Calculated vs real take off weights?
 

I was having an interesting discussion the other day, where we were talking about the assumptions made for passenger weights etc. Now, from what I understand the average male passenger weight assumed is 84kgs, with approx 3.4 kilos of hand luggage?

Obviously the aircraft weight is added to the load, then zero fuel weight added to the fuel load to give the COG & moment, plus AUW.

How close in the real world is calculated compared to actual AUW, assuming no silly mistakes, just difference between the industry standard assumed weights and the actual load on board?

Depends on the population statistics used and the relevance of the statistics to the particular population of passengers (or baggage) on any given day. This applies to any use of presumed weights including, for example, fuel loads.

(a) generally, for a given country, say, there will be national statistics which can be used to determine a rational set of standard weights.

For instance,

(i) the original 170lb weight generally used for adult males was derived from North American military population studies back in the 40's if my recollection is correct.

(ii) the current Australian schedule, CAAP235-1(1), dates to a study by a CASA (or whatever the name was that week) engineer by the name of John Klingberg. The study, based on national medical data, was quite detailed and gave a large sample base for the sums.

(b) providing that the population of passengers in question on any given day is consistent with the population in the sums, the use of standard weights should be reasonable - with two principal caveats -

(i) compatibility - if the study population is, say, national, then don't expect an aircraft load of sumo wrestlers or jockeys to present sensible data

(ii) due to the shape of population distributions (ie considering standard deviations) small passenger loads would be expected to show far greater variability than larger passenger loads.


If I recall back to the 70s, when I was flying F27s, we often elected to weigh the passenger and baggage loads in lieu of using standard weights. I cannot recall a single case where the total weights were inconsistent with standard weights.

FYI a recent passenger weight survey conducted for EASA:

http://www.easa.eu.int/rulemaking/do...95%20Final.pdf

We learned for this and other studies (e.g. done by the FAA) that weights are increasing. People are getting heavier and bringing more stuff with them.

A freighter aircraft of course has the most accurate calculated
weight - everything is weighed, as against standard weights
for pax trips which can have large differences in actual weight
depending on what race of humans there is down the back as
well as how many.

80kg is way too light for your average Western slob against a
Burmese peasant who couldn't ever weigh that much even if
you filled his boots with mud.

Not very easy to weigh 200 passengers but I have a few occasions been given actual baggage weights and they have always been more than the assumed weight would have been. On one occasion with a 144 seat A319 the actual baggage weight was over 600kg up on the assumed weight.

When working for BEA in LBG in the 60's/70's as Officer i/c of Load Control, we would use the average weights for all our flts, whatever acrft type : 78 kg for a male, 68 kg for a female and 12 kg for a child up to 12 years of age. Those weights included 5 kg for hand luggage. The baggage wts used were 12 kg per piece. The only times we had to weigh our pax/bags was for the Cambrian Airways flts operated by a DC3 with 32 pax. The reason being that in UK the max allowed TOW was 12700 kg and in France that DC3 had a restricted max TOW of 12200 kg. So of course once every 2 years when the Wales vs France rugby match took place in Paris, you can imagine what we were up to. Unable to legally load the bags on the DC3 return trips to CWL as TOW exceeding 12200 kg. So we topped up the loads on the Viscounts luckily.
I remember a little later having changed Cy and operating as Stn Mgr for a US airline, I requested several times the actual pax/bags wts for a few LBG/JFK flts operated by a DC8-63 252 seat config. sked to depart around 13:00Z in July/August. We gained each time around 2500 kgs that allowed the last minute top up fuel in order to fly non stop. Obviously, in those days the human beings were not as heavy as they are today.
Those were the good days.