Sunday, June 05, 2011

Balancing Act

Sorry for not posting, I was away last week. Here's a question for any aviation experts amongst you.

On boarding the plane (Ryanair!) I noticed that three rows of seats near the front of the plane were being guarded by a stewardess who would not let anyone sit in them. Being the inquisitive sort I enquired why this was so and she replied triumphantly:

"Captains orders! It's for balancing the plane."

Once again on the return flight, three rows were blocked off at the front of the plane, but this time the occupation of three rows at the back was not allowed either and I overheard same reason being given to several irate passengers.

Now whilst I admit that I do not have any qualification in aeronautical engineering, nor have I ever flown anything bigger than a paraglider. I do however possess a small amount of common sense, a basic knowledge of the principle of levers and loads of healthy scepticism.

I imagine that the mass of the plane should be roughly equally distributed around its centre of gravity so that it remains level in flight, but I don't believe for a moment that you can 'balance' an airliner by having three empty rows of seats when the luggage is still being loaded in the hold and you do not know the mass of the individual passengers. A small plane, say an eight seater would be that sensitive, but not a Boeing 737. (I'm even more certain that you can't balance anything by moving people from both the front and the back!)

I suspect that the real reason is either to reduce the amount of cleaning required (mind you, with a 25 minute turnaround do they really do any?) or more likely to speed up the trolley sales by having fewer rows of customers to deal with. (The damn thing seems to go up and down all through the flight). A third possibility might be to make it more difficult for families to sit together, thus persuading them to pay extra for 'priority boarding' next time.

If anyone knows the answer then please let me know...


paulsc said...

I don't know that leaving a few rows of seats clear would make much difference to the overall distribution of weight. I do recall that once, when flying between Hawaiian islands, the pilot asked everybody to move forward of row 17.

Anonymous said...

Apparently this is not uncommon:

Dafydd said...

Just googled this on and apparently it IS to do with load and balance calculations - with less than full pax loads they fill one freight bay and then balance the hull by leaving rows of seats vacant .
Its easier than shifting bags around - apparently

Dave said...

What Dafydd said. The balance of the aircraft is critical during takeoff and landing, less so in level flight though.

TonyF said...

Self loading ballast is easier to arrange than baggage, I believe it also allows them to carry less fuel (which is pumped to various tanks to maintain the Centre of Gravity) which means they can fly lighter, using less fuel, but still charge the ballast the same.

Anonymous said...

There are many calculations that should be performed before any aircraft takes off. Two critical factors are for 'weight' & for 'balance'. They apply equally to a light aircraft and to an Airbus 380, although the numbers will be a lot different.

Every aircraft will have a Maximum Take Off Weight and might also have a Maximum Landing Weight, depending upon things like the departure & destination elevation, temperature, atmospheric conditions, runway length available etc. This weight must not be exceeded, so it might mean a trade-off between fuel, freight & passengers.

It is also important that the centre of gravity (balance) sits within defined fore & aft limits, otherwise it could be impossible to control the aircraft during all phases of flight. So, even if the weight is within limits, you might have to distribute it appropriately to ensure balance.

Then again, it's Ryanair, so the laws of physics might have been set aside in favour of the dismal science.


Anonymous said...

its kind of a combination of both.

The weight does have to be balanced very carefully in an aircraft. Obviously the smaller the aircraft the more it matters.

When My OH flies his Cessna he has to manually caluculate the weight of the fuel , passengers luggae etc and work out what ( or who to put where) to balance things out

Airlines use a standard avergae weight for passengers , but its also the fuel and the cargo that they have to consider. Again most airlines have to claculte this for every individual trip. it is one of the reasons that doors close before flight and they won't let late passengers on , it screws up their figure ( they are not just trying to piss you off)

budget airlines like easy jet , that rely on a tight turnaround use simplified load sheets , which cut down on the calculations needed and thus the turnaround time

its all explained here