frankv:

 

joker97:

 

Dingbatt: I'm still struggling with the title of this thread. How is Air NZ's requirement to offload a passenger so they can carry more (required) fuel a maths fail? If anything it shows a failure by people to understand how an aeroplane works. As for 2 minutes of fuel, that equates to about 5 nautical miles at typical approach speeds, so I guess you would be happy to swim the last bit to the airport? Yes, an exaggeration, because of reserves are carried, but just as an airliner isn't allowed to takeoff overweight, it's not allowed to depart with insufficient fuel to get to its destination or a suitable alternate airport if it's destination closes unexpectedly. The article even references the fact that a more distant alternate was required than would normally have been used.
So there's some maths for you,

more distant alternate = more fuel required

So

Total Weight(W) = Empty Weight(E) + fuel(F) + payload(P)

Where the first two (W and E) are fixed, then maths says if F increases then P must decrease.

Oh, and @aredwood, your guess ^ is wrong

 

I didn't understand how they calculated 77 tonnes with such precision that a skinny lady had to be taken off. to meet the threshold.

 

[Thanks for the pointer I've amended the title]

 

 

I suspect that they have load cells in the landing gear to measure the actual weight of the aircraft, and calculate its centre of gravity. Since individual passengers aren't weighed, there's no way of knowing how much fuel can be loaded to keep the aircraft under maximum takeoff weight, and the fuel is loaded before the passengers. So the amount of fuel (& freight) to load has to be a guesstimate, based on the average weight of a passenger. The ICAO-mandated guesstimate is 70kg... if the actual average weight is only 1kg above that, you're 300+kg in error. Offloading 100kg of fuel isn't an option. 

 

I suspect also that it may not have been the pilot's decision... the airplane computers themselves probably won't allow it to start if it's overweight. I don't think it's too much to expect that the sensors have the precision to distinguish between 77000kg and 77100kg... that's .12%, so you could do it with a 10-bit A/D. Whether those sensors are accurate and repeatable enough to measure that weight to that accuracy is moot. I suspect that if they had got all the passengers to jump up and down a few times, they could probably have made it answer less than 77000.

 

I guess they could have offloaded the meals and/or drinks instead. Or sent all the passengers to use the toilets in the terminal. Or got some skinnier hosties.

 

 

 

Some do. But there's too many variables for them to be taken over and above estimated weights following standard guidelines. Gust of wind comes along while weighing? Oh look the leeward side just gained 500kg. Plane gets iced up before taxiing to the de-ice station - thats 200kg of ice. etc.

This is all a storm in tea cup over an article about a self-entitled whiner who doesn't appreciate the complexities around operating a safe airline.