1) Aircraft type capacity has traditionally been measured by seat count, but this is an unstable metric as seat configurations change frequently. 2) The document proposes using cabin area as a more stable way to measure and compare aircraft type capacities. It defines gross, net, and equivalent cabin areas. 3) Analyzing several aircraft types, it finds cabin area correlates better to seat count than gross area. Net or equivalent cabin area provide stable capacity measurements over time for forecasting and fleet planning.

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HOW TO MEASURE AIRCRAFT TYPE CAPACITY?
AN INNOCENT QUESTION WITH BIG CONSEQUENCES
By Daniel SALLIER
Aéroports de Paris
Bât. 530 – Zone Orlytech
9, Allée Hélène Boucher
Orly Sud 103
94396 Orly Aérogare cedex
France
Telephone: +33 6 82 84 12 56
daniel.sallier@adp.fr

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ABSTRACT
In this contribution I will introduce a new unit to measure aircraft type capacity. Aircraft type
capacity is a quantity used in long term fleet forecast the type Airbus and Boeing are publishing
every year or in long term forecast of movements by (generic) aircraft types the airports have to
perform for future infrastructure dimensioning (terminals, aprons, stands, etc.). Aircraft capacity is
downscaled at cabin level (1st, business class, etc.) leading to the contribution analysis of the
different market segments to flights revenue/profit.
Aircraft type capacity has been stated in number of seats for ever. Unfortunately the seat count of an
aircraft type is a very unsteady data to play with: airlines operate different seat counts even for the
same aircraft type which keep changing all the time. Isn't it an inadequate unit leading to incorrect
measurements which result in misleading analysis at the very origin of bad decisions?
To start with, we will have a critical look at how the aircraft type capacity is measured by the major
players of the air transport industry. Then we will look at how cabin area could prove to be a far
more adequate unit. Then we will question different ways of measuring it so that it can allow direct
and consistent comparisons between different aircraft types. To finish with we will look at how seat
counts and cabin areas can relate to each others and illustrate with an example how to reassess
market segment income/profit contribution per flight.
KEYWORDS: movement forecast, airlines economics, revenue/profit contribution
CLASSIFICATION:
1/ Airline Economics,
2/ Market Outlook & Future Development of Air Transport,
3/ Market/Capacity Measurement and Forecast

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1. INTRODUCTION
Attaching a number of seats to an aircraft type or to a specific aircraft sounds as the most
straightforward and obvious way to proceed in order to measure its (passenger) capacity. It is that
obvious that the literature refers to this or that aircraft as being a 250-seater short/medium haul or a
550-seater long haul for instance.
Doing so is fully relevant for a specific aircraft having a fixed cabin layout at a given date: i.e. Air
France 777-300 registered as F-XXXX accounted 303 seats on November the 28th
, 2009:
Figure 1: Air France B777-300 cabin configuration
But the same airline can have a sub-fleet of the same aircraft type – 777-300for instance – with
different cabin layouts resulting in a significantly different seat count; 468 seats for instance:
Figure 2: Air France B777-300 cabin configuration
Is the 777-300 in the Air France fleet a 300-seater or 470-seater? It does make a difference, doesn't
it!
Seat count as an aircraft capacity measurement is even far more dubious when dealing with aircraft
equipped with convertible seats allowing them to shrink from a 6-abreast to a 5-abreast or 4-abreast
configuration for instance. What is the aircraft seat count then? This is illustrated in the A320-200
Europe sub-fleet of Air France.

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Figure 3: Air France A320-200 cabin configuration
In addition airlines tend to change their cabin configuration every 5 years as an average.
So, how to measure the A320-200 seat capacity for instance and how does it compares with the
737-800? Is seat capacity a single figure attached to an aircraft type for ever or should it be
"adjusted" over the time with regard to the actual airlines product changes? Are seat count and its
related ASK (Available Seats Kilometres) the best units to measure aircraft capacity and airline
supply? These are not academic questions. Depending on the capacity unit definition which is used
the appraisal of the future developments of the world fleet can be quite different ending up with
quite different conclusions as for the types of aircraft likely to be required by the market.
A side aspect of this question is that using seats or ASK as measurement unit of the industry supply
affects any further economical analysis which will be conducted on the market profitability, the
market segmentation (i.e.: 1st
, business, coach class passengers).
We definitely favour capacity measurement derived from cabin area or cabin area kilometres such
as the net cabin area which is the actual cabin area minus all the cabin surfaces which the
certification rules demand to be kept free of any utilisation at any time such as the aisles for
instance. It offers the type of measurement steadiness over the time and the type of homogeneity
between aircraft types which represent data characteristics very comfortable to deal with any time
one is faced with long term issues.
2. CLASSICAL AIRCRAFT CAPACITY UNITS
We will focus mostly on long term forecasting issues and more specifically on fleet planning ones.
The main objective of a fleet planning exercise is to turn demand requirements into supply
requirements which are turned into aircraft types. Supply is generally expressed in number of seats
or ASKs (Available seats kilometres). In addition to future demand developments, supply
requirements derives from a set of general and specific conditions/rules such as the frequency
policy, the maximum number of different aircraft types which is acceptable in a sub-fleet, etc…
The question raised is to adopt a supply/capacity unit definition which:
1/ results in a steady measurement over the time. Same capacity figure attached for a given aircraft
type whatever the year the capacity is measured;

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2/ is homogeneous between different aircraft type and allows consistent comparisons between
each others. How an A330-300 compares with a 777-200 in terms of type capacity.
PHYSICAL CAPACITY OF A GIVEN AIRCRAFT
Measurement unit: seats.
The physical capacity measurement of a given aircraft at a given date is its number of seats,
commercial and technical crew dedicated seats excluded. This capacity measurement is likely to
change over the time further to the different cabin configurations the aircraft will be given.
We should point out that for aircraft equipped with convertible seats such as the ones allowing the
cabin or part of the cabin reconfiguration for each flight from 6 abreast to5-abreast or 4 abreast,
there is no single figure for the aircraft capacity but a full range of possible capacities.
COMMERCIAL CAPACITY OF A GIVEN AIRCRAFT
Measurement unit: seats.
Same as before with the exclusion of passengers seats which are reserved for the crew and of the
seats which are not put on sale whatever the reasons are (i.e.: further to range limitation, take-off
performance, etc…)
AIRCRAFT TYPE CAPACITY
This issue here is not to measure the capacity of this or that specific aircraft at a given date, but to
characterise an aircraft type by its capacity. The issue is no more to characterise this or that specific
Air France A320-200 (at a given date) but to characterise the capacity of the A320-200 aircraft
type.
Up to now they are 3 ways to do so, none of them being fully satisfactory:
TODAYS AIRBUS APPROACH AND DASA APPROACH (Former German partner of
Airbus)
Measurement unit: seats.
Dasa used to consider the actual number of physical seats of a given aircraft at a given date and to
categorise this aircraft accordingly. The major drawback of this approach is to prevent an aircraft
type from being categorised by its capacity.
This approach is illustrated in the fact that the French domestic airline, Air Inter, used to operate
single class, high density version of the A330-300 with 440 seats which would classify it, according
to Dasa rule, in the same category as Air France 747-400 (436 seats) in its latest configuration!
Dasa approach was never able to answer: "what is the A320-200 capacity/seating category?" and its
aircraft seating categories have never been "type homogeneous".
FORMER AIRBUS APPROACH (10 years ago).

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Measurement unit: seats.
Airbus uses the average number of physical seats accounted for the worldwide fleet of a given
aircraft type to define the type capacity. That's how the A320-200 can be categorised in former
airbus files as a 162-seater for instance.
The major drawback of airbus approach is to provide a type capacity measurement which is
unsteady over the time. To make a long story short, an A320-200 identified as a 162-seater in 2009
could likely be identified as 168-seater in 2040 for the very reason that most of the A320-200 would
be second hand aircraft at that time and be operated by charter airlines which definitely favour very
high density configurations.
BOEING APPROACH (10 YEARS AGO).
Measurement unit: seats.
Boeing categorise each aircraft type by it seat count in its single class highest density version. The
issue is that the maximum number of seats does not depend exclusively on the cabin geometry but
can result from emergency escape certification rules which can limit this number (i.e. 737-900
registered in Europe).
Nevertheless Boeing's definition offers a single value for each aircraft type and a steady one over
the time, not likely to change since it is based on the cabin type geometry and certification rules. By
far we consider it as being the best approach among the 3 ones quoted up to now.
The main drawback of Boeing approach is its lack of data homogeneity between aircraft belonging
to different categories such as single-aisles and twin-aisles or between single-aisles and regional jet
for instance. While this drawback is of rather minor importance when working on aircraft belonging
to the same category (i.e.: long-haul twin-aisles), it turns out to be pretty hard to overcome anytime
one is faced with fleet mix issues such as the routes which can potentially be operated by single-
aisle and twin-aisle aircraft.
3. OUR PROPOSITION: CABIN AREA (m²)
Measurement unit: square meters.
GROSS CABIN AREA.
We can define the cabin area as being the cabin floor area located between the rear bulkhead and
the flight deck rear panel.
This is illustrated in the following chart (grey-blue area):
Figure 4: Gross cabin area

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We define the cabin width as being the floor width measured in the internal constant section part of
the fuselage.
NET CABIN AREA.
Further to certification rules parts of the cabin floor should be left free of any utilisation: no seats,
no monuments (galleys, lavatories, etc.) allowed.
The areas of the aisles, cross aisle, assist spaces, (light yellow areas in the following chart) which
cannot be of any commercial use, should but cut off the cabin area calculation. The net cabin area
(grey blue area) is illustrated in the following chart:
Figure 5: Net cabin area
EQUIVALENT CABIN AREA.
An aircraft of a slightly larger cabin floor than another one, for instance the A320 family vs the
737NG series, cannot accommodate more seats abreast per row (6).
It means that in terms of aircraft capacity the net cabin area should be corrected in order to get as
much rid as possible of the bias comfort considerations may have introduced in the cabin geometry
design but which does not translate into additional or lower capacity.
We propose:
1/ to consider the maximum number of seats abreast which can be placed in the constant section
of the fuselage. Let us assume 10 seats abreast in the 777-300;

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2/ to consider the maximum number of aisles (1 or 2). 2 for a 777-300;
3/ to consider that a high density configuration coach class seat is 17" wide (0.4318m);
4/ to consider that the aisle width is 15" wide (0.381m);
5/ to calculate the area correction ratio as follows:
- the 777-300 actual floor width is 5.7074m ;
- the 777-300 floor width which can be used for capacity purposes: the net floor width is
4.9454m = 5.7074 – 2 x 0.381m : the actual floor width minus 2 times the minimum aisle
width ;
- the 777-300, a 10 abreast aircraft, equivalent width is 4.318m = 10 x 0.4318m ;
- the area correction ratio is 0.87313463 = 4.3180m / 4.9454m
6/ to define the equivalent cabin area as being the net cabin area time the area correction ratio:
229.11m² = 262.40m² x 0.87313463
The following chart illustrates the concept:
Figure 6: From gross to equivalent cabin area

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The following table provides the main cabin areas data for the most current Airbus and Boeing
aircraft types.
CABIN AREAS & CABIN SEAT-COUNT.
We will try to correlate number of seats, the traditional, measurement of aircraft capacity and cabin
areas.
We will consider 3 possible seat counts:
1/ average actual seat count worldwide for a specific aircraft type whatever the cabin
configuration (former Airbus approach);
2/ average actual seat count worldwide for a specific aircraft type for a representative layout
(single-class, 2-class, 3-class, … configuration). The data should be dated since it is a fluctuant
value over the time;
3/ maximum certified number of seat count (Boeing approach).

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Seat count data come from the Ascend database.
Gross cabin area versus seat count
Figure 7: Gross cabin area vs seat counts

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Net cabin area versus seat count
Figure 8: Net cabin area vs seat counts

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Equivalent cabin area versus seat count
Figure 9: Equivalent cabin area vs seat counts

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The 3 types of charts - equivalent, net and gross areas – demonstrate a rather better R² criteria for
the linear correlations between seats and cabin areas measured in equivalent or net cabin area.
Equivalent cabin area concept does not prove to provide a significantly better correlation between
seat count and cabin area.
Twin-aisle seat count for 3-class configured aircraft offers a much better correlation between seat
count and cabin areas than the one based on the maximum certified number of seats – Boeing
approach – or the one based on the average number of seats worldwide (whatever the cabin
configuration) – former Airbus approach.
For single-aisle aircraft none of the linear correlations between seats count and cabin areas end up
with a "better choice to make".
It should be pointed out that the study is done on a very small sample of aircraft types and would
require further studies based on a much larger one for a final conclusion to be driven. Our feeling is
that the net cabin area criteria is likely to be far sufficient and that further considerations such as
equivalent cabin area is not worth the additional cost of complexity it may require.
GENERIC SEAT COUNT & NORMALISED CABIN AREA.
We suggest that an aircraft type is credited of the generic seat count which is the seat count estimate
according the linear estimator between average seat count in the most common configuration
worldwide and the net/equivalent cabin area:

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The last issue is that moving from twin-aisle operation to single ones generally means moving from
one cabin configuration such as a 3-class product, to another one, let us say a 2 if not 1-class
configuration and to a lower standard of comfort. This represents a discontinuity in aircraft capacity
measurement which can be solved by introducing the normalised area concept: i.e. what would be
the (gross/net/equivalent) cabin area of the other aircraft family which would accommodate the
same number of generic seats: horizontal projection of the light blue dots on the left red line and
turning them into grey blue dots in the following chart:

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The following table provides the full set of capacity data attached to each aircraft type:
4. CABIN AREA & FLIGHT ECONOMICS
Some airlines tend to favour the high yield market and, more specifically, their business class
passengers.
The following example which is based on an actual B777-300 cabin layout seems to confirm this
view:
Two cases should be considered with regard to the average revenue per coach class passengers
relative to the average revenue per business class passenger.
If we were to base our accounting analysis on passenger revenue, the business class market - about
18% of the total number of passengers - is likely to generate between 37% and 44% of the
revenue/flight while at the same time the coach class passengers - 72% of the total number of
passengers (3 times as many!) – generates respectively 51% down to 43% of the trip revenue.

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But another way of accounting is to relate the flight revenue with the aircraft resources to be used:
i.e. (net) cabin area. If we adopt this axis of analysis, it results in that the business class product
appears as being less economically attractive: In the worst case the coach class revenue per m² is
70% of the one of business class. In the best case it is comparable. Comparable or even lower levels
of income do not tell us anything about profit contribution since a business class passenger is likely
to be (far) more expensive to "supply".
The following table provides seat density and seat count trade-off between business class seat and
any other class seats. This is how, in this very example, 2.5 coach class seat should be "sacrificed"
in order to install an additional business class seat. By the way, 2.5 is a very common trade-off
figure on twin-aisle aircraft worldwide.
5. DISCUSSION AND CONCLUSION
Shifting from seat-based capacity measurement to cabin area one's provides the measurement
steadiness and homogeneity across the different categories one can but dream of. Nevertheless we
have conducted very preliminary studies at this stage which would require:
1/ a database of aircraft types worldwide and over the time to be designed and "fed";
2/ a detailed and exhaustive analysis of seat countS versus cabin areaS to be done in order to
determine the best units to be selected as definitions of aircraft capacity.
In my opinion it is worth starting considering a per m² unit instead of per pax/seat one for further
aircraft economics calculation and analysis. It may change dramatically the way the market is
looking at itself which could lead to different choices both in terms of market segments, aircraft
type and consequently future aircraft design.
For instance, on a dollar per m² basis a high yield dedicated long haul 40 to 50-seater may compare
much more favourably with today's wide bodies with 3-class layouts.
6. ACKNOWLEDGMENTS
I would like to thank Richard Carcaillet, Stephan Boutonnet, Susana Martin-Romo and François
Keller former colleagues of Airbus Industrie and M. Roi who is working for Air France for their
very precious technical assistance and advices on these issues.