The banner headlines of the latest airliner orders catch the attention, but what is ordered today is not necessarily what gets delivered tomorrow.
The monthly listings of new orders from Airbus and Boeing also contain a series of notes about alterations to existing orders. There have been increasing numbers of these notes in recent months, as airlines and lessors change their minds about the exact size of the aircraft they actually need.
So far in 2011, the Ascend Online Fleets database has tracked 230 changes in jet orders.
The theme is definitely "more seats please", as customers upgauge their requirements and seek to lower their seat-mile costs. This is where the benefits of offering families of aircraft really come to the fore for both manufacturers and customers.
The sector under the most pressure is the 125-seat category, where the Airbus A319 and Boeing 737-700 have seen 109 orders switched to their larger siblings so far this year.
Most swaps have been to the mid-size narrowbodies - the A320 or 737-800 - although over 30 have been for the largest single-aisle variants, the A321 or 737-900ER.
In fact, it is interesting to look at how the firm orders backlog for 125-seaters has changed.
From a peak of almost 1,100 during 2007, there has been a steady decline to today's figure of under 550.
The better seat-mile costs of the larger aircraft, coupled with the increasing penetration of low cost carriers - which maximise seat counts - make it less surprising that upsizing is increasingly occurring.
When such a long-established proponent of this size of aircraft and operator of over 500 737-300s and -700s - Southwest Airlines - decides to switch some orders to larger 737-800s, it is sending a clear message.
In 2012, the carrier will take delivery of 20 737-800s and can switch more of its orders for -700s with 12 months notice. Similarly, EasyJet has converted 45 A319 orders to A320s in the past three years. It also maximises seats in its A319s, with the dual overwing exit option, increasing seat count to 156.
Market values of this size of aircraft have also been more sluggish in recovering after the downturn. The 737-700 is showing some signs of an increase in lease rates, as operators can't get the -800s they want, and so have to opt for the smaller -700. The competing A319 is yet to see any noticeable recovery, unlike the younger A320s. What implications do these moves to larger aircraft have for the future of the 125-seat sector? There is of course a new player in this market - Bombardier with the CSeries. The CS300 is firmly targeted at the A319 and 737-700 market, with a typical 130-seat configuration, and will be able to carry up to 160 in its highest density layout, which may attract the low cost players.
However, with a population of approaching 3,000, the 125-seaters still represent a significant replacement opportunity. Over 600 are the ageing Classic 737-300s, which are the first targets.
Bombardier's design is optimised for this size of aircraft, rather than a shrink of a larger design, and with its smaller sister - the 110-seat CS100 - offers airlines an alternative to a family built around an optimised 150-160 seater. The availability of the A319neo and now a CFM International Leap-X re-engined version of the 737-700 complicates the choice available to airlines, and decisions will no doubt depend upon cost, performance, timing and fleet strategy. A similar upsizing situation has emerged in the widebody sector, where the Boeing 787 and Airbus A350 XWB are also seeing a changing orderbook.
The delays to delivery of the 787-8 have, it can be argued, helped those airlines who really wanted the larger 787-9, but ordered the smaller -8 in order to gain earlier production slots.
At 242 seats, the 24 extra seats that the 787-8 has over the 767-300ER (in typical 3-class layout) may be now be less attractive to some than the 280 seats which the 787-9 can offer, with the added bonus of almost 400nm of additional range.
Korean Air and lessor ILFC have been the latest to change orders to 787-9s this year. Almost 100 orders for 787-8s have been upsized to the -9 in total.
Airbus is having a similar experience on the A350 XWB, where the lead variant, the 313-seat A350-900, has taken a 60% share of orders placed to date.
Its shorter fuselage sister, the 270-seat A350-800, has seen a quarter of its orders upsized to -900s and development has been put back by two years to 2016.
The "sweet spot" for the medium capacity twin-aisle types seems to be around the 300-seat mark. The size of these larger widebodies is also an advantage where more space is needed for up to three premium cabins.
The message here is perhaps: "more room for lie-flat seats".
Chris Seymour is head of market analysis at Flightglobal data and consultancy division Ascend