Instrument Procedures - Departures — Page 152, Lesson 227

Let’s start with the big picture, because this chapter is about why instrument procedures exist at all. The whole point is to permit all-weather operation — that means low-visibility take-off and landing. To make that safe, we have to establish procedures that give two things for departing aircraft: track guidance and terrain avoidance. For arriving aircraft, we need track guidance, terrain clearance, and — where special equipment is used — vertical displacement guidance. Now, a key definition. Low visibility operations, as ICAO defines them, are take-off and landing operations with RVR less than 800 metres. RVR is Runway Visual Range — the distance over which a pilot can see the runway surface markings or lights. So below 800 metres RVR, we’re officially in low-visibility territory. But here’s a separate, important rule to remember: the minima for take-off from an aerodrome in a CTR — that’s a Control Zone — is ground visibility not less than 5 kilometres, and cloud ceiling not less than 1500 feet. So even though low-visibility operations kick in below 800 metres RVR, the take-off minima in a CTR are set by ground visibility and ceiling. The criteria for which type of procedure to use are defined in terms of RVR and the limit to which a pilot is permitted to descend — that’s DA/H or MDA/H. DA/H is Decision Altitude or Decision Height; MDA/H is Minimum Descent Altitude or Minimum Descent Height. These are the altitudes or heights below which you may not descend without the required visual reference. Now, the fundamental assumption underpinning all of this: an instrument procedure — whether departure or arrival — will only be flown in conditions less than VMC. VMC is Visual Meteorological Conditions. So if you’re flying an instrument procedure, you’re in IMC — Instrument Meteorological Conditions — and that means you’re flying under IFR, Instrument Flight Rules, and therefore subject to ATC, Air Traffic Control. That leads to a critical operational point: prior to commencing any instrument procedure, you must obtain an ATC clearance. No clearance, no procedure. Now, procedures for departure and arrival are published, and you are required to have the necessary plates available on the flight deck. Plates are the printed representations of the procedures — the charts. But here’s the contingency: if ATC requires you to divert to an aerodrome you’re not familiar with and you don’t have the plates, ATC will read the procedure to you — including the loss of communications procedure and the missed approach procedure. So you’re never left without the information. Now let’s move to the abbreviations, because these are required knowledge. I’ll go through them systematically. C/L — Centre Line. That’s the runway centre line. MSA — Minimum Sector Altitude. This is the lowest altitude that provides terrain clearance within a sector around a navigation aid. DA/H — Decision Altitude or Decision Height. The altitude or height at which a missed approach must be initiated if the required visual reference hasn’t been established. NOZ — Normal Operating Zone. This is part of the obstacle clearance concept for ILS approaches — the area where the aircraft is expected to operate normally. DER — Departure End of Runway. The far end of the runway from which you depart. NTZ — No Transgression Zone. The area between the localizer and the glideslope where aircraft must not enter — it separates the normal operating zones. DME — Distance Measuring Equipment. A radio navigation aid that gives you slant range distance from the beacon. OIS — Obstacle Identification Surface. A surface used in obstacle clearance assessment for departure procedures. DR — Dead Reckoning. Navigation by calculating position from a known starting point, heading, speed, and time. PDG — Procedure Design Gradient. The minimum climb gradient required for a departure procedure to clear obstacles. FAF — Final Approach Fix. The fix from which the final approach segment begins. RTR — Radar Termination Range. The range at which radar service terminates. FAP — Final Approach Point. The point where the final approach segment begins, typically for non-precision approaches. SDF — Step Down Fix. A fix that allows you to descend in steps during an approach. FAT — Final Approach Track. The track flown on the final approach. SID — Standard Instrument Departure. The published departure procedure. IAF — Initial Approach Fix. The fix where the initial approach segment begins. STAR — Standard Arrival Route. The published arrival procedure. IF — Intermediate Fix. The fix between the initial and final approach segments. TAA — Terminal Approach Altitude. The altitude for the terminal area around the aerodrome. LHA — Lowest Holding Altitude. The minimum altitude at which you can hold. TP — Turning Point. A point where the aircraft changes heading. MAPt — Missed Approach Point. The point at which a missed approach must be initiated. VM(C) — Visual Manoeuvring Circling. The circling manoeuvre performed visually. MDA/H — Minimum Descent Altitude or Height. The lowest altitude or height for a non-precision approach. VM(C)A — Visual Manoeuvring Circling Area. The area within which the circling manoeuvre is conducted. Now, let me tie this together. The reason we have all these abbreviations is that instrument procedures are built around them. When you look at a departure plate, you’ll see the DER, the PDG, the SID, the MSA, and so on. Each one plays a role in ensuring you have track guidance and terrain avoidance. Let me also highlight the contrast between the two sets of minima we discussed. Low-visibility operations are defined by RVR below 800 metres. But take-off minima in a CTR are ground visibility not less than 5 km and ceiling not less than 1500 feet. These are different criteria for different phases — one for the overall operation, one specifically for take-off in a control zone. And remember the fundamental assumption: instrument procedures are only flown in less than VMC. That’s why ATC clearance is mandatory before you start any instrument procedure. And that’s why you must have the plates on the flight deck — or, if you don’t, ATC will read the procedure to you, including loss of comms and missed approach. So, to summarise the flow: all-weather operation requires procedures for track guidance and terrain avoidance on departure, and track guidance, terrain clearance, and vertical displacement guidance on arrival. The criteria are defined by RVR and DA/H or MDA/H. Obstacle avoidance is paramount. You fly these procedures under IFR, subject to ATC, with a clearance, and with the plates available. That’s the foundation. Now, when we move into the actual departure procedures themselves, we’ll build on these definitions — the DER, the PDG, the SID, and how the obstacle clearance surfaces work. But for now, make sure you’re comfortable with every one of those abbreviations, because they’re the vocabulary of the entire chapter.