Shrinking Margins

I just got back from a roundtrip flight to Central Florida for a speaking engagement, and even after all these years of flying 1,000-nm trips in light airplanes, I was still surprised by how starkly different the “out” and the “back” legs were.

This is one important lesson about transportation flying that no one ever taught me, either, and it should be a standard part of the New Private Pilot 101 curriculum. Plan for your return trip as though it’s an entirely different experience, because it very likely will be.

The flight out in the Cirrus SR22-T, with just myself and a very SR22-experienced pilot buddy aboard, was about as easy as they get. I say "just about" because we had marginal O2 reserves, and the new shop at the new FBO at the new airport—Austin Executive (KEDC) which is my new base here in Austin, doesn't yet have oxygen service.

That said, we did have some oxygen, the weather was expected to be severe clear for the entire trip, and the Perspective displays in the ‘22T have excellent O2 system information, down to every ten pounds of pressure. So we could fly high, use the O2 for as long as we had at 170 while checking our O2 sats religiously on the pulse oximeter, and then head down to 11,000 thereafter.

That was exactly how it worked out. Our groundspeeds were excellent — around 235 knots for much of the trip — the oxygen held out even longer than we’d anticipated, and the air even down at 11,000 was smooth. We made it nonstop in around 4:30.

After a great visit in the Orlando area with good friends and co-workers, it was time to head back home a few days later.

For the trip back home, we’d have more bags, one more passenger, some convective activity along the way, and…we’d be heading west and not east, so our 40 knots on the tail at 170 would be exchanged for about 25 on the nose at 6,000 feet.

These things all affect each other. The addition of the extra weight meant that we had to leave off fuel, which meant that we had to plan a stop along the way — I was thinking it would likely be two stops — and make sure we had plenty of fuel reserves for weather. Plus, our schedules meant that we’d have to head for home starting later in the day, with a 1 pm departure, so we’d be flying most of the last leg in the dark.

The headwinds were as forecast. The views along the Gulf Shore made up for our slow progress, however. It was as beautiful a day as I ever remember seeing there. Along the way Destin looked like a good bet, though I had to come back on the power to make it there with the required reserves. The amount of reserve fuel I like to arrive with is a figure that for me changes depending on the conditions. When the weather is fairly good with high temp/dew point margins, as it was in the Panhandle, I will go with an hour. My ability to accurately know how much fuel is on board a is easier and more accurate than ever with the Perspective G1000-based avionics. As you might know, there’s a range ring on the MFD that is based on fuel consumption and current ground speed--the ring comes in very handy for figuring reserves. You can expand and contract the ring with power, watching the ring grow as you reduce power and watching it shrink as you add power. The headwinds were slightly worse than forecast, but by coming back on the power, we made our first stop in Destin with an hour's fuel in reserve. Once on the ground, we added the precious little amount of fuel we could while still being within weight and balance limits, giving us enough for our next leg and then a little bit more in reserve.

The extra reserves were because the leg after Destin looked to be the complicated one. The weather — a loosely organized front--would start, the XM told us, around Mobile, Alabama, and continue on through Lafayette, Louisiana. It was a small town near there where we had been planning to stop again for fuel. The complication was, we'd previously set up a meeting there.

It had gotten dark, too, and the XM showed cells marching in close formation right through the heart of the little Louisiana town where we’d planned to stop. As the flight progressed I made the call to divert to Baton Rouge, which was in the clear. We'd land at BTR, take on fuel, and then continue on our way home to Texas. Our meeting would wait for another day.

And that's just what we did. It was the prudent call. I could only imagine a night IFR (LNAV+V) approach in the dead of night in the rain to a small airport (with less than ideal runway lighting). A lot can go wrong in a situation like that, so why put yourself into one when you don't need to, and you almost never need to if you plan well.

After Baton Rouge we passed through the front without incident and were met with only moderately stiffer headwinds along the way. We made it back to Central Texas and were greeted by a beautiful, starry night. (Turns out the stars at night here really are as they say deep in the heart of the Lone Star State.)

I felt glad for the way the flight went, especially since it had a number of potential traps within it. We had extra weight, less fuel than we would have liked, some convective weather, substantial headwinds and a dark night to contend with. It was nothing like our trip out to Florida had been. Just as I should have known it wouldn’t be.

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