aircraft cater to the shorter-range market sector – they provide better fuel economy than turbofans. The author considers that the future may show potential markets in the less affluent areas. Major countries with substantial population centers could fly more passengers within their borders, such as in China, India, Indonesia, Russia, and the United States.

The points in Figure 4.4 include the following aircraft: Lear 31A, Lear 45, Lear 60, Cessna 525A, Cess 650, Cess 500, Cess 550, Cess 560, Cess 560XL, ERJ 135ER, ERJ 140, ERJ 145ER, CRJ 100, CRJ 700, ERJ 170, DC-9-10, CRJ 900, ERJ 190, 737–100, 717–200, A318–100, A319–100, A320–100, Tu204, A321–100, 757–200, A310–200, 767–200, A330–200, L1011, A340–200, A300–600, A300–100, DC-10-10, MD11, 777–200, 747–100, A380, Short 330 and 360, ATR 42 and 72, Jetstream 31, Saab 340A, Dash 7 and 8, Jetstream 41, EMB 120, EMB 120ER, Dornier 328–100, and Q400.

Commercial aircraft operation is singularly dependent on revenue earned from fare-paying passengers and cargo. In the operating sector, load factor is defined as the ratio of occupied seats to available seats. Typically, for aircraft of medium sizes and larger, operational costs break even at approximately one-third full capacity (this varies among airlines; fuel costs at 2000 level with regular fares) – that is, a load factor of about 0.33. Of course, the empty seats could be filled with reduced fares, thereby contributing to the revenue earned.

It is appropriate here to introduce the definition of the dictating parameter, seatmile cost, which represents the unit of the aircraft DOC that determines airfare to meet operational costs and sustain profits. DOC is the total cost of operation for the mission sector (operational economics are discussed in detail in Chapter 16). The U.S. dollar is the international standard for aircraft cost estimation.

The higher the denominator in Equation 4.1, the lower is the seat-mile cost (i.e., DOC). The seat-mile cost is the aircraft operating cost per passenger per nm of the mission sector. Therefore, the longer an aircraft flies and/or the more it carries, the lower the seat-mile cost becomes. Until the 1960s, passenger fares were fixed under government regulation. Since the 1970s, the fare structure has been deregulated – an airline can determine its own airfare and vary as the market demands.

A careful market study could fine-tune an already overcrowded marketplace for a mission profile that offers economic gains with better designs. Section 2.6 addresses the market study so that readers understand its importance.

4.5 Civil Subsonic Jet Aircraft Statistics (Sizing Parameters and Regression Analysis)

This section examines the statistics of current aircraft geometry and weight to identify aircraft sizing parameters. Regression analyses are carried out to demonstrate a pattern as proof of expectations. With available statistics, aircraft can be roughly sized to meet specifications. This is the starting point; Chapter 11 discusses formal sizing to finalizing aircraft configuration.

Definitions of various types of aircraft mass (i.e., weight) are provided in Chapter 8; some are required in this section, as follows (payload could be passengers and/or cargo):

MEM is the design outcome from catering to the MTOM, in which fuel load and payload are traded. The trade-off between payload (i.e., passenger) and fuel is at the operator’s discretion, who has the choice to trade between them (see Chapter 13). Keeping the MTOM invariant, the operator can offload some passengers to increase the fuel load to the extent that the tankage capacity would allow a farther flying distance. Conversely, fuel could be offloaded to a shorter range, allowing an increase in passengers to the extent the aircraft can accommodate. Mass per passenger is revised to 100 kg (220 lb) from the earlier value of 90 kg (200 lb), which includes baggage allowance; there could be additional cargo load.

4.5.1 Maximum Takeoff Mass versus Number of Passengers

Figure 4.5 describes the relationship between passenger capacity and MTOM, which also depends on the mission range for carrying more fuel for longer ranges. In conjunction with Figure 4.4, it shows that lower-capacity aircraft generally have lower ranges (Figure 4.5a) and higher-capacity aircraft are intended for higher ranges (Figure 4.5b). Understandably, at lower ranges, the effect of fuel mass on MTOM is not shown as strongly as for longer ranges that require large amounts of fuel. There is no evidence of the square-cube law, as discussed in Section 3.20.1. It is possible for the aircraft size to grow, provided the supporting infrastructure is sufficient.