Originally Posted by ZapBrannigan

Well, to be fair what is the alternative?

Originally Posted by “FAA 8900.1”

B. Level B Differences. Level B differences are those differences in systems, controls, and indicators that have only minor procedural differences. Level B differences are of great enough degree to require formal training in general operational subjects, aircraft systems, or both, but are not of great enough degree to require systems integration training. An example of a Level B difference is a fuel system with additional fuel tanks, pumps, and gauges. Procedural differences are limited to the operation of transfer valves and pumps while an aircraft is in cruise flight. Appropriate instructional methods for Level B differences include, but are not limited to, audiovisual presentations, lectures, and tutorial computer-based instruction (TCBI). A task or systems check for Level B differences must be conducted after training. Appropriate methods include an oral or written exam or TCBI self-test.

C. Level C Differences. Level C differences are part task differences of flightcrew member knowledge, skills, and/or abilities. Level C differences are those differences of great enough degree to require a systems integration training module but that are not of great enough degree to require actual flight training (see Volume 3, Chapter 19, Section 5 for a definition and description of systems integration training). An example of a Level C difference is the installation of a flight management system (FMS) computer. Appropriate training methods in the systems integration module are dedicated part task trainers, interactive computer-based instruction (ICBI), or Level 4 or higher flight simulation training devices (FSTD). Level C differences require a check following training. Appropriate devices are the same as for Level C training. Checking methods appropriate to Level C differences are demonstrations of skill in the procedures affected by the difference. In the case of the installation of an FMS computer, checking might consist of preflight programming of the computer and a demonstration of its use in navigation, climbs, and descents.

D. Level D Differences. Level D differences are full task differences of flightcrew member knowledge, skills, and/or abilities. Level D differences are those differences for which there is a requirement for flight training modules in a Level 6 or higher FSTD. When Level D differences exist between two aircraft, general operational subject modules, aircraft systems modules, and systems integration modules may be required. An example of a Level D difference is the installation of an electronically integrated flight instrumentation display. Aircraft operations using such a display are required to contain flight training in most phases of flight. Level 6 or higher FSTDs are appropriate for conducting Level D differences training and qualification modules. Level D differences require a check following training. The check must be conducted using scenarios representing a real‑time flight environment.

E. Level E Differences. Level E differences are such significant full task differences that a “high‑fidelity” environment is required to attain or maintain knowledge, skills, or abilities. Level E differences are those differences for which there is a requirement for flight training, including landing events. An example of a Level E difference is the installation of a Short Takeoff and Landing (STOL) kit on an aircraft, resulting in a very different flare and landing attitude. A Level C or D full flight simulator (FFS) or an aircraft is required for flight training in Level E differences. Checking for Level E differences requires a full part 121 proficiency check or part 135 competency check in a Level C or D FFS or an aircraft.