Order 7110.65P, Air Traffic Control, with changes

7110.65P CHG 1 8/5/043. Reciprocal tracks:(a) Ensure that aircraft are vertically separatedfor a time interval equal to the applicableminimum required before and after the aircraft areestimated to pass. (See FIG 8−3−3.)FIG 8−3−3Reciprocal Courses(b) Vertical separation may be discontinuedafter one of the following conditions are met:(1) Both aircraft have reported passing asignificant point and the aircraft are separated by atleast the applicable minimum required for the samedirection longitudinal spacing; (See FIG 8−3−4.) orFIG 8−3−4Vertical Separation(2) Both aircraft have reported passingground-based NAVAIDs or DME fixes indicatingthat they have passed each other.8−3−3. MACH NUMBER TECHNIQUEThe use of Mach number technique allows for theapplication of reduced longitudinal separationminima. The following conditions shall be met whenthe Mach number technique is being applied:a. Aircraft Types: Turbojet aircraft only.b. Routes:1. The aircraft follow the same track orcontinuously diverging tracks, and2. The aircraft concerned have reported over acommon point; or3. If the aircraft have not reported over acommon point, the appropriate time interval beingapplied between aircraft exists and will exist at thecommon point; or,4. If a common point does not exist, theappropriate time interval being applied betweenaircraft exists and will exist at significant points alongeach track.c. Altitudes:1. Assign only a single cardinal altitude to eachaircraft.2. The aircraft concerned are in level, climbingor descending flight.d. Mach Number Assignment:1. A Mach number (or, when appropriate, arange of Mach numbers) shall be issued to eachaircraft unless otherwise prescribed on the basis ofICAO regional agreement.NOTE−1. The application of Mach number technique requirespilots to strictly adhere to the last assigned Mach number(or range of Mach numbers), even during climbs anddescents, unless revised by ATC. Turbojet aircraft shallrequest ATC approval before making any changes. If it isessential to make an immediate temporary change in theMach number (e.g., due to turbulence), ATC shall benotified as soon as possible that such a change has beenmade.2. When it is necessary to issue crossing restrictions toensure the appropriate time interval, it may be impossiblefor an aircraft to comply with both the clearance to meet thecrossing restrictions and the clearance to maintain asingle, specific Mach number.REFERENCE−ICAO DOC 9426−AN/924, Part II, Section 2, Para 2.3.4, Para 2.4.7, andPara 2.5.3.EXAMPLE−“Maintain Mach point eight four or greater.”“Maintain Mach point eight three or less.”“Maintain Mach point eight two or greater; do not exceedMach point eight four.”8−3−2Longitudinal Separation