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You're in cruise, you're facing a bigger headwind than expected, and the weather at your destination is at minimums.
That's the exact scenario we were in a few months ago on a flight from Grand Forks, ND (KGFK) to our home airport, Rocky Mountain Metro (KBJC).
At our time of departure, the weather was low at BJC, with 200 foot ceilings and 3/4 mile visibility.
But the weather was expected to lift by the time we got there, with the TAF calling for the clouds to be scattered at 1,200', overcast at 2,000'. No problem, right?
We also had plenty of fuel to make our alternate of Colorado Springs (KCOS), and well more than the required 45 minutes of reserve after that.
But as soon as we took off, we started facing some unexpected problems.
We planned our flight at 12,000', because the winds aloft were higher - up to 50 knots. And nobody wants to buck a 50 knot headwind if they don't have to.
Once we got in cruise, we realized the wind forecast was off, and we were facing about 10 more knots of headwind than we expected.
At this point, the wind still wasn't a problem, because we had enough fuel to make it to BJC, shoot the approach, and get to our alternate.
But then, problem #2 showed up. The weather wasn't lifting in BJC.
About an hour into our flight, the ceilings at BJC were supposed to start lifting to 1000', and then 2000' an hour after that.
But that never happened. As we monitored ADS-B and XM weather, the ceilings were bouncing between 200 and 300 feet.
The ILS approach would get us down to 200', but shooting an approach to minimums doesn't guarantee a landing, and if the ceilings stuck where they were, there was a real possibility that we would be going missed and heading to another airport. Notice we said "another airport" - not our filed alternate of Colorado Springs? That's the alternate we filed, but that doesn't mean that it would have been our best option once we arrived in the Denver Metro area. If you need to divert, you're not restricted to your alternate. Go where the weather's best.
The weather at Denver Centennial was better - above minimums and it was only a few miles from our destination. But the entire Front Range of Colorado was covered in a blanket of clouds, and most airports within 100 miles were low IFR.
With the combination of an increased headwind and widespread low weather, our 'outs' started becoming more limited.
By the time we were crossing southern South Dakota, we decided our fuel situation was going to be lower than we were comfortable with, even though we still had enough to fly an approach at KBJC and our alternate. But - had ATC issued holding, we would need an immediate diversion to an airport where a landing was guaranteed. So we took the next step and started looking for places to land and fuel up.
With a few clicks on the MFD, we found that Alliance, NE (KAIA) looked like a good option.
The weather at Alliance was decent, with light winds and 1,700' overcast ceilings. Shooting the approach and landing would be no problem.
Alliance was only a few miles off course, which meant our diversion wouldn't add much time to the trip. And at this point, we were seriously questioning whether our bladders would make the nonstop trip to BJC anyway, which made the decision to divert even easier.
With a quick call to Minneapolis Center, we asked to re-route direct to Alliance, and within about 60 seconds, we were on our way.
We shot the RNAV 12 approach in to KAIA, landed, and fueled up.
When we landed in Alliance, we had a chance to re-evaluate the weather on the ground. It did eventually lift at BJC, though it was a several hours later than the original forecast. And in the meantime, we got to wander around the airport, where we met the owner of an absolutely stunning 70's Piper Warrior. The paint and the interior - all the way down to the mint green overhead air vents - was perfect. Like it just came off the showroom floor. You never know what you'll find at an airport.
So - was this an anti-climatic flight? That's the point. We probably could have made it to Metro. And, had we diverted, we could have probably shot an approach at Centennial and made it in. But had those clouds dropped down, they could have taken every airport in the Denver area out of the picture. And if you're staring at the MFD, starting to wonder if you have enough fuel, landing is the easy option. Once those tanks were filled again, we could have held at nearly every fix in the Metro area and still had enough fuel to divert. (Ok - probably not every fix...) And when the low weather's widespread and not following the forecast, you can't beat full tanks.
Tell us what you think: how do you make your fuel planning decision on an IFR flight? When do make the decision to divert and gas up? Tell us in the comments below.
Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at email@example.com.