Contaminated runways
Joined: May 2003
Posts: 198
Likes: 1
From: france
hello catch up,
just from memory, a rwy is considered contaminated when more than 25% of its length is covered with:
more than 3mm (1/8 inch) of (standing) water or
slush of 1/8 inch or greater
wet snow of 1/4 inch or greater
dry snow of 1 inch or greater
to cope with these contaminants sop usually command a reduction in v1 & a reduction in max take off weight.
also max contaminant depths are defined equal to or above which take off is prohibited.
minimum equipment list (mel) relief is also more restrictive, eg: antiskid must be operative, all thrust reversers must be functional, no assumed temperature t/off thrust etc.
last remark: difference between wet & contaminated rwy is defined for following reasons: although both conditions increase the stopping distances required, first, wet rwy's are more common than contaminated rwy's & then on contaminated rwy's acceleration capabilities can be severely restricted, remember the infamous airspeed ambassador accident in the 1950ties in munich with the manchester football team aboard( "the matt busby babes"),bobby charlton was a survivor.
the probable cause of this accident was an attemted take off on a snow covered rwy & the aircraft never reaching rotation speed, so the aircraft overran the rwy end & broke up. but then, much if not everything had still to be learned concerning contaminated rwy's.
just from memory, a rwy is considered contaminated when more than 25% of its length is covered with:
more than 3mm (1/8 inch) of (standing) water or
slush of 1/8 inch or greater
wet snow of 1/4 inch or greater
dry snow of 1 inch or greater
to cope with these contaminants sop usually command a reduction in v1 & a reduction in max take off weight.
also max contaminant depths are defined equal to or above which take off is prohibited.
minimum equipment list (mel) relief is also more restrictive, eg: antiskid must be operative, all thrust reversers must be functional, no assumed temperature t/off thrust etc.
last remark: difference between wet & contaminated rwy is defined for following reasons: although both conditions increase the stopping distances required, first, wet rwy's are more common than contaminated rwy's & then on contaminated rwy's acceleration capabilities can be severely restricted, remember the infamous airspeed ambassador accident in the 1950ties in munich with the manchester football team aboard( "the matt busby babes"),bobby charlton was a survivor.
the probable cause of this accident was an attemted take off on a snow covered rwy & the aircraft never reaching rotation speed, so the aircraft overran the rwy end & broke up. but then, much if not everything had still to be learned concerning contaminated rwy's.
Last edited by blackmail; 19th February 2005 at 19:53.
Joined: Mar 2000
Posts: 97
Likes: 0
From: England
Hi catchup, if its not in any of your manuals and someone wants a reference you can direct them to JAR-OPS 1.480
(2) Contaminated runway. A runway is
considered to be contaminated when more than
25% of the runway surface area (whether in
isolated areas or not) within the required length
and width being used is covered by the following:
(i) Surface water more than 3 mm
(0·125 in) deep, or by slush, or loose snow,
equivalent to more than 3 mm (0·125 in) of
water;
(ii) Snow which has been
compressed into a solid mass which resists
further compression and will hold together
or break into lumps if picked up (compacted
snow); or
(iii) Ice, including wet ice.
Here's the link, go to page 61
http://www.jaa.nl/section1/jars/494174.pdf
Scally
(2) Contaminated runway. A runway is
considered to be contaminated when more than
25% of the runway surface area (whether in
isolated areas or not) within the required length
and width being used is covered by the following:
(i) Surface water more than 3 mm
(0·125 in) deep, or by slush, or loose snow,
equivalent to more than 3 mm (0·125 in) of
water;
(ii) Snow which has been
compressed into a solid mass which resists
further compression and will hold together
or break into lumps if picked up (compacted
snow); or
(iii) Ice, including wet ice.
Here's the link, go to page 61
http://www.jaa.nl/section1/jars/494174.pdf
Scally
Joined: Jul 2000
Posts: 67
Likes: 0
From: ionoshere
If the FCOM doesn't specify reducing V1 I would be very cautious about reducing V1 as failure after this new speed will require longer acceleration times to reach Vr therefore increasing TODR, possible reduction in your 35' screen height and therefore making the climb performance data invalid. Just something to think about .
