1 - Instrument approach procedure - Segments :

An instruments approach procedure is a set of predetermined maneuvers for landing shown on an instrument approach chart (IAC). The procedure is made of a maximum of 5 segments and may include a holding pattern.

These different segments and patterns are calculated in times or/and distances. For the calculations to match the aircraft performances, the aircraft are divided into 5 categories designated with letters according to their landing speed Vref (or Vat) at maximum gross landing weight and their initial approach speed.

Vref = Vat = 1.3 x Vso   (Vso is the Stalling speed with gear and flaps out) 

Note 1 : some other speeds may be taken into account (holding, final approach).

Note 2 :If it is necessary to maneuver at speeds in excess of the upper limit of a speed range for a category, the minimums for the next higher category should be used. For example, an aircraft which falls in Category A, but is circling to land at a speed in excess of 91 knots, should use the approach Category B minimums when circling to land.

a) Arrival, from the last enroute point (navaid or fix) to the IAF (initial approach fix), when no STAR is designed. It could be :

- omnidirectional (not really a segment, the IAF may be reached from any direction -  involves the IAF to be a navaid (not a fix) and the use of MSAs based on this navaid - see below).

- specified (the segment could be one or several straights and/or a DME arc - the minimum altitude is indicated on the charts, along each part of the arrival route).

b) Initial approach, from the IAF to the IF (intermediate fix) or to the procedure turn. The segment could be :

- Note: when no IF is designated, the initial approach ends at the end of the procedure turn (the last one, bringing the aircraft on the final or intermediate course).

c) Intermediate approach, from the IF or from the end of the procedure turn to the FAF or FAP (final approach fix / point).

- is usually horizontal because the aim is to give the pilot the time to prepare the aircraft for the final (reduce speed, lower gear and flaps).

- the minimum length is at least 30 seconds at the initial approach speed (according to the categories above).

d) Final approach, from the FAF or FAP to the DH (decision height) or the MAPt (missed approach point).

- this is the segment where alignment and descent for landing are accomplished.

- FAF and DH are for precision approaches only (see below). It could be designated fix or the end of the procedure turn or the point of interception with the final course.

- FAP and MAPt are for non precision approaches (see below).

- the optimum slope is 5.2 % (3°); the maximum is 6.5 %.

e) Missed approach, from the DH or MAPt, according to a trajectory indicated on the instrument approach chart (IAC).

- to be used when, for any reason, the aircraft can't land after executing the instrument approach procedure.

- the lowest point to start it is the DH (precision approach) or the MApt (non precision approach).

f) Holding pattern, based on  the IAF or another point, in case a delay has to be applied before starting the approach procedure (simultaneous arrivals, airfield not available due to weather, failure, runway occupied...).

- see L5-Charts for details about entering a holding pattern.

- a holding pattern is a race track with defined specifications which are usually all shown on the IAC :

. heading and length of outbound and inbound legs (by time, distance or limiting radial).

. maximum indicated airspeed.

. minimum and maximum holding altitudes.

- the race track is calculated with a minimum bank angle of 25°.

2 - Instrument approach  procedure - MSA = Minimum Safe (or Sector) Altitude :

MSAs are altitudes depicted on approach charts which provide at least 1,000 feet of obstacle clearance within a 25-mile radius of the navigation facility upon which the procedure is predicated. Sectors depicted on approach charts must be at least 90 degrees in scope. These altitudes are for emergency use only and do not necessarily assure acceptable navigational signal coverage.

This shows the minimum altitude to be used for an omnidirectional arrival, according to the distance and the sector the aircraft is coming from. It could look like this :

Whatever the arrival heading is, the MSA is 5400 ft 25 NM around the associated navaid.	Whatever the arrival heading is, the MSA is 3600 ft before 12.5 NM and 1200 ft within 12.5 NM from the associated navaid.	The MSA is : 1200 ft if coming from the south. 7800 then 4700 ft if coming from the west. 3700 then 2400 ft if coming from the east. 4700 ft if coming from the north.

3- Instrument approach procedure - Type of approaches, minima and parameters :

a) Minimums :

The minimums represent the weather condition requirements established for IFR take-offs and landings. They are based on differents parameters and shown at the bottom of approach charts.

The parameters are :

- DH / DA (Decision Height / Altitude) : a specified height or altitude in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established or if the position of the aircraft according to the runway does not enable a safe landing.

- MDH / MDA (Minimum Descent Height / Altitude) : the lowest height or altitude to which descent is authorized on final approach or during circle-to-land maneuvering in execution of a standard instrument approach procedure where no electronic glideslope is provided. The descent must not be continued if the required visual reference to land has not been established or if the position of the aircraft according to the position of the runway does not enable a safe landing.

- RVR (Runway Visual Range) : An instrumental value (from transmissiometers) representing the horizontal distance a pilot will see down the runway from the approach end. It is based on the sighting of either high intensity runway lights or on the visual contrast of other targets.

- VIS (Visibility) : Prevailing horizontal visibility near the earth's surface as reported by an accredited observer.

- ceiling : The height above the ground or water of the base of the lowest layer of cloud below 6,000 meters (20,000 feet) covering more than half the sky (cloudiness SCT, BKN or OVC, see L1-MetarSpeci).

The parameters to be taken into account depend on the type of approach to be used :

b) Precision approach :

A precision approach is an instrument approach procedure providing the pilot with a 3D information (bearing, slope, distance). In FS, there is only one of that type : the ILS approach (see L6-NavInstr).

=> 2 parameters : DH / DA and RVR. 

There are 3 categories :

For the ILS, the categories are as follows :

c) Non precision approach :

A non precision approach is an instrument approach procedure in which no electronic glideslope is provided. In FS, there are several of that type : VOR, VORTAC, NDB, L, LLZ, ILS with GS out approaches (see L6-NavInstr)

=> 2 parameters : MDH / MDA and RVR or VIS.

d) Circle-to-land :

A circle-to-land maneuver is initiated by the pilot to align the aircraft with a runway for landing when a straight-in landing from an instrument approach is not possible or is not desirable. At tower controlled airports, this maneuver is made only after ATC authorization has been obtained and the pilot has established required visual reference to the airport. See also L5-Charts.

=> parameters : MDH / MDA, VIS and ceiling.

A circle-to-land maneuver may be free (no chart for this, the pilot is free to maneuver around the airfield) or specified on prescribed tracks which the pilot has to follow (published on a specific chart).

e) Take-off :

=> 2 parameters : VIS and ceiling.

4 - Departure procedure - SID / DP (Standard Instrument Departure / Departure Procedure) :

A SID, also called DP, is a predetermined route for leaving an airport shown of SID/DP charts. It starts on the runway and ends at the first en route point. A single runway may have several SIDs/DPs, according to the direction of flight after take-off.

SIDs/DPs are designated by names, figures and letters as follows (examples : MTL 3N - MAZET 4S ) :

- The  name is the one of the first en route point to be found after departure, where the SID/DP ends. It is a navaid (MTL) or a fix (MAZET).

- The figure is the version of the SID/DP. Presently, MTL 3N and MAZET 4S are active. If they have to be modified for any reason, they will be renamed as MTL 4N and MAZET 5S, just to make sure that everybody will use the same version. Unfortunately, this is a problem in the sim world because a lot of pilots/controllers are using outdated charts and depending on the date of their charts, the versions may be quite different.

- The letter is relative to something specified on charts. Here, imagine we have a 18/36 runway. MTL 3N is for 36 departures (northbound) and MTL 3S for 18 departures (southbound). Idem for MAZET 4N and MAZET 4S. 

5 - Arrival procedure - STAR (Standard Terminal Arrival Route) :

A STAR is a predetermined route for joining the initial approach fix (IAF). It starts at the last en route point and ends at the IAF. A single runway may have several STARs, according to the sector the aircraft is coming from.

STARs are designated by names, figures and letters as follows (examples : MEN2V - LOGIS 2W) :

- The  name is the one of the last en route point to be found before IAF, where the STAR starts. It is a navaid (MEN) or a fix (LOGIS).

- The figure is the version of the STAR.

- The letter is relative to something specified on charts. Say V for runway 18, W for runway 36 for example.

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