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« on: May 08, 2012, 08:59:44 AM »
E’ tempo di neve, finalmente direi, ed è necessario decodificare il Metar
Es. EHAM 20017KT 9999 VCSH FEW025CB 00/M01 Q0997 R18C520394
R18C Pista 18 centro (e sinistra?!)
5 Neve bagnata
2 11% to 25% di pista contaminata
03 tre millimetri di spessore
94 azione frenante medio/buona
Non sempre però è così facile decifrarli, possiamo usare questo post per confrontarci e discutere i metar invernali.
Information on RWY conditions expressed by one or more 8-figure groups appended to the METAR.
MOTNE runway reports code AABCDDEE.
1st and 2nd figure RUNWAY DESIGNATOR AA
PARALLEL RWY:s The RIGHT RWY is identified by adding 50 to the Designator, e.g 77=27R, while the left RWY only the RWY figures appears e.g 27=27L
The figure 88 instead of a RWY designator indicates that conditions reported apply to all RWY at the Aerodrome.
The figure 99 instead of a RWY designator indicates that a previous RWY report is repeated.
3rd figure TYPE OF DEPOSIT B
0= CLEAR and DRY
1= DAMP
2= WET or Water Patches
3= RIME or FROST (<1mm)
4= DRY SNOW 5= WET SNOW
6= SLUSH
7= ICE
8= COMPACTED or ROLLED SNOW
9= FROZEN RUTS or RIDGES
/= TYPE of DEPOSIT NOT REPORTED, e.g due to RWY clearance/de-icing i progress.
4th figure EXTENT OF CONTAMINATION C
1= 10% or less of RWY covered
2= 11% to 25% of RWY covered
5= 26% to 50% of RWY covered
9= 51% to 100% of RWY covered
/= NOT REPORTED e.g due to RWY clearance or de-icing in progress.
5th and 6th figure DEPTH OF DEPOSIT DD
00= less than 1mm
01 to 90= depth in mm, e.g 23=23mm
92= 10cm
93= 15cm
94= 20cm
95= 25cm 96= 30cm
97= 35cm
98= 40cm
99= RWY not operational due to snow, slush, ice, large drifts or RWY clearance. Depth not reported.
//= Depth operationally not significant e.g with ice or rolled snow, or not measurable e.g RWY wet.
7th and 8th figure BRAKING CONDITIONS E
Either the measured Friction Coefficient or an estimated Braking Action is reported as follows
FRICTION COEFFICENT
Reported figures from 01 to 90 represent FC, e.g 05=FC 0.05, 28=FC 0.28
BRAKING ACTION Reported by following code figures
91= POOR
92= MEDIUM/POOR
93= MEDIUM
94= MEDIUM/GOOD
95= GOOD
99= UNRELIABLE, BA and FC not possible to assess, misleading, e.g in case of aquaplaning.
//= RWY not operational, BA and FC not reported.
SNOWTAM.
How to interpret a SNOWTAM.
SNOWTAM and MOTNE RWY reports are only provided for winter conditions (snow, ice etc) but not for other hazardous RWY conditions e.g RWY slippery when wet or, wet combined with dust.
Observations and measurements are made at routine intervals but only when RWY are contaminated and/or when there are significant changes.
There are certain definitions used in SNOWTAM and MOTNE.
DAMP
The surface shows a change of color due to moisture.
WET
The surface is soaked but there is no standing water.
WATER PATCHES
Significant patches of standing water are visible.
STANDING WATER
Standing water of significant depth and area which affects the braking action (aquaplaning).
FLOODED
Extensive standing water is visible.
DRY SNOW
Snow which can be blown if loose. If compacted by hand, will fall apart again upon release.
WET SNOW
Snow which, if compacted by hand will stick together and tend to form a snowball.
SLUSH
Water saturated snow which with a heel-and-toe slap-down motion against the ground will be displaced with a splatter.
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.
SNOWTAM example.
A)LSZH B)11070620 C)10 D)2200 E)40L F)4/5/4 G)20/10/10 H)30/35/30MUM J)30/5L K)YES L L)TOTAL M)0900 P)YES 12 S)11070920 T)FIRST 300M RWY 10 COVERED BY 50 MM SNOW, RWY CONTAMINATION 100%
A)LSZH
AERODROME LOCATION INDICATOR
B)11070620
DATE/TIME OF OBSERVATION (in UTC)
C)10
RUNWAY DESIGNATORS
D)2200
CLEARED RUNWAY LENGTH, if less than published length (m).
E)40L
CLEARED RUNWAY WIDTH, if less that published. (m; if offset left or right of center line add "L" or "R").
F)4/5/4
DEPOSITS OVER TOTAL RUNWAY LENGTH (Observed on each third of the runway starting from threshold having the lower runway designation number).
NIL - CLEAR AND DRY
1 - DAMP
2 - WET
3 - RIME OR FROST
4 - DRY SNOW 5 - WET SNOW
6 - SLUSH
7 - ICE
8 - COMPACTED SNOW
9 - FROZEN RUTS OR RIDGES
G)20/10/20
MEAN DEPTH (mm) FOR EACH THIRD OF TOTAL RUNWAY LENGTH.
H)30/35/30
FRICTION MEASUREMENT ON EACH THIRD OF RUNWAY AND FRICTION MEASURING DEVICE.
MEASURED or CALCULATED COEFFICENT
0.40 and above
0.39 - 0.36
0.35 - 0.30
0.29 - 0.26
0.25 and below
9 ESTIMATED SURFACE FRICTION
5 - GOOD
4 - MEDIUM/GOOD
3 - MEDIUM
2 - MEDIUM/POOR
1 - POOR
9 - Unreliable TYPE OF MEASURING EQUIPEMENT USED
BRD=Brakemeter-Dynometer
GRT=Grip Tester
MUM=Mu-meter
RFT=RWY friction tester
SFH=Surface Friction tester
(high pressure tire)
SFL=Surface Friction Tester
SKH=Skiddometer
(high pressure tire)
SKL=Skiddometer
(low pressure tire)
TAP=Tapley meter
J)30/5L
CRITICAL SNOWBANKS. If present, insert height (cm) / distance from the edge of runway (m) followed by L or R or LR if applicable.
K) YES L
RUNWAY LIGHTS (If obscured insert YES followed by L or R or both LR if applicable.
L) TOTAL
FURTHER CLEARANCE(If planned insert length (m) / width(m) to be cleared or if full dimensions insert TOTAL.
M)0900
FURTHER CLEARANCE EXPECTED TO BE COMPLETED BY...(UTC).
N)...
TAXIWAY (if no appropriate taxiway is available, insert NO).
P)YES 12
TAXIWAY SNOWBANKS (If more than 60 cm, insert "YES" followed by distance apart, m)
S) 11070920
NEXT PLANNED OBSERVATION/MEASUREMENT IS FOR (month/day/hour UTC).
T) First 300M RWY 10 covered by 50 mm
PLAIN LANGUAGE REMARKS (Including contaminant coverage and other significant information like sanding or deicing).
-----------------------------------------------------------------------------------------
TAKEOFF PERFORMANCE
When taking off from contaminated runways, it is not permitted to use FLEX thrust.
If anti-ice is used, the flight crew must apply the applicable performance penalty.
Slush, standing water, and/or deep snow reduce the effectiveness of aircraft takeoff performance, because of increased rolling resistance and reduction in tire-to-ground friction.
A higher flap setting increases the runway-limited takeoff weight, but reduces the second segment limited takeoff weight.
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