(c)
Particular cases
-If one IRS becomes in alignment status whatever the state of the other two IRS, then the ALIGN IRS prompt appears on the INIT A page so that the pilot may send the reference position to the IRS which requests for the alignment. The prompt is displayed until a position is sent through the ADIRS CDU or the MCDU INIT A page.
-Note that the reset of an IRS to NAV (which is the action to switch from NAV to OFF and then to NAV) is equivalent to a first request for alignment, and induces same mechanizations.
E. Leg Transitions
(1)
General The FMGC guides the aircraft in both lateral and vertical axes. The lateral guidance is responsible for the construction of a lateral path of the active primary flight plan. This lateral path consists of the active leg path geometry to be used to control the aircraft and the multiple leg geometry which is used for generating EIS displays. The lateral path is made of geometric legs and transitions between the legs. The available types of legs for which guidance may be provided are defined in 22-71-00 and are as follows:
-great circle course
-planar magnetic course
-magnetic heading
-circular arc (AF leg, HX legs).
(2)
Transition types There are five types of transitions.
(a)
Type I is a curved path transition between two fix referenced legs (FX or XF) that terminate and begin at the same point. (Ref. Fig. 018) It is performed with a constant turn radius. The nominal bank angle is then corrected to take ground speed evolution into account.
(b)
Type II is a next course capture between two fix referenced legs (which are not connected) or from a heading/course leg (VX or CX legs) to a fix referenced leg. (Ref. Fig. 019) Substitution of a type II transition for a type I transition can also occur under the following conditions:
-an overfly has been specified for the active leg
-a turn direction is specified for the next leg which causes course change of greater than 180 deg. (except for PX, AF, HX)
-course change between active and next leg is less than or equal to 3 deg. or more than or equal to 175 deg.
-distance between the termination of the active leg and the path
of the next leg is greater than 1 NM. The type II transition captures the path of the next leg by using the fixed path control law. A type II transition is used to capture the parallel offset path. When the parallel offset is cancelled, a type II is again used to capture the original flight plan. (Ref. Fig. 020) Transitions to holding patterns are also type II transitions. These are three types of entries:
-direct entry
-teardrop entry
-parallel entry
The type is determined by the region from which the aircraft will
cross the holding pattern fix.
(Ref. Fig. 021)
1_ Direct entry : The aircraft captures either turn number 1 or
outbound leg using a type II transition.
(Ref. Fig. 022)
2_ Teardrop entry : The aircraft captures a 30 deg. intercept
course from the holding pattern fix and holds this course
until the distance from the holding fix is equal to 1.15 times
the outbound leg distance (fixed path control law).
Type I Transition CF, TF
Figure 018
Type II Transition
Figure 019
Parallel Offset Capture
Figure 020
Transitions to Holding Pattern : Determination of Entry Type
Figure 021
Direct Entry
Figure 022
Then, the aircraft performs a circular arc (turn control law)
(constant turn radius, course change = 180 deg.) before
capturing the inbound leg using a type II transition.
(Ref. Fig. 023)
3_ Parallel entry : the aircraft captures a parallel course to
the inbound course using a type II transition (fixed path
control law).
Then, it initiates a circular arc (constant turn radius,
course change = 180 deg.) (turn control law) before capturing
the inbound leg following a type II transition.
(Ref. Fig. 024)
(c)
Type III is a transition onto a heading leg (VX legs). In that case, a capture is performed to the desired heading. (Ref. Fig. 025)
(d)
Type IV is a transition onto a direct type leg (DF). A circular arc path is used to capture the great circle course of a DF leg. This type of transition is also used to capture a fix referenced leg from a VI or CI leg. (Ref. Fig. 026)
(e)
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