A340 COLD WEATHER OPERATIONS
Introduction • Aircraft performance is certified on the basis of a clean wing. Ice accretion affects wing performance. When the wing is clean, the airflow smoothly follows the shape of the wing. When the wing is covered with ice, the airflow separates from the wing when the Angle-Of-Attack (AOA) increases. Therefore, the maximum lift-coefficient is reduced. As a result, the aircraft may stall at a lower AOA, and the drag may increase. • Even a small amount of ice and snow on the wings can reduce the stall AOA (and therefore increase the stall speed) dramatically. A stall may occur before any stall warning device signals it. • The flight temperature than 0 °C, temperature,
crew must keep in mind that the wing of the aircraft may be significantly lower after a flight at high altitude and low even if the OAT is higher than 0 °C.
• In such cases, humidity or rain will cause ice accretion on the upper wing, and light frost under the wing. (Only 3 mm of frost on the under-surface of the wing is acceptable.)
Anti-ice Fluids: _ The fluids lowers freezing point of precipitation on a/c surfaces. Contains ethylene glycol or propylene glycol, etc, plus wetting agent, corrosion inhibitor, water and sometimes dye (so you can see it). _ The fluids used for de-icing as well as for anti-icing. Depending on their characteristics, anti-icing fluids are divided into different types with quite different anti-icing properties: _ De-icing fluid is normally applied heated in order to assure maximum efficiency. _ De/anti-icing fluids do not provide any protection from contamination once the ACFT is airborne. These fluids have different characteristics: type I: Low viscosity/ Limited HOT/ Mainly for deicing type II, III, IV: High viscosity/ Longer HOT/ Used for deicing +anti-icing Type I fluids form a thin liquid wetting film, which gives a rather limited Hold-Over Time (HOT).
“ In all circumstances it is the Captain’s responsibility to decide whether or not to de-ice/anti-icing the aircraft, or to order a repeated treatment.
In precipitation, they are quickly diluted and give short HOT. Type I fluids are always mixed with water. The fluid/water mixture is selected to maintain freezing point at least 10°C below OAT. Increasing the fluid concentration does not improve HOT.
• Having stated the above, the Captain relies heavily on the ground engineers and the contractor who treats and inspects the aircraft surfaces.
Type II fluids contain a thickener and form a thicker film adhering to aircraft surfaces. Therefore, compared to Type I, the Type II fluids provide improved HOT especially under precipitation.
• A340 is certified for flight in icing conditions. DEFINITIONS Icing Conditions 1. OAT (on ground and for takeoff) or the TAT (in flight) is 10 °C or below and 2. Visible moisture in the air (such as clouds, rain, fog with low visibility of one mile or less, snow, sleet, ice crystals) or standing water, slush, ice or snow on the runways and taxiways. Warning Pilots must turn on the engine anti-ice system, when temperature and visible moisture meet these criteria, and not wait until they see ice build up. Freezing Conditions The conditions in which the OAT is below +3°C (37.4°F) and visible moisture in any form (such as fog with visibility below 1.5 km, rain, snow, sleet or ice crystals) or standing water, slush, ice or snow is present on the runway.
Before liftoff, the viscosity is drastically reduced by shear forces, allowing the fluid to run off the wing. Type II fluids are used undiluted or diluted with water and are identified according to the mixture ratio; e.g. “Type II 75" is a mixture of 75% (by volume) Type II fluid with 25% water. Higher concentrations allow use down to lower temperatures and improve HOT. Type IV fluids are similar to Type II, but provide even better HOT when used undiluted or slightly diluted.
Hold-Over Time (HOT) _ HOT is the estimated time the anti-icing fluid will prevent frost, ice and snow to form or accumulate on the protected (treated) areas of the aircraft. HOT starts at beginning of the final anti-icing treatment (or de-icing fluid is only using the 1-step procedure). _ Hold–over protection is achieved by a layer of anti-icing fluid remaining on the protected a/c surfaces for a period of time. _ A HOT table is published in RM/ PFL p.240, giving HOT as function of applied fluid, temperature and weather. For each condition the table gives a range of HOT (e.g. 30-45 minutes)
Critical Surfaces: wings (leading edges +upper surfaces of wings) & control surfaces (vertical & horizontal stabilizers, slats & flaps).
_ Generally, the low end of the range represents the estimated HOT in heavy conditions, the high end, the estimated HOT in light conditions.
De-icing is a process by which frost, slush, snow or ice is removed from the aircraft in order to provide clean surfaces.
_ In heavy weather conditions, the HOT can even be shorter than the lower end of the range and it is the responsibility of the P-i-C to determine what HOT can be expected under prevailing conditions.
Anti-icing is a precautionary process which provides protection against the formation of frost or ice and accumulation of snow or slush on treated surfaces of the aircraft for a limited period of time (hold-over time). De/anti-icing is a combination of de-icing and anti-icing and may be performed in one or two steps. De-ice Fluids mixes with the ice on the surfaces, lowers the freezing point of the ice so it melts and falls off with the excess de-ice fluid (which is sprayed under pressure).
_ HOT may shortened with high wind velocity, jet blast and a/c skin temp well below OAT. If the aircraft is treated and remains within the HOT there is still no guarantee of clean surfaces – the HOT is a guide. HOT is determined from tables in the RM/ PFL Winter Ops considering fluid type and ratio mix, nature and severity of precipitation.
PRE-FLIGHT & ENGINE STARTING Pre-flight
Check 1
_ All surfaces of the aircraft must be clear of snow, frost,
A340 COLD WEATHER OPERATIONS and ice for takeoff. _ Thin hoarfrost is acceptable on the upper surface of the fuselage (Thin hoarfrost is typically a white crystalline deposit which usually develops uniformly on exposed surfaces on cold and cloudless nights; it is thin that a person can distinguish surface features (line or markings) beneath it). _ On the underside of the wing tank area, a max layer of 3 mm (1/8 inch) will not penalize takeoff performance. _ Other than above, all parts of the aircraft must be free of ice, snow and slush. Other areas to inspect: • landing gear assemblies, tires, gear doors • engine inlet cowls, fans (check for rotation), fan exhaust ducts and reverser assemblies • drains, bleeds, outlets • pitots, static ports, TAT sensors, angle of attack sensors • radome • fuel vents • commercial water supplies not frozen _ Use ground power for APU start if OAT ≤ -15°C (5°F). _ Cold soak effect: OAT -2 to +15°C, ice or frost can form on a/c structure if airframe is below 0°C. _ ECAM and EFIS DU’s may not be available with OAT below -15°C (5°F) until cabin conditioning has warmed the avionics compartment and cockpit IRS’s may take up to 15 minutes to alignment. _ Freezing temp of JET-A1 is -47 °C and slightly higher for other common fuels. Add warm fuel if necessary. _ The PROBE/WINDOW HEAT switch is turned on in the preflight (PNF duty) for cold weather procedures – temp ≤0°C (otherwise left in AUTO which is lights out). Engine Start _ Minimum oil temperature for starting is -40°C. _ The PROBE/WINDOW HEAT switch is turned back to AUTO after engine start. It provides a low level of heating to the cockpit windows and some probe heating. The level of heating automatically changes to high when airborne. The TAT probe is not heated on the ground. _ EAI goes on after all engines started (PNF duty before APU shut-down). DE-ICING & ANTI-ICING TREATMENT Before departure the following actions shall be performed before every departure: _ The departure check person shall perform a check for need to de-ice. The P-i-C shall, if applicable in cooperation with the departure check person, state the necessary de-/anti-icing treatment of the aircraft or be assured that there is no frost, ice or snow on the critical surfaces of the aircraft If de-icing performed: – The de-/anti-icing release person shall perform a check after de-/anti-icing verifying that all frost, ice and snow accumulations are removed from the critical surfaces of the aircraft after completed treatment. Note If conditions are such that frost, ice or snow might accumulate on the aircraft: – After anti-icing, the P-i-C shall determine the HOT for prevailing conditions. See Determined Hold-Over Time (HOT) table. The P-i-C or a delegated person shall perform a Pre-takeoff Check within 2 min before takeoff.
_ Usually performed after engine start so as to :
+ maximize HOT + prevent de-/anti-ice fluid from entering the cabin through open doors _ Coordinate with ATC at busy airports regards a departure slot time so de/anti-icing may be done at the suitable time to extend HOT. _ During off-gate de-icing, two-way communication between pilot and de/ anti-icing operator/ supervisor must be established prior to de/anti-icing treatment. This shall be accomplished either by intercom or by VHF radio. _ The mixture ratio and de-icing procedure (1–step/ 2– step) is selected by the de-icing specialist. The selection of mixture ratio is based on the actual weather conditions and ISO/ SAE tables. _ The PIC usually has no influence on selection of mixture ratio and de-icing procedure. Should the PIC, however, insist on a mixture or procedure other than that selected by the de-icing specialist, he is obliged to report the reason to personnel in charge. _ All de/anti-icing actions must be entered in the a/c log. The appropriate information will be communicated by the ground personnel and the respective de/ anti-icing code (fluid type, mixture and the time the final de/ anti-icing step commenced, e.g. ”Type II, 75/25, 1155”), shall be entered by the flight crew into the Technical Log on the ”Complaint” side of the log slip. _ The HOT table must only be used as a guideline, as many factors affect the time of protection of the aircraft. _ Aircraft preparation for fluid spraying: See the procedure in FCOM 3.04.91 Supp Tech –Adverse Weather -Cold Weather. _ The following outlines the various procedures to be applied before and after spraying: + All ENG and APU BLEED pushbutton must be set to OFF and the DITCHING pushbutton must be set to ON, to prevent any engine ingestion of deicing/anti-icing fluid. + The aircraft can be deiced/anti-iced, with the engine and/or the APU running or off. However, the APU or the engine should not be started during spraying. (De-ice and anti-ice fluid should not be sprayed directly into engine or APU intakes or any other vent.) + The aircraft must be same deiced/anti-iced treatment symmetrically on both sides. + If spraying is performed with the engines not running, a small negative cabin delta P may appear for a short time, just after selecting the ditching pushbutton to OFF. During this time, do not open any door or windows. De-/anti-icing Treatment Depending upon the severity of the weather, the deicing/anti-icing procedure must be applied in one or two steps either: + In one step, via the single application of heated and diluted deicing/anti-icing fluid. The fluid used to de-ice the aircraft remains on the treated surfaces and provides anti-icing capability.: This procedure provides a short HOT, and should be used in low moisture conditions only. The HOT starts from the beginning of the application of the fluid. 1 Step Procedure Heated anti-icing fluid applied Type I , II & IV fluid. (type III fluid discontinued) Type I less effective and used for low precipitation case only .
+ In two steps, by first applying the heated de-icing
A340 COLD WEATHER OPERATIONS fluid, then by applying a protective anti-icing fluid. The second step (anti-icing) is an over spray with hot or cold anti-icing fluid. The correct fluid and concentration shall be chosen with regard to desired HOT, OAT or aircraft skin temperature (whichever is lowest) and prevailing weather conditions. These two sprays must be applied consecutively. The HOT starts from the beginning of the application of the second fluid. 2 Step Procedure De-ice with either hot water, mixture of hot water & type I fluid (low viscosity and shorter H.O.T), or heated concentrate of type I fluid applied. Then anti-ice with type II or type IV fluid (high viscosity an longer HOT) applied.
_ If repeated anti-icing is necessary, ground crew must de-ice the surfaces with a hot fluid mixture before applying a new layer of anti-icing fluids _ Aircraft wings are sprayed first. After Treatment
Check 2 / Check 4
_ Keep the APU running with the bleed off for a few minutes after completion of spraying and perform a visual inspection of the aircraft surfaces. _ The slats/flaps and flight controls can be moved, because they no longer have ice. _ A deicing/anti-icing report must be filled out to indicate the type of fluid and when the spraying began. _ The information from ground personnel who performed the treatment must include: + Type of fluid used. + The mix ratio of fluid to water. + When the HOT began. + Result of post application check. TAXI OUT & BEFORE TAKE-OFF Taxiing _ On contaminated taxiways, the taxiing speed should be limited to 10 knots on straight way ( max 5 kts around corners -less in icy conditions), and any action that could distract the flight crew during taxiing should be delayed until the aircraft is stopped. _ On slush-covered, or snow-covered, taxiways: Flap selection should be delayed until reaching the holding point, in order to avoid contaminating the flap/slat actuation mechanism. Then do the “before takeoff checklist down to the line” when reaching the holding point. _ Avoid high thrust settings. _ Allow more than usual spacing with taxiing aircraft in front and begin braking for a stop well before normal (~3 times earlier). _ Anti skid does not operate at speeds below 10 knots. _ The use of EAI increases ground idle thrust, so the pilot must use care on slippery surfaces.. _ To minimize the risk of skidding during turns: Avoid large tiller inputs and use minimum radius turns. _ Use smooth nose wheel steering inputs. _ On slippery taxiways: It may be more effective to use differential braking and/or asymmetric thrust, instead of nose wheel steering. _ Warm up procedure When on ground in icing conditions at idle and in temperature below + 1°C (34°F) for extended periods of time, or if engine vibration occurs,
thrust should be increased 50% N1 for ten seconds periodically (do this once every hour) and just prior before takeoff, to shed any ice from the fan blades. Pre-takeoff Check
Check 3
Pre-takeoff check is the P-i-C's final check that the aircraft is free from frost, ice and snow before takeoff. It shall be performed within 2 minutes of commencing takeoff roll whenever conditions are such that frost, ice and snow might have accumulated on the critical surfaces after the de-/anti-icing treatment. Mental review: A mental review of prevailing conditions including: 1. Anti-icing treatment and HOT 2. Precipitation type and rate and variations experienced since anti-icing was performed. 3.Temperature, normally OAT but also skin temp if aircraft has been cold soaked. 4. Relation of temperature/dew point. 5. Wind or experienced jet blast (especially for Type I fluid). 6. Visual cues as available from flight deck. Check of representative surface : A visual check of a representative surface from within the flight deck. The Pre-takeoff Check is passed satisfactorily if: + The determined HOT has not expired, and + It is visually confirmed that the representative surface is free from frost, ice and snow. Check of wings: A visual check of wings. It may be necessary to open flight deck windows or perform the check from the cabin. The Pre-takeoff Check is passed satisfactorily if: + The determined HOT has not expired, and + The visual check confirms that wings are free from frost, ice and snow. _ If it cannot be satisfactorily confirmed by the Pretakeoff Check, the aircraft shall return for a new de/anti-icing. 4 CHECKs BEFORE TAKEOFF “MAKE IT CLEAN AND KEEP IT CLEAN” Check 1 for need to de-ice : A visual check of the entire aircraft to determine whether the de-icing is required. Check 2 after de-ice/anti-ice treatment: A check to verify that frost, ice and snow has been completely removed out and the anti-icing treatment has been performed correctly. This is done by the authorized person who performs the treatment and issues the deice/anti-ice release statement. ** Check 3 pre-takeoff check ** : The check is performed before every departure as an item in the departure check. _ This check is the P-i-C's final check that the aircraft ( wings or a representative surface) is free from frost, ice and snow before takeoff. It shall be performed within 2 minutes of start commencing takeoff roll whenever conditions are such that frost, ice and snow might have accumulated on the aircraft after the de-/anti-icing treatment. _ Done by flight crew within the determined HOT from inside cabin to ensure wings & control surfaces clear of ice, snow, slush & frost. _ If there are only two pilots and one has to leave the
A340 COLD WEATHER OPERATIONS control seat on the flight deck to check the wings then the aircraft must be stopped and the park brake set. _ Switch on all aircraft lighting at night. Check as close as possible to T/O. _ If in doubt or the surfaces can’t be properly evaluated, get an external inspection (even it means taxiing back to the ramp). _ Special attention should be given to the flight control check, which is delayed until just before take-off. _ Before Take-off Checklist is completed at the holding point. Check 4 if re treatment is required : it is required when HOT has expired. HOT may be extended depending on weather conditions (see the charts in RM). TAKEOFF _ Before the aircraft lines up on the runway for takeoff, the flight crew must ensure that the airframe has no ice or snow. Then, before applying thrust, the Captain should ensure that the nosewheel is straight on the runway. _ On contaminated runways use TOGA thrust. _ ENG START SEL to IGN/START for takeoff in turbulence, standing water or heavy rain. _ Takeoff technique is normal. _ Take-off is not recommended from a runway which is: + icy (though can land under certain conditions) + has more than 2” (50 mm) of loose dry snow + has more than 1” (25 mm) of wet snow + has more than 1/2” (12 mm) of slush (no tables available for calculations)
limitations also. Takeoff roll _ If there is a tendency to deviate from the runway centerline, this tendency must be neutralized immediately, via rudder pedal steering, not via the tiller. _ On contaminated runways, the flight crew should ensure that engine thrust advances symmetrically to help minimize potential problems with directional control. Rejected Takeoff _ Maintain directional control with rudder and differential braking if necessary. _ Reverse thrust is most useful at high speeds. CLIMB & DESCENT _ Whenever icing conditions are encountered or expected, the EAI should be turned on. Although the TAT before entering clouds may not require EAI, flight crews should be aware that the TAT often decreases significantly, when entering clouds. _ In climb or cruise, when the SAT decreases to lower than -40 °C, EAI should be turned off, unless flying near CBs. _ If the recommended anti-ice procedures are not performed, engine stall, over-temperature, or engine damage may occur.
_ V1 (VR and V2) reductions apply for contaminated runways – see FCOM 2.04.10
_ If it is necessary to turn on the EAI, and if ice accretion is visible because EAI was turned on late, then apply the following procedure: + Set the ENGINE START selector to IGN. + Retard one engine, and turn on set the EAI. + Smoothly adjust thrust, and wait for stabilization. + Set the ENGINE START selector to NORM + Repeat this procedure for the other engines.
_ Use of EAI and/or WAI results in a reduction in PERF MTOW, the flight crew must apply the applicable performance penalty.
_ WAI should be turned on, if either severe ice accretion is expected, or if there is any indication of icing on the airframe.
_ Crosswind limits apply for contaminated runways with reduced braking Action (see limitations below)
HOLDING & APPROACH
Takeoff Performance
_ Anti-skid must be serviceable (contaminated RWY) _ Inoperative brakes may affect dispatch (contaminated RWY) _ Reversers must be serviceable (contaminated RWY) _ When taking off from contaminated runways, it is not permitted to use FLEX thrust. However, derated thrust may be used, as required, in order to optimize aircraft performance. When available, a derated takeoff thrust results in lower minimum control speeds and, therefore, in a lower V1. _ A reduction in the minimum control speeds can sometimes enhance takeoff performance. _ Slush, standing water, and/or deep snow reduce the effectiveness of aircraft takeoff performance, because of increased rolling resistance and reduction in tire-toground friction. _ A higher flap setting increases the runway-limited takeoff weight, but reduces the second segment limited takeoff weight. _ Low visibility take-off (if required) has a set of
Caution (FCOM 3.04.30) 1. The pilot should avoid extended conditions with the slats extended.
flight in
icing
2. If the pilot suspects that a significant amount of ice is accumulating on unde-iced parts of the airframe, the min speed should be: _ Green Dot + 10 kt in clean configuration. 3. If the pilot suspects that a significant amount of ice is accumulating on de-iced parts (WAI inoperative) of the airframe, use CONF 3 for landing, and the minimum speed should be: _ Green Dot + 10 kt in clean configuration. _ VLS + 5 kt in CONF 1,2,3. _ Multiply the landing distance by 1.1 on dry runway or 1.05 on a wet runway. Holding _ Holding in icing conditions should be done with a clean wing. _ If holding is performed in icing conditions, the flight crew should maintain clean configuration. This is because prolonged flight in icing conditions with the slats
A340 COLD WEATHER OPERATIONS extended should be avoided. Approach _ If significant ice accretion develops on parts of the wing that have not been de-iced, the aircraft speed must be increased (see above). _ When the temperature is lower than ISA -10°C , the target altitudes (provided by the ATC) must be corrected, by adding the values. ( see cold weather altitude corrections below) LANDING & TAXI IN Landing _ Consider autobrake mode 4 for short or contaminated runways ( mode LO,2,3 for long and dry runways). _ Consider contaminated runway matters for landing. Landing distance calculations and technique, crosswind limits. _ Do not land on a contaminated runway if the antiskid is unserviceable. _ Do not land on a runway where braking action is reported as POOR unless a greater emergency exists. _ Correct flare technique (do not float). _ Maintain directional control with the rudder for as long as possible and then use nosewheel steering with care.
_ Obviously, landings should be avoided on very slippery runways. However, if it is not possible to avoid such landings, the following factors (linked to operations on contaminated runways) should be considered: . Braking action . Directional control. Braking Action _ The presence of fluid contaminants on the runway has an adverse effect on braking performance, because it reduces the friction between the tires and the surface of the runway. It also creates a layer of fluid between the tires and the runway surface, and reduces the contact area. _ The landing distances, indicated in the QRH, provide a good assessment of the real landing distances for specific levels of contamination. _ A firm touchdown should be made and MAX reverse should be selected, as soon as the main landing gear is on ground. Using reversers on a runway that is contaminated with dry snow may reduce visibility, particularly at low speeds. In such cases, reverse thrust should be reduced to idle, if necessary. _ The use of autobrake mode 4 for A345,346 is recommended, when landing on an evenly contaminated runway. It is possible that the DECEL light on the AUTO BRK panel will not come on, as the predetermined deceleration may not be achieved. This does not mean that the autobrake is not working. _ In the case of uneven contamination on a wet or contaminated runway, the autobrake may laterally destabilize the aircraft. If this occurs, consider deselecting the autobrake. Directional Control _ During rollout, the side stick must be centered. This prevents asymmetric wheel loading, that results in asymmetric braking and increases the weathercock tendency of the aircraft. _ The rudder should be used for directional control after touchdown, in the same way as for a normal landing. Use of the tiller must be avoided above taxi speed, because it may result in nosewheel skidding, and lead to a loss of directional control. _ When required, differential braking must be applied by completely releasing the pedal on the side that is opposite to the expected direction of the turn. This is because, on a slippery
runway, the same braking effect may be produced by a full or half-deflection of the pedal.
_ Landing on a contaminated runway in crosswind requires careful consideration. In such a case, directional control problems are caused by two different factors: + If the aircraft touches down with some crab, and reverse thrust is selected, the side-force component of reverse adds to the crosswind component, and causes the aircraft to drift to the downwind side of the runway. + As the braking efficiency increases, the cornering force of the main wheels decreases. This adds to any problems there may be with directional control. _ If there is a problem with directional control: + Reverse thrust should be set to idle, in order to reduce the reverse thrust side-force component. + The brakes should be released, in order to increase the cornering force. + The pilot should return to the runway centerline, reselect reverse thrust, and resume braking. Taxi In _ After landing in slow, slush or ice do not retract the flaps. The engineer must inspect them for ice accumulation or damage and will retract the flaps. GREEN and YELLOW ELEC PUMPS are placed ON temporarily to retract the flaps. _ If the approach was made in icing conditions, or if the runway was contaminated with slush or snow, the flaps/slats should not be retracted until after engine shutdown, and after the ground crew has confirmed that flaps/slats are clear of obstructing ice. This is because retraction could cause damage, by crushing any ice that is in the slots of the slats. _ When the aircraft arrives at the gate, and the engines are stopped, a visual inspection should be performed to check that the slats/flaps areas are free of contamination. They may then be retracted, with the electric pumps. PARKING & SECURING At the end of the flight, in extreme cold conditions, cold soak protection is requested when a longer stopover is expected. _ Remove the APU battery in very cold conditions – below -15°C (it can Freeze otherwise). _ Drain water systems to prevent freezing and possibly split pipes. The water draining procedure is in FCOM. _ Aircraft external vents and ports are closed e.g. DITCHING P/B ON). _ Park brake should be left off (chocks in). _ pitot and other protective covers ON. AIRCRAFT SYSTEM Engine Anti-Ice (EAI) _ Descent with anti-ice - The FMGCS assumes anti-ice is on for a third of all descents. _ If anti-ice use is prolonged, increase descent speed (to that programmed) or use half speedbrake. Wing Anti-Ice (WAI) _ When switched ON on the ground, anti-ice valves open
A340 COLD WEATHER OPERATIONS for about 30 seconds (test sequence) and then close as long as the aircraft on ground until airborne. _ Detection by + ECAM “SEVERE ICE” or + ice accretion on central external cockpit post o + Ice accretion on the windscreen wiper or window external frame Wing anti-ice is only the outer portion of the leading edge slat. Equipment Failure Cases _ EAI valves remain OPEN if electrical failure (fail safe open). _ WAI valves CLOSE if electrical failure (fail safe close).
BRAKING ACTION vs RUNWAY CONDITION vs XWIND
The concept of equivalent runway condition is used to determine the max crosswind limitation. The following table indicates the max recommended crosswinds related to the reported braking actions: Braking action/ Rwy Friction Coefficient/ Equivalent rwy condition/ Max Xwind kt GOOD 1 32 GOOD/MEDIUM 0.39-0.36 1 27 MEDIUM 0.35-0.30 2/3 20 MEDIUM/POOR 0.29-0.26 2/3 20 POOR ≤0.25 3/4 15 UNRELIABLE *** 4/5 5 (*** do not land unless a greater emergency exists) Equivalent Runway Condition 1 = dry, damp or wet runway (less than 3 mm depth standing water) 2 = slush 3 = dry snow 4 = standing water (with aquaplaning risk) or wet snow 5 = icy runway or high risk aquaplaning
Example: Let’s assume an airport elevation of 1000 ft. The airport elevation is the same as altimeter setting source altitudes elevation = 1000 ft. The ISA temperature at 1000 ft is 13°C. Let’s now assume that the actual OAT is -2°C. The ISA deviation is then, ΔISA =(13°C)-(-2°C) = -15°C. It is assumed that the minimum required actual altitude to clear the obstacle is 1200 ft. Value to be added: In order to account for the ISA deviation, the terrain/ obstacle elevation has to be increased by: 1200 x 0.04 x 15/10 = 72 ft In other words, the altimeter must read 1272 ft in order to have an actual height of 1200 ft. 2. Tabulated corrections ICAO publishes the following tables in the «PANS-OPS Flight Procedures» manual. They are based on an airport elevation of 2000 ft; however, they may be used operationally at any airport.
Example: Aerodrome elevation: 1000 ft; Reported temperature:-40°C
ALTIMETER CORRECTIONS The altimeter is designed for ISA temperatures. When it is extremely cold, the altimeter under-reads (most dangerous case). It is worse as altitude increases. This means corrections to cleared altitude, minima, marker / DME check heights and glideslope intercept altitudes must be applied. _ The altimeter error may be significant under conditions of extremely cold temperature. _ Altimeter corrections during approach (The table is calculated for a sea level AP. They are conservative when applied at higher AP). It is assumed that the aeroplane altimeter reading on crossing the fix is correlated with the published altitude, allowing for altitude error and altimeter tolerances. The choice of a method depends on of the amount of precision needed for the correction. 1. Approximate correction : Increase obstacle elevation by 4% per 10°C below ISA of the height above the elevation of the altimeter setting source or Decrease aircraft indicated altitude by 4% per 10°C below ISA of the height above the elevation of the altimeter setting source _ This method is generally used to adjust minimum safe altitudes and may be applied for all altimeters setting source altitudes for temperatures above -15°C.
References 1. FCOM 3.04.91 -Supplementary Techniques - Adverse Weather - Cold Weather 2. FCOM 3.04.30 -Ice & Rain Protection 3. FCTM 04.010 – Adverse Weather 4. FOM 3.2.12 De/Anti-icing 5. Getting to Grips with Cold Weather Operations 6. Lido RM part LAT, PFL 7. www.a330jam.com edit by punn33567
[email protected]
14 Nov 08
