I was on a UA 747-400 flight with w/b issues a few years ago. The plane had a very light load of passengers. I was moved from Economy to First.

Same here -- they made all the non-revs disembark from C and F, and cleared the first three rows of E+. Captain said the choice was either to do that, or wait 2-3 hours for the cargo to be redistributed.

Last month, ORD-PHL on a US 320. Wintry mix was in effect and, when backing the jetbridge back the ground crew discovered it was frozen to the aircraft. Rather than wait for deicing/maintenance to come by and free us, all of the pax in F and the first few rows of Y were told to get up and walk to the rear of the aircraft. The shift in balance would put enough pressure on the ice to break its grip.

Sure enough, it worked and off we went. Very odd. We were assured this was perfectly fine and, having spent the 3 hour delay in the RCC working my way to cirrhosis, it sounded good enough to me.

Holding the rare pre-departure beverage while standing back in the aisle amongst the unwashed masses in Y was a bit awkward, though.

that's a great story! i'm (sadly) surprised they can do this without fearing litigation.

I'm sure the UA pilots here can provide a lot more insight than me, but I fly small single-engine props and we always have to do weight and balance calculations as part of flight planning. However, the principle applies regardless of aircraft type (as many have noted).

Essentially, you're computing where the center of gravity (Cg) is located based on the empty weight of the aircraft, fuel, passengers and cargo. Each aircraft has acceptable limits for the Cg, which are determined by things like the location of the center of lift and size of the elevators. Basically, for a given Cg, can you move the elevator enough to produce an angle of attack that allows you to climb (or descend).

To calculate the Cg, you multiply the mass of a component and its distance from a given reference point, e.g. the fuel weighs 72 lbs and is 37.4 cm from the reference point. By dividing the sum of those products by the total mass, you get the effective Cg relative to your reference point.

Typically, you calculate these for takeoff and landing based on your planned fuel burn (since that's hopefully the only change in mass during your flight!).

As an aside, I know the Concorde was particularly sensitive to changes in Cg and the flight engineer could change the selected tank and cross-feed fuel between the fore and aft tanks to control the location of the Cg for different phases of flight. There's an interesting article about it here: http://www.concordesst.com/fuelsys.html

I was very surprised as well, but common sense, and no doubt a manual somewhere, dictated the only thing having an issue was contact with the skin of the fuselage. No control surfaces, instruments, etc. Likely the torque of the jetbridge motor just wasn't equipped to handle that small amount of resistance.

I was on a United P.S. 757 LAX to JFK in C and the plane stopped right before takeoff. The lead FA came to me and asked me to move to F because of W/B. What was interesting to me was that I simply moved from 5a to 3d (essentially one row up) and I'm a pretty small person!
Anyway, I can imagine that even small fluctuations can change the W/B and the P.S. has an unusual configuration, but I was pleasantly surprised nonetheless!

This is seriously weird but it was an A380. On a flight CDG-LHR on AF they changed seating to adjust for W&B. the flights were really training flights but they sold seats. They had too much load aft and moved some passengers forward.

All A/C have such issues but I had not expected it in this context.

Light fuel load means it can't be used for W/B as much as normally. For "real" A380 flights this will never happen, as no airline will burn an A380 cycle for such a short flight in scheduled service. Quite interesting how much fuel is pumped around between tanks in flight and the beneficial effect, one area where computers have made a big difference in modern airplanes.

Interesting, I don't think I can recall this happening to me in the airbus in many many years, so it's not that frequent for larger aircraft. You might have had a lot of cargo in the forward cargo pit, and fully loaded with a lighter load, they needed pax moved back initially. All aircraft have weight and balance numbers they have to make work each flight.

AD

Triple-7 with a light load out of AMS. When we arrived at the gate, we were handed new boarding cards w/new seat assignments. The front of the plane was full, and most of the passengers in back originally were seated in the front part of coach - and were reassigned to deep steerage.

Sounds like the usual non-op 747 cabin on UA and w&b only being the justification/excuse for the mess.
Great handling of the situation by UA .

I think the guy did the right thing, I would not want to fly with a pilot either who notices unbalance at such a late stage.

During those two hours they could at least process the compensation for the F pax who were moved to C. That is after they convinced a sup that balancing a plane is not exempt as force majeure....

DC 10 flying from CDG to DTW. As we were heading out to the runway, pilot comes on and says that they didn't load/balance the weight on the plane correctly and that we'd have to return to the gate to rearrange the luggage. He was pretty upset.

W&B varies based on the load, operational requirements, and conditions at departure. An international widebody shouldn't usually have problems as the ground crew should already have a plan of what sequence and where freight cargo should be loaded. If a balance issue was found after pushback it's most likely related to how some of the weight/load data isn't complete until the flight is closed.

On some of our flights with ACARS, the crew can input thefuel load, # of pax and their bags (by zone or bag bay: x# zone 1, y# zone 2; a# aft bag, b# fwd bag), and send the data out and get a takeoff data for the current conditions which included the stab trim setting for W&B (certain range required for takeoff).

Environmental conditions can restrict weight which can require removing pax/bags due to WX (hot at departure location), or extra fuel needs to be carried for possible holding or diversions due to WX at destination.

boarded from the rear on a small twin engined plane in EIS bound for sju(something like sunshine or sun carib airlines) and sat near the rear door.. everybody else that boarded sat in the rear door. the nose came up(tricycle gear), and the tail hit the tamarack. the pilot came back and asked people to move forward. we did, nose wheel went down and we went to SJU. i opened their little magazine in the pocket, and the pilot was pictured there, as the president of the airline.