Winter Operations

It is in the interests of an airport to stay open so that airlines can operate their schedules. A lot of money is invested in the equipment need to keep the runways and taxiways clear of snow. The difficulty, of course, is that if there is constant snow then as soon as one part is cleared another may be contaminated. The runway has to be cleared and cleaned to certain standards. Some snow or slush is allowed BUT it has to be measured and regular reports are made to pilots about the ‘Runway State’ Different aircraft will have different requirements, so one plane may be able to take off and another not.

For example, if the runway can only be cleared along three-quarters of its length, then smaller planes could take off but larger ones not be able to. So the conditions vary minute by minute and although it may look chaotic and disorganised to you, there are in fact dozens of variables to take into account from one minute to the next,

For the snow clearance vehicles, there is very little traveling 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 organization at an airport means that a runway and its taxiways can be cleared very 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, 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. Other parts which MUST be de-iced are those which are associated with the aircraft’s instrumentation.

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. The de-icing method has to be entered into the aircraft Technical Log so that the Captain can confirm that the correct procedures have been used.

The procedures with de-icing a plane are complex and usually before de-icing commences those involved with the preparing the aircraft for flight will refer to the appropriate procedures. Consideration of 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.

The aircraft must now get airborne within that holdover time, as laid down in the Operations Manual. This may be anywhere between 30 minutes and two hours depending upon the ambient conditions and the type of de-icing fluid used. The Airworthiness Certificate of the aircraft would be invalid if any of these procedures were violated.

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. Normally reduced take off weights apply when the runways are contaminated with water, slush or snow. When landing, the Runway State Report has to be considered to calculate stopping distances and braking effectiveness.


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. There is more information on the Premium Level Membership. 

The message for fearful flyers 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.

HERE IS A NOTICE TO PILOTS ISSUED BY AN AVIATION AUTHORITY

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

1.3.3.1 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.

1.3.3.2 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

1.3.4.1 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.

1.3.4.2 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.

1.3.4.3 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.

1.3.4.4 The landing distance available should be the longer of that derived under paragraph 1.3.4.3 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.