Dec 30, 05, 3:18 pm
On my way back from SJU, I had a bit of a hang over and wanted to get some sleep. So I wondered from my spot in 1C to the last row which was empty I lay down across all three seats and fell a asleep. A few minutes later a FA woke me up and told me I had to go back to my seat because of weight balance. On an A319 does one person moving from the 1st to the last row really matter?
Dec 30, 05, 8:58 pm
Asked several pilots. It depends on load and where everyone and everything is. But yes it can. Most FAs don't have a problem with people moving as long as they report it to the captain and he says it's fne (assuming the numbers let you move).
Dec 30, 05, 11:06 pm
Center of Gravity (CG) is calculated at three points. Takeoff, landing and zero-fuel weight. It must be within limits at all three points. (CG will shift somewhat as fuel is burned off as the center of mass of the fuel is not exactly at the CG)
If the limit is 15.00% - 32.00%* and it calculates out to 14.99% then something has to be moved. Is there any noticeable difference between 14.99% and 15.00%? No, but the line has to be drawn somewhere. Moving a single passenger (probably about 190 pounds on paper) won't make a very big difference in CG but that difference can be enough to move you into limits and that is all that is required.
Usually, with a full-size jet like the A320, they would move some cargo/baggage instead of passengers but sometimes it's quickly to just move a passenger or two. On the smaller airplanes you frequently don't have cargo under the floor so you don't have the option of moving bags so passengers must be moved.
* FWIW, the CG is expressed as a percent of mean-aerodynamic chord. Aft CG's give you more efficiency and maneuverability at the expense of stability. Forward CG's give you more stability at the expense of efficiency and maneuverability. The forward limit is based on the point where you no longer have sufficient control authority to meet certification limits. The aft limit is based on the point where you no longer have sufficient stability. Probably more than you wanted to know.