jamesgao8

Can you yse VNAV on final approach?

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Hi,

I've been doing a flight on the 777 to Sydney and on final approach I was using VNAV to manage the speed of the aircraft during approach.

For some reason, on final approach the vnav set a speed of 250-240knts. It only reduced to 170knts when I reached the LAST VOR/DME waypoint FOR THE APPROACH.

From there the VNAV refused to slow down to lets sat 14-150knts. Therefore I couldn't expend the flaps to full.

 

So this leads me thinking that do you use VNAV to manage speed during approaches?

If so can anyone explain what went wrong?

 

Thanks,

James

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I just use speed intervene at that point. That said, if you were doing an ILS approach, you should have armed approach mode as you were approaching the localizer. Once the glideslope is captured, it would take you out of VNAV, at which point you have control of your speed via the speed window.

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You would need to specify, the approach type, which runway, and the currency of your navdata to get a more specific answer.

Normally either a STAR or ATC will determine the speed, but one can always specify speeds in the FMC for waypoints. Some RNAV (GPS) approaches specify min max speeds.

Flying into YSSY, all STARS specify min/max speeds 10 NM (or a specific waypoint) out: 185-160kt and 5 NM out:160-150kt 

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24 minutes ago, pracines said:

all STARS

approaches .....

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1 hour ago, vadriver said:

approaches .....

fly..t4&..ZZ--9...….

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Someone hasn't followed the tutorial flight yet maybe? 

🙂

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On 3/6/2019 at 9:14 AM, jamesgao8 said:

For some reason, on final approach the vnav set a speed of 250-240knts. It only reduced to 170knts when I reached the LAST VOR/DME waypoint FOR THE APPROACH.

From there the VNAV refused to slow down to lets sat 14-150knts. Therefore I couldn't expend the flaps to full.

VNAV follows the speeds that are indicated on the LEGS page on the CDU. The LEGS page typically indicates 170kts for the final approach.

 

On 3/6/2019 at 9:14 AM, jamesgao8 said:

So this leads me thinking that do you use VNAV to manage speed during approaches?

If so can anyone explain what went wrong?

On RNAV approaches, "VNAV PATH" mode is used. Ensure this mode is indicated on the Primary Flight Display. Press / click the speed knob and set Vref + 5.

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Being able to manage the levels of automation available to you is a skill set that is Paramount when flying transport category airplanes. 

Hell, it is a Paramount skill set even if you are in a Cessna.

VNAV is "great" for STARs. However not so much for an ILS. Actually, it most likely is agaisnt SOPs for the same reason you made a thread about your issue.

You need to determine what type of navigation you are using for any given type of approach.

For RNAV, you could use VNAV in PATH mode as mentioned above. 

For an ILS, use APPR mode, then manually dial in the speeds you want to fly. 

Using a level of automation that is to high for an approach will get you the result your asking about. 

When I'm flying IRL, I use the least amount of automation I need for any given situation in any given flight. If the workload starts to creep up on my crew and my self, I start increasing the level of automation as necessary. 

For approaches in particular, you need to use a level of automation diminishes workload while getting the airplane to do EXACTLY what you want it to do. If you are finding that you are having to fight the automation, then it's most likely at a level that is to high for what you are wanting to do. 

At the end of the day, if the autopilot isn't doing what you want it to do, turn it off and hand fly the plane. It's as simple as that.

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11 hours ago, ahsmatt7 said:

VNAV is "great" for STARs. However not so much for an ILS. Actually, it most likely is agaisnt SOPs for the same reason you made a thread about your issue.

In the 777 VNAV isn’t that great for STARS. Unlike the 737, the 777 doesn’t decelerate as you extend flap. That leaves it late to decelerate for the approach if you do nothing about it. You need to use speed intervene to manually decelerate as you extend flaps.

 

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3 hours ago, kevinh said:

In the 777 VNAV isn’t that great for STARS. Unlike the 737, the 777 doesn’t decelerate as you extend flap. That leaves it late to decelerate for the approach if you do nothing about it. You need to use speed intervene to manually decelerate as you extend flaps.

 

True but that should not be a problem during the actual STAR portion of the approach. You should not be using flaps at all until a few miles from the transition fix to the actual approach and then only 5 ready for intercepting runway heading. 

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5 hours ago, sloppysmusic said:

True but that should not be a problem during the actual STAR portion of the approach. You should not be using flaps at all until a few miles from the transition fix to the actual approach and then only 5 ready for intercepting runway heading. 

OK, so the problem actually occurs during the transition. Being pedantic doesn't change anything in terms of what the pilot needs to do.

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2 hours ago, kevinh said:

OK, so the problem actually occurs during the transition. Being pedantic doesn't change anything in terms of what the pilot needs to do.

Sorry but I don't think I was being pedantic at all. STARS are often 100-200 miles from the approach itself and the 777 will fly them perfectly. All you have to do is SPD INTV in the last 5 mins or so of flight. 

So the statement below is not true in the slightest and misinformation which I corrected politely. VNAV will descend perfectly throughout  the STAR, taking you from cruise mach speed (.82M/500 or so GS) down to a few thousand AGL and 240kts (default settings, slower if you wish to program it differently).

Once on the approach you HAVE to extend flaps and gear manually so it's no issue at all to just lower the speed to what the markers read on the PFD. A plane WITHOUT auto throttle, now THAT would be harder work on a STAR and a fair comment.

No offense meant at all Kevin.

 

11 hours ago, kevinh said:

In the 777 VNAV isn’t that great for STARS

 

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