I think we’ve talked a time or two about the importance of weight and balance when flying general aviation aircraft. The simple fact is that virtually no light plane ever manufactured can lift a full load of people as well as a full load of fuel into the sky at the same time.
If you want to carry more people, you need to carry less fuel.
If you want to carry more fuel, you need to carry fewer people.
That’s the weight in weight and balance. The whole balance part of the weight and balance dance is about ensuring that the load is placed in the airplane correctly so that it’s neither too tail-heavy nor too nose-heavy to fly safely.
I’ve been doing weight and balance since I was seventeen years old.
The military does it too, at least for cargo planes. And I’ve watched flight attendants juggle passengers on small commuter planes, but never in a million years would it have occurred to me that it’s an issue for airliners had I not been on a Southwest Airlines flight out of Houston, Texas on Super Bowl Sunday.
What? Did I attend the Super Bowl? No. Not my cup of tea. Houston just happened to be where I changed planes heading farther east. But I did enjoy the good-natured ribbing between Falcons and Patriots fans flying into the city.
The airplane was a Boeing 737, arguably the most successful airliner since the DC-3. Boeing has been making these short- to medium range twinjets since 1967. Over the intervening years there has been a blizzard of variations, including a military cargo version and a personal jet version, called the BBJ for Boeing Business Jet. Can you imagine owning a one hundred-foot long personal jet with a ramp weight of a hundred and fifty thousand pounds?
I wonder what the annual on that would cost? (The Plane Tales Plane is still in the shop for her annual, so thinking about such things actually cheers me up.)
Boeing has sold over ten thousand of these airliners to operators in 190 countries, according to Wikipedia. Stats there show 737s are operated by more than 500 airlines globally, and apparently, at any second on your wristwatch there are 1,250 of them in the air at the same time. All told, the 737 makes up a quarter of the global fleet of airliners.
And apparently it too is incapable of lifting both a full load of fuel and a full load of passengers into the air at once. I know this because after we’d sat—properly buckled in with our belts low across our laps as instructed—at the gate for the longest time, the Captain came on the intercom, and explained that we had, uh… a… you know… a problem.
Fuel is cheaper in Houston than it is in New Orleans or Orlando, the plane’s next two stops, he explained, so the airline topped up the tanks with cheap gas while on the ground in Texas. The problem was that the plane’s manifest showed a three-quarters full plane, but then the rest of the seats sold out at the last minute.
The plane was now too heavy.
Apparently, weight and balance matters to the big boys, too. Just like small planes, airliners aren’t always able to lift full seats and full tanks into the wild blue yonder.
The Captain told us that de-fueling takes forever so they decided the simplest solution was two fold. First, some people would need to de-plane. Then the rest of us would fly at lower than usual altitude to New Orleans, which is less fuel-efficient. He reported that by the time we got there this would get us within our max landing weight, which we’d exceed on takeoff.
I was surprised and delighted that he gave such a detailed explanation to his passengers.
First, the seven standby passengers were given the boot. But Southwest still needed five more passengers to take the next flight. After an offering of a $500 bounty, five hands shot up. Mine wasn’t one of them. I wanted to be on the barnstorming airliner. Typically, 737s fly at 35,000 feet. On this flight we’d be at 12-15,000 feet, according to the Captain. That I had to see.
But this really doesn’t sound like a good business practice, does it? To find out, I decided to run the math myself. A 737 can hold 7,837 gallons of Jet-A. I checked the price per gallon for Houston. Of course, my sources don’t show airline discounts, but I could fly in and buy a gallon for $5.50. At that price, if I flew in my personal BBJ—if I was rich enough to own one—and filled it up, I’d spend $43,103.50.
Farther east in the Big Easy, sure enough the price jumps to seven bucks a gallon. Now my tank-up costs $54,859.00—nearly $12,000 more. I have such small gas tanks in the Plane Tales Plane that I don’t bother to divert for cheaper fuel, but when you have big tanks to fill, it can really make a difference!
As we taxied out to the runway I was still amazed how little difference there is between Ercoupe and Airliner.
For more about weight and balance, read my article The Weight and Balance Jungle in the June 2015 issue of Flight Training Magazine. Even non-pilots will enjoy it. It has elephants and monkeys. And whiskey.