I know that typically RNAV navigation involves a list of waypoints, and the aircraft simply flies from one point to the next. What I'm curious about is if a procedure could be developed (as a special engine out procedure, for example) that would be something like

Depart on runway heading. At distance 2nm from FOBAR waypoint, turn direct to FOBAR. Track radial 090 outbound from FOBAR.

Would the instruments in an RNAV equipped aircraft allow a procedure like that to be flown? Would it require a certain system (say only from a certain manufacturer), or require additional systems (like an FMS)?

CLARIFICATION FROM COMMENTS: I understand that a procedure like the one above would not be typical or preferred, but in very hazardous terrain (for example) with no real other options, would the pilot simply have the tools available to be able to fly it?

If it matters, I'm particularly interested in commercial aviation and answers that would be applicable to any airport worldwide.

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    $\begingroup$ IFR engine-out is an emergency, and ATC will make sure to clear you direct wherever you want to go. I'm not sure why you would be departing with an engine out, IFR or not, unless you had a death wish. $\endgroup$
    – Ron Beyer
    Jan 12 '18 at 15:04
  • $\begingroup$ @RonBeyer I know of many airports at the bottom of a narrow valley, surrounded by large cliffs on all sides, where the safest way out could be following a procedure similar to the one I mention. $\endgroup$ Jan 12 '18 at 15:12
  • $\begingroup$ Even then, you say as a special "engine out" procedure, why would you depart an airport in the mountains with an engine out? If you are engine out coming in that may be different, however ATC will give you vectors, not waypoints. $\endgroup$
    – Ron Beyer
    Jan 12 '18 at 15:14
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    $\begingroup$ That may be true, however trying to do some kind of VOR-ish RNAV procedure with an already high workload is going to be a recipe for disaster. That is why ATC will just issue vectors/altitudes. In an emergency ATC's job is to make yours as a pilot easier. If I were flying engine out and declared on departure and heard that from the controller, provided I make it back alive I'd walk up to that controller and slap them. $\endgroup$
    – Ron Beyer
    Jan 12 '18 at 15:31
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    $\begingroup$ @RonBeyer Actually, it is the operators responsibility to develop emergency turn procedures where they are needed. They are typically referenced to navaids/RNAV-fixes. (Sometimes as simple as "Passing 1.5 DME, turn right TRK 120", but sometimes more complex, involving multiple navaids and possibly climb in hold). ATC can assist you with vectoring above their MVA, but the emergency turn procedure is required to get to MVA/MSA safely. At those low heights, you might not even be visible on radar. $\endgroup$
    – Waked
    Jan 12 '18 at 16:32

In a modern B737 (NG/MAX) (and probably most other comparable aircraft), this is trivial. The simplest (and most realistic option for an emergency turn procedure) would be to fly the procedure in HDG SEL:

  • Enter FOBAR on FIX page
  • Add a 2 nm range ring for FOBAR on the FIX page. This ring will be displayed on the ND (Navigation Display)
  • Add the 90 radial for FOBAR on the FIX page. This radial will be displayed on the ND.
  • Fly the procedure in HDG SEL, monitoring the ND.
  • $\begingroup$ I figured it would probably be possible with modern aircraft, thanks for confirming. But what if you only had older equipment, say one of the earliest RNAV systems and no FMS? $\endgroup$ Jan 12 '18 at 18:52
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    $\begingroup$ Technically, as long as you can define custom waypoints, either by lat/long or radial/distance from existing fix, sure. Is it something that you would see in practical use? Not so sure. $\endgroup$
    – Waked
    Jan 13 '18 at 10:39

One of the aircraft that I fly has dual Avidyne IFD540 GPS units onboard. I can select any waypoint that is in my database and treat the waypoint as though it were a VOR in-so-much-as I can set the GPS in OBS mode and then manually select any "radial" to track to or from that waypoint no different than if it were an actual VFR.

I believe that the Garmin units can do the same thing.

Once I have this dialed in, the autopilot will follow the "radial" that I have selected no different than a VOR.

In the situation you are describing I think if they were going to be tracking outbound from FOBAR you would be going "somewhere" and instead of tracking outbound they would simply be going to their next waypoint.

Ultimately, while not something that one would normally do, with modern navigation equipment, it can be done.


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