• Destination alternate. An aerodrome to which an aircraft may proceed… — Page 16, Lesson 20

Let’s start with the destination alternate, because it’s a term you’ll use constantly in flight planning. A destination alternate is an aerodrome to which an aircraft may proceed should it become either impossible or inadvisable to land at the aerodrome of intended landing. So think of it as your backup airport at the end of the flight. If, for whatever reason, you can’t get into your planned destination — weather, runway closure, an emergency — you have a nominated alternate you can divert to. And there’s an important note here: the aerodrome from which a flight departs may also be an en route or a destination alternate aerodrome for that flight. In other words, your departure airport can double as your alternate, either for the middle of the flight or for the destination, as long as it’s suitable. Next, altitude. This is a precise definition you need to lock in. Altitude is the vertical distance of a level, a point, or an object considered as a point, measured from mean sea level. So the key here is the reference datum — mean sea level, which we abbreviate as MSL. When we say an aircraft is at an altitude of 5,000 feet, we mean 5,000 feet above mean sea level, not above the ground. That distinction matters because terrain and obstacles are also referenced to MSL, so altitude is what we use to ensure vertical separation from the ground and from other traffic. Now, two financial definitions that come straight from the regulations. The first is annual costs, in relation to the operation of an aircraft. This means the best estimate reasonably practicable at the time of a particular flight, in respect of the year commencing on the first day of January preceding the date of the flight, of the cost of keeping and maintaining, and the indirect costs of operating, the aircraft. Let me unpack that. It’s an estimate you make at the time of a specific flight, looking back at the calendar year that started on the first of January before that flight. It covers two things: the cost of keeping and maintaining the aircraft, and the indirect costs of operating it. And there are two exclusions built in. First, these costs exclude direct costs. Second, they must be costs actually and necessarily incurred without a view to profit. So we’re talking about genuine, necessary expenses, not anything speculative or profit-driven. The second financial term is annual flying hours. This is the best estimate reasonably practicable at the time of a particular flight by an aircraft, of the hours flown or to be flown by the aircraft, in respect of the year commencing on the first day of January preceding the date of the flight. So again, it’s an estimate made at the time of a specific flight, for that same calendar year starting on the first of January before the flight. But here we’re estimating the hours the aircraft has flown or will fly in that year. Notice the wording — hours flown or to be flown — so it can look backwards at hours already completed, or forwards at hours projected. Now we move into air traffic control terms. The approach control office is a unit established to provide air traffic control service to controlled flights arriving at, or departing from, one or more aerodromes. So this is the facility, the physical or organisational unit, that handles traffic coming into or leaving an aerodrome. And closely tied to it is the approach control service, which is the air traffic control service for arriving or departing controlled flights. So the office is the unit, and the service is the actual control function it provides. Both are limited to controlled flights — that’s flights operating under an air traffic control clearance. Finally, we have approach to landing. This is a defined portion of the flight. It means that portion of the flight of the aircraft, when approaching to land, in which it is descending below a height of 1,000 feet above the relevant specified decision height or minimum descent height. So once you’re on the approach and you descend below 1,000 feet above your decision height, or above your minimum descent height, you are now in the approach-to-landing phase. The decision height applies to precision approaches, where you have a glide path, and the minimum descent height applies to non-precision approaches. The moment you cross that 1,000-foot threshold above whichever one is relevant to your approach, you’ve entered this defined phase of flight. So to tie it together, we’ve got the destination alternate as your diversion option, altitude as your MSL-referenced vertical position, the two annual cost and hour estimates for regulatory purposes, the approach control office and service for terminal traffic management, and the approach-to-landing phase defined by that 1,000-foot-above-threshold descent. Each of these is a precise regulatory definition, and you’ll see them referenced throughout your flight planning and operations.