Thursday, January 17, 2013

On Tuesday's flight home, we did something unusual, and I want to share it.

It was a pretty short leg home, about 400 nautical miles in total.  The winds were insane at our normal altitude though - basically 190 knots directly in our face at 35,000'. The computer model also showed that the winds died down at around 40,000'-  if it was a longer trip it would have been a consideration but as it was a short one, we knew there was zero chance that Air Traffic Control would let us climb that high.  For their own operational reasons, 35,000' is as high as ATC will let us fly on this particular leg.

At 35,000' we fly through the air in the Citation Ultra at about 430 knots. That would leave us with an average ground speed (airspeed - headwind) of 240 knots.  At 35,000' we burn about 1600 pounds of fuel per hour on average.  The 400 mile trip would take 1 hour 40 minutes, and we would burn 2660 lbs of fuel.

However, the winds at 22,000' was only blowing directly in our faces at 120 knots.  At 22,000' we can only fly at about 400 knots though. That left us with an average ground speed of 280 knots.  At 22,000' we burn about 2000 lbs of fuel per hour - our jet is pretty great, but the engines really suck gas down low.  The 400 mile trip would take 1 hour and 25 minutes, but we would only burn 200 more lbs of fuel despite the markedly higher fuel burn, because we would be burning fuel for less overall time.

Doing the math showed us that we'd save 15 minutes by flying at the lower altitude.  Each 6 minutes in our plane costs us roughly $210 (fuel, maintenance and money for the engine overhauls), so we'd save about $525 by going lower. We still have to factor in the extra fuel burn though.  Our gas costs us about $4.35 per gallon, or about 65 cents per pound.  The 200 lbs of extra fuel will cost us about $130, so our overall savings would be about $395 by flying at the lower altitude.

$395 isn't a whole lot in the world of jet travel, but it's more than zero dollars, and combined with the time savings, it made our decision a no-brainer. We only climbed to 22,000', and the lower true airspeed and extra fuel burn was more than offset by the lighter headwind and correspondingly shorter trip length.. We confirmed the stronger headwind by getting ATC to talk to people who were up that high, and it was exactly as the computer models predicted. We landed in Toronto 1 hour and 26 minutes after we departed, feeling quite pleased with ourselves, having saved both time and money (it's usually one or the other).

See, I'm not just a pretty face - I can do math too! Or at least I can read the math that the computer model displayed for me, and agree with it.

To be clear - these calculations are simplified, but I wanted you to get the general idea of one of the many things we did to earn our outrageous pilot salaries on Tuesday :)

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