A review of published articles has shown that many researchers use financial reports as the main source of information in regard to airline business models. A study of accounting policies and other external information, however, has highlighted the differences in assumptions as to useful lives and the residual values of aircraft, which are the principal assets of airlines. While the considerable, unexplained differences in the accounting policies of enterprises with similar business models indicate there may be risk in using this data, the risk can be eliminated by making appropriate adjustments in the financial statements.