Saturday, April 10, 2010

A Little Ice & A Lot of Wind

The flight last evening from KBDR down to KVKX was, shall we say, interesting. In more ways than one. The cold front, with associated precipitation, had come through Bridgeport overnight but the forecasts insisted that by late afternoon the rain would end and cloud cover would be going from broken to scattered. Well, that didn't exactly happen.

I'm thoroughly trained, so I filed for my usual route.[1] On departure at 2045Z in light rain, KBDR was reporting scattered clouds at 4,200 and a broken ceiling at 8,000. I knew I was going to find the freezing level at around 6,000 feet. New York Approach cleared me to 6,000 and gave me a heading of 290 in the direction of SAX. (You can see the initial track on the plot from FlightAware.com above. Click to enlarge.) As expected, the Outside Air Temperature (OAT) instrument indicated 32F. In a few miles, the ceiling came down to meet me and it was time to make myself unpopular with the controller.

I know the drill. The controller handling the White Plains sector needs to get me above the KEWR arrivals so I'll get "climb and maintain 7,000" and then, usually crossing the Hudson, "climb and maintain 8,000". But the ceiling looked thick and dark and gave every indication that if I poked N631S's nose in there I'd be thoroughly iced up in short order. So I told Approach, "Skylane 631 Sierra is in IMC at the freezing level. I will be unable to accept any higher altitude."

That got a reaction. The controller said, "Cessna 31S, 6,000 is just not going to work. We'll have to reroute you up over Huguenot and V162 at 4,000." That would be a pretty extensive loop to the north and would add about a half hour to my trip, but it sure beat picking up ice. I said, "That'll be fine, 31 Sierra."

Then the controller demonstrated why controllers are wonderful, by asking, "31 Sierra, are you going to be OK there at 6,000 for a few miles while we work this out?" I love these people. I replied, "31 Sierra is doing fine at 6,000." Of course, within a minute the OAT dropped to 30F and I began to pick up a bit of light rime ice on the strut and wheel fairing.

My best friend the controller soon came back to me and said, "Cessna 31 Sierra, y'know what, we're going to send you direct to JFK and then down V16 all at 6,000 feet, does that sound OK?"

I could see breaks in the clouds to the south and the ice was not accumulating so I replied affirmatively and heard, "31 Sierra, cleared direct JFK, maintain 6,000 and the next controller will have your full route." I entered JFK into the GPS-530W and turned to the south, soon to find myself just below the ceiling (see photo above). As the controller handed me off to JFK I said, "120.7 for Skylane 631 Sierra. Thanks very much for your help today." He replied, "No problem; I've been there myself."

Heading down toward JFK I noted that N631S was getting about 5 or 6 fewer knots of true airspeed than normal for the throttle, prop and fuel flow setting I was using. The small amount of ice I'd picked up was having an affect on performance.

I leaned forward and looked at the left wing. There was a narrow line of rime, perhaps 1/2 inch wide and 1/4 inch thick just below the leading edge, along the stagnation line where the incident airflow divides to pass above and below the airfoil. Kind of neat! And there was a small amount of rime on the struts (click to enlarge) and the gear fairings as well. Not hazardous, not getting worse, but something to get rid of at an early opportunity.

So when I was handed off by New York I checked in with "McGuire Approach, Skylane 631 Sierra, level 6,000, requesting 4,000 when and if you can." I was advised to expect 4,000 in a couple of miles and so it came to pass. At 4,000 feet the OAT was 41F and all of the rime disappeared in about a minute.

McGuire handed me off to Atlantic City Approach who, in their turn, turned me over to Dover. I knew that the forecast had called for breezy conditions in the DC area so I thought to check the METAR's for Andrews and Washington National.[2]

Here's what the XM Weather system had to say:
KADW 092155Z AUTO 32023G30KT 10SM CLR 12/M02 A2990 RMK AO2 PK WND 32030/2152 SLP129 P0008 T01161016 $
KDCA 092152Z 32013G29KT 10SM SCT060 12/M03 A2992 RMK AO2 PK WND 30033/2135 SLP133 T01221033

Well, clearly the flight was not through being interesting. The wind at Andrews would be almost a direct crosswind for the 6/24 runway orientation at VKX. And I'm not at all sure that either N631S or I can handle 23 knots of crosswind.[3]

If there was any consolation, it lay in the fact that the wind on the ground at KVKX is nearly always less than is current at either KADW or KDCA. My little airport is in a valley and surrounded by trees, and the terrain and forestation act to shield the runway environment from the worst of the wind. I'd need to press on until I could pick up the automated on-field weather information from the local traffic frequency (CTAF).

About 10 miles out I checked the weather - by switching to the CTAF and clicking the microphone three times. This triggers an automated weather statement and it reported "Winds Variable 270 to 050 at 12; caution, crosswind; caution, wind shear." Well, that was less bad. The wind was swirling around like a confused squirrel but at the surface it was just 12 knots.

I calculated that the wind would sort of favor Runway 6 and set up for a straight in approach. At about 1,000 feet I was holding a 45 degree crab angle to stay on the extended runway centerline. At about 250 feet the swirling ground effect tossed N631S about quite a bit - keeping on a path toward the runway and ensuring that the airspeed stayed somewhere near 75 knots was a bit challenging.

As we dropped below the tree line (about 100 feet AGL), the handling got a little less sporty. I put in the last notch of flaps and flared just a bit. As the left main gear touched the runway the ground speed must have been about 45 knots and so the rollout was short. I made my usual turnoff, stopped on the taxiway and took a deep breath. It was 2305Z, and it was good to be home.

[1]As regular visitors here already know, that means radar vectors west to Sparta, NJ, thence airways south to Solberg, NJ, west to East Texas in PA, south to Lancaster, PA, southeast to Baltimore and then direct to Potomac Airfield. It reads: SAX V249 SBJ V30 ETX V39 LRP V93 BAL and that is what the ATC computer will give me regardless of what route I request.(back)
[2]KVKX doesn't issue a METAR but Andrews (KADW) is about 4.5 miles away and National (KDCA) about 6. So while enroute, those two give a reasonable idea of what's going on around home plate.(back)
[3]N631S's Pilot's Operating Handbook (POH) says that the Maximum Demonstrated Crosswind for landing is 15 knots. Now, that is not a Limitation, and I believe I have managed about 17 knots of crosswind - but that pretty much used up all of the rudder and more than 20 knots of crosswind would be good cause for a diversion to a better oriented runway.(back)

1 comment:

Eric said...

Nice article, I enjoyed reading it!

Thanks for sharing it with us!