RNAV approaches

[Richard McDonald Woods 168]

I am ashamed to say that I have never attempted an RNAV approach.

Without being able to tune nav radios, I feel that I am failing to understand important flying practices. Searching online, so far, has not produced any solution for me.

Can anyone tell me what I need to do to make a successful RNAV approach?

Hints are most welcome.

[Paul_Smith 92]

I am sure someone will correct me if I am wrong, but doesn't the 737 tutorial flight use an RNAV approach?

[gregmorin 199]

Richard

1. Research the available RNAV approaches at the airport you wish to fly the approach.

2. Select either an approach relative to the runway wind or one that you wish to try if you are using a calm wind situation.

3. Program a local flight into the FMC. I suggest you plan direct to the transition fix then load the approach. Use the transition altitude as the flight altitude.

4. Program the auto pilot for departure.

5. Select LNAV and VNAV upon engaging the auto pilot on climb out.

6. I would suggest that you let the 737 fly the approach the first couple of times so you can see how the indicators perform on the PFD.

7. to hand fly the approach simply follow the indications on the PFD as you would for an ILS approach.

I think you will be very impressed with what can be done with a RNAV approach, especially in mountainous conditions. I suggest the RNAV (RNP) Z Rwy 08 at LOWI as being spectacular. Use XEBIX as the transition fix. The RNAV (RNP) Y Rwy 05 or Rway 23 at NZQN as also very impressive. Like everything in the sim; we can learn from trial and error.

Have fun,

Greg

 

[Budbud 227]

Hello Richard,

In addition to the info above, the 737 is equipped with a nav function that simulates a pseudo-ILS but based on the GNSS instead of a ground based guidance system.

When you are close to intercept the inbound course to the runway, you can arm the APP mode. On the FMA, FAC and GP will be displayed in white when it is armed. This mode will allow you to fly the rnav approach very much like an ILS.

[kevinh 409]

Hi Richard,

I would learn the basic RNAV approach technique first before using 737’s IAN system to help you. The 747 and 777 can both perform RNAV approaches too, though don’t have IAN, unlike the 737.

Essentially an RNAV approach uses VNAV and LNAV to control the final approach path. The FMC will show what that vertical path angle from the approach fix is on the legs page. It should be close to 3 deg.

Energy management is important. You need to make sure that the AP is in VNAV PATH as you descend and decelerate. If VNAV is controlling speed it won’t follow the glidepath to the runway.

As in all things practice makes perfect.

[downscc 1,327]

5 hours ago, Richard McDonald Woods said:

Can anyone tell me what I need to do to make a successful RNAV approach?

There is a wealth of information in the NGX FCTM on how to fly a non-ILS approach, including RNP using LNAV/VNAV beginning on page 5.42.  I suggest it  is required reading for students of this aircraft, and a good review for weathered veterans.

(I tend to avoid RNAV approaches in the 777 because it lacks IAN, and the 747 because it is not qualified for RNP0.5 ((to my knowledge)), so basically my focus for RNAV approaches in restricted to the NGX, which unfortunately cannot do RNP0.30 (RNP0.50 only).

Edited February 23, 2018 by downscc

[Richard McDonald Woods 168]

Dan has suggested that my 777 should not attempt to use RNAV approaches. I do not know what 'IAN' stands for as I am not a 737 flyer. Thanks, Dan.

So, apart from avoiding RNAV approaches, I now have the problem of having no ILS on rwy 34 at YMML. I had to land on the shorter rwy 27 with ILS. If ATC had been staffed at the time, presumably they should know of the 777 restriction, or I could 'unable' instructions to use rwy 34?

In the real world, is the RNAV restriction applicable, or is it just the PMDG implementation?

Thanks for your replies so far.

[Driverab330 74]

7 hours ago, Richard McDonald Woods said:

I am ashamed to say that I have never attempted an RNAV approach.

Without being able to tune nav radios, I feel that I am failing to understand important flying practices. Searching online, so far, has not produced any solution for me.

Can anyone tell me what I need to do to make a successful RNAV approach?

Hints are most welcome.

 

What you need is an onboard GPS and position monitoring system. And during the approach make sure there is no NAV UNABLE RNP, POSITION DISAGREE MSGS. 

Other than that you just need to trust the system and manage your speed in accordance to the approach chart.

Most importantly, only select the RNP (RNAV) approach from the FMC database. 

 

 I recommend reading the FCOM3 which has a very detailed MCP altitude setting procedure involving all the non precision approaches using VNAV.

 

The only problem in real life is that the VNAV PATH assume ISA temp deviation, therefore will resulted in steeper descent path in a hot day and a shallower descent path in a cold day. Thats why there is a temp limit to all the RNP (RNAV) approaches to ensure terrain clearance in a cold day with a shallower descent path. And to some places like dubai, to ensure the descent angle in a hot day does not exceed aircraft limit. 

 

I agree with all the comments above, it is easier to understand how RNP approaches works with IAN because it works like an ILS at the beginning. IAN approach is the equivalent of the FINAL APP mode on the Airbus where the airplane follows the LNAV VNAV PATH as if it is flying an ILS app. like Airbus, once FINAL APP is engaged, one may set Miss Approach Altitude straight away. (See the airbus video below and see how FINAL APP work which has pretty much the same logic as IAN)

 

Since the 777 does not have IAN, there is a complicated MCP altitude setting procedure to follow. 

 

The way I see it, it is no different to doing an VOR approaches on the 777, just keep everything in LNAV and VNAV PATH, and disconnect the AP when you can see the rwy. The only thing is there is no ground nav aid for you to reference to on the RNP approach. 

 

 

https://www.youtube.com/watch?v=6r7QsQ6WHbA

 

 

I found two youtube video which may help understanding the theory and actual practical application behind the RNP approaches (RNAV approaches). 

 

https://www.icao.int/MID/Documents/2016/PBN SG2/2.PBN Charting - ICAO.pdf

also the ICAO recommendation is to rename all RNAV (GPS / GNSS) app to RNP approach and what we used to called RNAV (RNP) APP into RNP (AR) APP which AR stands for Authroization Required. 

 

Edited February 23, 2018 by Driverab330

[Budbud 227]

Hi Richard, 

The T777 can fly RNAV approaches (both GPS and RNP) with no issues both PMDG's and the real beast. What Dan says in he post above is just that since the T7 doesn't have the IAN feature, he prefers not doing RNAV approaches but it is a personally taste. I flew some RNAV approaches with the PMDG's just fine.
 

IAN stands for Integrated Approach Navigation. You can find some info on internet about it like here:

http://www.boeing.com/commercial/aeromagazine/aero_22/737approach_story.html

Basically, it is a system that gives you a ILS like guidance (FAC replaces LOC and GP replaces GS) when there is no ILS. It is a GNSS based system. But it is irrelevant for the T7.
Sorry for the confusion I made bringing it into the discussion. For some reasons, I don't know why I assumed that you were talking about the 737 but you actually didn't specify the aircraft in your initial post.

 

Edited February 23, 2018 by Budbud

[Mike777 163]

8 minutes ago, Driverab330 said:

The only problem in real life is that the VNAV PATH assume ISA temp deviation, therefore will resulted in steeper descent path in a hot day and a shallower descent path in a cold day. Thats why there is a temp limit to all the RNP (RNAV) approaches to ensure terrain clearance in a cold day with a shallower descent path. And to some places like dubai, to ensure the descent angle in a hot day does not exceed aircraft limit. 

Richard, this is a very interesting thread you started!  I've flown such approaches, and there has been some discussion about them elsewhere on this forum.  One thing I learned is don't tune, or at least don't follow, the ILS, as the horizontal and vertical paths can be different -- for example at KSFO 28R.

Wing Lai (or someone else),  I wonder if you would explain in greater detail why temperature affects the vertical path?  Also, is this simulated (or simulatable, if there is such a word)  in FSX or P3D?  Finally, couldn't one compensate for an incorrect vertical descent path by using the radio altimeter and checking at each waypoint?

Thanks,

Mike

[scandinavian13 5,192]

Gents,

Based on this Richard's response, I'd ask that you all be careful in properly wording responses, as it seems as if some misinformation has been put out there, which has confused Richard (and potentially others who pass through this thread). If you don't fully understand RNAV, please be careful to note that, so that people don't assume you are speaking from a position of authority/knowledge.

Again, please be extremely careful when sharing knowledge, or, if you are not particularly knowledgeable (or are sharing an opinion or preference), please make that abundantly clear.

RNAV is actually incredibly simple - just like ILS.

Basic RNAV approaches are simply GPS-driven approaches. Anything with LNAV can fly a basic RNAV approach.
RNAV Auth Required is basically the ILS CAT III of ILS.

-----

Richard,

No. You should not avoid RNAV approaches in the 777. I can fly basic RNAV approaches all day in a GPS-equipped Cessna Trashhawk if I wanted to. The only procedures that you cannot fly in the 777 (our version, since we don't have the proper nav format for RTF) are those with radius-to-fix (curved) legs, often with the special verbiage "AUTHORIZATION REQUIRED" written on them. This isn't always the case, but it is common (FAA).

As for YMML, the RNAV 34 approach is the most basic RNAV approach out there: LNAV and LNAV/VNAV. You can fly that in a 172 (you can even fly the LNAV/VNAV mins if your GPS has vertical guidance on it).

Keep in mind that an approach is only necessary when the airport is IFR, too. The huge simmerism that instrument approaches are flown all the time is a massive misconception, particularly in the States.

[Mike777 163]

4 minutes ago, scandinavian13 said:

Basic RNAV approaches are simply GPS-driven approaches. Anything with LNAV can fly a basic RNAV approach.

So if you only have horizontal GPS guidance you simply rely on your altimeter at each waypoint?

Mike

[scandinavian13 5,192]

2 minutes ago, Mike777 said:

So if you only have horizontal GPS guidance you simply rely on your altimeter at each waypoint?

Yep. Note the verbiage in the mins section for an LNAV approach. DA or DH? Why?

[cagrikartal 8]

7 hours ago, Richard McDonald Woods said:

I am ashamed to say that I have never attempted an RNAV approach.

Without being able to tune nav radios, I feel that I am failing to understand important flying practices. Searching online, so far, has not produced any solution for me.

Can anyone tell me what I need to do to make a successful RNAV approach?

Hints are most welcome.

Hello

in glass cockpit aircraft with 3 IRS cuppled with GNSS it is too pricise to live these kind of approaches. All you will do is to fallow the magenta line and check your alt points. How aver if you can get an analogue cockpit aircraft (without EFIS) with a RMI and CDI or HSI so that you will have to chase needles for alignement and direction rather than a a line on navigation display. But since we are talking about state of the art pmdg aircrafts, you can use nd with full vor ils mode without entering the whole approach on fms and fly it by the plates. This is how you learn the basics.

Good luck and enjoy 

[Driverab330 74]

51 minutes ago, Mike777 said:

Richard, this is a very interesting thread you started!  I've flown such approaches, and there has been some discussion about them elsewhere on this forum.  One thing I learned is don't tune, or at least don't follow, the ILS, as the horizontal and vertical paths can be different -- for example at KSFO 28R.

Wing Lai (or someone else),  I wonder if you would explain in greater detail why temperature affects the vertical path?  Also, is this simulated (or simulatable, if there is such a word)  in FSX or P3D?  Finally, couldn't one compensate for an incorrect vertical descent path by using the radio altimeter and checking at each waypoint?

Thanks,

Mike

The first part of Second Video I posted explained why temperature has an effect on VNAV PATH. 

 

Basically the 777 VNAV system uses something called Baro-VNAV. The FMC computes a path from a point 50ft over the runway waypoint (which is the threshold) backwards to the FAF assuming the ISA weather condition (15 deg C on the ground with a standard lapse rate), and VNAV solely depends on the altimeter reading. (unlike the G/S of and ILS which defined a fix geographical path independent of the altitmeter, hence it is called a precision approach)  

 

in on a cold day, the air is more dense, and the altimeter reading is pressure sensitive so 100ft change in altimeter reading only results in let say 80ft of change in real (True) altitude. And the opposite applies in a hot day. 

 

Therefore in real life, for the same approach let say the RNP Z 07R appr into HKG which we normally do during early morning arrival, it is very common to see 3 whites on the PAPI when visual when the temp is 25c or above. 

 

Put it simply, just fly it like any other non precision approaches using LNAV VNAV PATH, I think it is good enough as a normal simmer. 

 

To be able to qualify as a pilot to do the RNP / RNP AR APPR requires at least one simulator exercise and one simulator check as part of our bi-annual proficiency check. And before that a self-study PowerPoint package which takes about 3 hours to complete. 

 

It is is never an easy topic to be able to explain with one to two hundreds words here in a forum. 

 

I am sure those who have flown the 777 RNP approach in various airports around the world real life, RNP AR APPR is not as accurately as it “depicts” on the charts becuase it is still largely subjected to a temperature issue which requires quite a bit of correction at minima, and it is also very common to see the airplane not quite line up the rwy as well. 

 

I have yet to try the RNP AR APPR WITH LPV minima on the A350. I Will definitely see how it work in about 1 year time. 

 

 

 

 

 

 

 

 

 

Edited February 23, 2018 by Driverab330