PDA

View Full Version : Question about W&B and average pax weight


Pugachev Cobra
28th Mar 2010, 01:11
Hello folks!

I was thinking about the average weight companies use for passenger plus hand luggage, 75kg. Is that correct?

First, it seems a little too low.

But what strikes me is why companies, at least to my knowledge, never tried to weight passengers (the same way baggages are) for accurate payload weight.

This way couldn't the company save more on, e.g. fuel?

And would anyone here know who determined the 75kg/pax ? (or any other value)

Any thoughts on this are appreciated!

411A
28th Mar 2010, 03:05
...at least to my knowledge, never tried to weight passengers

Oh, it's been tried, alright (in the past, especially with charter airlines) however...the punters get quite upset, especially those of the female gender.
Sometimes (and I have seen it, personally) the ladies (often elderly) start to argue, as in...'fix your scale, dummy, it's way off.'
Four letter words often follow...:}

Denti
28th Mar 2010, 03:23
Even more weird when you fly both charter and scheduled service but use very different weights depending on which of both it is. Quite often the same passengers on both, but on one they "weigh" 13kg more than on the other.

Tinwacker
28th Mar 2010, 07:22
I was thinking about the average weight companies use for passenger plus hand luggage, 75kg. Is that correct?

That may well be for some budget companies but I have heard as 411 mentioned, the screams on the scales.

10kgs of hand baggage that leaves 65kgs for the pax, my wife would just scrape in so there is no hope for me..

My company uses 100kg as their base figure, and doing my maths on a A330 as an example, that turned out very close to the actual departure weight.
The difference is probably all the unaccounted carry on bags and duty free....

TW

Genghis the Engineer
28th Mar 2010, 09:12
I did a survey of this some years ago. I don't have the results any more, but my recollection is of a very wide (20kgish) range of masses used by various operators - there doesn't seem to be much of a standard.

Equally worrying is that the airworthiness standards for big jets are only using around 77kg per seat to determine crashworthiness. To my mind, ludicrously low. (Pilot seats use 86kg, which is a little better, but still frankly too low.)

G

rudderrudderrat
28th Mar 2010, 09:44
Hi,

I believe our actual take off weights can be more than we've calculated because of the different standard weights we assume. (20 kgs difference was noted by Genghis).

On A 320 series the VLS is computed by the angle of attack probe & FAC. The FMGC VLS & VAPP is computed using Fuel remaining + the Zero Fuel Weight (entered from Weight & Balance calculation). There is often a difference in the two VLS values of about 3kts when on the approach; i.e. the aircraft's VLS FAC calculation thinks we are heavier than the weight & balance calculation.

If it was just a random error in the way the angle of attack vane is mounted on the aircraft, then we'd see + and - speed differences. I've only ever noticed that we seem to be heavier than we think we are.

Retired Redcap
28th Mar 2010, 11:19
I have been retired a while now but from what I remember BA used 88kg for a male passenger and 70 kg for a female passenger. This was for economy passengers. For first and club class a further 12kgs was added to cover the increased cabin baggage allowance.
Ever so often a series of flights are subject to a check weighing of passengers (plus ccabin baggage) to verify that the authorised weights reflect the true state of affairs.
In the 1960s 70s and 80s the figure of 75 kgs was faily common around the world but since then the population has definitely become heavier and the current authorised weights reflect that fact.

john_tullamarine
28th Mar 2010, 11:29
The earlier 170lb/77kg came from a study of US military personnel many, many years ago.

The main point is that ANY standard weight schedule needs to be based on a sensible statistical study of a population typical for that style of flight .. ie, there is no reason why an operator cannot use several different sets of standard weights in different circumstances.

The Australian regulatory suggested weights are based on a study done by John K quite some years ago and the report is still floating around.

It is a bit useless not to base weights on stats otherwise the outcome is a bit silly at times .. eg a charter for a football team using mums and dads weight schedules.

If the population is representative, the use of standard weights works out quite well ... I can recall, as a young buck on Fokkers, occasionally weighing the punters for a critical takeoff ... invariably the then use of 170lb gave very good results just about every time. ...

kenparry
28th Mar 2010, 12:00
Each regulatory authority seems to have its own idea. In Europe, EU OPS 1.620 defines pax mass according to type of flight and size of aircraft. See page 125-126 of

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:254:0001:0238:EN:PDFd

for more detail.

When the CAA decided these things in the UK, the weights/masses were raised every few years as the result of surveys of real pax at check-in. During my airline years, the figures we used seemed to be fairly realistic in that the aircraft performance was pretty much in line with expectations. Without an on-board aircraft weighing system, I think there is no other way of the crew being aware of true mass - and of course only gross errors would show up that way.

fireflybob
28th Mar 2010, 13:45
Had passengers weighed twice in my career - on both occasions actual weight was below the weight we would have been using had we used the official assumed weights. This was fortuitous since we were on fuel critical sectors which meant we could load some extra fuel to avoid a technical stop for fuel.

On the other hand when I first flew A320 in 1990 we would sometimes get airborne and we would get a "Check Gross Wt" message as the system had detected that we were heavier than the entered ZFW plus fuel etc. We were using assumed weights for hold baggage. The company decided to weigh all hold baggage and we discovered that we were indeed heavier!

That said in this day and age I would have thought some bright spark would come up with a way of automatically displaying (whilst on the ground) actual weight and CG position which was accurate. Am aware that such systems are in place on cargo a/c as a gross error check.

ft
28th Mar 2010, 16:48
In Europe, 1.620 EU-OPS Subpart J (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:254:0001:0238:EN:PDF) tells us that 75 kg is only close for holiday charters >30 seats. Otherwise, it is low.

In the US, 75 kg equals 165 lbm and is, again, low. The official word comes from AC120-27E (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%20120-27E/$FILE/AC120-27E.pdf) and states 190 lbs for a mixed pax load in the summer, 195 in winter. Without carry-ons, the summer weight goes down to 184 lbm.

The standard weights are determined by weighing pax and bags and applying statistical methods. They are revised every now and then, although chances are they are not revised often enough.

75 kg will probably only be valid in Asia these days, where they are blessed with significantly lower average pax weights.

muduckace
28th Mar 2010, 17:00
Last time I did AMC/MAC runs 220 lbs was the weight for a soldier.

john_tullamarine
28th Mar 2010, 23:45
.. the 170lb dates back a LONG time .. would have to dig out the paper to get the actual date but certainly not overly relevant to the modern and larger folk.

Point is the numbers have to be based on a sensible population sample or else they are useless.

Checkboard
29th Mar 2010, 02:03
John, if I remember correctly, the Australian CAA brought out a CAAP (Civil Aviation Advisory Publication) on weights, where they listed different weights for different sized aircraft. The idea was to stop a guy on a Navajo using an "airliner" 75kg weight when he knew he had eight 100kg passengers on board.

In any case, the regs were written "thou shalt not fly overweight" - use of average weights did not absolve the pilot from that dictate.

john_tullamarine
29th Mar 2010, 04:15
The CAAP was based on John K's study - quite a useful document on the subject and worth a copy in the pilot's tech bookshelf.

The varying weights reflected differing sigmas relevant to the aircraft seating capacity (as I recall) .. the intent was to have an acceptable probability that the aircraft would not be overloaded .. rather than an attempt to preclude mischief in the operational camp. It is incumbent on the operator/pilot not to misuse standard weights deliberately if it is reasonably known that the population study is not reasonably representative of the population on board. (Yes, yes, I know .. and if you believe that fiction I have a bridge to sell you ..).

In general, the larger the sample size the less the problem. Overall, it is more useful to weigh the load for a smaller aircraft to avoid the associated penalty involved in using the CAAP data.

rudderrudderrat
29th Mar 2010, 09:11
Hi ventus45,

I can see problems of only excluding your weigh scales to one person at a time. You'll probably have additionally someone else's foot on the weigh bridge.

We have always used Male, Female and Child standard weights. Are you saying that some operators only use a standard 75kg per passenger? If so, then no wonder the calculations can be significantly out.

john_tullamarine
29th Mar 2010, 11:15
regulatory bodies got off their collective rears and fixed this problem once and for all ?

the problem lies only with the lack of will to do what is required .. the solution itself is simple ... either you weigh all load or use a statistically based schedule(s) of standard weights ..

the cause of the crash was: "significant overloading and / or CG out of range,

operator risk management problem .. just like it is at the moment

A weigh-bridge unit need only be built into the floor

would be feasible for gross weight summing and a swipe of the pax boarding pass would take care of CG

the display could even "flash" individual seat icons

not really much use as the variation per flight essentially is a normal distribution so a significant number of folk will be outside the mean value

all aircraft were deigned to maximise the number of seats

... as might follow from a desire to maximise revenue ?

How close to the "absolute limit"

each certification establishes a maximum number of occupants so that is the readily obtained limit

"standard pax weights" under the old rules are no longer representive

then redo the sums - QED

they also included a "standard mix" of adult males, adult females, and children.

can you provide any evidence to support this idea ?

Brian Abraham
29th Mar 2010, 17:55
Now that airlines are beginning to charge quite hefty fees for baggage over the allowed limit I recon they should be charging pax by weight. Why should a slim lass weighing in at 45kg dripping wet and being a kilo or two over the baggage limit be required to cough up whereas a 136kg lard arse who is within the prescribed baggage limit is OK.

john_tullamarine
31st Mar 2010, 12:54
pass, friend ... glad I'm not the only one to have the odd mental infarct ...

Bullethead
31st Mar 2010, 13:25
Back in my previous life flying RAAF B707s we used standard weights which was fine until we carried a plane full of fighting fit soldiers and all their kit out of Honolulu bound for Richmond. We were at MAUW on departure and the poor old thing only just got airborne and then staggered into the sky and took ages to accelerate and would not reach the planned cruise level. We did some head scratching after we eventually settled in the cruise and worked backwards through the performance chart to discover were somewhere like 8,000 lbs over max weight on take off. :eek:

We used to weigh them after that and couldn't generally plan PHNL - YSRI non-stop with a full load of soldiers.

Using standard weights in airline operations I'd wouldn't be surprised if the actual wieght of the aircraft varied from the planned weight by by a minimum of several tonnes, up or down, most of the time. I'm not sure whether the 'standard' pax weights vary depending on the departure point, some races are generally of smaller stature than some others, I'll have to check next time I'm at work.

Regards,
BH.

decurion
31st Mar 2010, 14:02
I recently worked on a project for EASA together with a company called NEA on a survey on standard weights of passengers and baggage.

Here is the link to the final report of this survey:

http://www.easa.eu.int/ws_prod/r/doc/research/Weight%20Survey%20R20090095%20Final.pdf

Storminnorm
31st Mar 2010, 16:16
Due to the increase in average weight due to the "Obesity"
plague that we seem to be in at the moment, I have been
thinking of starting a new business to prevent industrial
injuries in the Undertaking industry.
Pall-bearers are having to shoulder weights in excess of
any safe limits whilst carrying out their duties, and need
to be removed from potentially hazardous situations whilst
carrying out those duties.
I am proposing the replacement of Pall-Bearers by suitably
quiet electrical fork-lift trucks to carry the dear departed on
their final trip into the Cemetery or Crematorium.

BBQ12345
31st Mar 2010, 17:57
Thanks Cobra for starting this thread coz I've been scratching my head over this subject for a long time. EU and FAA regulations and methodology are quite complicated. I've been thinking whether there are easier alternatives. Wonder if something like weighing the aircraft on the ramp, deducting the known load, then averaging out the pax weight. ANy thoughts? A survey to weigh the pax are both costly and impossible. I agree that the IATA and ICAO or maybe the ACI should work together and look into a more effective solution.

john_tullamarine
31st Mar 2010, 22:59
A survey to weigh the pax are both costly and impossible

Some of the posters are missing the important bit ..

(a) if you are going to use standard weights, the weights used MUST be representative of the population form which you are drawing your passenger loads

(b) standard weights usually are drawn from population studies (eg John K used NHMRC Australia wide population study data, as I recall). One could weigh all passengers for a period but that would be both a pain and take a moderate time before the sample set was sensible

(c) the 707 incident simply highlights a deficiency in the squadron's weight control procedures

(d) the fall back always remains .. if the commander considers that the passenger mix doesn't reflect the population studies then weigh them on the day

(e) there is NO reason why appropriately derived and applied standard weights will not give a pretty accurate figure, especially as the size of the aircraft increases .. other than operator/crew use of inappropriate protocols.