What and Balance?

The latest issue of Aviation Safety Letter (or at least the latest one that I have managed to be home to receive) reprints an article on weight and balance that surprises me. His thesis is that only five percent of private pilots do a weight and balance calculation before a flight, and that eighty percent couldn't do the calculation correctly if their lives depended on it. His narrative implies that W&B isn't even taught as part of the licence, and is not tested as part of the flight test. A Canadian pilot licence candidate would fail a flight test if she couldn't produce a very accurate weight and balance for the proposed flight.

Now I'm not expecting that a private flyer would whip out an operational flight plan every time he came out in the evening to do a few circuits between dinner and sunset. If you own or regularly rent the same kind of airplane, you know, for example, that your own weight plus full fuel is well within limits. You'll know perhaps from repeated calculations, or careful examination of the graphs, that a passenger in the seat next to you cannot put the airplane out of balance limits, so you only need to count weight. Or perhaps you've determined that with 200 pounds in each passenger seat you can carry 50 lbs of bags, but they have to go in the forward compartment. I wouldn't fault someone who knew his airplane taking on loads like this without doing any calculations.

The example given in the article of the pilot not asking the heaviest person to sit in the front with him seems bizarre to me. If he was shy about mentioning weight to a female passenger, then just say, "Hey Susan, Sara has sat up front lots of times, why don't you sit up here." Or offer here the front seat for more "hip room." Myself I would have just sized up the passengers and assigned seats, no excuses, no explanations. My own family might know that I was doing it to get the weight in the front, but no one needs to be told if they are going to be embarrassed by it.

The thing is, an airplane loaded out of the manufacturer's limits probably will fly. It probably won't even crash. But in some configuration there is some otherwise reasonable maneuver that your airplane is no longer able to perform. Maybe it becomes unstable in the slow flight regime. Maybe it makes it harder to maneuver with a distraction. With an overweight airplane, turbulence puts more stress on the airframe and could lead to an in-flight break up. Maybe it won't climb out of ground effect or won't give you the published rate of climb. Maybe there's some attitude or or maneuver from which it won't be recoverable. it happens to commercial pilots too. This airplane has flown a couple of legs with an unknown elevator rigging problem, but it only killed people on the leg that they had an aft C of G.

The last example above departed with paperwork showing it within limits, but that is because the paperwork took into account standard passenger weights, based on a fifty year old survey. People weigh more now, and that accident was the last straw. Americans don't use quite the same standard weights Canadians do, but within twenty days after that accident, Transport Canada had issued new standard passenger weights to be used by all operators. If your passengers aren't standard, don't pretend they are. One method a reader mentioned for discreet but accurate weight and balance on small private airplanes is for the pilot in command to enter the moment of the empty airplane on a calculator, hit the plus key, then to tell each passenger to enter his or her honest clothed weight multiplied by the arm (obviously you tell the passenger the arm of their seat), hit the plus key and hand the calculator to the next passenger. You'd want to assume reasonable calculator skills on the part of the passengers, and ensure your calculator used the proper precedence of operations.

You'll notice that in almost all of these fatal accidents, the out of envelope condition was not the only factor in the accident. It's a little like "speed was a factor" in automobile accidents. In the car, once you're going too fast, any other thing that goes wrong, or any other mistake you make, is more likely to lead to a crash. In the airplane, once you're loaded out of weight and balance you've deliberately given yourself a penalty for anything you have to do. Not being within weight and balance limits is like not sending all six players onto the ice for a hockey shift. Yes, you may successfully skate out the penalty, and sometimes you even score a goal shorthanded, but in sudden death overtime, everyone should know enough not to take unnecessary penalties.

I'm guessing that pilot readers of Cockpit Conversation, being biased towards the smart and geeky, can all do the simple arithmetic required to determine the centre of gravity of a loaded airplane, and mostly do check the balance limits if they are putting an unusual load in their airplane. if any non-pilots (or any of those hypothetical eighty percent of pilots) is now curious how to do a weight and balance calculation, leave a comment and I'll be happy to explain in a future post.