DISCONTINUITIES, VECTORS AND CONSTRAINTS
A flight-plan discontinuity is a break between two portions of the route. The message can look untidy, especially after you have carefully entered a long list of fixes. Resist the immediate urge to remove it. First read the legs before and after the gap and compare them with the chart. The same-looking break can represent two very different situations, and the distinction determines what we do next. [26, PDF pp. 331-337]
One possibility is an unintended gap: two parts of the intended route have not been joined. Another is a deliberate end to a published path, followed by radar vectors. During vectoring, air traffic control gives headings to take the aircraft towards the next part of the flight. A MANUAL termination or discontinuity can therefore be part of the intended procedure. It is information to interpret before it is something to edit. [26, PDF pp. 331-337]
If the two portions are intended and cleared to connect, use the appropriate clearing action and inspect the resulting temporary route before INSERT. The new line needs to join the correct fixes in the intended order. If the gap belongs to a vectoring phase, retain the relevant structure until the actual continuation is established. We are trying to represent the flight accurately, rather than produce the tidiest possible page. [26, PDF pp. 331-337] [26, PDF pp. 312-314]
After a revision, look a little beyond the point you changed. A local repair can reveal a doubled waypoint or an unexpected turn a few legs later. Scroll the neighbouring legs and inspect the ND again. This is one reason to make one understood change at a time: it remains possible to connect the result on the screen with the action that produced it. [26, PDF pp. 331-337] [26, PDF pp. 312-314]
The route also contains constraints, or restrictions on speed and altitude at particular points. An exact altitude differs from an at-or-above or at-or-below restriction; an altitude window has two bounds. Read what the chart requires and what the coded flight plan actually says. Recognising the number is only part of recognising the instruction attached to it. [26, PDF pp. 394-395,404-410]
The FCU, Flight Control Unit, sets an immediate guidance target, including the altitude selected for the current clearance. That clearance and the route's coded restrictions must be understood together. A lower altitude later in the flight plan does not grant permission to descend to it now. The practical exercise keeps these three views connected: the charted restriction, its MCDU representation and the actual clearance limit in the FCU. [26, PDF pp. 394-395,404-410]
IN PRACTICE: Resolve a gap without losing the procedure
Before you begin: The flight plan and applicable chart are open. Work on one identified discontinuity or constraint at a time.
1. Identify what surrounds the gap
Action. Find the waypoint immediately before the discontinuity and the first leg after it. Compare them with the chart and the intended route, including any MANUAL termination or vectoring phase.
Check. You know what the discontinuity represents. You are no longer treating all breaks as identical formatting errors. [26, PDF pp. 331-337]
2. Retain an intentional vectoring break
Action. Where the procedure terminates for headings or radar vectors, retain the relevant manual/vectoring structure until the actual continuation is established. Brief where the published route ends and what guidance you expect next.
Check. The MCDU still represents the intended procedure. It has not been made continuous by adding an unbriefed direct leg across a vectoring phase. [26, PDF pp. 331-337]
3. Remove only a justified discontinuity
Action. If the two route portions are intended and cleared to join, use CLR on the discontinuity entry. Inspect the proposed connecting leg before selecting the offered INSERT.
Check. The temporary geometry connects the correct fixes in the correct order. If it does not, abandon the proposal and correct the route construction. [26, PDF pp. 331-337] [26, PDF pp. 312-314]
4. Inspect the restriction itself
Action. At a constrained waypoint, open the relevant vertical revision and compare its speed and altitude condition with the chart. Distinguish an exact altitude, an above/below condition and an altitude window.
Check. The coded condition means what the chart requires. A familiar number has not distracted you from the restriction attached to it. [26, PDF pp. 394-395,404-410]
5. Keep the clearance limit independent
Action. Compare the FCU altitude with the current clearance. A flight-plan restriction is part of the route; it does not authorise climbing or descending beyond the cleared altitude.
Check. The FCU limit and the charted restrictions can be explained together, including which one will limit the next manoeuvre. [14, PDF pp. 1074-1077] [26, PDF pp. 394-395,404-410]
6. Recheck the surrounding route
Action. After insertion, scroll several legs on either side and inspect PLAN mode again. Check for a duplicate waypoint, an unexpected turn or a restriction lost during the revision.
Check. The local repair has not created a new problem just beyond the page you were editing. [26, PDF p. 128]
Complete when: Every remaining discontinuity has an operational explanation, every removed one has a justified connection, and chart restrictions remain correctly represented.