Runway Contamination Flashcards
Define Dry
Surface not affected by water, slush, snow or ice
Define Damp
When the surface shows a change of colour due to moisture
Define Wet
When the surface is soaked but no significant patches of standing water are visible
Define Water Patches
When significant patches of standing water are visible (more than 25% of the runway surface area to be used is covered by water more than 3mm deep)
Define Flooded
When extensive standing water is visible (more than 50% of the runway surface area to be used is covered by water more than 3mm deep)
How would you pass an unofficial observation to pilots?
“Unofficial observation from the control tower/pilots report. The runway surface condition appears to be damp/wet/water patches/flooded.”
What are the effects of water on aircraft operations? (5 things)
- Additional drag
- Possibility of power loss or system malfunction due to spray ingestion or impingement
- Reduced wheel-braking performance (the problems of aquaplaning)
- Directional control problems
- Possibility of structural damage.
Define dry snow
A condition where snow can be blown if loose or, if compacted by hand, will fall apart again upon release.
Define wet snow
A composition which, if compacted by hand, will stick together and tend to form a snowball.
Define compacted snow
Snow compressed into solid mass resists further compression, holds together or breaks into chunks if picked up.
Define 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.
What are Significant Changes in runway contamination?
- Any change in surface deposit (snow to slush, water to ice) and effect on braking action where appropriate
- Changes in depth greater than 20mm for dry snow, 10 for wet snow, 3mm for slush
- Any change in available length/width of runway of 10% or more
- Any change in type of deposit or coverage which requires reclassification on snowtam
- Any change in distance apart of snowbanks from initial report
- Any change in serviceability of runway lighting due obscuring, particularly threshold
- Any other conditions known to be significant locally.
When shall measurement of contamination begin?
As soon as the presence of snow, slush, ice & associated standing water is detected or observed and is expected to be operationally significant
When should further runway contamination measurements take place?
Whenever it appears from observations or pilot reports that there is a significant change in conditions.
Braking action & snow depth are to be measured asap after:
Any accident or incident in which snow, slush or ice on a runway may have been a contributory factor.
Where should an assessment of braking action be made & how is this info disseminated?
Each side of & 3 metres from the runway centre line. Measurement on one side only accepted if time is pressing.
Snowtam: values for each third of r/w
METAR: single mean value for full length
Pass to pilot on RT assessment for each third
Random very high/low figures to be ignored.
How is snow/slush depth measured?
Using standard depth gauge approx 3m each side of centre line, close to a/c wheels but clear of rutting, at 300m intervals. If not possible, distance can be increased to 600m.
Mean reading for each 3rd of runway.
How is runway contamination disseminated? (3 things)
- By SNOWTAM over AFTN
- By adding 8 figure code to WX report transmitted over OPMET system
- Important that reports are dispatched as soon as a runway is clear of deposits.
What is included in a SNOWTAM? (8 things)
- Runway cleared length/width
- Runway contamination including depth
- Runway braking action (thirds)
- Snow banks
- Runway lighting situation
- Taxiway & apron situation
- Further planned clearance
- Next observation.
(Max validity period: 24hrs)
An 8 figure runway state group for each runway in use is required to be appended to METAR or SPECI appearing in OPMET bulletins
True
A fresh runway state report should be prepared for each METAR
True
When should runway state reports be changed?
- When snow is judged to be turning to slush
- It is apparent that snow depth has increased
- It is considered that braking action is deteriorating & a braking test cannot be made immediately.
