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A and B weather. Controllers will be unable to see aircraft from the tower cab. The technique adopted might also be adaptable for ground guidance of aircraft during Category III C weather conditions. If so, Category III C would appear to be much more promising.

Criteria for Category III A/B Ground Installations
The basic criterion used herein for the installation of Category III equipment is that economic benefits exceed costs. If the airlines equip for purposes other than an all-weather landing capability, e.g., for safety during VFR and IFR landing, this criterion reduces to a requirement that benefits exceed the cost of the ground equipment.
AWLS benefits have been assigned in this study only to SST and jumbo jet aircraft. A secondary criterion, then, is that the airport be an SST/jumbo jet use airport.
Instrument approaches to an airport reflect both the amount of traffic at the airport and the occurrence of instrument weather. Based on forecasts of airport instrument approaches (AIA) at specific airports, not reproduced herein, it appears that 10,000 air carrier instrument approaches a year would justify Category III A/B installations at SST/jumbo jet use airports, if the aircraft were equipped to use them. This compares with present planning standard criteria of 5,000 total AIA's for Category II installations, and 700 AIA's for Category I installations.

CONCLUSIONS
1. Most of the costs of an AWLS program are airline costs. Airline equipment decisions, therefore, affect FAA program decisions. 
2. If total ground and airborne costs are assessed against the AWLS program, it probably cannot be justified on economic grounds alone. If one-half or less of the costs of Category III A Airborne equipment are charged to the program, the installation of ground equipment becomes quite attractive.