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I have flown a bunch of times on a Bombardier Dash-8 Q400 on a couple of different airlines, and several times I have flown a shuttle flight that is basically empty.

I have been instructed to change seats on these flights, reportadly to balance the plane better.

It appears as though the request comes from the cockpit relayed back to the cabin staff.

The plane appears to be static in place, so how do they determine that they need to balance the plane? Does the landing gear report this sort of info?

A Dash-8 is a reasonably 'large' airplane that it seems sort of surprising that the balance is so delicate that the weight of a few people can make the difference.

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Back in to mid-80s I was a first officer flying Metroliners for a commuter airline. If there were few passengers, they had to be seated aft of the wing mid-point or your c.g. would exceed the aft limit. It was the job of the first officer to stand at the cockpit entrance, just forward of the entry door, and tell passengers where to sit when there was a light load. A very large African American came up the steps, and I had to tell him to go to the back of the airplane. Realizing what I had said, I hurriedly explained way. I recognized the man, he was Rosey Grier. Google him if necessary. –  Terry Jan 14 at 3:36
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In the late 80s I was flying F-27 with no autopilots. We had a captain who weighed in excess of 250 lbs. He was a prankster, and when he was deadheading, he never failed at some point in the flight to make three or four circuits of the cabin. You always knew when he was doing it; the airplane just wouldn't stay in trim. –  Terry Jan 14 at 3:41
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1 Answer

up vote 5 down vote accepted

Before the main cabin door is closed, the ramp personnel will deliver a cargo sheet that lists

  • number of checked bags
  • number of gate checked bags
  • number of heavy checked bags
  • pounds of commercial cargo
  • pounds of company cargo

With numbers broken down by cargo bin where accurate.

The flight attendant will deliver a sheet with passenger count in zones.

The FMS or EICAS screens can tell you how much fuel is on board.

From there, some airline have ACARS programs that you plug those numbers into and it will give you weight information (to turn #bags and #people into pounds). Other have worksheets to calculate the weights. In the EMB-145 we then had to spin a special wheel with the weight information to get the balance info. This can vary by operator.

Some operators will have the W&B calculated by dispatch and all of the numbers I mention above are put into the computer system by various people and the dispatcher will deliver the W&B and takeoff reference data to the pilots via ACARS.

What if there is a problem?

Problems can be overweight overall, overweight in the cabin, overweight in the bag compartments or out of balance.

For overweight, remove people or bags as necessary. If fuel has not arrived and you can do without some, call dispatch to revise the numbers and load less fuel.

If you are out of balance, you move people or bags around. This was rarely an issue and if it does happen you just ask a passenger from zone X to sit in zone Y for takeoff.

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