(c) Along Track Offset (PLACE/DIST) The along track offset (ATO) waypoint is a pilot-defined waypoint that may be entered only on the F-PLN pages. However, a waypoint defined as an ATO is included as one of the twenty pilot-defined waypoints. An ATO waypoint is inserted into the flight plan by entering a PLACE/DIST into the scratchpad and pressing the left LS key adjacent to the revised point. Insertion of this waypoint is per the following rules:  The PLACE entry must be identical to the revised point. An ATO cannot be entered at the FROM waypoint. The DIST entered to define the ATO cannot exceed the distance of the leg on which it is inserted. A distance may be entered up to 9999 NM as long as it satisfies the rules herein. A positive DIST entry results in an ATO inserted on the leg following the revised point while a negative DIST entry results in an ATO inserted on the leg preceding the revised point. If "+" or "-" is not specified, a positive entry is assumed. Once an ATO waypoint is inserted, the distance of the ATO from the revised point becomes the upper limit for the DIST entry for any other ATO in the same direction from that revised point. An ATO waypoint cannot be inserted less than 1 NM from any existing flight plan waypoint. If such an entry is attempted, the entry is rejected and the NOT ALLOWED message is displayed. ATO waypoints are only allowed on CF, DF or TF legs. Inserting an ATO waypoint into the flight plan divides an existing flight plan leg into two fixed legs. The first leg (ATO) is a DF or TF leg, depending on the termination of the preceding leg, and the second leg (existing fix) is a TF leg. A discontinuity is not created and there is no course change between the two legs. If an ATO is defined within a transition between two waypoints, the ATO lies on the great circle path between the waypoints and not on the curved path. This may introduce short legs. ATOs are allowed on the active leg between the aircraft position and the active waypoint. An ATO waypoint cannot be inserted less than 5 NM from the current aircraft position. This ensures that the waypoint is not immediately considered for sequencing or is not placed behind the aircraft. For normal cases, one can consider that for an entry of TO/-XXX at an active waypoint (TO), the distance XXX must satisfy the following rule: XXX < (direct distance from the aircraft to the active waypoint)

 -5 NM.
 However, in cases where the aircraft is flying manually off the
 active leg, such a rule may still place the waypoint behind the
 aircraft position with respect to the active leg. In these cases,
 it is acceptable to limit XXX as follows:
 XXX < (direct distance from aircraft abeam point to the active
 waypoint) - 5 NM.
 If entry within this region is attempted, the entry is rejected
 and the NOT ALLOWED message is displayed.
 If an ATO is defined within a gap between two CF legs, the entry
 is not allowed.
 If an ATO is entered on a DF leg, the ATO lies on the great
 circle path between the waypoint preceding the DF leg and the
 termination of the DF leg.

 (d) DIRECT TO page (Ref. Fig. 054, 055)
 1_ Access
 DIR mode key on the MCDU while Backup Navigation is inactive.
 If the DIR mode key is pressed while the aircraft position is
 invalid, then the scratchpad message A/C POSITION INVALID is
 displayed and the DIRECT TO/INTERCEPT page is not accessed.
 If a DIRECT TO/INTERCEPT page is displayed and aircraft
 position becomes invalid, with or without a pending Direct To,
 Abeam Points or Intercepts, the Direct To/Intercept/Abeam
 Point is cancelled, the F-PLN A page is displayed and the
 scratchpad message A/C POSITION INVALID is displayed.
 2_ Purpose
 Allows access to the DIRECT TO/INTERCEPT function.
 3_ Data fields
 The DIR TO page is initially displayed with brackets in 1L,
 prompting entry of a Direct To fixed waypoint.
 - Title
 The flight number, as entered on the INIT A page, is
 displayed in small font in columns 12-21. If no flight
 number has been entered, then this field is blank.
 - 1L-DIR TO prompt
 Allows selection of the desired Direct To/Intercept
 waypoint. This waypoint can be selected from the ACTIVE
 primary flight plan via an adjacent left LS key, if the
 scratchpad is empty, or it may be manually entered into 1L
 by the flight crew through the scratchpad. Additionally, a
 pending DIR TO/INTERCEPT allows changing of the selected
 waypoint and/or intercept radial until the Direct
 To/Intercept is activated.
 - 1R-2R: Intercept radial prompts
　
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