Definitions — Page 20, Lesson 25

We're starting a new section of the book — the formal Definitions chapter. This is where Air Law stops being prose and becomes precise, legal language. Every single word in these definitions matters, because these are the exact terms that appear in regulations, in your exams, and in operational documents. Let's work through them in order. First, Crew. The definition here is very specific: a member of the flight crew, or a person carried on the flight deck who is appointed by the operator of the aircraft to give or to supervise the training, experience, practice and periodical tests as required, in respect of the flight crew or as a cabin attendant. So note — "crew" isn't just anyone on board. It's either operational flight crew, or a designated person, appointed by the operator, whose job is training or supervising the crew's training and periodic tests. That appointment by the operator is the key legal hook. Next, Critical Power-Unit(s). This is the power-unit or units whose failure gives the most adverse effect on the aircraft characteristics relative to the case under consideration. In plain terms: when you're calculating performance, you have to assume the worst engine fails at the worst possible moment. The critical power-unit is the one whose failure hurts the aircraft's performance the most for the specific situation you're analysing — take-off, climb, landing, whatever the case may be. Then Cross-country. This is a flight between the point of departure and a point of arrival, following a pre-planned route using standard navigation procedures. So it's not just any flight from A to B — it must follow a pre-planned route, and you must use standard navigation procedures. That's what distinguishes a cross-country from a local hop. Cruise Climb is an aeroplane cruising technique that results in a net increase in altitude as the aeroplane mass decreases. Think about it — as you burn fuel, the aircraft gets lighter, so it can climb while maintaining the same power setting. That gradual, continuous climb is the cruise climb technique. Cruising Level is simpler: a level maintained during a significant portion of a flight. Not a momentary altitude — a level you hold for a meaningful part of the journey. Danger Area — this is an airspace of defined dimensions within which activities dangerous to the flight of aircraft may exist at specified times. So it's a defined block of airspace, with specific dimensions, where dangerous activity might happen — but only at specified times. Outside those times, it may not be active. Now Day — and this one is precise. Day means the time from half an hour before sunrise until half an hour after sunset, both times exclusive, with sunset and sunrise determined at surface level. So the legal definition of day is wider than daylight — it starts half an hour before sunrise and ends half an hour after sunset. And note "both times exclusive" — the half-hour points themselves are not included. And it's surface level, not your altitude. Decision Height — in relation to the operation of an aircraft at an aerodrome, this is the height in a precision approach at which a missed approach must be initiated if the required visual reference to continue that approach has not been established. So on a precision approach, you descend to a specific height. At that height, you must either have the visual reference to continue, or you must initiate a missed approach. That height is the decision height. Then we have three design masses. Design Landing Mass is the maximum mass of the aircraft at which, for structural design purposes, it is assumed to be planned to land. Design Take-off Mass is the maximum mass at which the aircraft, for structural design purposes, is assumed to be planned to be at the start of the take-off run. And Design Taxiing Mass is the maximum mass of the aircraft at which the structural provision is made for load liable to occur during the use — and the excerpt cuts off there, but you get the pattern. These are structural design limits, not operational limits. They tell the manufacturer what the airframe must be built to withstand. Let me pause there — we've covered the definitions in order