Does anybody knows is there any document where is described the nav accuracy during STAR and SID? I mean, how far can I deviate from the path as much as possible?


2 Answers 2


TSO-c129 define the requirements for non-WAAS GPS receivers. In these receivers, TERMINAL (T) mode is equivalent to RNAV 1 and extends from the departure and destination 30NM.

Between those two airports, ENROUTE mode is activated (> 30 NM from departure or destination airport). ENROUTE mode is equivalent to RNAV 2 procedures.

APPROACH mode starts at the capture fix and on these non-WAAS receivers, it is equivalent to RNAV 0.3 mode.

SIDs and STARs are RNAV 1 requirements. This means the receiver needs to have a 95% confidence that it knows where you are with 1NM of where you actually are. Also, full scale deflection of the GPS needle is 1NM.

Enroute structures like Victor and Jet airways, and Q and T routes are RNAV 2 procedures and the receiver needs to know where you are within 2NM just like the previous example.

As another answer pointed out, SIDs and STARs can extend greater than 30NM from the departure or destination airports, but they are still RNAV 1 procedures. The crew must be aware and monitor "actual navigational performance" to ensure it meets RNAV 1 criteria.

TSO-c146 WAAS GPS receivers account for the distance on SIDs and STARs and will stay in TERMINAL mode (RNAV 1) until the end of the SiD or the beginning of the arrival.

AC 90-100A change 2 describes this pretty well

(5) The navigation standard (for example, RNAV 1 or RNAV 2) required for all RNAV procedures/routes will be clearly designated on all appropriate charts. However, SIDs, ODPs, and STARs will be flown with RNAV 1 procedures. (page 6)

On RNAV SIDs and STARs, the plate will typically remind the pilot of the RNAV RNP.

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For non-RNAV SIDs and STARs, the airway extends 4NM from the centerline until 4.5° radial change intercepts the 4NM area at 51NM. At that point, the airway obstacle clearance expands at 4.5°.

FAA TERPS Order 8260.3F

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This is an interesting question, because the FAA docs, like many large complex organizations, often have vague or contradicting definitions.

RNP APPR, the navigational precision required for final approaches, narrows starting at 1 NM from the runway, down to .1 NM near the runway.

RNP 1 (full CDI deflection is 1NM either side of the course) is required for “arrival and departure in the terminal area, and the initial and intermediate approach phase.”

RNP 2 (full CDI deflection is 2NM either side of the course) is required for enroute operations in the US.

(It’s worth noting that there several technical criteria that define RNP 1 or 2, and the CDI sensitivity is merely the visible indication to you as the pilot, there’s a lot more to it.)

The problem is that the definition of a SID or STAR’s normal lateral dimensions don’t exist. A large arrival could start hundreds of miles from the runway. Does this constitute the “arrival and departure in the terminal area” that points to RNP 1? Probably not.

The FAA defines the “Terminal Area” as “A general term used to describe airspace in which approach control service or airport traffic control service is provided.” By that definition, you would switch from RNP 2 to RNP 1 when you leave the ARTCC sector and enter into the approach controller’s sector. That line may be very clear to the controllers, but will be very vague to the pilot.

So you are actually flying the inner 20-30NM of the SID or STAR under RNP 1, and the outer part under RNP 2.

  • $\begingroup$ Where are you getting these definitions for navigation specifications? There are many errors in this response, starting with the first one listed. RNP APCH has, as a total system error, a 1 NM for many segments but is down to 0.30 NM for the final approach segment. Meanwhile, US RNAV DPs and STARs require RNAV1, not RNP1. Likewise, enroute RNAV requires RNAV2. $\endgroup$
    – Timbo
    Commented Apr 29 at 9:22
  • $\begingroup$ @Timbo Information comes directly from the AIM, see Chapter 1, Sections 2… Specifically 1-2-1-b-2-E. And then really all of 1-2-2, with special focus on Table 1-2-1, and paragraphs 1-2-2-b-1-a. $\endgroup$
    – Max R
    Commented Apr 29 at 15:55
  • $\begingroup$ Thanks for your answer! $\endgroup$ Commented Apr 30 at 6:49
  • $\begingroup$ @MaxR, thanks… though you have misrepresented RNP APCH as RNP APPR. Likewise, RNP 1 is NOT required in the US for arrival and departure. RNAV1 would be the correct NavSpec for an RNAV procedure. Finally, RNP 2 is NOT required in the US for the enroute phase. I believe you’re just misquoting the AIM. $\endgroup$
    – Timbo
    Commented Apr 30 at 22:53

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