Flying the Fuel Mule to Seattle
Pace yourself: a Seattle turn is 1,600 miles northwest, then 1,600 southeast. Seduced by the 12 day work month, you’re about to find out how 90 flight hours can be logged in so few days. And, for W2 purposes, you’ll pick up another day of voluntary flying, to top out near 100 hours–in only 13 days. Looks good on paper, fly it.
First, consider the illusion: 8.2 hours of flying turns into an 11 hour work day–if all goes as planned. Here’s how it unfolds: report at 11:40 for preflight duties, pushback at 12:40. If, that is, the inbound arrives at the gate on time. Arrival weather can slow that down considerably, and so can maintenance requirements on the $55-million dollar air machine. That could happen before it leaves wherever it started its flight day–Miami, in our case–which will put it on our gate late. Regardless, your day starts on schedule no matter when you eventually pushback.
Until you get your hands on the jet, consider the route, the weather, and the winds. That last element is crucial, because wind variance from planned can easily add 10-15% to your fuel burn. DFW to Nashville? Barely 2 hours, so plus or minus 10% is nominal. But over 4.5 hours? You can’t ignore the extra fuel burn, which could easily be 1,000 pounds or more. on longer flights, you have to be mulishly stubborn about fuel. Here’s how.
The winds used by the flight planning computer program are fairly accurate, but not perfect. They are a blend of historical data, predictive calculations, and some real time pilot reports. But consider their “Best if Used By” label: they were fresh 3 or 4 hours ago when reported, but with the sun that many hours higher since, you know wind patterns and intensity will change.
Which brings up another wild card: the front range of the Rockies. You have to cross that ridge northwest bound, probably just west of Pike’s Peak. The old rule of thumb says you’re vulnerable to mountain wave turbulence half again as high as the mountain range, so if you figure between 15,000 and 20,000 on top of a generous average for the range, you’d figure to be a smooth cruise in the upper 30-thousands, right? Seldom works that way and in fact, often the ride is worse higher and better lower. That’s due to many variable factors: the jetstream pattern, heating and temperature bands in layers, and the orographic effect of the uneven range peaks themselves. Plus, the higher sun angle throws adiabatic heating into the mix, adding convection to the orographic disruption. End results: riding a dump truck down a dirt road.
Add those concerns to your awareness of the slimmer margin between high and low speed buffet at the higher altitudes, particularly early in cruise when fuel quantity and thus aircraft weight is the highest. Sometimes, lower than optimum cruise altitude is a wiser choice if there’s a possibility of significant turbulence. Again, there will be a higher fuel burn for that segment of cruise.
So there’s another possible fuel penalty, and it’s not as simple as the increased incremental fuel burn at a lower altitude for the front range transit time, although that is substantial. You also have to add the fuel burn for another climb back to optimum cruise altitude for the remainder of the flight.
Plus, if anywhere in the 1,600 mile route we discovery that a lower altitude is a better ride compared to a turbulent optimum cruise altitude, we’re going to descend and accept a higher fuel burn. Again, short flight like Nashville? No worries–just stay low. But not for 2-3 hours as in the Seattle flight.
So, in your head, you’re computing a comfortable arrival fuel, plus an extra 15% for wind and turbulence options. And “comfortable” depends on current and forecast Seattle weather. Yes, “current” weather in Seattle is important for a couple reasons. First, if their weather is causing flight delays there now, there’s a good chance for the imposition of arrival metering–unless it clears in the 5 hours before your planned landing time. That could mean an outbound (YOU) ground stop, or even enroute metering, vectoring or slowdown–all of which cost fuel.
The ground stop eventuality saves jet fuel, but burns YOUR energy, adding an hour or more to what’s typically an 11-12 hour workday for a Seattle turn. That type of delay on top of any maintenance or inbound delay can make your day an endurance contest: just getting to Seattle in 5-ish hours is only half of the game–you still have to juggle all of those factors and the same mileage southbound.
There are a few windfalls that will likely come your way, too. Frequently, the cargo load will drop off, sometimes the passenger count too, but that’s very unlikely for Seattle. But the cargo weight dropping a thousand pounds or more will allow an early climb to a higher cruise altitude with a lower fuel flow and more favorable winds.
Today we’re actually flying longer route on a more northerly course, passing east of Denver, and I can see why: there the jetstream becomes more of a crosswind than the headwind we’d get on a more westerly route. The typical westerly route is shorter mileage on a map, but not in the sky where the flow of the air mass acts like a treadmill: it’s already moving against us, whereas on the more easterly course, it’s not. No treadmill effect, or at least significantly lower.
So, here’s the numbers game for today: SEATAC’s landing south (grumble: longer arrival and approach) with variable winds (could switch to north, you hope) and neither poor weather nor delays. Ceiling 700 to 1,000 and, with the trend data, improving. Good. 6.0 arrival fuel will be fine, and it will likely balloon to 7 if all goes well but comprises a good pad if not. Worst case, we visit McChord AFB twenty-some miles south.
Weather at DFW makes for outbound delays, not due to the heavy rain so much as the convective (read: spring thunderstorms) cells dotting the radar, disrupting the standard departure routing and forcing all jets into a 10 mile in-trail spacing to allow radar vectoring after takeoff. More grumbling: sure don’t want our southbound leg to be delayed or god forbid, ground-stopped in Seattle. But the steadily moving frontal line snarling DFW will be well clear by the time we return around 10 pm. We’ll worry about that later.
Somewhere over Wyoming at take-off plus two hours, you share a wry observation with the First Officer: “We’re not even halfway yet.” She laughs: “And even that’s only halfway to halfway.”
True enough. Because every single step of analysis, planning, preflight and execution repeats itself sure as Bill Murray’s Groundhog’s Day as soon as you set the brakes in Seattle.
Pace yourself: it’s going to be a long day. If you’re lucky, you’ll get home 12-13 hours after you left for the airport this morning, allowing you to get a good rest in order to do it all over again tomorrow.