Originally Posted by
Adlerdriver
Fair enough, JB. I can understand the "sim-ism" of having to re-cruise the box in certain circumstances. However, it's also a potential real-world task in the event of a MAP and re-attempt at another approach requiring VNAV. So, a clear understanding of the, why, when and how is required, regardless of the more common times it might be required in a training sim.
Absolutely, I agree.
Originally Posted by
Adlerdriver
I've flown a lot of non-precision approaches using VNAV and not once have I "protected" the FAF using the MCP in the last 15 years, at least. That was back in dive and drive days. Now FAF is protected by a large font altitude restriction in the FMS. In the "old days" we set mins in the MCP. Now, once cleared, established on the approach and protected by such large font FMS entries, the MCP is rolled down to TDZE rounded up. That allows a VNAV descent to mins that are treated like a DA, not an MDA. I can't imagine a modern 121 airline is currently teaching to protect the FAF using the MCP. But, maybe I'm wrong.
There are operators who do this. They may require protection of an intermediate fix on the MCP until the fix is passed, then the FAF, and then approaching the FAF, insertion of minimums in the MCP, until inside the FAF and below the missed altitude, when it's set in preparation for the missed. Such would be an individual company technique. One should be able to fly the procedure using only the altitudes in the box once on VNAV Path, but there are operators who insist on stepping it down in the MCP, too. Likewise a STAR, with resetting the MCP at each crossing. Obviously the potential to mismanage or get behind/distracted, and get in an offpath situation exists, such as winding up in VNAV SPD, and high, or low. VNAV, in any case, does seem to be one of the more misunderstood subjects.
With regard to resetting the MCP to minimums rounded-up, there are also operators that set the next lowest even altitude below minimum, in the MCP (rounded down). It would certainly be important with such a technique, to understand what is being done, and why.