Although some MLS systems became operational in the 1990s, the widespread deployment envisioned by some aviation agencies never became a reality. There were two reasons: (economic) while technically superior to ILS, MLS did not offer sufficiently greater capabilities to justify adding MLS receivers to aircraft equipage; and (potentially superior third system) GPS-based systems, notably WAAS, allowed the expectation of a similar level of positioning with no equipment needed at the airport. GPS/WAAS dramatically lowers an airport's cost of implementing precision landing approaches, which is particularly important at small airports.