Hi all

I haven't flown the -700 in quite a while now. I did a quick flight yesterday from KLGA La Guardia to KDCA Washington Natl. 

I chose an RNAV approach into rwy 19. The issue is that I never saw any indication to start the glideslope. I thought this would happen just before reaching SETOC, which is the final approach point. Now - it could be that I messed up, since I haven't flown it in a while. I was at SETOC at 1500' as per the charts, so naturally I had to do a go-around. Not enough time to correct the mistake at that low altitude. On the second attempt I descended in V/S after FAP and disconnected the autopilot early. 

RNAV approaches should be working fine in the -700, right? I'll probably try the approach again today to see what went wrong. 

Edited July 28, 20223 yr by Cpt_Piett

I am waiting for the 737-800, but I use Zibo mod quite a bit.  I prefer to use IAN mode for RNAV. Were you using IAN mode?

For IAN, select the RNAV approach in the FMC. Set your inbound course (187) on the MCP.   When descending for the approach, look for the the RNAV and runway info to display on the PFD in the top left corner. At this point go ahead and press the APP button. You should see FAC and GP armed (but not active). FAC should turn to active in a minute or two as you start the approach. Keep descending down to 1500 before SETOC. Then you should see GP go active. At this point you can fly the approach similar to ILS but instead of LOC, G/S it shows FAC, GP (Final approach course, Glide Path).

Edited July 28, 20223 yr by Greazer

Well first of all it's a glidePATH on RNAV approaches (technically on the 737 it's called IAN approach).
Did you press the APPR button?

11 minutes ago, Fiorentoni said:

Well first of all it's a glidePATH on RNAV approaches (technically on the 737 it's called IAN approach).
Did you press the APPR button?

I want to say "of course I did", but to be honest I can't remember for sure. I was a bit flustered during the approach as I'm a bit rusty on airliner flying after being on holiday and flying mostly GA before that. 

When do you recommend pressing APPR during this approach? Just before FAP? And then there should be an indication on the display that glidePATH is armed?

Another question: The aircraft would descend in VNAV all the way down to the FAP, right? If I have selected 1500' as the target altitude. So let's say I completely disregard ATC, could I teoretically let the autopilot handle the descent from cruise FL all the way down to FAP, then glidepath down to the runway?

Edited July 28, 20223 yr by Cpt_Piett

40 minutes ago, Greazer said:

I am waiting for the 737-800, but I use Zibo mod quite a bit.  I prefer to use IAN mode for RNAV. Were you using IAN mode?

For IAN, select the RNAV approach in the FMC. Set your inbound course (187) on the MCP.   When descending for the approach, look for the the RNAV and runway info to display on the PFD in the top left corner. At this point go ahead and press the APP button. You should see FAC and GP armed (but not active). FAC should turn to active in a minute or two as you start the approach. Keep descending down to 1500 before SETOC. Then you should see GP go active. At this point you can fly the approach similar to ILS but instead of LOC, G/S it shows FAC, GP (Final approach course, Glide Path).

Prior to this I hadn't even heard of IAN mode 🙂 But thanks for the info. I had selected the RNAV approach in the FMC, but I had not set the course to the final approach course. 

You're flying an RNP approach with RF legs (both LT/ left turn and RT/ right turn). You are not allowed to use IAN if there is no constant approach course from FAP (in other words IAN is suitable for straight in approaches)

Rather Fly this approach in LNAV/VNAV instead.

IAN is a Boeing term, and not all Airlines have chosen this avionics option. It must be more than 20 years of age now, and since then new types of RNAV procedures have evolved, making IAN less attractive.

Edited July 28, 20223 yr by SAS443

22 minutes ago, SAS443 said:

You're flying an RNP approach with RF legs (both LT/ left turn and RT/ right turn). You are not allowed to use IAN if there is no constant approach course from FAP (in other words IAN is suitable for straight in approaches)

Rather Fly this approach in LNAV/VNAV instead.

IAN is a Boeing term, and not all Airlines have chosen this avionics option. It must be more than 20 years of age now, and since then new types of RNAV procedures have evolved, making IAN less attractive.

Thanks for your explanation. You're right, this approach has several course changes after FAP. I'll fly it in LNAV/VNAV then. 

5 hours ago, Cpt_Piett said:

Thanks for your explanation. You're right, this approach has several course changes after FAP. I'll fly it in LNAV/VNAV then. 

There's basically no practical difference between flying RNAV approaches in IAN or LNAV/VNAV, which is why some airlines didn't even bother getting the IAN option. They have the same minima and are to be flown manually on short final (no autoland obviously). The only practical difference is that, since IAN imitates an ILS approach, you can set the missed approach altitude once you are on the glidepath. But that's it.

As for your question: If you use IAN, press the approach button before the FAP, like you would on an ILS approach. The plane will start descending automatically after the FAP.
If you use LNAV/VNAV, you set the minimum as the selected altitude and press VNAV (if you haven't already). The plane will start descending after the FAP. Keep in mind that the plane will want to level off at the minimum, so you have to turn the altitude selector again to 0 feet (once you decided to "continue") so the flight director keeps the vnav path.
Or you disconnect the AP at the minimum, recycle the FDs (off->on) and fly it down visually, like most pilots do.

5 hours ago, Cpt_Piett said:

Thanks for your explanation. You're right, this approach has several course changes after FAP. I'll fly it in LNAV/VNAV then.

I have not been able to dial in this approach either. Flying in LNAV/VNAV (not hitting Approach button) and I am also not capturing the path down...

After all this great information I'm going to try it again. 

5 minutes ago, Flic1 said:

I have not been able to dial in this approach either. Flying in LNAV/VNAV (not hitting Approach button) and I am also not capturing the path down...

Did you set the altitude to the minimum (or to 0)? If it's still set to the FAF altitude (e.g. 1500 feet), the plane won't descend in VNAV mode.

RNAV in the PMDG 737 is flown in VNAV, not aproach mode. MCP altitude needs to be set at least down to mins or field level.

Be sure the VNAV mode is showing VNAV PATH, if it's VNAV SPD you are off path and it won't work correctly.

Once you are past the FAF and descending (in VNAV PATH!) you can reset the MCP altitude BUT (IMPORTANT), you must first be more than 300ft below the missed approach altitude first.

To practice, it may be best at first to just set the MCP altitude to field level and leave it there to ensure the plane doesn't level off during the approach.

Also, if the RNAV is an RNP approach, you may want to set the RNP deviation limit (PROGRESS page 4) to that shown on the RNP plate. It is usually at 4.0 by default, but the approaches are usually around 0.4.

1 hour ago, rjquick said:

Also, if the RNAV is an RNP approach, you may want to set the RNP deviation limit (PROGRESS page 4) to that shown on the RNP plate. It is usually at 4.0 by default, but the approaches are usually around 0.4.

Flying the mentioned approach in this thread, when I look at PROG page 4, the actual RNP is 0.06nm. 

2 hours ago, Fiorentoni said:

Keep in mind that the plane will want to level off at the minimum, so you have to turn the altitude selector again to 0 feet (once you decided to "continue") so the flight director keeps the vnav path.

What is more prudent is to set the MCP to DA(H) or MDA(H) approximately 2 NM before the FAF to prevent level off at platform altitude. 

When the airplane is at least 300 feet below the missed approach altitude and stabilized in VNAV PTH, set the MCP to the missed approach altitude.

No need to dial altitude down to zero, just spin the alt knob quickly.

 

I just repeated the approach, and it worked well in LNAV/VNAV mode. I had to deploy the speed brakes in order to slow down to flap 10 speed. But VNAV did a great job bringing the plane all the way down to DA(H) on a continuous descent, meeting all the altitude restrictions on the STAR as well as the approach. 

It's not the easiest approach, considering there's a 40 degree turn to the runway below 500ft. I guess it's also possible to mistake rwy 15 for rwy 19 if one is not paying attention.