Slippery When Wet...?

[JABBARA]

Hi Guys,


I usually come across with a phrase in the notams for Munich Int(EDDM) such as "Runways may be slippery when wet"

"Being slippery" is a natural conclusion after "becoming wet".

Or,
Does that phrase imply another meaning which I am unaware?

What dou you think it implies?


Thanks in advance

[TheOddOne]

Jabbara,

'Liable to be slippery when wet'

This means that the friction co-efficient of the runway falls below a pre-determined value when measured in the wet, or by a device which artificially wets the runway as it is measuring the friction. A typical friction value (referred to as 'mu') of .7 would be very good, but less than .55 would require the warning as above.

At the moment, there is no official direct correlation between runway friction and braking action. Lots of work is being done at present to try and rectify this situation, including high-speed trials with a variety of aircrft types and different measuring devices. However, it is still felt that in general, a poor 'mu' will result in poor braking action and therefore a longer than expected stopping distance, both when landing and rejecting a takeoff.

For many years, especially in adverse weather such as ice, snow and slush, reduced friction values have been passed to crews who have then adjusted their performance figures to suit. The UK CAA have intimated that until the unified friction value/braking action thing is sorted out, we shouldn't be passing the results of our friction runs to aircrew.

Many runways that have transverse grooves for drainage suffer from rubber buildup and it is this that causes the reduced wet friction. I don't know if this is the case at EDDM but it takes a lot of hard work and considerable expense to clean the rubber out of the grooves.

Cheers,
The Odd One

[BEagle]

If the runway is classed as 'Slippery when wet', it means that you must use 'icy runway' values if it's wet, not just 'wet runway' values - no matter what the temperature.

MRTOW will undoubtedly suffer.

[mutt]

BEagle,

Boeing aircraft normally have "SLIPPERY" and "ICY" charts available, they are based on vastly different MU values. Why would you expect people to use the ICY charts and not the SLIPPERY charts?


Mutt.

[Loose rivets]

If they can do it on newly washed restroom floors, wouldn't you think they'd put a few of those yellow cones down the centerline to warn us poor unsuspecting aviators.

[BEagle]

"When a runway is notified as 'liable to slippery when wet', take-offs or landings in wet conditions should only be considered when the distances available equal or exceed those appropriate to the conditions, or, where none are specified, those required for a very slippery or icy runway, as determined from information in the Aeroplane Flight Manual" is the precise answer....

'Slippery' is probably not the same as 'very slippery', so if there's no actual information available concerning the runway surface friction or braking action, safety would suggest using the icy runway factors.

[catchup]

This phrase is so helpfull like

"dark at night."

regards

[80/20]

It means that runway information is not standardized even within JAA.
Two questions are affected:
(1) Will it affect max weights?
(2) Can reduced thrust be used?

It might affect weights of large heavy aircrafts. It will not affect the weights for a normal 737CL or NG because the runway at EDDM is 4000mtr.

Most airlines use computer runway analysis from EFB, FLT OPS or a vendor. These are based on Boeing Airplane Flight Manual-Digital Performance System and will give numbers that are less conservative than the QRH and cost saving reduced thrust when permitted by regulations.

Reports such as "runway dry and braking action good" or warnings such as "slippery when wet" are of little use unless the person who makes the note use the same terminology as aircraft certification rules and manufacturers performance definitions. Reduced thrust takeoff will save millions for your airline. It should be used when conditions permit. Unfortunately well intended non standard reports can make it difficult to determine if it is safe to make reduced thrust takeoffs. Not a problem if it happens a few times each year. Big problem if it happens on a daily basis.

Wet or damp runway – may use reduced thrust but reduce V1 on short runways
Standing Water (more than 3 mm depth) - reduced thrust not permitted

In the EDDM example a maximum assumed temp takeoff with wet runway would give a medium weight B737NG 2300 mtr stopping margin* and about 1300 mtr stopping margin at MTOW.

(*) Stopping margin = runway remaining after the aircraft stops following RTO at V1. No credit for reverse thrust on a dry runway/reverse thrust is on for wet as per FAA/JAA approved calculations.

[oldebloke]

In view of the fact that it's always slippery when wet(as advised)enquire from tower the latest 'braking' pireps,or where did they(the proceeding traffic) clear the runway...In view of the fact that no authority 'certifies' to ICY'conditions- don't go there.All one can rely on are the latest comments of 'experienced' conditions......For the landing case and on Taxiing out......:ok:

[JABBARA]

The Odd One and all the guys who reply;

Thank you all for these valuable posts.


Jabbara.