Air NZ - how they get plane weights?

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tdgeek

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#1547422 6-May-2016 07:41

Aredwood:

Since the flight was going to Tonga. My guess is that they completely fill the planes fuel tanks. So the plane can fly NZ - Tonga, and Back to NZ without needing to refuel. If that was the case they could easily have removed quite alot of fuel to save weight. And then refuel in Tonga, but I bet the reason is jet fuel is probably expensive there.

I think the plan is what fuel is required, taking into account worse case scenarios, head winds, etc, available alternative landing spots if there was a problem, plus 10%

IIRC

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#1547509 6-May-2016 10:36

tdgeek:

Aredwood:

Since the flight was going to Tonga. My guess is that they completely fill the planes fuel tanks. So the plane can fly NZ - Tonga, and Back to NZ without needing to refuel. If that was the case they could easily have removed quite alot of fuel to save weight. And then refuel in Tonga, but I bet the reason is jet fuel is probably expensive there.

I think the plan is what fuel is required, taking into account worse case scenarios, head winds, etc, available alternative landing spots if there was a problem, plus 10%

IIRC

Sorry, this is not correct.

Flight planned fuel is very specific for every individual flight. Flight plan fuel requirements are run based on very specific forecast winds and the legal requirements for a alternates whether they are EDTO, weather or other (due to lighting, nav aids serviceability for example). There is no 10% added or worse case scenarios.

For anyone interested in the process for loading an aircraft you can read CAR Part 121 here.

It has the requirements for fuel and passenger loading requirements including standard weights.

Cheers, Matt.

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empacher48

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#1547512 6-May-2016 10:47

As I pilot with a well known international airline, operationally the payload we can put on our aircraft varies on a number of things.

The aircraft will have an empty weight, which when the aircraft leaves the factory it will be weighed with all the parts in it which make it fly. (but less things like useable fuel, galley contents and the operating flight crew). Then you can add on things like the weight of all the food and drinks and other nice things that airlines might want to give the SLF (Self Loading Freight - passengers, those who pay our salary), plus the weight of cabin crew and pilots. This weight becomes the Aircraft Operating Weight.

During flight testing, and the design of the aircraft by Boeing, Airbus, Bombardier or ATR they work out the maximum certified taxi weight, maximum certified take off weight, maximum certified landing weight and the maximum zero fuel weight. These weights are usually structural, which means if you exceed these weights when the aircraft is operating in its normal design envelope and upto 150% of the design envelope for turbulence, the aircraft won't break up around you in flight.

Using these figures the manufacturer will then provide performance figures for us to work out whether we can take off or land on a runway of a certain length (if it is shorter, we have to reduce the maximum weight so we don't run off the end). This also takes into account things like wind component (headwind helps), temperature (lower temperature helps), atmospheric pressure (higher pressure helps). Also these figures will give us the safe speeds to which the aircraft will fly, and also climb even if we have an engine failure on the runway. Its not a good look when a flight runs off the end of a runway, or crashes because it can't fly on one engine.

When it comes to maximum weights, those of us flying the line aren't test pilots and having weights above the maximums means you are flying the aeroplane somewhere that no one designed or tested it to go. You are now a test pilot with up to 400 crash test dummies in the back.

We then work out how much fuel we need to take, to make sure we can fly from point A to point B, plus allowances to weather deviations, and then any fuel to fly to another airport should the weather at our destination to below certain limits, there will be an allowance for engine start, taxi and shut down and a certain amount as a minimum reserve.

Once we get our aircraft operating weight plus fuel and what our maximum take off weight will be, the difference is payload (or how many SLF's and bags and freight, if any) we can carry.

Should the weather and departure or arrival mean we have a lower take off or landing weight - we have less payload (we only know that on the day of the flight, weather forecasting is not good enough to know what the temperature, wind direction and atmospheric pressure 6 months out when people book tickets). Should the weather enroute or at the arrival airport means we have to carry more fuel - we have less payload (once again we don't know that until the day). Then other things like minor problems with the aircraft, which mean it is still safe to fly (like one of the three air conditioning systems) means you have to fly lower, which means higher fuel burn, means more fuel need, means less payload (usually happens at an airport without maintenance support).

There are a lot of things that have to be balanced out to make sure we don't exceed the maximum weights and don't end up either a smoking hole in the ground, break up in the air or run off the end of a runway. So yes, sometimes we have to offload passengers or freight or bags to stop you all dying. But I just assume that the public do like living and I am the one with the legal responsibility that you all do. If you would rather risk the chance of dying in the firey plane crash and not be offloaded, that is fine. But I won't be flying that flight.

djtOtago

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#1547518 6-May-2016 11:15

The real problem here is Airbus designed an aircraft that can't have a full load of fuel and a full load of passages.

Technofreak

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#1547519 6-May-2016 11:22

djtOtago:

The real problem here is Airbus designed an aircraft that can't have a full load of fuel and a full load of passages.

Who said it was an Airbus?

Very few if any aircraft can take full fuel tanks and a full load of passengers.

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#1547549 6-May-2016 11:39

djtOtago:
The real problem here is Airbus designed an aircraft that can't have a full load of fuel and a full load of passages.

Huh? It depends on what full is. A full fight of certain ethnicity and a whole cargo load of Apple cables (you know how they box their stuff right) would probably be very light vs a full flight of world's strongest men competitors and a cargo full of gold bars.

hairy1

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#1547552 6-May-2016 11:40

I think @djtOtago was joking.

My views (except when I am looking out their windows) are not those of my employer.

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djtOtago

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#1547557 6-May-2016 11:50

hairy1:

I think @djtOtago was joking.

Correct.

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#1547567 6-May-2016 12:12

Completely by the by ... Are you using Donald Trump's initials ;p ?

sbiddle

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#1547650 6-May-2016 14:36

I'm still slightly confused by the actual story. I'd love to know if she simply accepted the $350 to actually be bumped.

nate

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#1547695 6-May-2016 16:00

empacher48: You are now a test pilot with up to 400 crash test dummies in the back.

I'm definitely not here to help add to this conversation, however this sentence above is pure gold.

bmt

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#1548049 7-May-2016 20:26

Aircraft can be stripped of non-essentials and fuel, jacked, lowered onto scales and weighed to get the basic weight of the aircraft. This would typically only happen during a major servicing (perhaps every 2-3 years). Everything that goes back on will have a known weight and gets included in the total for the pilots to work with before fuel, freight and passengers are even considered.

Centre of gravity is also calculated which has an effect on weight distribution (would more likely be for freight in a large aircraft). This is why if flying on a smaller turboprop plane that isn't full, passengers will be seated in specific locations to spread the load and you may be denied permission to change seats.

As for this situation, could seem frivolous over 1 person and their baggage, but you never know.. It could be the final hole in the cheese being lined up for something to go wrong. Rules are rules, regulations are regulations.

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