When to switch from GPS Nav to Ground Based?

S

SierraPilot123

Well-Known Member
Part 121 Airline environment.

KMFR airport. "Cleared Direct Ashie, cleared LOC DME-B back course"

At this point we are navigating GPS direct to ASHIE, an IAF using our "white needles" GPS.

**At what point must you switch and be navigating off of the "green needles", the actual Localizer back course to be legal?

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Most people leave the autopilot synced up to GPS until passing ASHIE. It makes for a nice transition and turn so you don't blow through the course at all. At this point they will select HDG, switch to LOC needles and than sync the autopilot to the LOC BC. BUT I've heard that this is not correct and a few people have failed a line check in this area.

Can someone please chime-in on what you think is the most correct/legal procedure and why?

mfr2.jpg


MFR.jpg


Thanks
 
Maurus said:
Why not flip it to LOC during the turn onto final?
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That is what I usually do. I usually keep GPS on my side and have the monitoring pilot switch their needles to the LOC so I can see it come alive. But I see a lot of Captains wait until the plane is stabilized a little past ASHIE, than switch. And I think this is where people have gotten in trouble during a line check. And you certainly can't switch to early because that you are just navigating on your own assigned heading, hoping to intercept.

This one can't be flown as a GPS overlay for us
 
Not sure what system you are using, so.....it depends. As far as a line check, you only have to be "green" before crossing the FAF.

The system I use switches automatically. Preview needle (gray) is selected to the "front" course. GPS LNAV engaged and BC selected (stby). As soon as the FD/AP intercepts the final approach course, the Magenta needle (GPS) turns Green, preview needle (gray) disappears, BC becomes active and the plane continues on it's merry way. So in your example, the Magenta/Green switch would occur outside of ASHIE, or right after the arc turn to the final app course.
 
Just do what your FM-1 or ops specs dictates to do. Everyone has a little different take on when to switch.
 
Rocketman99 said:
Nothing wrong with leaving it on GPS past ASHIE as long as you are using the real loc at HOXOR.
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That's how I'd do it. OpSpecs may vary at some places, but for us, as long as we are in short range nav by the time we cross the FAF we are good.
 
At my previous airline we had to be on conventional nav (green needles) no later than crossing the initial approach fix. Under their rules, you'd need to leave LNAV(GPS), go to heading mode just prior to ASHIE, arm the B/C, and let the flight guidance track the B/C beginning at ASHIE.

At my current airline the plane does it for us (I've still got the greatest enthusiasm and confidence in the mission. And I want to help you. :) ). Assuming you've set up your FMC correctly, the 747 FMC will not use a B/C for navigation until it's within 12 NM of the navaid. ASHIE is at least 15NM from IMFR. So the 747 would track inbound for a few miles using GPS prior to using the B/C.

I'd say you're legal and correct using either technique described in the original post. You can go ahead and track the conventionally tuned B/C inbound if you're getting a signal with a good identifier it prior to ASHIE. If you prefer to stay coupled to GPS until you're closer to the navaid, that would be OK too....at least Boeing seems to think so. It all depends on your equipment's capability and/or company's requirements.

Now if someone wants to correct anything I've said here, feel free. I'm still a complete NOOB when it comes to flying with HAL :)
 
Having flown this approach at Horizon, we can actually fly this approach with the FMS/GPS, have "Localizer Steering" engaged, and VNAV to MDA. It was a pretty slick system that we have to use. The only time you ever do a "dive and drive" approach is in the sim, and even those are going away soon.

All approaches at Horizon have VNAV available.
 
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