SECTION 2: CHAPTER 8 SNOW AND SLUSH

Question 1

The measurement of snow, slush, ice and associated standing water is the responsibility of the Aerodrome Operator. The ATC unit is responsible for

Answer 1

issuing reports to pilots of aircraft directly under their control, but the general dissemination of information is the responsibility of the Aerodrome Operator. However, special arrangements may be made at some aerodromes for the measurement and reporting of snow and slush to be delegated to the ATC unit.

Question 2

The following terms are to be used to describe deposits on the surface of an aerodrome:

Answer 2

(1) Ice – water in its solid state, it takes many forms including sheet ice, hoar frost and rime;
(2) Dry snow – a condition where snow can be blown if loose or, if compacted by hand, will fall apart again upon release;
(3) Compacted snow – snow which has been compressed into a solid mass, that resists further compression and will hold together or break-up into chunks if picked up;
(4) Wet snow – a composition which, if compacted by hand, will stick together and tend to, or does, form a snowball;
(5) Slush – a water saturated snow which, with a heel and toe slap down action with the foot against the ground, will be displaced with a splatter;
(6) Associated standing water – standing water produced as a result of melting contaminant in which there are no visible traces of slush or ice crystals.

Question 3

The following changes, relating only to runway conditions, are classed as significant:

Answer 3

(1) Any change in surface deposit, i.e. snow turned to slush, water to ice, etc., and the effect on braking action where appropriate;
(2) Changes in depth greater than the following: 20 mm for dry snow, 10 mm for wet snow, 3 mm for slush;
(3) Any change in the available length or width of runway(s) of 10 per cent or more;
(4) Any change in the type of deposit or extent of coverage which requires reclassification in item F of the SNOWTAM;
(5) Any change in the distance apart of snowbanks from the criteria declared to be the value from which reporting begins;
(6) Any change in the serviceability of runway lighting caused by obscuring of the lights, with particular reference to the threshold;
(7) Any other conditions known to be significant according to local circumstances.

Question 4

Runway Surface Condition Reporting

Answer 4

It is CAA policy that Continuous Friction Measuring Equipment (CFME) should not be used on runways contaminated with wet snow, slush or water, and controllers must not pass runway co-efficient of friction measurements to pilots take in such conditions. The reason for this is that readings obtained from CFME equipment such as ‘Griptester’ and ‘Mu-meter’, unless used only on compacted snow and ice, are considered unreliable and in some cases may indicate a surface condition that is better than the actual condition. UK runways contaminated with compacted snow and ice are not normally made available for use, with Aerodrome Operators applying a ‘back to blacktop’ policy.

Question 5

Feedback from aircraft operators has shown that data relating to type, depth and extent of contamination reported for each third of the runway is useful to aircrew for performance calculations.

Answer 5

Each runway in use should be divided into a Touchdown Zone, a Mid Point, and a Stop end for reporting purposes. Within each of the three zones the % coverage, the type of contaminant, and the depth of contaminant together with the cleared runway width and length, should be recorded and promulgated. The Aerodrome Operator or its delegated Air Traffic Service Unit should promulgate runway surface condition using the following format.