Question about RNAV approach

[ajcbakker 0]

Dear sir/madam,

After a long period of performing ILS approaches we started recently to perform RNAV approaches with the PMDG 777. A/T, FD, LNAV and VNAV on. However we encountered some problems here. Every time when we reach the MDA the A/T will increase throttle so the descent has to be aborted because the plane does not descend anymore. We use a throttle quadrant but at that moment the levers are on idle. Surely we do something wrong but we can not figure it out at this moment. Can someone help us with this? Many thanks in advance.

Kind regards,

Alje Bakker

[ph-cxz 28]

Look at your fma. What is it saying. What does the speed say. Idle, spd or hold.

[downscc 1,327]

When you reach the MDA you should hand fly the rest of the approach.  You should not allow the A/P to take you below minimums.  Disconnect A/P and you may elect to either use or not use A/T to landing.  Boeing recommends that A/T be used when manually landing the 777.

Edited November 26, 2018 by downscc

[01A045 9]

You need to set the MCP altitude to miss approach altitude before reaching MDA. Also you should disconnect the autopilot before MDA.

[downscc 1,327]

3 hours ago, 01A045 said:

You need to set the MCP altitude to miss approach altitude before reaching MDA. Also you should disconnect the autopilot before MDA.

That works with the 737/747 with the IAN option but not in the 777 where there is no IAN.  See FCTM 5.40:  MCP should be set to DA(H) or MDA(H) before the FAF and the descent will be using VNAV PTH.  When at least 300 feet below the missed approach altitude set the MCP to the missed approach altitude.  If you don't wait until at least 300 feet below the missed approach altitude the airplane may level off.

[ajcbakker 0]

Hi guys,

Many thanks for all your responses. We will continue to perform RNAV approaches with the 777 and take into account the remarks you have made downscc. Hopefully things are going smoother and no level off anymore at DA(H) or MDA(H). At ph-cxz: our fma displays spd. We keep you posted with the results.

Kind regards,

Alje Bakker

[xkoote 57]

For RNAV Approaches in the 777;

- Set platform altitude, and make sure you are in SPD | LNAV | VNAV PTH when approaching FAF. Speed is controlled manually in the 777 in final approach

- About 2 NM prior to FAF, set the MDA on the MCP

- After leaving platform altitude on the way down, make sure to be at least 300' below the missed approach altitude, THEN set MisAp altitude in MCP

- Autopilot MAY be left on to at the lowest 200' above ground, provided that the runway itself is coded as a waypoint on the approach. This check is done during approach preparation. If not, disconnect the autopilot at MDA.

[jrw4 624]

With regard to the original post, what may be happening is that you have set the MCP altitude to the MDA and left it there after passing the FAF and  instead of changing it to the altitude required by the missed approach procedure as noted by several of the other posters. That causes the autothrottle to spool up the engines as  the a/c approaches the MDA, etc. Believe me, I made the same mistake several times before watching how it is actually done on a tutorial video.

With regard to the suggestion that these approaches be flown by hand, the FCTM states on page 5.27 that the autopilot should be used for non-ILS approaches. Of course, no one is actually watching, so go for it if you like!

 

[Gnacino 48]

What is the MDA?  What do the initials stand for ?

George Nacino

[Adrian123 1,015]

Safe level. Minimum Descent Altitude

[downscc 1,327]

5 minutes ago, Gnacino said:

What is the MDA?  What do the initials stand for ?

George Nacino

Adriana is correct, but also the MDA is your decision point.  When descending and reaching the MDA you must either 1) see the runway environment and continue to landing, or 2) execute missed approach.

[Gnacino 48]

Thanks, I always set it at radio 200.

George Nacino

 

[icaruss 18]

11 hours ago, downscc said:

Adriana is correct, but also the MDA is your decision point.  When descending and reaching the MDA you must either 1) see the runway environment and continue to landing, or 2) execute missed approach.

Not very familiar with the 777, but the MDA is not your decision point (proper name “missed approach point”) on an RNAV(GPS) with an MDA, approach with LNAV minimums.  The MAP is the end of the runway unless otherwise specified.   

That being said, if a calculated vertical path by the FMS is flown, the MDA and MAP will mostly likely be reached at the same time.  This is the easiest way of doing these type of approaches.  The approach can also be flown with any other vertical mode such as vertical speed, in such cases the aircraft will have to be leveled off at MDA, which is not your decision point.

In reality, in a non-precision straight-in approach such as this one, the VDP is really the key.  Once the VDP is reached and a landing can’t be made, seeing the runway later at the MAP leveled at MDA will not allow a stabilized approach.

And of course, LNAV/VNAV or LPV both have DA, decision altitudes

[downscc 1,327]

15 hours ago, icaruss said:

Not very familiar with the 777, but the MDA is not your decision point (proper name “missed approach point”) on an RNAV(GPS) with an MDA, approach with LNAV minimums.  The MAP is the end of the runway unless otherwise specified

You are technically correct, but if you are IMC at the MDA you should start your missed approach and not motor along at that altitude hoping to break out.  Continuing on and then suddenly getting visual and diving for the runway before running out of runway is not a safe maneuver.  To be precise, I carefully avoided using the MAP term.

I think we agree this is just a difference of splitting definitions.

Edited January 10, 2019 by downscc

[icaruss 18]

3 hours ago, downscc said:

You are technically correct, but if you are IMC at the MDA you should start your missed approach and not motor along at that altitude hoping to break out.  Continuing on and then suddenly getting visual and diving for the runway before running out of runway is not a safe maneuver.  To be precise, I carefully avoided using the MAP term.

I think we agree this is just a difference of splitting definitions.

Actually even before that, at the VDP you don’t see the runway you most definitely will be doing a go around at the MAP.

Agreed, just splitting hairs here.