Seat reassigned at gate.....to help balance the plane??!!
 

Hi,
I travel every week on EI from AMS to DUB. A couple of weeks I was boarding in AMS and when my BP was scanned, the machine made a funny sound and I was asked to step aside. The gate attendant came back a couple of minutes later, after fiddling round on the computer, and told me my seat had been reassigned. I originally had 3E (a middle seat, but it's just a 1h10min flight and it's usually very full, so I'll take a middle seat up front over an aisle seat down the back) and I was reassigned to 33F!! I asked why, and was told that the seating had to be adjusted to 'help balance the plane'.

I boarded the plane last and noticed it was only about 70% full. Seat 3E was empty. So were many of the middle seats and plenty of window and aisle seats from about row 15 onwards. Rows 31 and 32 were also completely empty. I felt like the naughty schoolkid on my own at the back of the class.
I asked one of the stewardesses and she told me it seemed completely bizarre and apologised but couldn't explain it. She said she hadn't heard of a plane being trimmed for weight in this way since the 70's.
Any idea why this happened?

Cheers.

This is understandable as it is the pilots' responsibility, not the stewardesses (thank goodness) to calculate Weight & Balance (as it is known in the trade), and also the dispatcher at the gate plays some part.

It is sort of precalculated beforehand but can change during loading, eg freight turns out not to fit in the rear hold, has to go in the front one, or passengers expected in the rear cabin misconnect and do not get on board. The balance required to be within limits is actually quite fine.

The easiest way to rebalance is to move the minimum number of people (maybe just one) the maximum distance from one end of the aircraft to the other, as happened to you. Looks like it had been nose-heavy on the initial calculation.

The pilots up front are professional folks, they are not going to leave the gate with the plane out of balance. Did you thank them when disembarking for their careful arithmetic ? It's not the easiest to do (if you remember your physics classs in school, bending moments, lever action, and all that, it's the same thing).

It has to do with affecting the plane's center of gravity (CG) and its effect on the controllability of the aircraft.

I have messed around in FTD's and simulators with the CG everywhere but where it should be, and given the out of whack flight handling characteristics that can ensue you will have to take my word on it that you were done right.

It is definitely not an archaic issue limited to the 1970's.

So what if the passenger chosen was a tiny person who only weighs about 55 kilograms (not sure what that is in pounds but not many :)) whereas I am 140 kilos (not good:eek:).

Surely actual weight would have to be involved as well? Therefore, they would need to view you rather than just moving you because of your seat number.

There is a "standard weight" of around 90kg per passenger used for flight planning purposes. However, believe me that the pilot or the dispatcher would almost certainly have had a look at those involved (thought probably not saying so) to see such a gross anomaly from the standard weight was not happening.

An accident in the USA some years ago was initially (though incorrectly) believed to be due to a large load of sportsmen in the aircraft which could have upset the balance, and procedures were redefined after that to ensure the standard weights did not in themselves lead to imbalances.

The substantial change in aircraft gross weight during the flight as the fuel is consumed is not significant as the fuel tankage is designed so it lays equally forward and rearward of the nominal centre of gravity of the aircraft no matter how much or little fuel is on board.

Wow....thanks for all the answers. I really didn't know that modern aircraft required such fine-tuning in terms of weight distribution.
I didn't complain or anything as it was highly unlikely to get me anywhere in the circumstances, just politely asked the stewardess. It did feel at the time, somewhat irrationally I know, that I was being singled out in some way!

One thing that confuses me though, is that when on a flight with a lot of free seats I've seen a total free-for-all once the doors are shut. I've seen the cabin crew actually encourage this. If weight distribution can be such a fine thing how is this allowed?

The flight crew really do get to feel everyone moving round the plane through their Trim Control, which they roll back and forward during the flight. It is a minor adjustment on the elevators. If they feel things are getting towards the limits of the controls they will put a stop to it, or alternatively move the fuel round a bit (by say burning off the rearward tanks to both engines) to keep their Trim in the centre. The key thing though is to get the balance correctly within limits before you start. This is all written on the documentation and left with the dispatcher at the gate, if any issue happens with the flight this is where the investigation will start. I always like it to be right in the middle of the allowable range before starting, it looks like you have been precise.

Pilot's adage is that flying is a science but trim is an art :)

I have seen this fairly commonly in RJs and turboprops, but not in full size airliners. What kind of plane was it?

WHBM, thanks again. That's very interesting.
When you say 'put a stop to it' I take it you mean they stick the safety belt light on?

djk7, it was an A320.

Just out of interest, here's a discussion among flight crews about automatic trimming versus doing it yourself. There's some jargon in there but you can probably follow the general line.

http://www.pprune.org/forums/archive...hp/t-9346.html

A "scarebus" by the way is Boeing pilotspeak for an Airbus !

Regarding the point about putting the seat belt sign on, if you think about it that is not the thing to do. Once the crew feel an imbalance which is significant, you do not want to freeze the passengers in such a position, you want it back as it should be. So a quick discussion on the interphone with the lead FA to ask what is going on, as crews cannot look back down the cabin nowadays, and then an announcement for passengers to please resume their original seats. It doesn't happen often because things do tend to balance out and there is in truth quite a margin. Incidentally there is trim both fore-and-aft, and also left-and-right.