toseq: there seems to be still a little confusion over the terminology because VNAV is used for two independent things. Let me try to split them so we can be certain of reading the same page. Most likely I'd be preaching to the converted, reader's patience is appreciated.
a) The LNAV+
VNAV sub-version of RNP APCH. A stand-alone type of instrument approach procedure. Different from the others in its own manner, similar as with CAT II being different from a simple CAT I approach. Procedures for RNP LNAV+VNAV which is a 3D approach type (=with vertical guidance) require specific design, need to be published as such and operator must be authorized by their CAA to fly them, with all the bells and whistles normally associated such as training for the specifics of the operation.
Maybe it is possible to call this "3D APCH (LNAV+VNAV)" for the purpose of this conversation.
Note 1: The a) above is somewhat obscured by the fact that the printed chart is normally combined for "3D APCH (LNAV+VNAV) and "2D APCH(LNAV only)", the only visible difference being the two boxes of different minima. But they are fundamentally different, just like ILS and LOC approaches that also commonly share one page.
b) The
VNAV mode of autoflight vertical guidance. If the on-board system is capable of generating a vertical profile, a mathematical glide path for the final approach, the Flight Director may be set up to follow that guidance and provide steering commands for AP / human at controls.
I'd call this VERTICAL GUIDANCE OF FMS/FD FOR FINAL APPROACH SEGMENT but it is such a mouthful. Settle for VNAV (FD mode)?
Note: This b) is a widespread technology, commonly used to fly NDB and VOR approaches for decades. We let the machine calculate the profile and follow it, whilst checking from the underlying decisive NAVAID approach chart that the altitude / distance is reasonable. Just let the clever box sort out the guesswork of target and desired vertical speed values.
These points should be visible now:
- For 3D APCH (LNAV+VNAV) the availability and use of VNAV (FD mode) is a technical pre-requisite. Many other rules apply as well.
- A 3D APCH (LNAV+VNAV) may only be flown within the published temperature envelope which actually is an integral and critical part of the procedure's design. In certain cases, only if temperature compensation feature is embedded into the internal logic of VNAV (FD mode), it may be permissible fly 3D APCH (VNAV+LNAV) below the procedure's LO TEMP limit. Or maybe not, rules do vary.
- There is no temperature envelope for 2D APCH (LNAV only), similar to VOR APCH. But cold temp corrections, the ordinary variety with ground OAT <= 0 should be applied to all minimum altitudes.
- It is entirely possible and actually desirable to fly 2D APCH (LNAV only) using the VNAV (FD mode) feature.
If I read the thread and your questions correctly:
Topic 1 (closed): Can you perform a 3D APCH (VNAV+LNAV) approach outside temp envelope? ->> NO.
Topic 2 (your last posted question): Please re-phrase.