and minimum obstacle clearance are markedly different. Sidestep maneuver A visual maneuver by a pilot performed at the completion of an instrument approach to permit a straight-in landing on a parallel runway not more than 1,200 feet to either side of the runway to which the instrument approach was conducted. Rate-of-descent formula A useful formula pilots use to calculate descent rates (for the standard 3° glide slope): Rate of descent = (ground speed ⁄ 2) × 10 or Rate of descent = ground speed × 5 For other glideslope angles: Rate of descent = glide slope angle × ground speed × 100 / 60, where rate of descent is in feet per minute, and ground speed is in knots. The latter replaces tan α (see below) with α/60, which has an error of about 5% up to 10°. Example: 120 kn × 5 or 120 kn / 2 × 10 = 600 ft/min The simplified formulas above are based on a trigonometric calculation: Rate of descent = ground speed × 101.27 × tan α where: α is the descent or glideslope angle from the horizontal (3° being the standard) 101.27 (ft/min⁄kn) is the conversion factor from knots to feet per minute (1 knot = 1 NM⁄h ≈ 6076 ft⁄h ≈ 101.27 ft/min) Example: Ground speed = 120 kn α = 3° 120 kn × 101.27ft/min/kn × tan 3° ≈ 640 ft/min Airport requirements Special considerations for low visibility operations include improved lighting for the approach area, runways, and taxiways, and the location of emergency equipment. There must be redundant electrical systems so that in the event of a power failure, the back-up takes over operation of the required airport instrumentation (e.g., the ILS and lighting). ILS critical areas must be free from other aircraft and vehicles to avoid multipathing. In the United States, the requirements and the standards for establishing instrument approaches at an airport are contained in the FAA Order 8260.3 "United States Standard for Terminal Instrument Procedures (TERPS)". ICAO publishes requirements in the ICAO Doc 8168 "Procedures for Air Navigation Services – Aircraft Operations (PANS-OPS), Volume II: Construction of Visual and Instrument Flight Procedures". Mountain airports such as Reno–Tahoe International Airport (KRNO) offer significantly different instrument approaches for aircraft landing on the same runway, but from opposite directions. Aircraft approaching from the north must make visual contact with the airport at a higher altitude than a flight approaching