LNAV/VNAV minimums setting

[Green Banana]

At Alaska,............Even a Cave Man Could Do It!!!

Baja.

And they do, have you seen some of the crusties in ANC?

 

[Whine Lover]

"My God!! Even w/ a fresh cup of coffee that gave me a head ache. I feel for all of you ATA guys. That POI should be shot."

Agreed.

But it wasn't all that bad...At ATA the "procedures" changed almost bi-weekly and were never really etched in stone, so as long as you did at least something that had been taught in the last 2-3 years you were good to go.

Seriously.

It was a fun place....Can't figure out why they went out of business.


YKMKR

 

[Toobdrvr]

In the Airbus (F9), when you get "Final Approach" FMA, we set missed approach alt. DH is in the FMS and the A/P disconnects when you reach DH...

I Think...

 

[boman]

Just on the 737. The 777 I know you set field elev, and the 756 I think is the same. Some software limitation on the 'ultra modern' 737.

Thanks for the correction.

That Guppy has all kinds of limitations and half measures... I am looking forward to the switchover to speed/alt. tapes instead of the electronic representation of the round dial. Its sure to happen soon.

Cheers

 

[BlueandWhite]

At ATA on the B737, when we were setting up these approaches, we'd leave the FMS alone, as it would take us to the runway. The MCP would be set to the nearest increment above MDA. That would usually be a little be higher than the MDA, next 100' above. No big deal, you could set it to the field once you have visual, or you could bump the yoke and it would continue. Then, our POI made the "brilliant" observation the if you hit TOGA on path, at MDA, the airplane would still descend below MDA while executing the miss. So his solution was to set the MCP up to 140' above MDA. Here's how it worked: you set the MCP to the next highest altitude increment above MDA as determined by the FMS. If this resulted in less than 50' increase, we set it another 100'. This was a royal pain in the a$$. Really FUBAR. When you reached (captured, but not hold) your MCP MDA the NFP would then spin up the MAA. The FP would "bump" the yoke to continue the descent, on path, to the published MDA. If you "timed" it right, you'd stay on path. Like I said, really screwed up. All that magic only to be trick-f@cked at the most crucial point.

Assuming we're still talking LNAV/VNAV, I don't think this POI had any idea what LNAV/VNAV was. The LNAV/VNAV uses a DA, just like an ILS DA/DH. It is the point along the descent path where the missed approach begins. If you commence the missed approach and hit TOGA at the DA, you are guaranteed obstacle clearance, even if the aircraft dips below the DA on a missed approach. DA is not a "minimum altitude". MDA is for LNAV-only approaches, and will not guarantee obstacle clearance if you descend below.

Setting MCP to TDZE or missed approach altitude will vary depending on company, aircraft or avionics software load, but it should not normally be set at or near the DA. That will cause most aircraft to start to level off prior to reaching the DA. If that happens, you have no way of determining where your missed approach point is.

I personally like the "dial to the dirt" for the MCP, and reset as part of the go-around/MAP flow.

 

[ableone]

The ATA POI is not the only one and he is not necessarily incorrect.

If you are flying an RNAV approach you may have an MDA or a DA. If you have Baro V-nav capability (LNAV/VNAV on the plate) you may have a DH. If so you can descend below DH on the missed. If, however, you are using just LNAV minimums or the LNAV/VNAV has an MDA you can not descend below MDA.

(If an airline ever installs WAAS then they will be able to use LNAV/VNAV minimums without the temp and baro restrictions and will also be able to use the LPV minimums.)

At USAirways if you are flying an RNAV approach with an MDA something called a DDA or Derived Decision Altitude is used. This is MDA+50ft. This ensures that the aircraft does not descend below MDA on the missed.

On the bus the MA altitude is selected and the autopilot will indeed disconnect at whatever altitude is inputed into the DH prompt.

(The plates airlines use may depict DH for LNAV/VNAV minimums but you may have to treat it as an MDA depending upon your ops specs. The LNAV/VNAV DH was designed for WAAS GPS equipped aircraft but most airlines meet the LNAV/VNAV equipment requirements through their FMS systems [Baro V Nav] and are not necessarily legal for the DH)

 

[wahoo250]

Unfortunately our ops specs dont have a defined procedure, but the QRH does and its TDZE. Had to dig for it but its there. Ive flown at a few different companies 91 and one 121 company and everyone does it differently. i dont really see a difference between airport elevation and 0000. Either way if you dont touch anything your flying into the ground. The only benefit to TDZE I see is on a missed in say Denver you dont have to twist your wrist as much dialing in a missed approach altitude when executing a missed approach...

 

[Dogwood]

If you set missed aproach altitude and arm vnav, you will never get the airplane to decend to the DH...at least in the GV. I think you guys have the updated software that allows you to set a dh and still set a missed approach altitude...like an ILS. I was told it was an FAR to set DH. I didnt think it was and have been trying to find it... Im guessing the parameters that you are speaking of are the FMS going to aproach mode once near the FAF...thanks for the replies

This question will vary by aircraft and airline. We refer to the VNAV approaches as RNAVs, and we fly them just like an ILS. Load it in the box, clean it up, get vectors, and push the APP button when cleared. When it indicates FINAL APP, meaning it's ready to capture the database driven glidepath, we then set the Missed App Altitude.

 

[Pilot Knob]

Nav and Prof to the LNAV or LNAV/VNAV minimums, whichever is lower. They are set in BARO rounded up to the nearest 10 feet(1895=1900, FMS precludes anything other than 10's) Runway in sight,disconnect autopilot and set vert speed to 800 ft./min. descent and preset M.A. altitude. Missed is made as soon as "Hold" is shown in the FMA and runway is not in sight. LPV's are not authorized. All of this assumes the approach is in the database. No building your own using the fixes and altitudes.

 

[mach none]

My God!! Even w/ a fresh cup of coffee that gave me a head ache. I feel for all of you ATA guys. That POI should be shot.

At Alaska: On a published part of the appch, at or past IAF, LNAV/VNAV Path, Dial the dirt and watch the magic.

That Easy - Even a Cave Man Could Do It!!!

Baja.

A cave man or someone from the -200 in ANC.