Plane too Heavy!!!

General Questions
#1

Hi everybody - 1st post coming up!!

I recently went on a flight from the UK to the south of Spain. We were all on board, and there were one, maybe two spare seats.

The head steward then piped up on the mic saying that the plane was not the one that we were supposed to have been using, and so the plane was overweight. He asked for 6 people to get off and take a flight the following morning.

My questions are these:

How come a plane has been designed with a capacity which it cannot carry?

And how come the planes are flown so close to their weight tolerance limit?!!

Cheers, FBF

#2

I can tell you tat most single engine planes cannot carry full fuel and all seats filled (unless they are children) Typically either the seats are left unfilled or less than a full fuel load is carried.

I don’t know if the same thing applies to commercial planes - I would expect they would be desighed to carry a full passenger load with a resonable fule load. Maybe the trip was longer (and/or there were headwinds) than the plane was designed for and so they needed to carry more fuel.

Brian
PP-ASEL

#3

Welcome, fbf20003!

I suspect that the planes are designed assuming a certain number of seats. If the airline squeezes in more seats and fills them, that could take the plane overweight.

There have been several airlines in Canada that did this kind of thing.

Canada 3000 packed the seats so tightly that when I sat in one with my butt all the way back, my knees brushed the back of the seat in front of me. And I am only of average height. It would have been physically impossible for my father to sit in that seat and still keeps his legs straight.

I remember a news story about Air Canada packing its short-haul planes so full that they couldn’t carry a full load of fuel.

#4

Too many door-to-door anvil salesmen, that’s my theory.

#5

The length of the runway matters as well.

The Lexington Bluegrass Airport (Lexington, KY, may have mistitled it slightly) is not a very large airport. So it’s runway is short, and airlines size the planes which fly there around those limits.

But in the fall, when Keeneland Racetrack is in season, it is not unusual to see a couple of 747s parked at the airport. These are private 747s owned by men from Dubai. They (or their pilots) know what weight a 747 can carry and still land on the short runway. They limit the number of people and the amount of luggage to that which can safely land and take off there.

As of a few years ago when I got this information from the newspaper, it costs about a hundred dollars a day to park your 747 at the Lexington Bluegrass Airport. Sounded cheap to me–relative to the price of the 747 and fuel and all that.

#6

It isn’t just the number of passengers, the pilot also has to consider the amount of cargo, amount of fuel, length of runway, altitude above sea level, temperature and humidity. The number of passengers that a plane can safely carry varies quite a bit depending on those conditions.

#7

This is correct. It’s also worth noting that the necessary fuel depends not only on the length of the flight (and anticipated headwinds/tailwinds) but also on the distance to suitable alternate airports (if destination proves unusuable, must be able to reach these with acceptable fuel reserves).

So for essentially every passenger aircraft there will be flights it can accomplish partially loaded, but not fully loaded.

#8

does location of the passengers make a difference too?
I flew on Continental “Express”–a small jet with 19 rows of 3 seats. The flight attendant filled out a little card with a diagram of the seats, marking an X for each one occupied, and then gave the diagram to the pilot.

What was this for?

#9

That was for his Weight and Balance calculations. The aircraft must not only be below max weight, but that weight must be correctly distributed fore and aft. The aircraft CG must fall between certain limits. or the aircraft will be unstable in flight, If it makes it into the air at all.

There’s a video on You Tube of an overweight aircraft in South America that made it about 100 feet from lift off before crashing.

#10

Anybody know how they measure it? I’m guessing an LVDT (linear variable displacement transducer) on the landing gear suspension, a piezoelectric, or a strain gauge on a spring, in varying order of likelihood.

#11

A co-worker once took a flight on a small plane, perhaps 12 seats or so. On boarding, she was asked her weight so that everyone would be properly distributed throughout.

When I told this story to my wife, her response was, “If they ever ask you that, just turn around and look for a train or bus. I don’t care if they fire you, you are not getting on a plane so fragile that they have to ask your weight.”

#12

The key to this is that “the plane was not the one that we were supposed to have been using”. The substitute plane was most likely designed for fewer passengers. And, in this case, probably a lot fewer, so the things pointed out by the others don’t really apply.

Planes are flown close to their weight limit because you can’t make money flying empty planes.

#13

That seems rather silly to me. As mentioned in the OP, “why is a plane designed with a capacity it cannot carry”. If the plane was designed for fewer people, it would have had fewer seats. The things others are pointing out are other things that do really apply, and had to be taken into consideration. Otherwise, it wouldn’t have been a problem.

#14

Jet aircraft are in many ways like a car that is stuck in high gear. They work fine at speed, but have trouble accelerating from a stop. Takeoff performance is thier weak point.

In addition to runway length, density altitude can become a limiting factor. Temperature in particular has a huge effect on a jet aircraft’s takeoff performance. It is not uncommon for PHX to be closed to takeoffs during a few hot afternoons each summer, while this is all but unheard of at ABQ. PHX runway altitude is about 1200’, while ABQ is about 5000’ MSL. High temperatures reduce turbine engine effiency, and high density altitude requires more speed to produce lift.

Beyond just getting off the ground, aircraft need enough runway to safely stop if something goes wrong just before they have attained enough speed. It is not a precise calculation, but part of the pre-takeoff drill is for pilots to figure “If I am not flying by point X, then I need to abort the takeoff”

#15

It’s been many years since I’ve done a weight and balance, and that was for general aviation aircraft, but at that time the passenger weight used was 170 pounds each. Now as I said that was many years ago, but the point is that an aircraft with say 100 seats at 170 pounds apiece will give quite different results with the NFL all star team on board. :smiley:

A friend who used to fly for Ozark Airlines when they were still around used to fly charter for some of the St. Louis sports teams. They were very careful with their weight and balance calculations because many of those folks were a lot heavier than average folks back then.

#16

So did you get off the plane?

#17

OK, then I will agree with what mks57 and Xema said: the amount of cargo + passengers allotted to the original plane exceeded the limits for the replacement one.

#18

Sorry I wasn’t clear. I was never in such a situation. That story was retold by the co-worker after she returned to the office.

#19

Further to my original question:

The plane we took was the Airbus A310 which had a capacity of 180 passengers. 6 people getting off the plane is only ~3% - Surely theyre not THAT confident in their planes that they fly with these low tolerances?!!

(on a side note, the passengers who got off got £250 compensation, a 5* hotel room for the night, and a flight to the same location 12hrs later. I was scrambling for the door, let me tell you!!)

#20

This was going to be my observation as well.

A couple of weeks ago, there was an article in the New York Times written by a reporter who had worked “undercover” as a flight attendant for a couple of days.

One part of the article said: