designated via NOTAM as either a TFR or stationary ALTRV. Unless otherwise specified, the vertical limits of an AHA are from the surface to unlimited. 

(See CONTINGENCY HAZARD AREA.) (See REFINED HAZARD AREA.) (See TRANSITIONAL HAZARD AREA.) 

AIRCRAFT WAKE TURBULENCE CATE- GORIES- For the purpose of Wake Turbulence Recategorization (RECAT) Separation Minima, ATC groups aircraft into categories ranging from Category A through Category I, dependent upon the version of RECAT that is applied. Specific category assign- ments vary and are listed in the RECAT Orders. 

AIRMEN'S METEOROLOGICAL INFORMA- TION (AIRMET)- In-flight weather advisories issued only to amend the Aviation Surface Forecast, Aviation Cloud Forecast, or area forecast concerning weather phenomena which are of operational interest to all aircraft and potentially hazardous to aircraft having limited capability because of lack of equipment, instrumentation, or pilot qualifications. AIRMETs concern weather of less severity than that covered by SIGMETs or Convective SIGMETs. AIRMETs cover moderate icing, moderate turbu- lence, sustained winds of 30 knots or more at the surface, widespread areas of ceilings less than 1,000 feet and/or visibility less than 3 miles, and extensive mountain obscurement. 

(See AWW.) (See CONVECTIVE SIGMET.) (See CWA.) (See SIGMET.) (Refer to AIM.) 

AIRPORT- An area on land or water that is used or intended to be used for the landing and takeoff of aircraft and includes its buildings and facilities, if any. 

AIRPORT ADVISORY AREA- The area within ten miles of an airport without a control tower or where the tower is not in operation, and on which a Flight Service Station is located. 

(See LOCAL AIRPORT ADVISORY.) (Refer to AIM.) 

AIRPORT ARRIVAL RATE (AAR)- A dynamic input parameter specifying the number of arriving aircraft which an airport or airspace can accept from the ARTCC per hour. The AAR is used to calculate 

the desired interval between successive arrival aircraft. 

AIRPORT DEPARTURE RATE (ADR)- A dynamic parameter specifying the number of aircraft which can depart an airport and the airspace can accept per hour. 

AIRPORT ELEVATION- The highest point of an airport's usable runways measured in feet from mean sea level. 

(See TOUCHDOWN ZONE ELEVATION.) (See ICAO term AERODROME ELEVATION.) 

AIRPORT LIGHTING- Various lighting aids that may be installed on an airport. Types of airport lighting include: 

a. Approach Light System (ALS)- An airport lighting facility which provides visual guidance to landing aircraft by radiating light beams in a directional pattern by which the pilot aligns the aircraft with the extended centerline of the runway on his/her final approach for landing. Condenser- Discharge Sequential Flashing Lights/Sequenced Flashing Lights may be installed in conjunction with the ALS at some airports. Types of Approach Light Systems are: 

1. ALSF-1- Approach Light System with Sequenced Flashing Lights in ILS Cat-I configura- tion. 

2. ALSF-2- Approach Light System with Sequenced Flashing Lights in ILS Cat-II configura- tion. The ALSF-2 may operate as an SSALR when weather conditions permit. 

3. SSALF- Simplified Short Approach Light System with Sequenced Flashing Lights. 

4. SSALR- Simplified Short Approach Light System with Runway Alignment Indicator Lights. 

5. MALSF- Medium Intensity Approach Light System with Sequenced Flashing Lights. 

6. MALSR- Medium Intensity Approach Light System with Runway Alignment Indicator Lights. 

7. RLLS- Runway Lead-in Light System Consists of one or more series of flashing lights installed at or near ground level that provides positive visual guidance along an approach path, either curving or straight, where special problems exist with hazardous terrain, obstructions, or noise abatement procedures. 

8. RAIL- Runway Alignment Indicator Lights- Sequenced Flashing Lights which are installed only in combination with other light systems. 

