Saturday, November 28, 2009

Finally, About the Ice...

Now, a fourth and last post about my flight on Wednesday afternoon from KBDR to KVKX.

In the first post in the series, written while planning for the flight, I observed that the routing usually given me by ATC had some issues with potential icing. The clearance always starts like this: vectors to SAX, V249 to SBJ, V30 to ETX. The cruise altitude is 8,000 MSL. Their idea is to take me westbound to the north of the New York Class B airspace and then southbound to central New Jersey while above the EWR arrivals, and thence west toward Allentown. The freezing level forecast for that routing was in the band from 7,000 to 9,000.

As an aside, it seems to me that forecasts of freezing levels are usually very accurate. I've found that freezing level and temperature aloft maps from Aviation Weather Center offer remarkably good guidance even two or three days before a flight.

I considered saying "unable" and trying to insist on a routing over JFK and south along the New Jersey shore (along V16) at 6,000 MSL - but I knew that the negotiation would be time consuming and I was equally concerned about changing conditions at my destination (see post #2). So I decided to accept the clearance and work it out en route if I found any ice.

After departing into the murk I was cleared initially to climb to 5,000 MSL and then stepped up to 8,000 as I approached the Hudson River. I was watching the Outside Air Temperature (OAT) gage closely. At 8,000 feet it showed an OAT of 35 Fahrenheit degrees. OK so far, but I knew that the freezing level was sloping downward to the west so I was not out of the woods.

Understanding that the OAT gage might be optimistic, I watched the left strut and the nose of the left main gear fairing out my side window for any sign of ice accretion.

The OAT dropped to 34 degrees and I figured I'd better give the controller a "heads up". I transmitted, "New York, Skylane 631S," and got a quick "31 Sierra, go ahead."

"31 Sierra is IMC and very close to the freezing level. If I lose a degree or two we will have to work out lower," I said and the controller responded with "OK, 31 Sierra, keep me advised."

I felt better because I was sure that the controller was already thinking about how he'd deal with me if I needed to descend into airspace that was typically used for EWR inbound traffic. But fortune smiled on him (and me), the OAT held steady, and no ice formed. I made the left turn at SAX, got handed off to another sector and as I neared SBJ I was turned to the west and told to contact Allentown Approach.

Still in the clouds, I noted the OAT drop to 33 degrees. Well clear, now, of the flow of EWR arrivals, it was time to do something. I transmitted, "Allentown, November 631 Sierra, Request."

"31 Sierra, say request," came back. "31 Sierra is going to need lower to avoid icing conditions. Is 6,000 available?"

Without delay, I was cleared, "Skylane 31 Sierra, descend and maintain 6,000 feet." N631S and I descended immediately and when we leveled at 6,000 we found the OAT to be 44 degrees. I stopped worrying about ice and devoted all available worrying to ceiling and visibility at my destination.

Here's my take-away lesson from this: It's often said that if you encounter icing you need to do something about it IMMEDIATELY! I'd now add that it is even better to do something about likely icing even before the white stuff starts to collect. You'll be happier and your friendly controller will be happier.

No comments: