I need some help!!! I am wondering from a legal point of view...if you can add or delete waypoints fron your selected approach procedure in the FMS...my Flight Manual states I can only do it before the FAF, but I am reading internet articles that says you can do it even after the FAF,other say that you cant modify it at all...???

 

If you're with a 121/135 carrier, I would go with what your manuals say. Otherwise, unless you're shooting an FMS/RNAV/GPS/WAAS approach, I don't see anything wrong with deleting waypoints. If an FMS isn't required for the approach, it can be turned off for all intents and purposes.

 

I know that in the GPS-fitted airplanes I fly (mostly G1000-fitted 172s and GNS 430W-equipped everything elses), you *can* make waypoint changes after the final approach fix. The question is, "should you" - and I'm not a fan of doing so although I can't find any regulatory guidance either way (Part 91 here).

 

Nav Data bases are coded according to a ARINC 424 spec. and use path terminators to do the coding. ie a heading to a altitude then turn etc. When you insert a waypoint you are only creating a direct segment. If you are flying a approach in nav then you should not modify a approach from the FAF inbound.

RNAV LEG TYPE DESCRIPTIONS.

a. Initial Fix (IF). This is the point or fix where a flight segment begins. An IF is not a route segment and does not define a desired track in and of itself. It is used in conjunction with other leg types such as a TF leg in order to define the desired segment.

Note: "IF" in this context is not to be confused with initial approach fix (IAF) or intermediate fix (IF); however, it may be located at one of these locations for coding purposes.
b. Track-to-Fix (TF) Leg. This designates a track or geodesic path between two fixes. If the TF leg is the first route segment of a flight path, the TF leg begins at an IF; otherwise, the first fix of the TF leg is the termination fix of the previous route segment. The TF leg is the primary straight route segment for RNAV.

c. Constant Radius to a Fix (RF) Leg. An RF leg defines a curved path route segment about a defined turn center that terminates at a fix. The RF leg begins at the termination fix of the previous route segment. The previous segment is tangent to the arc of the RF leg at that fix. An RF leg is the primary curved path route segment for RNAV RNP procedures. Waypoints defining the beginning and end point of the RF turn must be designated as “Fly-by.”

d. Course-to-Altitude (CA) Leg. The CA leg is used to code the initial leg at the beginning of the missed approach segment. This leg type requires a stated course and altitude at the beginning of the missed approach. This altitude will be the lowest of DA, MDA, or 400-ft above airport elevation (for helicopter point-in-space procedures, use lowest DA or MDA). A DF leg must always follow a CA leg.

e. Direct-to-Fix (DF) Leg. A DF leg is used to define a route segment (geodesic path) that begins at an aircraft present position, or unspecified position, and extends to a specified fix.

f. Heading-to-an-Altitude (VA) Leg. The VA leg is used in a departure route segment where a heading rather than a track has been specified for climb. The VA segment terminates at a specified altitude without a terminating position defined.

g. Course-to-Fix (CF) Leg. The CF leg is defined as a magnetic course that terminates at a fix. Although the CF leg is used in many traditional approach and departure procedures, this leg type is to be avoided in the design of RNAV procedures.

h. Vector-to-Fix (VM) Leg. A VM leg is used for whenever a departure route description specifies a course or heading to fly in expectation of a radar vector.

i. Vector-to-Intercept (VI) Leg. A VI leg defines a specified heading to intercept the subsequent leg at an unspecified position.

 

Per my company's manuals (and yours may be different), no changes inside the FAF and no changes to RNAV sids and stars.

 

The restriction from entering a waypoint after the FAF has more to do with required navigation performance (RNP), and how an RNAV/GPS approach is designed. All aircraft certified for RNAV/GPS approaches are designed to maintain an RNP of 1.0 NM prior to the FAF. RNP after the FAF is reduced to 0.3 NM. Inputting a waypoint after the FAF "corrupts" the approach stored in the Nav database and may keep it from changing to RNP 0.3 after the FAF. Not a big deal if you are on a visual approach, but you would be illegal to fly an RNAV/GPS approach in the weather. Deleting a waypoint after the FAF may not necessarily change the RNP but depending on what is deleted, it could affect how the both the lateral and vertical/glide paths are calculated and potentially compromise obstacle clearance during final approach. All this is dependent on the type of aircraft/avionics package and the the specific approach flown. Remember, not all RNAV/GPS approaches are straight-line. from the FAF.

 

if you manually add a fix after the FAF you won't get GPS Approach RNP of .3. The CDI will stay in term with the CDI sensitivity of 1.

 

There are aircraft and air carriers, I believe your company is one, that are certified to go well below 0.3NM. RNP0.3 is old school.

 

Entering waypoints manually is forbidden when flying P-RNAV routes. When shooting a final approach which relies on the FMS, a change of waypoints does not make sense and most operators would probably not allow it.