0 0 LOW INSTRUMENT FLIGHT RULES - CEILING < 500 FEET AND/OR VISIBILITY < 1 MILE
1 1 INSTRUMENT FLIGHT RULES - CEILING < 1000 FEET AND/OR VISIBILITY < 3 MILES
2 2 MARGINAL VISUAL FLIGHT RULES - 1000 FEET =< CEILING < 3000 FEET AND/OR 3 MILES =< VISIBILITY < 5 MILES
3 3 VISUAL FLIGHT RULES - CEILING >= 3000 FEET AND/OR VISIBILITY >= 5 MILES
7 7 MISSING VALUE
