Acceptable Lateral Deviation

[aviationluver]

When it comes to flying a Federal airway in the US, a lateral deviation of greater than 4NM from the centerline of the airway is considered off course.

However, what is considered off-course when flying a course which is not an airway? For example, point-to-point, present-position direct to a point, etc.?

Also, what is considered off-course when flying over the ocean such as Atlantic or Pacific routes?

Thank you.

[CallmeJB]

In the US, 4nm is the rule for Victor Airways. Jet Airways have no defined width. I would be interested if you have found a reference which assigns a width.

My understanding is you are expected to be right on the centerline, or as close as your navigation equipment can get.

[MarkerInbound]

A Gross Navigation Error on the NATs is being 25 miles off course.

[aviationluver]

@MarkerInbound

I'm assuming NAT = North Atlantic Track, is that correct?

Also, do you have a reference for your 25NM answer?

[safelife]

In europe it would be measured with BRNAV (basic area navigation) requirements. Those are 5 NM.

[Skyjob]

Different airways have different requirements.

The PBN Manual

The PBN Manual (http://www.ecacnav.com/downloads/PBN%20Manual%20-%20Doc%209613%20Final%205.10.08%20with%20bookmarks.pdf) (Doc 9613) comprises two Volumes.
Volume I of the PBN Manual is made up of two parts: Part A describes the PBN Concept, The Airspace Concept and how the PBN Concept is used in practice. Part B provides Implementation Guidance for ANSPs in the form of three processes.
Volume II of the PBN Manual is also made up of three parts. Part A describes on-board performance monitoring and alerting and Safety Assessments, whilst Parts B and C contain ICAO’s RNAV and RNP specifications which are to be used by States as a basis for certification and operational approval.

The B-RNAV standard contained in EASA AMC 20-4 is identical to the RNAV 5 specification in ICAO PBN. The term B-RNAV has been replaced by RNAV 5. RNAV 5 is now required for operation on all ATS routes in UK airspace.

The UK P-RNAV standard is not identical to the ICAO RNAV 1 specification but may be viewed as a European Application of the RNAV 1 specification. The difference between P-RNAV and RNAV1 centres on the allowable ground navigation aids and the PBN Manual identifies additional requirements for obtaining RNAV 1 approval for an operator already having approval against JAA TGL 10.

[aviationluver]

@Skyjob,

If different airways have different requirements, wouldn't it be unreasonable to expect a pilot to know the lateral deviation for all the different types of airways and situations that they find themselves in?

[Intruder]

Regardless of the RNP of a particular route or airway, these days ATC expects you to be ON CENTERLINE unless cleared otherwise (e.g., SLOP or other offset, or weather deviation). Effectively, the "acceptable" lateral deviation is ZERO, or the resolution of the ATC radar.

Best example I can think of is to try a 1 mile deviation just after takeoff on an RNP 1 SID. Think you'll win any argument based on the RNP1 designation?!?

[Green Guard]

..and why on earth do you want "1 mile deviation just after takeoff"...to test ATC? Of course they will see it. But anywhere further then SID or STAR i.e further then ~25 NM from Airport, for 1 NM offset they will not warn you...nor mention anything about ZDH ("zero deviation hysteria")...Guaranty

[Pub User]

Intruder.
If you're on an airway, then ATC have no business questioning you if you wander a couple of miles from the centreline. However, 1 mile off centreline 'just after takeoff' would indicate some sort of gross navigational mistake, equipment failure or mishandling, and I would both hope and expect that ATC would enquire as to the nature of your erratic flying

[galaxy flyer]

While ICAO standard for radio nav was +\- 1 dot, the FAA standard was "on course" or correcting, there was no tolerance or ability to wander around the 4 nm either side. Remember the 4 nm, includes "flight technical errors", so at the edge of 4 nm and be outside the airway due to other errors in the budget.

[flyboyike]

If different airways have different requirements, wouldn't it be unreasonable to expect a pilot to know the lateral deviation for all the different types of airways and situations that they find themselves in?


No, what's unreasonable is to pay us what they do, but I digress. I don't care what the airways width is, I care if my CDI is centered up or not. If it's not centered up, something is clearly amiss.

[MarkerInbound]

AL,

The definition of a GNE is in the North Atlantic Operations and Airspace Manual (NAT Doc 007).