initious
Posts: 943
Joined: Tue Dec 16, 2008 5:54 am

How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 12:31 pm

This is a question I been fretting for some time.

If I am correct, the ZFW determines the amount of fuel needed for a flight. Lower ZFW means lesser fuel needed and vice versa. However, how do you calculate the ZFW for each and every flight? Each passenger's weight varies greatly and of course their luggage weight may also vary greatly, although already weighed at check-in. Do they have sort of a built-in weighing machine at the ramp, or something? Thanks in advance! 
One day I will fly around the world!
 
Luftfahrer
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RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 12:36 pm

ZFW = Zero Fuel Weight

composed of

DOW (Dry Operation Weight) + Payload

Quoting Initious (Thread starter):
Each passenger's weight varies greatly and of course their luggage weight may also vary greatly, although already weighed at check-in.

Standard weights are used for passengers/baggage and they seem to be pretty accurate. I haven't heard of other practices thus far.

[Edited 2010-03-31 05:39:49]
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initious
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Joined: Tue Dec 16, 2008 5:54 am

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 12:41 pm

Quoting Luftfahrer (Reply 1):

Standard weights are used for passengers/baggage and they seem to be pretty accurate. I haven't heard of other practices thus far.

What's the standard weight used for each passenger and baggage? Does it vary according to region? (Like certain regions might have people who are of a larger average size)
One day I will fly around the world!
 
planefixer
Posts: 61
Joined: Fri Nov 10, 2006 7:59 am

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 12:45 pm

IATA have generalised weights for Men / Women / Children. Luggage is all weighed and these figures are added to the Dry weight of the aircraft, bearing in mind not all aircraft of the same type weigh the same, so each aircraft has a weight and balance certificate. That figure is the ZFW.
 
initious
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RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 12:49 pm

Quoting planefixer (Reply 3):
IATA have generalised weights for Men / Women / Children. Luggage is all weighed and these figures are added to the Dry weight of the aircraft, bearing in mind not all aircraft of the same type weigh the same, so each aircraft has a weight and balance certificate. That figure is the ZFW.

That was a detailed answer! Thanks a lot! 
One day I will fly around the world!
 
migair54
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Joined: Thu Jun 14, 2007 4:24 am

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 1:29 pm

Quoting planefixer (Reply 3):
IATA have generalised weights for Men / Women / Children. Luggage is all weighed and these figures are added to the Dry weight of the aircraft, bearing in mind not all aircraft of the same type weigh the same, so each aircraft has a weight and balance certificate. That figure is the ZFW.

Very good answer........

Usually is pretty acurate because pilots use the weight and balance data to ge take off speeds, centre of gravity and postion on the trim for take off..........

Inside the payload data you have, paxs, baggage and cargo........baggage and cargo could be more accurate if the airline wants, but usually the only real weight is the cargo......I think is for billing purpose..........as mentioned above pax and baggage are standard values......
 
airtran737
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Joined: Mon Apr 05, 2004 3:47 am

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 2:38 pm

Quoting planefixer (Reply 3):

In our operation almost 100 percent of our flight are for AMC, and they do not fit in with the average weights. The average weight of a civilian is 190 lbs in the summer, and 195 in the winter. AMC weighs each passenger, their carryon, and their baggage. This gives us an even more accurate weight than the IATA standard. The average soldier weighs between 223 and 231 lbs. So we take the pax weight, bag weight, aircraft OEW, and add them all up to get the ZFW
Nice Trip Report!!! Great Pics, thanks for posting!!!! B747Forever
 
sirloin
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Joined: Sun Mar 11, 2007 12:13 pm

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 2:45 pm

Standard weights in the US:

Pax (Summer Weight): 190 lbs. (carry-ons included)
Pax (Winter Weight): 195 lbs. (carry-ons included)
Standard Bags: 30 lbs.
Heavy Bags: 60 lbs. (generally calculated as 2 standard bags)
Cargo: Actual weight, converted to corresponding # of bags

Keep in mind, this is how my airline does it. I'm not sure if it's universally done this way.
 
ThePinnacleKid
Posts: 497
Joined: Wed Feb 23, 2005 9:47 am

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 2:58 pm

Quoting sirloin (Reply 7):
Keep in mind, this is how my airline does it. I'm not sure if it's universally done this way.

It's not universal. If an airline wants to, they can get certified to get their own average weights approved for use FAA... my carrier has them and a proprietary weight and balance program/system.
"Sonny, did we land? or were we shot down?"
 
CALMSP
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RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 5:04 pm

Quoting ThePinnacleKid (Reply 8):

correct. CO uses different baggage weights for a number of flights, and even had different baggage weights for mainline aircraft and COEX on flights to MEX. Almost every destination heading south uses a specialized bag weight set forth from research on the average bag weight per flight..........PTY, SAL, GUA, LIM, etc etc.
 
simairlinenet
Posts: 720
Joined: Sat Oct 29, 2005 2:24 am

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 5:24 pm

The standard weights vary by regulatory agency. In Australia for example, it is based primarily on gender.

If the carrier has reason to believe that standard weights should not apply though, they should determine an alternate means of determining payload. When carrying a sports team for instance, they could use the player's listed weight.
 
Viscount724
Posts: 19287
Joined: Thu Oct 12, 2006 7:32 pm

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 6:16 pm

One of the contributing factors to the Air Midwest (operating as US Airways Express) Beech 1900D crash at CLT in 2003, that killed all 21 aboard, involved the average weight assumptions. I believe the FAA conducted a survey after that accident that involved weighing each passenger and their baggage on a sampling of flights. If not mistaken it resulted in increasing the weight assumptions. See item 5 in the last paragraph listing the contributing factors.
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030110X00049&key=1

[Edited 2010-03-31 11:21:25]
 
Tristarsteve
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Joined: Tue Nov 22, 2005 11:04 pm

RE: How Is The ZFW For Every Flight Calculated?

Wed Mar 31, 2010 6:54 pm

Quoting Initious (Thread starter):
Do they have sort of a built-in weighing machine at the ramp, or something?

Well no, but aircraft are weighed to get the Basic Weight.
This is for an airline A320.
This is the weight of the aircraft ready for service. Toilets are serviced, water tank full, All the seats, galleys and equipement fitted, but no catering, and the fuel tanks empty. This is done every two or three years for every aircraft.
When I did it we used a set of scales, one for each undercarriage. The results are printed on a Basic weight and index table, which is fixed to the cockpit door.
Then you add the operating crew and their baggage, the catering, the passengers, baggage and freight to get the ZFW.
This has to be done an hour or two before departure, so that the flight plan can be prepared. This weight is called the EZFW (estimated). Using the EZFW, the computerised flight plan system can work out the fuel required, which is checked and agreed by the pilots.
Then the plane is readied for service. Hopefully the EZFW will be near enough! If the actual ZFW goes up, at a certain point the Flight Plan will become invalid, about 2 tonnes is allowed for a narrowbody, or 5 tonnes for a wide body before a new calculation has to be performed.
When the flight is closed after the standbys are given boarding passes, then the actual ZFW is calculated. If this is in limits then off you go.

Airlines operate hundreds of flights and get good at producing an EZFW that works.
We operate short haul, flights of around two hours. The ZFW is the factor that limits us, never TOW and rarely LDW. The tricky one for the dispatcher is the B763. Lots of freight in the fwd hold, and a nearly full load of pax and bags, can give you a ZFW limit, and especially a nose heavy CG. Quite common to close the flight and find you have exceeded the fwd CG limit, especially when there are few business class pax.. Then you have to move a couple of pax from front to back to balance the plane and close the flight.

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