Figure 3-17. Altitude restrictions.  Airspeed  3-20  During the arrival, expect to make adjustments in speed at  the controller’s request. When pilots fly a high-performance  aircraft on an IFR flight plan, ATC may ask them to adjust  their airspeed to achieve proper traffic sequencing  and separation. This also reduces the amount of radar  vectoring required in the terminal area. When operating  a reciprocating engine or turboprop airplane within 20  NM from the destination airport, 150 knots is usually the  slowest airspeed that is assigned. If the aircraft cannot  maintain the assigned airspeed, the pilot must advise ATC.  Controllers may ask pilots to maintain the same speed as  the aircraft ahead of or behind them on the approach. Pilots  are expected to maintain the specified airspeed ±10 knots.  At other times, ATC may ask pilots to increase or decrease  airspeed by 10 knots, or multiples thereof. When the speed  adjustment is no longer needed, ATC advises the pilot to “…  resume normal speed.”  Remember during arrivals, when cleared for an instrument  approach, maintain the last assigned altitude until  established on a published segment of the approach or on  IFR en route descent procedures should include a review  of minimum, maximum, mandatory, and recommended  altitudes that normally precede the fix or NAVAID facility  to which they apply. The initial descent gradient for a low  altitude instrument approach procedure does not exceed  500 ft/NM (approximately 5°), and for a high altitude  approach, the maximum allowable initial gradient is 1,000  ft/NM (approximately 10°).  a segment of a published route. If no altitude is assigned  with the approach clearance and the aircraft is already on a  published segment, the pilot can descend to its minimum  altitude for that segment of the approach. There are numerous exceptions to the high performance  aircraft arrival procedures previously outlined. For example,  in a non-radar environment, the controller may clear the  flight to use an approach based on a NAVAID other than  the one aligned with the landing runway, such as a circling  approach. In this case, the descent to a lower altitude  usually is limited to the circling approach area with the  circle-to-land maneuver confined to the traffic pattern.  below 5,000 feet above the airport elevation.  NO T FOR NA VIGA TION "  "Piper 6319K, cross PENNS Intersection at 6,000, maintain 6,000.  NE-2, 21 OCT 2010 to 18 NOV 2010  If you are at RACKI Intersection at 12,000 feet  MSL, you must adjust your rate of descent so  you can reach 6,000 feet MSL in the distance  available. At a groundspeed of 180 knots (3  NM per minute), you will reach PENNS  Intersection in approximately 8 minutes (23 ÷ 3  = 7.6). You must descend at least 750 feet per  minute to cross PENNS at 6,000 feet MSL  (6,000 ÷ 8 = 750).  You are at HAYED Intersection at 12,000 feet MSL. Your planned rate of descent is 500 fpm and your groundspeed  is approximately 180 knots (3 NM per minute). You should begin your descent no less than 36 NM from PENNS  Intersection ([6,000 ÷ 500] x 3 = 36). NE-2, 21 OCT 2010 to 18 NOV 2010 