheelpants will also allow you a clearer view to inspect tire condition and the possibility of leaking fluid

Icing Effects on Aircraft Control and Performance:

  • Structural icing, referring to the accumulation of ice on the exterior of the aircraft, will have impacts on control and performance
  • Forms on the external structure of the aircraft when supercooled droplets impinge on them and freeze
  • Small parts of the aircraft will develop ice (Pitot tube) before larger parts (wing)
    • Icing in strange places such as the wind screen is indicative of super-cooled droplets
  • The quicker you move, the more friction on the skin of the airplane, and thus the less icing would be expected; so a jet will not ice as fast as a Cessna in the same conditions
  • Icing decreases lift, thrust, and range, and increases drag, weight, fuel consumption, and stall speed
  • The most hazardous aspect of structural icing is its aerodynamic effects
  • Lift:

    • We know from our principles of flight that lift is generated mostly on the first 25% of our wingtip which is the same location ice will tend to build
    • [Figure 2-19] 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
  • However, note that the ice significantly reduces the CL-MAX, and the angle of attack at which it occurs (the stall angle) is much lower
  • Thus, when slowing down and increasing the angle of attack for approach, the pilot may find that ice on the wing, which had little effect on lift in cruise now, causes stall to occur at a lower angle of attack and higher speed
  • Even a thin layer of ice at the leading edge of a wing, especially if it is rough, can have a significant effect in increasing stall speed
    • Its like flying at a very high altitude
  • 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 in effective
  • 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

Icing Effects on Aircraft Systems:

  • 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
    • 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
      • This may occur at temperatures between 20°F (-7°C) and 70°F (21°C)
      • The problem is remedied by applying carburetor heat, which uses the engine's own exhaust as a heat source to melt the ice or prevent its formation
    • On the other hand, fuel-injected aircraft engines usually are 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 that may be selected in case the normal system malfunctions
    • In turbojet aircraft, air that is drawn 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 occurs when ice breaks off and is ingested into a running engine, which can cause damage to fan blades, engine compressor stall, or combustor flameout
    • When anti-icing systems are used, run-back water can refreeze on unprotected surfaces of the inlet and, if excessive, reduce airflow into the engine or distort the airflow pattern in such a manner as to cause compressor or fan blades to vibrate, possibly damaging 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 quick to accumulate ice and typically do not have protection leading to navigation and communication problems or failures
  • Flight Instruments:

    • Flight instruments rely on data from external sources such as the Pitot tube, static ports and stall warnings
    • This will result in instrument failures

Conclusion:

  • Always consult the aircraft's Pilot Operating Handbook for special procedures and limitations (such as engine starting) regarding cold temperature operations
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References: