PRECAUTIONS DURING WINTER FLYING-Aviation Safety Management Society of India
Winter season is already here and it is time to be refreshed related to the associated flying hazards during Winter Season. Number of accidents/serious incidents have occurred around the world during winter months. The accident of Air India, Air Bus 320, at Jaipur, on 05 Jan 14, which fortunately did not result in casualties, highlights the need for involvement by all stakeholders to prevent any accident/incidents. Unfortunately, no lessons are learnt from the investigation reports of the accidents and history continues to repeat itself.
Aviation Safety Management Society of India, which is dedicated to promote Safety and Efficiency of Aviation Operations in the country, wishes to disseminate certain precautions which should be taken by the Operators/Pilots during winter flying, to prevent any incident/accident.
Hazards During Winter Flying.
Low clouds and Fog leading to almost zero visibility conditions, wet, slippery runways, frost, icing and snow blindness/white out are some of the major flight safety hazard during winter months particularly in Northern, North Eastern and to some extent in Western parts of India.
Formation of fog, its thickening leading to poor visibility conditions are quite unpredictable.
Most of the times, the fog thickens at sunrise and may last for long hours before clearing or may not clear for hours or even days.
Whenever the surface temperature and dew point temperature are very close to each other, dense fog can be expected.
There may be occasions when the fog is very widespread and it may be difficult to find a diversionary airfield in hundreds of kilometres of the destination airfield.
Low clouds may form quickly as the fog lifts and cover large areas, particularly in the hilly regions, they can cover the entire valleys, without any gaps for penetration.
Lack of Visual reference due Poor Visibility can lead to Visual Illusions, Spatial Disorientation, Loss of Situational Awareness and consequent CFIT accidents.
Western Disturbances in Northern India/North East Monsoons in Tamilnadu Region, associated with Thunderstorms, low clouds, poor visibility and wet/contaminated Runways present flight safety hazards.
Precautions during Winter Flying.
The Accountable Executives/Managers should ensure that all the Pilots have gone through the necessary flying and ground training with added emphasis on Low Visibility Operations.
All the pilots should be current in instrument flying, should have undergone Low Visibility Operations Training (LVO) and clearances etc. as per DGCA CAR. Good knowledge of DGCA CAR and circulars on All Weather Operations is essential for safety.
In depth knowledge about the aircraft, systems, procedures, understanding the phenomenon of visual illusions, spatial disorientation, recovery from unusual situations, strict adherence to SOP’s, rules, regulations and good CRM are key to successful accomplishment of the mission.
Operators/Accountable Executives, Air Crew, Ground Crew and Dispatchers should be fully aware about the winter hazards, particularly, phenomenon of fog and human factors limitations.
It is essential that the Accountable Executives, Supervisors and Operations staff closely monitor the operations during marginal weather conditions to ensure the safety of operations.
Professional planning and preparation for the flight is an inescapable necessity and should not be ignored. Pre Flight briefing for operations during poor visibility conditions should be much more comprehensive and the pilots must plan for contingencies for sudden deterioration of weather/visibility.
Thorough weather briefing and knowledge of the terrain and obstructions around the runways must be ensured before undertaking any flying. Briefing from the Met Department and various Weather Sites should be complemented with the experience of having operated in particular area or region. Knowledge of typical weather phenomenon affecting particular areas during winters is of paramount importance
Although most of the time the Met Forecast is reasonably accurate yet there have been instances when pilots have got caught in very poor visibility conditions, may be due to inaccurate Met forecast or lack of intelligent weather analysis on the part of the Pilots. Hence, these aspects must be kept in mind while planning flying during winter months.
A very high level of situational awareness must be achieved related to prevailing weather and its trends, terrain, availability and serviceability of Nav, Approach aids, watch hours and weather conditions at the neighbouring airports.
Continuous Monitoring of the weather situation at the destination with particular emphasis on visibility and RVR through ATIS, RT communication and other aircraft operating in the general area of your route and destination, is strongly recommended.
Pilots must be aware about the timings, extent, duration and severity of fog.
Special precautions need to be taken while flying during night, Dawn / dusk and Circadian Low. Night flying during winters should be undertaken with extra caution since poor visibility due fog during night flying is a serious hazard.
Use of landing lights during approach in foggy conditions should be as per SOP and situation, since it may degrade the visibility, lead to visual illusions and disorientation.
Timely and sound decision making based on the overall situational awareness, should be inculcated among the pilots. Overconfidence and complacency must be kept under check.
Operations to and from Delhi airport during winter months foggy conditions are very challenging and pilots need to be very alert, vigilant and plan diversions well in time lest they get caught into complicated situation.
Meticulous fuel planning as per the CAR is of paramount importance and must not be ignored. Contingency fuel to cater for unexpected delays/diversions due weather may be considered. Remember fuel is life.
Fuel planning and close monitoring of the fuel state is of great importance since one may be forced to divert due to poor visibility conditions and most of the time a diversion may not be easily available due to widespread fog.
Runway condition must be monitored very closely and special care taken during taxiing, take-off and landing to avoid slipping, skidding, runway excursion and overruns (Hydroplaning).
Do not succumb to the commercial pressures, on time performance, passenger related pressures, inconvenience, job demands and always evaluate the factors related to self, aircraft, weather, terrain and the associated risks, before undertaking or continuing the flight.
Follow standard operating procedures meticulously and do not hesitate to go around if unstable approach or divert in time if situation demands.
Additional points for Helicopters.
Generally, Helicopters fly at low levels below 2000 Ft AGL and Pilots in their eagerness to complete the task, tend to descend below minimum safe altitude when faced with fog or low clouds to stay in ground contact.
Most of the Helicopter pilots do not have the advantage of the EGPWS, Auto Pilot, reliable instruments or the Co Pilot
By virtue of their operations at low levels to helipads particularly in the hills and over water, the chances of Helicopter Pilots getting disorientated, with consequent CFIT accidents are high.
Helicopter pilots should be aware of the limitation of the Helicopter and their own limitations and must plan and prepare thoroughly with particular emphasis on weather, terrain and minimum safe altitude.
Ground contact flying should be the rule for helicopter pilots unless the Helicopter is suitable for IFR flight and the Pilots are qualified and IR rated. For IFR flights both the departure and arrival airport should be equipped with suitable IFR aids.
Spatial disorientation and loss of Situational Awareness are some of the serious challenges and hazard during poor visibility conditions. Hill shadows and flying into sun can result in late siting of obstructions or terrain. Be knowledgeable about these hazards.
While flying with reference to instruments, resist the temptation of looking outside, while flying on instruments. This can lead to spatial disorientation.
Single pilot operations particularly in the hills are much more challenging and the need for Single pilot to be very thorough in his/her planning, preparation, knowledge and timely decision making cannot be overemphasized.
Know the terrain and route safety altitudes well and plan your levels accordingly. Check, recheck and double check the altitude and make sure the altimeter setting is correct and the readings on pressure and Radio Altimeter are matching.
Know the obstructions in your area of operations. Pylons, communication/chimney towers, electric/telephone cables, trolley cables particularly in hilly areas pose a major hazard and knowledge of these is important for helicopter pilots.
Trolley cables come up in hilly areas to cart apples from one hillock to other and vigilance is required to look out for the same. Kindly intimate other operators in your area of operations about the existence of such hazards and mark them on maps.
Operations in snow bound areas require special skill levels. Special briefing and training is essential for safe operations in these areas. Snow blindness (white out), blowing snow during pick up, hover and sit down, skids/wheels getting stuck in snow, slippery conditions while on snow or melting of snow during long hours of operations and disorientation (White out) are some of the aspects which need to be taken into account for snow bound area operations.
Ice formation at high altitudes is a serious hazard. Anti-icing measures like serviceable and available ice detectors, heating elements, need for frequent movement of controls to prevent jamming of controls due ice formation, knowledge about freezing level and potential of ice formation are some of the areas which require the attention of the Operators/Pilots.
Before take-off at high altitudes and low temperature conditions, ensure that the main, tail rotor blades and other surface areas are free of ice and frost formation.
Check the manufacturer’s instructions about adding anti –icing additives in the fuel and use proper additive as required.
Check and ensure the serviceability of wind screen wipers, pitot heaters. Do not forget to switch on pitot heaters whenever required and switching them off on landing.
Be aware that snow fall can change the appearance of the terrain and perspective during take-off/landing.
Helicopter batteries need to be maintained properly and protected during night from extreme cold temperatures by keeping them in warm rooms or wrapping in blankets etc.
Cracking of various seals can take place and must be checked periodically.
Engineer and technicians should ensure thoroughness during their maintenance and servicing activities. Tendency to take short cuts due to very cold temperatures should be avoided.
Low light conditions during winter months may result in minor cracks or other small defects getting overlooked. Ensure adequate lighting for servicing and maintenance work.
Maintenance staff should be careful while climbing on the helicopter for maintenance work since surface may be slippery due to frost, icing etc.
Take special precautions during taxiing and maintain very good look out for obstructions, aircraft and vehicles.
Do not succumb to commercial pressures, VIP pressure, peer pressure, Self-imposed pressure, job demands, and personal convenience. Never take chances with the poor weather conditions and don’t be overconfident or macho. Overconfidence has taken the lives of many pilots.
There may be occasions when frustration may set in because of the delays and postponement of departure timings/dates and long wait on ground due prolonged bad weather spells. Number of pilots have taken chances with weather under such conditions and have met with serious /fatal accidents. Please be aware of the grave danger under such conditions and take very considered decisions.
Further Reading-Additional Points.
Airplane operation in cold weather conditions can cause special problems because of the effects of frost, ice, snow, slush, and low temperature.
The airplane maintenance manual (AMM) provides procedures for removal of contaminants from the airplane and the prevention of subsequent accumulation of frost, ice, snow, or slush. In addition, the operator must ensure that the maintenance procedures for winter operations are appropriate for the weather conditions.
When thickened airplane de-icing/anti-icing fluids (i.e., SAE International Types II, III, and IV fluids) dry, they may leave a very fine, powdery residue in critical areas in wings and stabilizers. This residue can rehydrate and expand into gel-like materials that can freeze during flight and cause restrictions in the flight control systems.
Be aware of how frequently airplanes are being de-iced/anti-iced.
Be aware of whether a one- or two-step application process is being employed.
Ensure that proper procedures, including storage, handling, and application of fluids, are being followed by airline personnel or contracted de-icing service providers.
Establish an inspection and cleaning schedule for thickened fluid residue to help ensure that no flight control restrictions will occur.
Examine areas such as wing rear spar, wing leading edge devices, horizontal stabilizer rear spar, vertical stabilizer, auxiliary power unit bay, control tabs and linkages (when applicable), and the bilge area of the tail cone.
Visually inspect for dry or rehydrated residues in these areas. This inspection and cleaning should be performed in accordance with the recommendations found in the AMM for the specific airplane model involved.
Apply lubricants and corrosion inhibitors as necessary to the areas where residue cleaning occurs.
Airplane de-icing/anti-icing fluids and many runway de-icing fluids are not compatible — interaction between the two may contribute to the formation of gel residues.
When these fluids combine, the salts in some runway fluids enhance the separation of the polymers contained in thickened airplane fluids, leading to a more rapid formation of gel residues.
When runway de-icing fluid contaminates thickened airplane anti-icing fluid, there can be significant degradation of the fluid’s performance.
HOT values can be reduced and adherence or unacceptable flow-off may result. Runway de-icing fluid can get onto the wings and tails by various means, such as spray from the nose gear, spray kicked up by the engine exhaust of other airplanes, or from activation of the engine thrust reversers.
Runway de-icing fluids are hydroscopic fluids, so they don’t dry out very quickly, causing them to leave a thin wet layer on the wing that can be difficult to see. This implies that the use of hot water or Type I fluid to clean the wing prior to the application of thickened anti-icing fluid (i.e., Type II, III, or IV) is even more important than previously thought. On September 14, 2010, EASA issued Safety Information Bulletin 2010-26 on this subject, recommending the use of the two-step application process.
Catalytic oxidation of carbon brakes may result from exposure of the brakes to alkali metal (i.e., organic salt)-based runway de-icers. This may cause severe damage to the brakes and drastically shorten their service life. These runway de-icers have also caused corrosion of electrical connectors and hydraulic system components.
CONSIDERATIONS FOR FLIGHT CREWS
Winter or cold weather operations are generally associated with a combination of low temperatures and frost, ice, slush, or snow on the airplane, ramps, taxiways, and runways. The airplane flight manual (AFM) defines icing conditions as when the outside air temperature (OAT) on the ground or total air temperature (TAT) in flight is 50 degrees F (10 degrees C) or less and any of the following exist:
Visible moisture (e.g., clouds, fog with visibility of one statute mile [1,600 meters] or less, rain, snow, sleet, or ice crystals).
Ice, snow, slush, or standing water on the ramps, taxiways, or runways.
On runways contaminated by slush, snow, standing water, or ice, the use of fixed derate reduced thrust is permitted, provided that airplane-take-off-performance planning accounts for the runway surface condition. Use of the assumed temperature reduced thrust method, alone or in combination with a fixed derate, is not permitted on contaminated runways.
Boeing does not recommend take-offs when slush, wet snow, or standing water depth is more than 0.5 inch (13 millimetres) or dry snow depth is more than 4 inches (102 millimetres).
Boeing recommends that flight crews make themselves aware of the following recent developments in the area of winter operations:
Starting with the 2010 winter season, HOT guidelines for Type I fluids include a new set of times to be used when the fluids have been applied to composite surfaces. Testing performed during the last three winter seasons has shown that HOT values for Type I fluids on composite surfaces are significantly shorter (on the order of 30 percent) than for aluminium surfaces. Although this topic has been discussed in the FAA Notice of its “FAA-Approved De-icing Program Updates” for the last two winter seasons, this year both the FAA and TCCA are publishing separate HOT guidelines for composite surfaces. In addition to extensive use of composites on newer models, many older models also have numerous composite surfaces (e.g., spoilers, ailerons, flaps, slats, etc.).
During taxi-out, avoid using reverse thrust on snow- or slush-covered runways, taxiways, or ramps unless absolutely necessary.
Using reverse thrust on snow- or slush-covered ground can cause slush, water, and runway de-icers to become airborne and adhere to wing surfaces.
General Maintenance Precautions-Winter
Ice that has accumulated on the fan blades while the airplane has been on the ground for a prolonged stop is called “ground-accumulated ice” and must be removed before engine start.
Ice that has accumulated on the fan blades while the engine is at idle speed is called “operational ice” and is allowed to remain on the fan blades before taxi because the ice will be removed by engine run-ups prior to take-off.
The right and left sides of the wing and horizontal stabilizer (including the elevator) must receive the same fluid treatment, and both sides of the vertical stabilizer must receive the same fluid treatment.
Treat the wings and tails from leading edge to trailing edge and outboard to inboard.
Treat the fuselage from the nose and work aft. Spray at the top centreline and work outboard.
Do not point a solid flow of fluid directly at the surfaces, gaps in airframe structure, or antennas. Instead, apply the fluid at a low angle to prevent damage, while pointing aft for proper drainage.
Make sure that all of the ice is removed during de-icing. There may be clear ice below a layer of snow or slush that is not easy to see. As a consequence, it may be necessary to feel the surface to adequately inspect for ice.
Do not spray de-icing/anti-icing fluids directly into auxiliary power unit (APU) or engine inlets, exhausts, static ports, pitot-static probes, pitot probes, or TAT probes.
Do not spray hot de-icing/anti-icing fluid or hot water directly on windows as it may cause damage.
Ensure that ice or snow is not forced into areas around flight controls during de-icing.
Remove all ice and snow from passenger doors and girt bar areas before closing.
Cargo doors should be opened only when necessary. Remove the ice and snow from the cargo containers before putting them on the airplane.
If SAE Type II, III, or IV fluids are used, remove all of the de-icing/anti-icing fluid from the cockpit windows prior to departure to ensure visibility.
De-icing/anti-icing fluid storage tanks must be constructed of a compatible material. For thickened fluids, the tanks must be of a material that is not susceptible to corrosion (e.g., stainless steel or fiberglass). This is particularly important for thickened fluids because their viscosity can be permanently decreased if they are contaminated or exposed to excessive heat or mechanical shear during handling and application.
When there is ice, slush, snow, or standing water on the runways or taxiways during taxi-in, examine the airplane when it gets to the ramp. Look for any damage to the airplane surfaces and for contamination that may have collected on the airplane. Carefully remove the contamination.
Proper maintenance procedures for landing gear during cold weather operation as defined in the AMM can help reduce degradation of the structural joints and ensure optimal shock strut performance.
Operating during cold weather can adversely affect the ability to properly lubricate the landing gear joints. Where possible, perform scheduled lubrication at maintenance bases where the temperature is above freezing.
A heated hangar is the next most effective means of ensuring proper lubrication. If lubrication must be accomplished outside a heated hangar in temperature below freezing, the landing gear structure itself should be heated by blowing hot air directly onto the structure or into an enclosure around the structure.
Do not point a spray of deicing/anti-icing fluid directly onto wheels or brake assemblies.
Remove contamination (e.g., frost, ice, slush, or snow) from the area where the main and nose gear tires will be positioned when the airplane is parked at the gate. If tires are frozen to the ramp, the airplane should not be moved until they are free.
General Guidance for Flight Crew
PRIOR TO TAXI.
Carefully inspect areas where surface snow, ice, or frost could change or affect normal system operations.
Perform a normal exterior inspection with increased emphasis on checking surfaces, pitot probes and static ports, air-conditioning inlets and exits, engine inlets, fuel-tank vents, landing-gear doors, landing-gear truck beam, brake assemblies, and APU air inlets.
Take-off with a light coating of frost (up to 1⁄8 inch [3 millimetres] thick) on lower wing surfaces caused by cold fuel is allowable. However, all leading-edge devices, all control surfaces, the horizontal tail, vertical tail, and upper surface of the wing must be free of snow, ice, and frost.
Perform the normal engine start procedures, but note that oil pressure may be slow to rise. Displays may require additional warm-up time before engine indications accurately show changing values. Displays may appear less bright than normal.
Engine anti-ice must be selected ON immediately after both engines are started, and it must remain on during all ground operations when icing conditions exist or are anticipated.
Do not rely on airframe visual icing cues before activating engine anti-ice. Use the temperature and visible moisture criteria.
Operate the APU only when necessary during de-icing/anti-icing treatment.
Do not operate the wing anti-ice system on the ground when thickened fluids (e.g., SAE Type II, III, or IV) have been applied. Do not use the wing anti-ice system as an alternative method of ground de-icing/anti-icing.
If the taxi route is through ice, snow, slush, or standing water, or if precipitation is falling with temperatures below freezing, taxi out with the flaps up. Taxiing with the flaps extended subjects flaps and flap devices to contamination.
Check the flight controls and flaps to ensure freedom of movement.
If there are any questions as to whether the airplane has frozen contamination, request de-icing or proceed to a de-icing facility. Never assume that snow will blow off; there could be a layer of ice under it.
In rainy conditions with OAT near freezing, do not assume that raindrops on surfaces have remained liquid and will flow off; they could have frozen onto the surface. A similar issue can occur due to cold-soaked fuel in the wing tanks.
Ice that has accumulated on the fan blades while the airplane has been on the ground for a prolonged stop is called “ground-accumulated ice” and must be removed before engine start.
Ice that has accumulated on the fan blades while the engine is at idle speed is called “operational ice” and is allowed to remain on the fan blades before taxi because the ice will be removed by engine run-ups prior to take-off.
DURING TAXI
Allowing greater than normal distances between airplanes while taxiing will aid in stopping and turning in slippery conditions. This will also reduce the potential for snow and slush being blown and adhering onto the airplane or engine inlets.
Taxi at a reduced speed. Taxiing on slippery taxiways or runways at excessive speed or with strong crosswinds may cause the airplane to skid. Use smaller nose-wheel steering and rudder inputs. Limit thrust to the minimum required.
Use of differential engine thrust assists in maintaining airplane momentum through a turn. When nearing turn completion, placing both engines at idle thrust reduces the potential for nose-wheel skidding. Differential braking may be more effective than nose-wheel steering on slippery or contaminated surfaces.
Nose-wheel steering should be exercised in both directions during taxi. This circulates warm hydraulic fluid through the steering cylinders and minimizes the steering lag caused by low temperatures.
During prolonged ground operations, periodic engine run-ups should be performed per the Flight Manual or SOP.
BEFORE/DURING TAKEOFF
Do the normal Before Take-off Procedure. Extend the flaps to the take-off setting at this time if they have not been extended because of slush, standing water, icing conditions, or because of de-icing/anti-icing. Verify that airplane surfaces are free of ice, snow, and frost before moving into position for take-off.
In icing conditions, refer to the guidance in the Flight Manual/SOP regarding static engine run-up before take-off.
Before brake release, check for stable engine operation. After setting take-off engine pressure ratio (EPR), or N1, check that engine indications are normal, in agreement, and in the expected range. Check that other flight deck indications are also normal.
Rotate smoothly and normally at VR. Do not rotate aggressively when operating with de-icing/anti-icing fluid.
Retract flaps at the normal flap retraction altitude and on the normal speed schedule.
A larger temperature difference from International Standard Atmosphere (ISA) results in larger altimeter errors.
When the temperature is colder than ISA, true altitude is lower than indicated altitude. Consider applying the Cold Temperature Altitude Corrections, especially where high terrain and/or obstacles exist near airports in combination with very cold temperatures (-22 degrees F/-30 degrees C or colder). Operator coordination with local and en-route air traffic control facilities is recommended.
DESCENT
Unless the airplane has fully automatic activation of ice protection systems, anticipate the need for activating the engine and/or wing anti-ice systems at all times, especially during a descent through instrument meteorological conditions or through precipitation.
When anti-ice systems are used during descent, be sure to observe minimum EPR/N1 limits (if applicable).
LANDING
The flight crew must be aware of the condition of the runway with respect to ice, snow, slush, or other contamination.
Follow the normal procedures for approach and landing. Use the normal reference speeds unless otherwise directed by the Flight Manual/SOP.
Arm the autobrake and auto spoiler systems, if available, before landing.
The airplane should be firmly flown onto the runway at the aiming point.
Immediately after main-gear contact with the runway, deploy the speed brakes if not already deployed by the automatic system.
Without delay, lower the nose-wheel to the runway to gain nose-wheel directional control. Do not hold the nose gear off the runway when operating on slippery or icy runways.
Use of autobrakes is recommended. They will allow the pilot to better concentrate on directional control of the airplane. If manual braking is used, apply moderate to firm steady pedal pressure symmetrically until a safe stop is assured.
Let the anti-skid system do its work. Do not pump the brake pedals.
Do not use asymmetric reverse thrust on an icy or slippery runway unless necessary to arrest a skid.
When using reverse thrust, be prepared for a possible downwind drift on a slippery runway with a crosswind.
During winter operations, it is even more important than usual that the flight crew not attempt to turn off the runway until the airplane has slowed to taxi speed.
Taxi at a reduced speed. Taxiing on slippery taxiways or runways at excessive speed or with strong crosswinds may cause the airplane to skid.
The Cold Weather Operations Procedure specifies how far the flaps may be retracted after landing in conditions where ice, snow, or slush may have contaminated the flap areas.
If the flap areas are found to be contaminated, flaps should not be retracted until maintenance has removed the contaminants.
Use the engine anti-ice system during all ground operations when icing conditions exist or are anticipated.
Although efforts have been made to include as many precautions to be taken during winter flying, as possible, yet some points may have been missed out. Operators may like to add some aspects which may be typical to their area of operations.
Operators should always endeavour to match the man with the machine, mission and weather conditions. Adequate instrument flying practice, simulator flying, currency, recency in area of operations, comprehensive briefing covering the entire spectrum of the various aspects of the operations, maintenance and monitoring performance are key to the successful conduct of the operations.
Respecting the weather and courage of conviction to say no if the safety of the flight is likely to be compromised must be impressed upon the pilots.
ASMSI wishes you all safe and efficient flying operations during winters.
Many Many Happy landings.
Air Commodore BS Siwach AVSM YSM VM
Director General, ASMSI
