Originally Posted by
Capn Bloggs
Does the ILS itself cost a lot?
I don't know, however, the FAA report does do a cost benefit analysis. I suspect, the difference is that a single GBAS installation is required to do a ~20nm radius area. This limits the expense of each physical ILS installation. Ongoing calibration requirements & costs of ILS vs GLS are covered in the FAA report, page 9:
The approach information integrity in GBAS is digital and unchanging, unlike the analog signal from ILS which can change over time with component aging, and changes in the local environment through urbanization and construction. ILS requires regular flight inspection to ensure the approach path is repeatable and accurate. Once a GLS approach is defined and verified, its position does not change. Therefore, the flight inspection requirement (and cost) is reduced to approximately 50% of the ILS flight time requirement. For GLS, the requirement is 2.5 hours per station, 1.5 hours per approach (IAH example – 6 approaches with 11.5 hours total), ILS requires 10 hours per approach (equating to 60 hours for the IAH example). Annual maintenance/operations cost of GBAS for all runways is estimated at $75,000 whereas ILS operations cost per runway is over $90,000 (based on a 2010 GBAS program office assessment). For an airport like Houston with 6 ILS systems this amounts to $540,000 for ILS ops cost versus $75,000 for GBAS.