Load Classification Number Method

The ICAO, as an international agency, established ground rules to match aircraft and runway performance requirements. The ICAO developed the strength classifi­cations of Type 2 and Type 3 runways by designating a load classification number (LCN) that represents the extent of load that a runway can accommodate based on construction characteristics. All Type 2 and Type 3 runways must have a LCN and the aircraft undercarriage design must comply with it. The LCN range of the airfield’s type is grouped under the load classification group (LCG). For example, an aircraft with the LCN 62 can operate on any airfield with an LCG of I to III. Table 7.2 provides the LCN range for the types of runways.

The relationship among the LCN, tire pressure, and ESWL is presented in Figure 7.13. The procedure is to first obtain the LCN of the airfield in question. Then, compute the ESWL of the undercarriage (see Section 7.9). Finally, find the tire pressure required using Table 7.6 (see Section 7.11); this provides a guideline to choose tire size. Section 7.13 outlines the methodology followed by worked-out

Table 7.3. Aircraft weight to comply with LCN and corresponding tire pressure

Aircraft

MTOM (lb)

Tire pressure (psi)

LCN

Fokker F27

45,000

80

19

McDonnell DC-9

65,000

129

39

B737-200

110,000

162

49

B757

210,000

157

50

B707

300,000

180

80

examples (see the references for more details on other types). Typical examples of aircraft complying with the LCN and the corresponding MTOM and tire pressures are given in Table 7.3.

The B757, which is twice as heavy as the B737, maintains nearly the same LCN by having more wheels to distribute load per tire.

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