The onset of winter brings reminders of the 'dangers' of flying. Perhaps you think that flying is like motoring, and the mayhem that occurs as soon as a drop of snow settles on the roads. You can't compare flying and driving.
De Icing

The less we know about a subject the more risky we tend to believe it is, the more we know the less risky we think it is. But when we are experts in a subject we then are able to assess the risks as they really are and, what’s more important we can see them in context.

So it doesn’t ever surprise me that anxious flyers have extra things to worry about as winter approaches.

But before I explain about the precautions we take in flying let’s have a more detailed look at how we think about winter hazards like snow.  I want you though to see snow and ice  in context because to a  winter holiday makers, snow is good.

Let’s start by looking from a new pilot’s point of view. See Premium

… It’s called the availability heuristic, which works on the principle that  “if you can think of it easily, it must be important”.

Let’s look at an airport during ‘bad’ weather. See Premium.
For the snow clearance vehicles there is very little travelling time to the area where snow clearance is required. Aircraft do not bump into each other on the runway because one doesn’t land until the runway is clear.
All in all the organisation at an airport means that  a runway and its taxiways can be cleared relatively quickly. This is very different from the roads where problems mount up.
The law says that aircraft cannot take off when there is snow or ice on certain parts of the plane, (see here) this means that the plane is able to fly just as it does when it isn’t covered in snow or ice. Every aircraft has to have its wings free of ice at the time of take-off. See Premium fear of flying.
The procedure for de-icing a plane would either be the responsibility of the captain directly, or an airline may have a department responsible for it, which may be  airline engineers or a ground handling department.  See Premium for more help
The airworthiness certificate of the aircraft would be invalid if … see Premium for more The procedures with de-icing a plane are complex and usually before de-icing commences those involved with the procedure will … see Premium  for more help. The next thing to consider is the type of fluid to be used and whether or not it is to be used hot or cold. These factors determine the holdover time …that is to say the length of time that … see premium for more information
The aircraft must now get airborne within …
Pilots and airlines use a performance manual to determine the conditions and the maximum weight at which an aircraft can take off and at which it can land. When the runway is described as contaminated restrictions are imposed so that the same safety margins are achieved. Usually this means … see Premium for more information.
How well can a plane brake on an icy runway? … see premium for more information See para 1.2.2 in the following section.
At the take-off point we will decide whether we meet all the criteria for take-off under the prevailing conditions and then take off. … see Premium for more information. The message is that under these conditions there may be delays but there are very good reasons for them … keeping everything as safe as possible for you.
1.1 Introduction
1.1.1 The purpose of this FODCOM is to review and refresh some of the procedures and best practice that operators should adopt during winter operations.
1.2 Braking Action – General
1.2.1 Runways that are dry or wet with less than 3 mm of water will normally provide good braking.
1.2.2 Braking action is assumed to be poor on a wet runway that is notified as one that may be slippery when wet. Operators should ascertain from aerodrome operators the location and dimension of the part of the runway that has fallen below the minimum friction, ‘slippery when wet’ trigger level, in order that they can assess whether aeroplane performance is affected.
1.2.3 Braking action will not be measured or reported at UK licensed aerodromes on contaminated runways except on those covered in compacted snow and ice as described in the UK AIP AD 1.2.2 Snow Plan.
1.2.4 There is no reliable correlation available between the readings of Continuous Friction Measuring Equipment on a runway contaminated with water, slush and snow and aeroplane braking performance. Performance calculations must not be based on such readings. They will not be made available at licensed aerodromes in the UK.
1.2.5 Contaminants that aerodrome operators are unable to clear will be reported as depth and type of contaminant. These can be used with approved contaminated performance data to make a calculation of the landing or take-off distance required.
1.3 Aeroplane Performance Calculations for Operations on Contaminated Runways
1.3.1 Operators should avoid using contaminated runways whenever possible. All performance calculations for both take-off and landing on contaminated runways should be based on the depth and type of contaminant on the runway in accordance with approved contaminated performance data in the Flight Manual or approved supplement. The maximum depth of contaminant for operations can be found in AIC 15/2006 ‘Risks and Factors associated with Operations on Runways, affected by Snow, Slush or Water’. However, the aircraft Flight Manual limit should be used if more restrictive.
1.3.3 Take-Off Flight crews should be aware that in changing winter conditions the performance calculation carried out at the planning stage may no longer be appropriate at the time of take-off. A further calculation, based on the latest prevailing conditions, may be needed. Flight crews should also be made aware that using Electronic Flight Bag products for performance calculations on a contaminated runway often produces optimum flap setting performance where the computer uses the available runway length to accelerate the aeroplane to a higher speed in order to improve the climb performance. This is unlikely to be appropriate in such conditions where a shorter ground roll would be preferred.
1.3.4 Landing To compensate for operational variability JAR-OPS 1.515 and 1.520 specify factors that must be applied at the planning stage to the Flight Manual landing distance. In addition JAR-OPS 1.400 requires that prior to commencing an approach to land commanders must satisfy themselves that the weather and condition of the runway do not prevent a safe approach, landing or missed approach having regard to the performance information in the Operations Manual. If the flight proceeds as planned, the planning stage safety factors should remain valid. However in winter operations a scenario of rapidly changing conditions is possible. If conditions (including runway, meteorological, surface, aeroplane weight and configuration, and planned usage of decelerating devices) change or the aeroplane is required to land on a different runway, or in conditions that were not expected at the planning stage, it is still necessary to comply with JAR-OPS 1.400. JAR-OPS 1.400 does not specify additional factors in the same way as JAR-OPS 1.515 and 1.520. Operators should ensure that policies and procedures are in place to enable flight crews to assess whether sufficient landing distance is available at the time of arrival. The landing distance available should be the longer of that derived under paragraph above or that required by a non-normal configuration. However, in emergencies or abnormal configurations the flight crew needs to know the absolute landing distance (unfactored Flight Manual distance) for the aeroplane configuration in order to evaluate whether to land immediately or to divert to another aerodrome.
1.4 Contaminated Runway Clearance and Reporting Runway State
1.4.1 Aerodrome operators are responsible for clearing contaminants from runways and manoeuvring areas and keeping them clear as far as is reasonably practicable. Aerodrome operators should also measure and report the depth and type of contaminant present. Conditions will be reported by SNOWTAM, OPMET, RUNWAY STATE MESSAGE or RTF on request.
1.4.2 Contaminant is measured every 300 metres, between 5 and 10 metres either side of the runway centre-line and away from the effects of rutting. The measurement is reported in millimetres as a mean for each third of the runway. The contaminant will be described as Ice, Dry Snow, Compacted Snow, Wet Snow, Slush or Standing Water.
1.4.3 UK AIP AD 1.2.2 Snow Plan requires runway conditions to be reported every 30 minutes for as long as such conditions prevail, catering for a scenario of changing weather. In addition, the AIP requires the contaminant depth and type measurements to be carried out every 30 minutes. However, flight crews should be extremely cautious in rapidly changing conditions. Snow depth can increase rapidly and in typical UK conditions a slight thaw can also turn wet snow rapidly to slush. Flight crews should use the most adverse report available in such conditions.

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