Minimums Question

JeffDG

JeffDG

Touchdown! Greaser!
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JeffDG
OK...scenario for you all...

You're inbound to KDKX (Knoxville Downtown Island Airport), and you're flying the RNAV (GPS) RWY 26 approach (http://155.178.201.160/d-tpp/1308/06102R26.PDF)

Now, for whatever reason, you're not flying LPV, but you're flying it as an LNAV/VNAV approach. You reach the LNAV/VNAV DA of 1872' and have no runway environment in sight.

Can you then continue your descent to LNAV minimums (1600')? Indeed, for Category A, the visibility minimum for LNAV is lower than for LPV.
 
So, why not make the LNAV/VNAV minimums the same as the "less precise" LNAV-only minimums? Doesn't make much sense to me...
 
HighFlyingA380 said:
So, why not make the LNAV/VNAV minimums the same as the "less precise" LNAV-only minimums? Doesn't make much sense to me...
Click to expand...

That's what got me!

That's a strange set of mimimums, with the least precise having the lowest vis, and it having lower minimums than the LNAV/VNAV.
 
Each set of minimums are designed to a specification. When obstacles are close in to the runway, these kind of anomalies occur. An approach with a GS considers the dip below the DH as the missed occurs, the MDA doesn't.
 
There's a couple of towers around the airport! :D
 
HighFlyingA380 said:
So, why not make the LNAV/VNAV minimums the same as the "less precise" LNAV-only minimums? Doesn't make much sense to me...
Click to expand...

Approaches with vertical guidance use different concepts than the simple 250 feet of ROC used for NPAs. Vertically guided height minimums will typically be lower than NPA heights, but not always. Obstacle penetrations, if in a critical area, truncate DAs at that point on the approach. Not so, with NPAs.

In transport airplane operations training and FAA approved operating procedures often will not permit switching from a DA IAP to a MDA IAP inside the FAF; i.e., different flap setting, crew procedures, etc.

As to visibility being higher on DA IAPs than MDA IAPs when the DA is higher than standard, that is "TERPs 101" that every CFI-I should know.
 
Why were you flying to LNAV/VNAV in the first place? If you had WAAS, you would have flown to LPV minima. With few exceptions, there would be no reason to fly L/V minimums.
 
Definitely a lot of towers... one of my favorite airports though. If I have to make a fuel stop on the way to Nashville, I land at DKX.

KDKX.jpg


5222626730_78eba884d1_z.jpg
 
LNAV/VNAV typically have lower mins than stand alone LNAV. That is not always the case though. If the LNAV gets you lower then just shoot that. It doesn't make sense from a safety standpoint to switch approaches past the FAF.
 
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