3 minutes ago, mspencer said:

If the weather is good in the US you’re more likely to get a visual approach than an ILS or RNAV. 

That's a U.S. specific thing though because it allows for tighter sequencing and gives responsibility of spacing to the pilot.

 

49 minutes ago, anavsun said:

I don't understand. What is the purpose of an offset? Why? 

We have special types of RNAV approaches in Southeast Alaska that contain RF segments (radius-to-fix, a way to make the airplane fly a tightly defined arc) literally to the runway, to get around terrain.  You're rolling wings level as you begin your flare, over the threshold. 

The reason for any approach geometry is terrain / obstacle clearance.  There's a complex set of criteria that in the US is called TERPS that specifies allowable proximity to obstacles on each segment of each type of approach.  Offsets, RF legs, steeper than normal glidepaths, glidepaths that intercept the runway beyond the standard 1,000ft mark... All of these are tools for navdata engineers to construct procedures that can meet TERPS requirements for any given runway.  It's cool stuff if you're into it, but is mostly beyond the scope of what pilots need to worry about.  From a pilot perspective, you don't need to worry about the "why" if you don't want to; just fly the procedure as charted / coded in your navdata.

As far as the percentage of ILS vs non ILS approaches, it really depends on the operator.  The 737 is a very versatile airplane.  There are pilots at some airlines that haven't landed at a non-ILS airport in years.  There are pilots flying 737s who rarely do ILSs.  Just depends where you are and what you're doing.  That's one of the reasons I like my job... Could be doing a transcon to JFK one day, an ETOPs leg the next, and a day of 20 minute flights curving through terrain to short runways with no public approaches in Alaska the next.  Variety is fun.  👍

Auto brakes - this will be policy that varies by operator.  Some airlines mandate the use of auto brakes if they're working.  We don't; we use them when appropriate (crosswind, wet/contaminated/short runway), and leave them off on a nice day to a long dry runway.  This is all determined by landing performance calculations and is well beyond what's done in a desktop sim.  Just set them to 2 every time and call it good 😉.

19 minutes ago, Farlis said:

That's a U.S. specific thing though because it allows for tighter sequencing and gives responsibility of spacing to the pilot.

 

Which is why I qualified it by saying in the US…

6 hours ago, Farlis said:

From a short glance I see you are in FAC and GP mode so you have pushed the APP button at some point. 

Don't. You stay in LNV/VNAV for an approach like this.  This is why your lateral guidance was off.

I have pressed the APP button for every RNAV approach that I have ever flown. After checking, it seems that this puts the aircraft in IAN mode. All I know is that the approaches have worked perfectly every time (apart from one or two very rare cases where it has picked up an ILS frequency of another nearby airport). If I want to land in purely RNAV mode, is selecting the RNAV approach enough to get the job done?

Edited February 16, 20251 yr by Christopher Low

6 hours ago, Farlis said:

Ermmm, you switched off the AT 2:30 into the video, which is correct, because when you land a 737 manually you are not supposed to leave it on. At 2:46 you begin to retard the throttles (looks to me like you are idling them) and drop below final approach speed. This is the moment where you start to screw up the landing.

I set the approach course to 172° which is what is noted on the approach chart.  On final, I noticed that the plane was apparently aiming at that offset runway(?) to the right of the main runway. Not knowing any better, I turned off the AP and the AT to hand fly the plane to steer it to the left for the main runway. Had I not hand flown the aircraft I think it would have continued on using the IAN approach as @Christopher Low later mentioned he has been successfully using based on his experience flying RNAV. 

If the recommended approach course is for the main runway and the approach course is indicated the same in the aircraft as noted in the approach chart, and the offset is to be used only when there is a reason not to use the main runway, why would the aircraft fly towards the offset without input from the pilot? Also, was there an explanation in the chart that I missed to use the offset?

 

6 hours ago, Stearmandriver said:

The reason for any approach geometry is terrain / obstacle clearance.  There's a complex set of criteria that in the US is called TERPS that specifies allowable proximity to obstacles on each segment of each type of approach.  Offsets, RF legs, steeper than normal glidepaths, glidepaths that intercept the runway beyond the standard 1,000ft mark... All of these are tools for navdata engineers to construct procedures that can meet TERPS requirements for any given runway. 

I get it that TERPS is for obstacle clearance. How would a pilot know if an airport falls under TERPS criteria (do pilots need TERPS  certification?).  I don't see TERPS mentioned in KTVL's approach chart. KTVL is in a mountainous obstacle rich environment. Shouldn't it require a TERPS procedure?

9 minutes ago, anavsun said:

How would a pilot know if an airport falls under TERPS criteria

Simple - all of them do! TERPS is simply the name of the rules that are used to construct instrument approaches in the US.

Every single published approach is surveyed for terrain and obstacle clearance. If a straight-in, 3 degree glideslope gives the required clearance, that's typically what you'll get. If not, as at KTVL, the procedure designer needs to get creative.

The pilot doesn't need to know why the approach looks the specific way that it does (though you can usually guess) - they just need to follow the published approach.

43 minutes ago, martinboehme said:

Simple - all of them do! TERPS is simply the name of the rules that are used to construct instrument approaches in the US

A quick glance on the chart's lower left corner reveals what design criterias is being used (TERPS/PANS-OPS etc), if OP wants to know.

 

2 hours ago, anavsun said:

If the recommended approach course is for the main runway and the approach course is indicated the same in the aircraft as noted in the approach chart, and the offset is to be used only when there is a reason not to use the main runway, why would the aircraft fly towards the offset without input from the pilot? Also, was there an explanation in the chart that I missed to use the offset?

Not sure exactly what you mean. There is just one runway surface at KTVL?

The final approach course is not just recommended, but required. There is no case when you would use a different final approach course.

The term "offset" here refers to the fact that the final approach course is different from the runway heading. Maybe you're confusing this with the "lateral offset" you can enter in the FMC, which we were discussing in a different thread? These two things have nothing to do with each other.

3 hours ago, Christopher Low said:

I have pressed the APP button for every RNAV approach that I have ever flown.

Then you've flown them all wrong.

3 hours ago, Christopher Low said:

If I want to land in purely RNAV mode, is selecting the RNAV approach enough to get the job done?

Yes.  Just look at the videos posted at the top of this thread.

3 hours ago, anavsun said:

. Not knowing any better, I turned off the AP and the AT to hand fly the plane to steer it to the left for the main runway.

Then you did instinctually right what you were supposed to do. Like I said in the very first post in this thread, this approach is flown manually after the missed approach point. I was not taking issue with you flying it manually, your throttle management was the problem.

And no you can't fly this approach in IAN it would have steared you into the ground next to the runway.

Edited February 16, 20251 yr by Farlis

2 hours ago, anavsun said:

I get it that TERPS is for obstacle clearance. How would a pilot know if an airport falls under TERPS criteria (do pilots need TERPS  certification?).  I don't see TERPS mentioned in KTVL's approach chart. KTVL is in a mountainous obstacle rich environment. Shouldn't it require a TERPS procedure?

Yup, every single procedure falls under TERPS (or a different organization's set of rules that is effectively the same thing.). Instrument approach procedures aren't optional or voluntary.  If you're cleared for the visual, you can maneuver however you want to get to the runway... But if you're cleared for a named procedure like the "RNAV 14", you have to fly the procedure as charted.  If it includes an offset final approach course then you fly it, with the last minute small correction to line up with centerline. 

3 hours ago, Christopher Low said:

have pressed the APP button for every RNAV approach that I have ever flown. After checking, it seems that this puts the aircraft in IAN mode. All I know is that the approaches have worked perfectly every time (apart from one or two very rare cases where it has picked up an ILS frequency of another nearby airport). If I want to land in purely RNAV mode, is selecting the RNAV approach enough to get the job done?

What you have to understand about IAN is that in reality, it can only be used in a strictly defined type of RNAV approach.  It can only accept a straight in final with no (or very little) offset, and it cannot handle RF legs or other RNP (AR) specific requirements.  Its only purpose is to allow crews to fly extremely simple, straight-in non-precision approaches in a mode that's using FMC guidance to mimic a precision approach, so that a separate approach profile does not need to be trained or evaluated. 

In other words, IAN is a very dumbed-down version of RNAV approaches that has no operational benefits, but several drawbacks and limitations.  This is why most airlines do not have it installed, and fly all their RNAV procedures in LNAV/VNAV.  

3 hours ago, anavsun said:

If the recommended approach course is for the main runway and the approach course is indicated the same in the aircraft as noted in the approach chart, and the offset is to be used only when there is a reason not to use the main runway, why would the aircraft fly towards the offset without input from the pilot? Also, was there an explanation in the chart that I missed to use the offset?

The final approach course is defined on the approach chart.  If it differs from the runway heading, then it's offset.  But you don't do anything to make that happen; in fact, it's forbidden to modify courses or altitudes on an approach procedure inside of the final approach point.  The correct course will be loaded in your FMC when you load the procedure.  (As an aside, while setting the MCP course window to final approach course can be a useful SA tool, it is irrelevant from a technical standpoint on an RNAV approach flown in LNAV / VNAV.  The plane doesn't use the value in the course window at all in this case.)

10 hours ago, martinboehme said:

Not sure exactly what you mean. There is just one runway surface at KTVL?

The final approach course is not just recommended, but required. There is no case when you would use a different final approach course.

The term "offset" here refers to the fact that the final approach course is different from the runway heading. Maybe you're confusing this with the "lateral offset" you can enter in the FMC, which we were discussing in a different thread? These two things have nothing to do with each other.

Yes, I am confusing this with lateral offset. Perhaps because I'm reading the word "final" and "offset" literally?  I don't get it. Why would there be an offset or a deviation from the "recommended" final approach course over obstacle-free lake or body of water?  Is it a recommendation or a requirement?? "Final" by definition is a requirement, isn't it? That is, there can be no deviation from a final approach. As you mentioned "There is no case when you would use a different final approach course" which is why I don't understand why there is a need for an "offset".

This reminds me of something I was told visiting a town in an island in a "3rd world" country.  Red lights in traffic lights are just ... get this.... "suggestions". Lol.

10 hours ago, martinboehme said:

The term "offset" here refers to the fact that the final approach course is different from the runway heading.

Why would the final approach course be any different from the runway heading? Shouldn't I have entered 172° as the course heading in the MCP? Did I get this wrong? If not 172°, what should I have used as the course heading on the MCP instead?

Incidentally, is CMD-B only used concurrently with CMD-A auto-landing in ILS approaches or are there other instances when both CMD-A and CMD-B are also used?

Edited February 16, 20251 yr by anavsun

11 hours ago, SAS443 said:

A quick glance on the chart's lower left corner reveals what design criterias is being used (TERPS/PANS-OPS etc), if OP wants to know.

 

Thank you. Yes, I'd like to know. Looking at the lower left corner of the chart, how does one know if TERPS or PANS-OPS is used? How are they shown differently in the chart?

Incidentally, are figures in approach charts in Skyvector always in Imperial units or can they be metric also?

10 hours ago, Farlis said:

Then you've flown them all wrong.

Yes.  Just look at the videos posted at the top of this thread.

Then you did instinctually right what you were supposed to do. Like I said in the very first post in this thread, this approach is flown manually after the missed approach point. I was not taking issue with you flying it manually, your throttle management was the problem.

And no you can't fly this approach in IAN it would have steared you into the ground next to the runway.

In your reply to @Christopher Low above, I don't understand your statement that he has flown it all wrong since he's almost always landed the aircraft without crashing. I'm assuming you meant he was wrong technically in the strict sense that he didn't follow the rules ie. dotting his 'i's and crossing his 't's in doing RNAV.  Do I have that correct?

To unravel this, let's start here:

1 hour ago, anavsun said:

Why would the final approach course be any different from the runway heading?

Because if the final approach course was the same as the runway heading, the final approach would go right through a mountain (or dangerously close to it). 😉

So the final approach course needs to go over the lake instead, but that means it's not lined up perfectly with the runway.

(Why didn't they build the runway so it can be lined up with a final approach that goes over the lake? I don't know - but the answer may simply be that a suitable plot of land wasn't available.)

This is all there is to it.

The term "offset" here simply means that the runway isn't lined up with the final approach. There's nothing special that you need to enter into the FMC. You fly the approach exactly as it is depicted on the chart and as it is contained in the FMC's navdata, as you would any other RNAV approach. The only thing that's different is that when you get close to the runway, you won't be lined up with the centerline, so you need to maneuver manually to get onto the centerline and land.