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Hi all,
anyone help me understand this one?
was listening in JFK tower last night during the little snowstorm we had, and they were using 4L for departures.
AA135 kept on asking for runway contamination reports and was asking if he can use some other runway instead,
AA135 also referenced the fact that its destination is HND
are there certain limitations in a snowstorm for different planes depending on one's destination??
Thanks
there are limits on the amount of contamination that can be on a runway before it becomes unusable for takeoffs and landings. there's MU values that are measured by a purpose-built car or simple braking action reports given by pilots after landing. one MU readings fall below a certain level, or a braking action report of Poor is recieved the runway has to be plowed/ swept/ treated etc.
i'm fairly certain that each carrier has it's own requirements for contamination and what's acceptable and what isn't.
AA going to HND means that it's going to be very heavy. Heavy plane means longer to brake which means that the V1 speed will be reduced. Contaminated runway will reduce the V1 speed even further to a point where there will be a significant gap between when the plane is committed to fly and when the plane can actually fly. A longer or less contaminated runway would reduce that gap to the standard 3-5 knots.
a contaimated runway also means your limitations for crosswinds is lowered, sometimes forcing you to takeoff on a runway that is less than preferred due to runway length, obstacles, etc.
Just running a quick comparison for a contaminated runway at JFK on the 747-400 could mean as much as a 90,000lb reduction in maximum takeoff weight for a runway which is just reported as wet vs one with a thin layer of wet snow.
That could be the difference between having to bump a significant amount or revenue or force a fuel stop
Thanks for the numbers. Didn't realize it was that drastic!
it is huge,the only time we never really sweated it was the DC3 ,with those big fat tires and low takeoff speeds she ATVed her way aloft through all sorts of muck and mire,ditto for landing.
If I remember correctly, at MTOW our Citation 650 needs over 12,000' for takeoff field length in a quarter inch of slush. Mind you, that's in a hot rod of a mid sized corporate jet!
Thank you all for the helpful info.
now I can understand also why the pilot asked for the 13 runway, because its longer....
wow, that's surprising!!Quote:
Originally Posted by threeholerglory
You're talking Critical Field Length, not actual takeoff distance, right?Quote:
Originally Posted by threeholerglory
Braking action reports play a big role in what's going to happen as well. Aside from an airline's rule (ie: 1/8" of snow on a runway can have it be considered contaminated), pilots telling the tower how effective their braking was on landing is info that gets passed on to upcoming arrivals. As I dispatcher, I call the tower and ask for those reports. So if I hear that a 747 landed ahead of my 757 with "good" braking action, I feel confident. If braking action on a smaller plane was "poor", I may get nervous (as will the pilot) and could consider diverting until the airfield operations folks have done a runway cleaning.
Braking action can either be Good, Fair, Poor or Nil.
There is also equipment that the airfield can use to test the braking action on the runway, which can often literally be a truck that has an aircraft tire that gives a numerical friction value which translates into the above four categories. These are known as an "mu" rating, and is more common in Europe.