Sleekjet From United States of America, joined Jul 2001, 2054 posts, RR: 20 Posted (14 years 4 months 3 weeks 5 days 9 hours ago) and read 1688 times:
Assuming an a/c has been properly de-iced, what are the runway parameters during winter storms? In other words, how much ice or snow on a runway does it take to scuttle a flight? And who decides? The pilot? The airport? The airline management?
OPNLguy From , joined Dec 1969, posts, RR:
Reply 1, posted (14 years 4 months 3 weeks 5 days 6 hours ago) and read 1635 times:
Each type of aircraft has different acceptible performance parameters, so it's difficult to give you a one-size-fits-all type of answer. If I can, what I'll do is give you a general example, which may then vary for a specific type of aircraft.
Snow (or slush) on a runway (commonly referred to as runway "clutter") affects both takeoff and landing performance. For takeoffs, clutter retards normal rates of acceleration, and for landings, braking (DEacceleration) distances are lengthened. The effect of both is that it makes a runway of X-length perform as if it's LESS than X-length, and since the airport folks can't come out and pour additional concrete to extend the runway on short notice ,aircraft weights must be reduced to keep the aircraft with safe allowable limits. Sometimes, this means that some folks get left behind even though there was an empty seat for them.
Generally speaking, an aircraft may not operate (that's takeoff or landing) on any runway covered by more than 1/2 inch of slush, 1 inch of wet snow, or 4 inches of dry snow. Anything beyond that, and the aircraft does not operate.
For takeoffs below the clutter levels mentioned above, the normal calculated runway takeoff weight is reduced by a factor of 5% or 10%, whether the clutter is minimal, or is closer to the max allowable values.
For landings, the clutter affects the "braking action" of the runway. A dry runway would (obviously) be the best for braking action, and is known as "dry" or "normal". As braking action deteriorates, the classifications range downward from "good", then "fair", then "poor", and finally, "NIL". Aircraft operations are prohibited on "NIL" surfaces, and it should also be noted that operations with "fair" and "poor" reported braking action also entail increasinly more restrictive crosswind limitations.
How is all this stuff measured? That's where things get interesting, as there are both OBjective and SUBjective methods in place.
The airport operator has the responsibility (here in the US, anyways) to have a snow control program in place, and they are generally pretty good about keeping everyone up-to-date of local field conditions. Some of this accomplished via issuance of a NOTAM (notice to airmen), but some stuff changes so quickly, that tower issues the information.
For takeoffs, snow depth is mostly commonly reported (objectively) by airport folks actually out there. A pilot can certainly make a depth determination, but obviously, doing so from from purely within the cockpit is a more subjective endeavor.
For landings, braking action can be assessed by either specially-equipped vehicles (that provide a numerical reading like MU, or other, that can be converted to good/fair/poor/NIL), or the pilots of any landing aircraft can report the braking action they experienced when they landing. Given the above two mechanisms, it's easy to see that one has more opportunity for subjectivity than the other.
Considering all the information above, who makes the decision? It sort of depends. If the airport operator decides that the clutter has exceeded limits and then closes the runway for plowing/brooming/de-icing, it's a no-brainer. That aside, here in the US, under FAR 121 Domestic/Flag rules, the captain and/or aircraft dispatcher make the call. If one of those two thinks they have limits, but the other has more current info that says they don't, the most conservative info takes precedence. I know there are probably some crews out there who will disagree, but I can assure you that within my 23-year career, I have personally told crews NOT to land on occasion because I had more timely info than they did. Does't happen often that way, but it does happen.
Sorry to be so long, but a complicated question...
OPNLguy From , joined Dec 1969, posts, RR:
Reply 3, posted (14 years 4 months 3 weeks 5 days 4 hours ago) and read 1595 times:
Another related factor in winter ops is plowing. At BUF last week, it was coming down so hard that they couldn't even see enough to plow, so off the runway they came. Once they eventually got back out there, there was so much accumulation (2-4 inches per hour) that it took them forever to get the runway, taxiways, and ramp areas cleared off enough to operate. Oh yeah, more heavy snow off and on the entire week. Something like 80 inches total...
Bicoastal From , joined Dec 1969, posts, RR:
Reply 4, posted (14 years 4 months 3 weeks 5 days 4 hours ago) and read 1578 times:
Prague had plenty of snow when I departed there on Sunday around noon. The runway was closed off and on most of the morning, but the equipment (BA 767) on which I was to fly out arrived on time. On my take-off, the British Airways 767, fully loaded with passengers, had a very short take off roll and handled the snowy runway just fine. I was supposed to be on a Lufthansa flight back to the USA via Frankfurt, but their equipment never left Frankfurt for Prague due to the snow storms. Hmmmm....do British pilots have more ability than Lufthansa's.....???? In any case, Lufthansa's personnel in Prague handled the cancellation very well. They rebooked me on BA to London then on my favorite United Airlines from London to the USA.
Maniac From United States of America, joined Apr 2001, 111 posts, RR: 0
Reply 5, posted (14 years 4 months 3 weeks 5 days 2 hours ago) and read 1561 times:
I had a flight out of PWM when the pilot went out in a plow truck with the snow removal crew to check the runway. He said that on landing the previous flight, the braking action was not good enough, and he wouldn't take off until he saw the runway.