Instrument departures

Read procedure terminology

A chart describes a protected path using defined fixes, references and areas.

Position, path and reference

Track is the projection of the flight path on the earth; heading is the direction of the aircraft’s longitudinal axis. A bearing is the angular direction to or from a point. A fix is a geographical position determined by visual reference, navigation aids or other means; a waypoint is a specified geographical location used to define an RNAV route or path. A fly-by waypoint anticipates the turn; a fly-over waypoint is crossed before turning.

Altitude is vertical distance above mean sea level; height is above a specified datum; elevation is the vertical distance of a point on the earth above mean sea level. OCA/H is obstacle clearance altitude/height; MOC is minimum obstacle clearance; MSA is minimum sector altitude; DER is departure end of runway. SID and STAR mean standard instrument departure and arrival. IAF, IF, FAF/FAP and MAPt mark approach functions developed in the next chapters.

Protection has conditions

Procedure design assumes specified navigation accuracy, tracking, aircraft speeds, turn performance, wind allowances and altimeter practices. Primary areas receive full MOC; secondary areas generally taper the clearance to the outer boundary where applicable. An obstacle surface is not an aircraft climb-performance guarantee.

CDFA is a continuous descent final approach technique; APV has vertical guidance but is not the traditional precision category; PBN specifies performance requirements, with RNAV and RNP navigation specifications. RNP adds onboard performance monitoring and alerting. Check the chart’s specific coding and limitations instead of assuming every RNAV path has the same protection.

Climb gradient and obstacle protection

A higher groundspeed requires more feet per minute for the same gradient.

The departure design

A SID connects the runway departure to the en-route structure. Design considers terrain, obstacles, airspace, noise, navigation facilities and the aircraft performance assumptions. A straight departure keeps the initial track within 15 degrees of runway alignment; a turning departure exceeds that. Unless published otherwise, the normal aeroplane procedure design gradient is 3.3 percent, based on a 2.5-percent obstacle identification surface plus a 0.8-percent margin.

The design normally assumes crossing DER at least 5 m (16 ft) above its elevation and climbing straight to at least 120 m (394 ft) above DER before a turn, unless the procedure specifies otherwise. A published higher gradient must be assessed for the actual aircraft and conditions. The SID is not an engine-out performance procedure; the operator must address that separately.

Omnidirectional does not mean unrestricted

Omnidirectional criteria are used where no suitable track guidance exists or where operational flexibility is needed. The design establishes a climb-out and turning area with minimum heights and possibly sectors or restrictions. The pilot still observes the charted gradient, turn height and prohibited or restricted sectors.

To convert gradient to vertical speed, multiply groundspeed in knots by gradient percent and approximately 1.013. At 150 kt, 3.3 percent is about 502 ft/min. Use groundspeed rather than IAS; a tailwind increases required vertical speed. The interactive profile shows this conversion and whether a selected rate reaches the schematic gradient, not an operational dispatch calculation.

Can you apply the rules?

Four original questions. Choose from the facts, then review the explanation.