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.
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.
The box should automatically skip the cruise phase when you activate/sequence a leg on the arrival/approach, it will then also calculate TOD without having to recruise it as it will then go to descent phase and then approach logic.
If you reach the missed approach altitude, there is no need to recruise the box as you recruised it by pressing TOGA. The only time that's required is if you get vectored off the missed, you never climb to the missed approach altitude, and then get vectored and you don't sequence the box correctly.
Setting mins to MCP does pretty much exactly the same as setting TDZE, as long as you set the missed approach altitude to your MCP after crossing FAF. VNAV will keep descending in approach logic even when MCP altitude is set to an altitude above you. The only difference in how it flies it is if you forget to set the missed approach altitude, it will then level off at mins (which is what you dont want assuming you have the runway in sight at that point).