Instrument Procedures - Departures — Page 159, Lesson 237

We're starting a new topic now: Instrument Procedures, specifically Departures. This is where the rubber meets the road for IFR flying — how we actually get from the runway into the en route structure. Let's dig into the published information. First, the foundation. Departure routes and SID charts — SID stands for Standard Instrument Departure — are published according to standards in Annex 11 and Annex 4 to the Chicago Convention. Annex 11 covers air traffic services, Annex 4 covers aeronautical charts. So when you see a SID plate, it's built to those international standards. Now, a key label. A departure route is labelled as RNAV — that's Area Navigation, based on VOR/DME or GPS — but only when RNAV is the primary means of navigation. If you're flying a conventional SID using raw VOR and NDB signals, it's not an RNAV SID. The label tells you what the primary navigation source is. For omni-directional departures — that's a departure where you can leave in any direction, not tied to a specific track — the restrictions are expressed as sectors. You'll see sectors to be avoided, or sectors where minimum gradients and/or minimum altitudes are specified. The purpose is to enable an aeroplane to safely overfly obstacles. So the plate is telling you: in this sector, you must maintain at least this gradient, or stay at or above this altitude, to clear the terrain and obstacles. Then we have the Minimum Sector Altitude, abbreviated MSA. This is depicted on the plate and gives the lowest safe altitude for a defined sector, based on a navigational facility, out to a range of 25 NM from the aerodrome or facility. So within that 25 nautical mile radius, divided into sectors, the MSA is the floor you can use for obstacle clearance. Let me show you a typical SID plate — Figure 7.10 shows one for Heathrow. This plate details the departures from the runways at Heathrow and specifies that the point of joining the ATS route structure is the Compton VOR, designator CPT. ATS is Air Traffic Services. So the SID takes you from the runway to the point where you join the ATS route structure — in this case, the Compton VOR. Here's a fundamental definition: all SIDs start at the DER — that's the Departure End of Runway — and end at the point of joining the ATS en route system. So the SID is the bridge between the runway and the airway system. Each route has a specific designator — for example, CPT3G. That's the Compton 3 Golf departure. In the ATC clearance for IFR flights, departure instructions will include a SID to the first airways point. The ATCO — Air Traffic Control Officer — will refer to the SID by its designator. So when you hear "cleared via CPT3G departure," that's the designator. Now, how is track guidance applied? In a normal aeroplane fully 'airways fitted' for IFR, the SID can always be complied with, because there will be a minimum of two VOR/NAV boxes and one ADF. VOR is VHF Omni-directional Range, NAV boxes are the navigation receivers, and ADF is Automatic Direction Finder, which tunes to NDBs — Non-Directional Beacons. The Compton SID specifically requires radio navigation using the LON and CPT VORs and the WOD NDB. DME — Distance Measuring Equipment — is also specified. The SID specifies DME distances to or from the facility, with radials from VORs, or QDMs for NDBs. A radial is a bearing from a VOR; a QDM is the magnetic bearing to the station for an NDB. The SID also specifies altitude restrictions in the form of "Above ....." or "At ....." — so you might be told to cross a certain point at or above a specific altitude, or at a specific altitude. Plus there's a diagram of the procedure on the plate. A narrative is always given in English. That's the textual description of the procedure, and it's always in English — that's the international standard for aviation. At the end of the SID, the aircraft should be well placed to continue en route climbing in the airway or under radar control. So the SID positions you to transition smoothly into the en route phase. One more critical point: at any time during the procedure, the pilot may be ordered to comply with radar vectoring, requiring abandonment of the SID or abbreviation of the procedure. In such cases, the pilot will be told that the aircraft is under radar control. So if ATC vectors you off the SID, they'll explicitly tell you you're under radar control — that's your cue that the SID no longer applies and you're being guided by radar. Let me show you the figures — Figure 7.10 is the typical SID plate for Heathrow, and Figure 7.9 shows the departure route structure. So to tie it together: the SID is a published, standardized departure procedure that takes you from the DER to the en route structure, using specific navigation aids, with specific altitude and track restrictions, all designed to keep you clear of obstacles and position you for the climb out. And it can always be overridden by radar vectoring if ATC needs to.