I got a NAV1 question

Hello,

Why do switching from GPS to NAV1 sometimes changes our obvious path? Plane turns to the north instead each time.

Even when we’re inside the cone and aligned prior to switching it on. Sometimes it works sometimes it doesn’t.

Thanking y’all for your answers, have a happy flight, cheers! :)

GPS follows your flight plan, while when Swtiching to NAV it sets it to the ILS you select on the airport.

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Yes, I was on the NAV1 designated approach runway. Sometimes all goes according to plan, but half the time - my aircraft runs away elsewhere! :D

Even when switching it on inside the cone, aligned with runway that I had set NAV1 on. Why on earth does that happen?

Autopilot in IF is quite aggressive, so it might just be that it overcorrects it

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Aha, speed! That could be one clue…

But I was on 180kts, 35% load, flaps full and manually had followed the middle line of the cone before switching to NAV1 just to overkill my perfect approach… but it went underkill so fast lol.

How fast should I be just inside the cone on a 737?

Having LNAV set with NAV 1 after being on GPS you can expect some new corrections since there’s new values for your aircraft to follow under LNAV since you still have it on I’m assuming.

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If you are perfectly aligned with the cone, then your speed only determines your descend rate

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Onboard computer malfunctioning! (aka coding related)… interesting. I will try switching LNAV off next time, switch to NAV1 and turn LNAV back on.

Yep with what you have set on NAV 1 your LNAV will follow. It takes you straight down the cone.

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Not sure if this was a factor, but on almost every airplane going 180kts doesn’t require full flaps. It can mess up the rate of descent a little bit. In an Airbus usually flaps 3 is appropriate and somewhere around 25 degrees in Boeings. However, disregard if you were in a 747 or A380.

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Right, except when following waypoints at speed when you are still heavy minutes after take-off! (LNAV took me in circles too at +250kts lol)

Will try putting that into account next time, thank you!

That’s because your going too fast to intercept the next waypoint and your aircraft circled around attempting to intercept that next waypoint but is unable to since your going too fast. It’s like trying to make a turn in a car going too fast. You miss the turn and… yeah.

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Well to be honest most SIDs don’t allow 250kts at times when there is a risk of a situation like this, so I would recommend check the maximum speeds for your desired SID next time

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Guys, could it be that NAV1 was coded in IF similarly or as sensitive as APPR? Where you’ve got to be at certain altitude, weight and speed, also at the right timing located near the cone area in order for it to work?

Might have messed up my NAV1 approach due to approaching at the wrong altitude?

For example, the last time it happened I was about 4000 feet a third way into the cone at KLAX

Your altitude has nothing to do with how your NAV 1 will work. It’s just like LNAV but selected for a certain runway or VOR.

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That’s a good point that I personally haven’t really looked into but you might be onto something. It do think that NAV1 is a bit more sensitive due to the fact that you need this sensitivity to fly VORs or ADFs. So I’d believe that if the course is adjusting, going from GPS to NAV1 is going from low sensitivity to high sensitivity.

And, I’m not sure if it was covered already but if you’re flying a GPS approach you stay in GPS and allow VNAV and LNAV to fly your approach for you… all the way to the runway.

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But there must be some strict conditions to be met though in order to use NAV (for example distance from airport). I’m sure something I did messed it up. My pathway was perfect, rest to blame are speed, weight and altitude inside the cone area…

Woah, thanks so much for this input! But I just love this new feature. So when would NAV1 be necessary?

Really NAV 1 is the same as LNAV as I kind of said earlier it just is to a certain runway or VOR. It goes by aircraft location in regards to the localizer center line information and will turn you to intercept that. So it intercepts the actual heading of the runway with your aircraft to be aligned with the center of the localizer or to be on the center line of the localizer.

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