Now that we know the basic work flow model realistic payware addons are built on we should also discuss the real world method most commercial airlines and aviators in general follow when doing an actual flight.
The Shortest Distance Between Two Points Is...
We should start our discussion with the basics: The shortest distance between two points on the ground is a straight line. However, the Earth is not flat. Therefore, when flying between two points the shortest distance is an arc. An arc is a semi-circle with a radius of 180 degrees (1/2 of 360 degrees). An arc also just happens to be the basic model that managed flights are based upon. It is a physical representation of the actual climb, cruise and descent the aircraft does while performing the flight. This should come as no surprise because...
What Goes Up...
The aircraft starts out on the ground at the departure airport (the point of origin), it takes off and climbs toward the cruise altitude. Once it reaches cruise altitude (Top of Climb), it stays there for as long as needed (the majority of the flight). This can be hundreds and hundreds of miles on long trips like Transatlantic Flights. Eventually, the airplane reaches a point where it must descend (Top of Descent), so that it can eventually land at the destination airport.
...Must Come Down
After the aircraft reaches the Top of Descent, it descends from the cruise altitude and lands at the destination airport thus, completing its journey.
This arc-model flights follow has a formal name: Vertical Profile.
A vertical profile is simply a snap-snot of all of the altitudes the plane climbs and descends during the flight. Vertical profiles are very important because this is what the FMGC (Flight Management Guidance Computer) uses as its basic model to calculate the appropriate altitudes and thrust ratings (speed) the plane needs to be at to achieve and maintain those altitudes. It also takes into account the distance between the origin and destination (the way points in between) and factors this into its planning of the vertical profile to make sure it the plane is making the most efficicent use of fuel as well.
The Difference Between Real World Flight and FSX
Now that you know the basic model managed flight follows, we need to discuss how you can apply this when flying in FSX... And how real world flight operations differ from the model FSX uses.
1) Flying with ATC (Air Traffic Control)
FSX air traffic control aims to simulate the interaction real pilots and air traffic controllers would have during a managed flight. Meaning, even if you have a full route of way points in your FMC, you will somtimes be requested by ATC to deviate from your set course just as real planes are often required to do. This is because there might be incoming traffic where you need to go, and/or because they are trying to keep a safe distance between you and other aircraft in the vicinity, etc.
For example, one reason ATC might have you deviate from your flight plan is because the flight plan itself requires ATC to give you specific instructions at certain points. Those instructions might depend entirely on what is happening at that moment e.g. how much traffic is present, weather conditions, unforeseen events, etc. The most common of all reasons for ATC interaction is for final approach vectors when nearing airports to land.
After you are familiar with FSX and operating the aircraft of your choice... You will quickly find the simulated ATC has a lot to be desired, unfortunately. In fact, it is down right unusable in its current form.
The bulk of the problems come from the fact that a lot of times ATC will have you deviate too far from your original flight plan, for no apparent reason at all. Not only that, but the ATC in FSX is programmed to not give virtual pilots enough time to perform the requested maneuvers. It will keep asking you do what it instructed over and over until you do it even if there is no physical way to perform the maneuver any faster (like transtition to a specified altitude).
The major bug in the ATC that makes it unsable for commercial flight is it doesn't know how to properly line aircraft up (vector) for IFR approaches. VRF approaches are usually "on the money", but for whatever reason, IFR approaches are completely useless, or non-functioning.
The other major problem with ATC in FSX is it is very limited in its overall interaction with virtual pilots. For example, you can't declare in-flight emergencies and follow real world procedures for emergency landings and diversions to alternate airports. This lack of interaction is a problem common to all MSFS titles and it is yet to be seen if FS11 will properly address this when it is released.
Therefore, because of all these ATC problems and limitations this leaves virtual pilots with only one option...
2) Flying the Flight Plan and Vertical Profile Solo
This is the only real option virtual pilots can use in FSX, if not online. Meaning, they can simply ignore ATC (don't activate it) and fly their own vertical profiles based on the specific operating procedures certain aircraft use to climb, cruise and then descend. As stated, realistic payware aircraft have simulated FMCs that use the vertical profile to fly the plane from point A to point B, so all they have to worry about is following the instructions and procedures the FMC gives.
For instance, if you know how to operate the Boeing 747-400, you can takeoff, climb, engage the VNAV and LNAV, cruise and descend to your destination as long as you know all the procedures required to complete the flight on your own.
However, this then becomes the major difference between real world flight operations and FSX flight operations and lessens the "simulation" aspects. The absence of ATC is obviously not very realistic, but given the limitations of the default ATC that ships with FSX, not using it might become your chosen method of flight simply because of its massive shortcomings mentioned above.
I usually fly without ATC simply because I would rather learn the aircraft itself vs. how to follow ATC orders while in the air. The two things go hand in hand, but if you are learning a complex aircraft like the A320, I strongly recommend not using ATC until you know the A320 inside and out. Then, you can add the multi-tasking of not just operating the plane properly, but also following ATC instructions if you so choose.
So, I hope this entry has proven informational and interesting. Whether or not you fly with ATC, or by yourself should be secondary to acknowledging what Vertical Profiles are and their importance in the world of avation in general across all types of aircrafts and varied flight operations.
