He said those kinds of changes typically have been added to new engines as supplements to their original certificates. With these engines, our plan is to certify once and get it right the first time. The AS907 and AS977 engines are identical except for software differences in their Fadec processors, which account for the difference in takeoff thrust ratings. AS900 design drivers, Redenbaugh said, were ease of maintenance, inspection and servicing to achieve the lowest possible cost of ownership. The market discriminators today are direct operating cost, simplicity and ease of maintenance.
Cost of ownership is the name of the game.
Honeywell engineer Mike Bevans pointed out that several simplified component designs drastically reduce the parts count. For example, the TFE731 engine combustor contains 62 parts, while the AS907 combustor has just three. One maintainability enhancement in the AS900 series is provision of 29 borescope access ports, three to five times more than previous designs, and the ability to rotate the turbine for inspection using a standard quarter-inch ratchet. Component accessibility improvements have greatly reduced the need for extensive disassembly compared with earlier engines. An example of Honeywell's push to simplify and reduce parts inventory requirements is its use of standardized fasteners of the same size and length.