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Tuesday, December 14, 2010

Winter Ops

Winter operations present a challenging environment that demands thorough planning, continuous assessment of conditions and careful management of options. N631S's flight last Friday from KBDR to KVKX brought all of that home for me.

I'd been watching the weather carefully for a day or so. It had been cold and dry in the northeast but an approaching system was promising to make things interesting. The low would pass to the north but we'd be getting a sequence of warm front, precipitation and cold front. The warm front was due at about flight time and might have precipitation associated with it.

Here are excerpts from 12Z Friday morning Terminal Area Forecasts (TAF's) with the expected weather for the time period that I'd be interested in.

 
TAF KBDR 101122Z 1012/1112 ...
FM101800 17006KT P6SM BKN080 OVC100
FM102200 17006KT P6SM BKN040 OVC070...

TAF KJFK 101122Z 1012/1118 ...
FM101700 17008KT P6SM BKN080 OVC100 
FM102100 17008KT P6SM BKN040 OVC070... 

TAF KABE 101131Z 1012/1112 ...
FM101700 18008KT P6SM SCT030 BKN060... 

TAF KRDG 101131Z 1012/1112 ... 
FM101700 18008KT P6SM SCT030 BKN060 
FM102300 00000KT P6SM BKN100... 

TAF KMDT 101134Z 1012/1112 ... 
FM101700 16008KT P6SM BKN060 
FM102000 18007KT P6SM BKN050...

TAF KBWI 101132Z 1012/1118 ... 
FM101800 19009KT P6SM SCT035 SCT060 BKN120 
FM102300 16004KT P6SM SCT150=

TAF KDCA 101132Z 1012/1112 ... 
FM101700 18011KT P6SM SCT050 SCT080 BKN150 
FM102300 17005KT P6SM SCT150=
(Note: Prior period TAF's (and a cornucopia of other climatological data) can be gotten from Ogimet, a wonderful resource developed by Guillermo Ballester Valor, meteorologist from the Spanish Meteorological Institute (INM).)
All that is not so bad. I was particularly interested in Allentown (KABE), Reading (KRDG) and Harrisburg (KMDT) because the weather would be approaching from the west and anything unpleasant would get there first. Those stations were showing some lower clouds (SCT030, scattered at 3,000) than the New York area. So on general principals I filed for an eastern route over New Jersey: KBDR DPK V16 ENO V312 OTT direct. Not that I expected to get that.

Things got a little more interesting as the day progressed. When the 18Z TAF's came up (a bit before 1:00 PM local time), the Pennsylvania stations had gotten a bit more pessimistic:

 
TAF KABE 101732Z 1018/1118 17007KT P6SM SCT030 BKN060
FM102300 VRB03KT P6SM BKN120...
 
KRDG 102222Z 1022/1118 17008KT P6SM SCT030 BKN060
TEMPO 1022/1024 P6SM -SN... 

TAF KMDT 101740Z 1018/1118 18010G15KT 1 1/2SM -SN OVC017
TEMPO 1018/1019 3SM -SN OVC025
FM101930 19008KT P6SM BKN060 FM102000 18007KT P6SM BKN050...
The Harrisburg (KMDT) TAF got my attention. At 18Z they were having continuous light snow with a mile and a half visibility under a 1,700 foot overcast. That's not good at all. The snow was gone from the forecast by 1930Z...but did I want to bet that way? I took another look at Atlantic City:
 
TAF KACY 101732Z 1018/1118 15008KT P6SM SCT030 BKN060 
FM102300 VRB03KT P6SM BKN080=...
That looked a whole lot better than Pennsylvania, with scattered to broken layers improving to a high ceiling by 23Z. The forecasts for KBWI and KDCA were holding up nicely and the departure was looking acceptable:
 
TAF KBDR 101737Z 1018/1118 08006KT P6SM SCT040 BKN110 BKN250
FM102100 15006KT P6SM VCSH BKN040 OVC070...
 
TAF KJFK 101737Z 1018/1124 13007KT P6SM SCT040 BKN110 OVC250
FM102100 16008KT P6SM BKN040 OVC070...
The one thing in the KBDR TAF that would need watching was the "VCSH" (showers in the vicinity) after 21Z. And, of course, I'd had an e-mail from FltPlan.com advising me to expect the routing over Pennsylvania as my clearance. I resolved to (a) be on my way prior to 21Z, and (b) insist on the New Jersey routing.

I had called the FBO earlier and asked them to plug in N631S's Tanis pre-heat system by noon. When I got to KBDR about 20Z, the engine was all toasty and ready to go. I quickly accomplished the pre-flight inspection and picked up the hand-held radio:

Me: "Bridgeport Clearance Delivery, November 631 Sierra."

KBDR: "631 Sierra, go ahead."

Me: "631 Sierra is filed IFR to VKX. I'm advised that you're going to read me a clearance via Sparta to Solberg to East Texas, etc. I am going to say "Unable" to that clearance due to icing conditions over Pennsylvania. Request you go back to Appraoch and get something for me that starts out 'vectors to Deer Park, V16...'"

KBDR: "631 Sierra, stand by."
I started the engine, to allow it to warm up while I waited for ATC to figure out what to do about me. I was a bit surprised (in a pleasant way) when Bridgeport tower came back to me with an excellent clearance: Vectors to DPK V16 ENO V268 SWANN Direct. ENO is the Smyrna VOR near Dover AFB; V268 departs ENO to the west and SWANN is 35 miles along that airway. This was good!

I entered the route into the Garmin GNS-530 and called for taxi clearance. As I taxied toward Runway 6 it began to snow. The forecast "VCSH" was a bit early.

This was the METAR in effect when I got to the airport:

 
KBDR 101952Z 09005KT 10SM OVC085 M02/M10 A3037 RMK AO2 SLP284
Snow? What snow? But the NEXRAD display on my GPS-396 showed there were bands of light snow, oriented N-S, crossing the area. And one band had arrived at KBDR. I sat at the hold-short line waiting for a Baron that was on the ILS 6 approach, and thinking about the snow. I heard the voice of my old instructor, Bob Parks, almost as though it was coming from the unoccupied seat next to me:
"Snow's not a problem as long as it's dry snow. It doesn't stick to the airplane. But it makes it very hard to see."
The Baron emerged from the cloud on short final. After it touched down, tower asked the pilot for flight conditions and braking action. He reported, "Flight visibility is three miles, ceiling indefinite. Braking action is good."

As the Baron turned off I reviewed my situation.

  • First, the snow was powdery and not adhering to the aircraft.
  • The outside temperature (OAT) was 29F.
  • The Baron had reported no problems.
  • As soon as I got a turn to the west I'd be out of it in minutes.
  • Ol' Bob had said you could fly in this if you didn't mind not being able to see.
  • And if N631S picked up any ice I could loop right around to the ILS 6 in short order.
Press on!

As N631S and I lifted off at 2028Z the following METAR was posted for KBDR:

 
KBDR 102028Z 08003KT 4SM -SN OVC026 M02/M08 A3037 RMK AO2 SNB24
The AWOS system thought the ceiling was at 2,600 feet but we were in the schmoo at about 900. It had been snowing for four minutes. I'd been given a heading of 090 by the tower and told to contact Approach. The New York controller cleared me up to 3,000 feet and turned me to the south.

Climbing out in IMC, I added two things to my normal scan: the leading edge of the wing strut and the OAT. If any ice began to adhere to the airframe it would show up first on the strut. And, as long as the temperature kept dropping with altitude, I would probably be in good shape. If I saw a rise in temperature (indicating an inversion), I'd be concerned that the snow might change to mixed precipitation and result in ice accumulation.

The OAT dropped steadily, to 20F at 4,000 feet. I got a turn to 220, then "Cleared direct Deer Park." Soon, near the Long Island shore, N631S and I flew out of the snow clouds.

The screenshot at left shows the snow band I'd just left behind, moving off to the east. Other precipitation appears downrange beyond JFK, but at 6,000 feet (and later back down to 4,000) it was never a factor for the flight. The forecasts of improving weather from southern New Jersey into the DC area verified nicely. The remainder of the trip, as evening fell, was quite pleasant.

Below, the flight track courtesy of FlightAware.com. The weather depiction in that image corresponds to the time that N631S and I were about 50 NM past JFK.

In spring, summer and fall, the question usually seems to be, "How shall we deal with this flight we wish to make?" In winter it becomes, "Can this flight we wish to make be accomplished with acceptable risk? If so, how?" The difference may be small, but I regard it as important.

4 comments:

Stephanie said...

Great minds think alike, or so it would seem.

Frank Van Haste said...

Dear Stephanie:

Indeed! I admit to failing always to dress for the possible emergency landing...perhaps I'll review my procedures.

Warm (heh) regards,

Frank

Karlene Petitt said...

Frank, So many extra challenges during winter for sure. Be aware. Be prepared. And never underestimate the power of mother nature when she's cold and irritable!
Happy Holidays!

Frank Van Haste said...

Karlene, thanks for reading, and adding your comment! Your words are especially important to me given your vast store of experience.

One of my goals is to expand the envelope of utility of my little airplane prudently, always respecting adverse weather. Your advice, "Be aware. Be prepared," is central to my planning process.

Mother nature is lots colder in the places where you go, and maybe even more irritable, so...

Fly safe(ly),

Frank