What's A Diverse Departure
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IFR DEPARTURES—RULES AND PROCEDURESIFR DEPARTURES—RULES AND PROCEDURES Departure Obstacle and Terrain ClearanceIFR departure procedures can be ground into two broad categories—procedures that are specified and procedures that are unspecified. Unspecified Departure ProceduresIncluded in the category of airports with unspecified IFR departure procedures are departures from airports not listed in the Canada Air Pilot or the Jeppesen Airways Manual. It is quite legal to make an IFR departure from these so-called “VFR” airports, but there are no specified IFR departure procedures to follow. Conversely, there are also airports that appear in CAP/JEP with published instrument approach procedures, but which have not been assessed with respect to IFR departures—i.e., obstacle and terrain clearance required.
Obstacle Departure Procedure
The IFR departure procedure for these airports is published as “not assessed.” “Not assessed” airports are becoming more and more rare.Where IFR departure procedures are unspecified, it is the pilot’s sole responsibility to ensure terrain and obstacle clearance. Specified Departure ProceduresAirports with specified IFR departure procedures, in contrast, are grouped on the basis of whether or not terrain and obstacles in the vicinity of the airport requires special restriction. Essentially, the airport is assessed as to whether or not terrain and obstacles meet what is described as the minimum climb gradient for IFR aircraft. The assumptions used to assess the minimum climb gradient are as follows:After take-off, an IFR aircraft will.
cross the departure end of a runway by at least 35’;. climb straight ahead to 400’ AAE prior to commending any turns; and. maintain a climb gradient of at least 200’ per NM throughout the climb to a minimum IFR altitude for en route operations.In conjunction with the minimum climb gradient of 200’/NM, obstacles and terrain around the airport are assessed as to whether or not they penetrate specified slope or plane that is projected in all quadrants around the airport. The slope, which appears as an inverted cone, is based 35’ above the departure end of the runway, and subsequently extends upward at a rate of 152’ per 1 NM. If this slope is not penetrated by vicinity obstacles or terrain, Transport Canada will not publish special departure procedures in CAP, and the departure procedure is simply identified on the basis of the standard IFR visibility requirement— ½ SM. By comparison, if this slope is penetrated, Transport Canada will publish specified IFR departure procedure designed to avoid the obstacles or terrain. The specified procedures are identified in CAP by the appearance of an asterisk—.—which refers the pilot to the text description of the procedure.½The departure procedure does not present any abnormal or unusual hazards.
If the departing aircraft conforms to standard performance criteria, a departure can be conducted with ½ SM. The aircraft may safely turn in any direction after climbing straight-out to 400’ AAE, provided the minimum climb gradient of 200’/NM is maintained to vicinity MEAs.The departure procedure does present potentially abnormal or unusual hazards. To ensure safe terrain and obstacle clearance for an IFR departure, specified procedures—indicated by the asterisk—must be adhered to.NOT ASSESSEDAs implied, the departure requirements for the airport have not been assessed. The pilot is solely responsible to ensure safe separation from terrain and obstaclesInformation pertaining to an airport’s IFR Departure Procedure is found on the Aerodrome Chart page, and in particular the box that appears in the lower left-hand corner marked Takeoff Minima.Appearing in the Takeoff Minima box, the published IFR Departure Procedure will therefore take one of three forms, summarised above. Unrestricted IFR Departures (½)The “½” depiction means “ takeoff, climb on course” for the specified runway or runways.
This is the case, for example, with respect to an IFR departure from any of the runways that appear at Fort St. John Airport—see the Takeoff Minima box in the lower left-hand corner. It is implied, therefore, that the terrain surrounding Fort St. John Airport presents less terrain and obstacle hazards then, for example, an IFR departure from an airport located in a mountainous area. Specifically, based on the ½ depiction that is published for Fort St.
John, we can assume that no obstacles penetrate the reference slope or plane extending upward in all quadrants at a rate of 152’ per nautical mile. The bottom of this “inverted cone” is based 35’ above the departure end of the runway. Since all of the runways are rated as simply “½” we know that this clearance requirement is met for all for runway departure ends that appear at this airport. Restricted IFR Departures (.)The appearance of the asterisk for a specified runway implies that reference must be made to required published procedures to ensure obstacle and terrain clearance, which may include specified climb gradients, routings, and/or visual climb requirements. An example of this is the specified departure procedures for Prince George.Examining the departure procedures you will note two types. First there are those runways where the minimum ½ SM visibility is specified, but for which prescribed routing must be followed—this is the case, for example, with respect to the departures from Rwys 15, 33, and 06.
In contrast, the departure from Rwy 24 requires not ½ SM, but specified visibility—SPEC VIS— to a specified altitude—in this case, 2700’ ASL. In the case of the ½ SM departures, only visibility governs, and cloud ceiling has nothing to do with it. In the case of the SPEC VIS departure from Rwy 24, however, both visibility and cloud ceiling govern.In the case of ceiling that is required, this of course will vary with each specified departure. In the case of visibility, however, we must return to the prescribed aircraft category based on manoeuvring speed:Remember that the manoeuvring speed specified here does not relate to Va, but instead relates in this case to the planned speed the pilot will manoeuvre the aircraft during the departure phase of flight. Based on the speed category, the Specified Takeoff Minimum Visibility (SPEC VIS) is prescribed as follows:Accordingly, an IFR departure off Rwy 24 requires in the case of Category B aircraft—aircraft with a departure manoeuvring speed of between 91 and 120 KTS—a reported surface visibility of 1½ SM. In contrast, Rwys 15 and 33 are less restrictive to IFR departures, requiring only ½ SM.
Note that IFR departures are not mentioned with respect to Rwys 19, 01, and 06. Departures off these runways will not be authorised for IFR aircraft; instead, the aircraft would have to depart VFR with the intention of activating an IFR clearance once in the air.The Prince George departure procedures are somewhat unusual as normally the appearance of a SPEC VIS component is provided as an alternative to ½ SM departures with higher than normal climb gradient.
Thus, aircraft that cannot meet the required higher climb gradient or gradients can choose the SPEC VIS alternative. It is important to remember, however, the minimum IFR climb gradient of 200’/NM still apply to SPEC VIS departures after cloud has been entered (the prescribed altitude to which a visual climb is specified).More commonly, the SPEC VIS departures are provided as an alternative to the ½ SM departures that have higher than normal climb gradients. This is the case, for example, with the departures that are published for Cranbrook Airport, as depicted below.All of the departure options from Cranbrook have specified routings, owing to the imposing height of surrounding terrain.
Pilots are nevertheless given two options.The first option to take the ½ SM departures. Careful consideration must be given to the climb gradient capabilities of the aircraft and whether those published can be sustained to the en route MEAs. A Category A or B aircraft requires only 270’ per NM climb to depart off Runway 16, but to depart off Runway 34 will require a more demanding 420’/NM. The advantage of these departures is that consideration must only be given to visibility, which is the governing factor—only ½ SM ground visibility on departure is required, irrespective of the ceiling. The disadvantage of these departures pertains to whether or not the required climb gradients can be sustained—in a light twin, for example, it is quite likely that the failure of an engine will quickly render the aircraft unable to comply.Accordingly, careful consideration must be given to the ability of the aircraft to meet or exceed the increased climb gradients.
To do this, the climb gradient chart that appears in CAP GEN must be consulted. This graph, depicted below, enables the conversion of a “feet per nautical mile” value to a “feet per minute” value, based on the anticipated groundspeed during the departure phase.
Be sure not to mix up the scales posted on either side of the graph. Note also that a multi-engine pilot should plug in the published single-engine climb performance valued (assuming one of the engines has failed). The example shown demonstrates the application of the Cranbrook climb gradient required for the ½ SM departure off Runway 16; the climb groundspeed is assumed to be 120 KTS. For some airports, the climb rates, based on the specified climb gradients, are set out in table form on the CAP plates; these are always provided in JEP plates.In the case of the SPEC VIS procedure for Cranbrook Airport, climb gradient is of course not specified in the text description. Don’t let this create any confusion, however, as the assumed minimum climb gradient of 200’/NM still applies. This requirement, however, only kicks in after the aircraft has climbed visually over the airport to the specified altitude—in the case of Cranbrook, 4400’ ASL. Thus, ceiling limitations govern SPEC VIS departures.
When evaluating the latest METAR sequence, be sure you properly convert the SPEC VIS altitude—published in height above sea level—to the METAR ceiling values—height above ground. To conduct the SPEC VIS departure from Cranbrook, then, the minimum ceiling requirement that must appear in the METAR is 4400’ minus the elevation of the airport—3082’ (as published in the Canada Flight Supplement).