Debates are a mainstay of hangar-flying discussions. Those debates can become particularly compelling and energized when the weather is below minimums or the wind is sending small structures and the occasional passerby tumbling across the ramp. You’ll often hear conflicting statements from different pilots, many even beginning, “Well, the examiner on my last checkride said…”
One common debate is what constitutes being “established” on a final approach course. This is important because being established often allows you to do something important, like, well, descend for a landing.
A good place to look for a definition is the Pilot/Controller Glossary. It defines established as “To be stable or fixed on a route, route segment, altitude, heading, etc.” “To be stable or fixed…” should jump out as a key component of being established. Note that established applies to altitudes, too, not just lateral courses.
Many debaters will claim you’re established when the needle leaves the peg—”course alive.” If pressed, one of the phrases you’re likely to hear in defense of this viewpoint is “positive course guidance.”
To have positive course guidance, you have to be established on the course, complete with positional awareness, right? In the case of a VOR, you have a measurable horizontal distance based on the needle’s deflection and your distance from the VOR station. With a localizer, it’s a little trickier since it varies between three and six degrees wide, but the greater precision helps.
TERPS defines positive course guidance as “A continuous display of navigational data which enable an aircraft to be flown along a specific course line.” The Instrument Procedures Handbook adds, “… (e.g., radar vector, RNAV, ground-based NAVAID).” This gives us clear guidance that we can be established even on a heading. We’d think a moving needle could quite easily be interpreted as a “continuous display of navigational data” so course alive has some merit.
I always set the heading bug. It’s much easier to see a brightly colored bracket coming around the dial than just another number. Most heading bugs are 10 degrees wide with your selection in the center. Staying within the bug can certainly help you be stable or fixed on your assigned heading, but it sure doesn’t constitute a continuous display of navigational data.
The needle-alive definition of being established overlooks the Pilot/Controller Glossary’s “To be stable or fixed…” It’s common to have a needle off the peg, yet remain far from stable on the selected course. Even a 90-degree crossing of a course provides a brief needle action without a hope of being stable. So, positive course guidance doesn’t appear to be enough. We have to dig deeper.
PTS and FARs
Often, the debate defining “established” uses the Practical Test Standards (PTS) for the permitted tolerance when tracking a navaid. The PTS for the Instrument Rating allows a -scale deflection of the needle when tracking a course. However, the PTS for the ATP practical test allows for no more than -scale deflection. Since the definition of “established” isn’t scaled to the certification level of the pilot flying, we can dismiss the PTS as a reference defining established.
The best regulatory guidance, of course, comes from the regulations themselves. In this case, 14 CFR 91.181(a) reads: “Unless otherwise authorized by ATC, no person may operate an aircraft within controlled airspace under IFR except as follows: (a) On an ATS route, along the centerline of that airway.”
An ATS route is an ICAO term that means “A specified route designed for channeling the flow of traffic as necessary for the provision of air traffic services. Note: The term ‘ATS Route’ is used to mean variously, airway, advisory route, controlled or uncontrolled route, arrival or departure, etc.” Since 91.118(a) specifically mentions “airway,” this note defining ATS should silence the loophole-seekers who claim the regulation doesn’t apply to approaches.
Could it be then that we are only considered “established” when we are on the centerline of a selected course? While “centerline” is what we should be flying, per the reg, we now should look at allowable navigation errors.
Two VOR receivers in the same panel are legally allowed to show “centerlines” of a course up to four degrees apart. Thus, they both could be established on the centerline, yet miles off of an imaginary line on the ground showing the physical centerline. It seems like we’re getting further from a definition. Couldn’t there be a more concrete metric?
More from ICAO
The International Civil Aviation Organization (ICAO) predates the present-day FAA by 17 years. Compliance with ICAO recommended practices is expected in order to facilitate seamless operation by other member states within each other’s jurisdiction. The U.S is a member state and, while slow, is gradually adopting most ICAO practices, phraseology and procedures.
ICAO, in a document called “Doc 8168—Procedures for Air Navigation Services—Aircraft Operations. Volume I—Flight Procedures” at the end of Paragraph 3.3.4, titled “Descent,” says “An aircraft is considered established when it is: a) within half full-scale deflection for the ILS and VOR; or b) within 5 degrees of the required bearing for the NDB.” That’s the first place we’ve seen an actual metric. Remember, however, that this ICAO definition only tightens up positive course guidance, replacing needle alive with needle half-scale. We still can’t forget the “stable or fixed” clause from the glossary, or the “centerline” goal of 91.181(a).
Combining all these disparate sources, we can assemble a workable and measurable definition of being established: To be stable or fixed, with a continuous display of navigational data showing no more than half-scale deflection for an ILS and VOR or five degrees off the required bearing for an NDB, of the centerline of an ATS route.
Throw that out there the next time you’re stuck by the coffee maker waiting for that 800 RVR to lift. Now all we need is a definition for an RNAV course.
Evan Cushing is a former regional airline training captain who now teaches at an aviation university. He considered himself established when they gave him a coffee mug with the school logo on it.