The way I have seen it works better with students is having them think in terms of "what for", why that button is there and why we need it.
Ask them what they are going to do when they fly the airplane into the approach plate.
Make them realize, through their own thinking, that you need the airplane to bank angle 25 degrees in order to remain in the protection areas of the approach, or the holding, and you need to bank while maintaining the minimum legal margin over the stall speeds (you may introduce the definition of Characteristic Speeds here).
Let them reach the conclusion that the legal margin over the Vapp speed is much lower (when you land you need to be able to stop the airplane on a finite runway) than over the maneuvering speeds (you just need the airplane to sustain some load factor, nothing more), that is why they'll see different margins over Vls in each flaps configuration.
And then, and this part is tricky, give them the chance to understand that, while the angle of attack at each one of those speeds happen (maneuvering and Vapp) is the same, the IAS at which it happens will depend on the WEIGHT. And such, instead of having to recalculate each set of speeds in flight (let's say, when you are in the holding, waiting to start the approach, your set of speeds while get lower with each ton of fuel you burn), you can just activate the Approach Phase in the the PERF PAGE, and voila, the FMGC just gave you the set of speeds you need to fly, to maneuver the airplane through the approach chart, it will calculate them for you, accurate to your actual GW, and with a Vapp that follows the weight of the airplane when it lands, following the FOB predicted.
So, the answer is - and I have found that they understand this term better - the Approach Phase is a energy managing tool that will allow you to get the set of speeds you need to 1) fly the airplane through the approach plate and 2) land the airplane on the runway, by giving an instant calculation of those speeds following the GW at the moment of activating it.
Many FO's I fly with now activate the Approach Phase as soon as ATC gives a speed reduction, because the associate it with "reducing speed for the approach", showing that they haven't been explained what is the internal process of the FMGC.
As an epilogue, you can also explain them that, depending on the FMGC version, MSN, etc... some airplanes with calculate the set of characteristic speeds as a figure from the expected GW (following the EFOB at the time of the approach), while other airplanes will calculate the value of such speeds with date from the FAC, that is, the value of the speeds will constantly be changing when the fuel burns and the GW gets lower. But despite this, they should always follow the same procedure: let the Approach Phase autoactivate, or activate it manually when you start your approach, but not earlier, to make sure your characteristic speed are as accurate as possible.
It doesn't reduce speed to GD or Vapp, looking at it from that point of view makes it more confusing, me thinks.
Last edited by iggy; 28th Mar 2024 at 08:06.