View Full Version : MOCA; Minimum Obstruction Clearance Altitude

12th Jul 2006, 04:22
MOCA provides what terrain clearance?
i.e on the GPS RNAV/GNSS jeppeson plate between two waypoints (2450T)=MOCA

I think the answer is 1000' plus 360ft which is the highest permissable altitude of an unmarked obstacle. Making terrain clearance of MOCA 1360 ft on Australian charts.

Need a Jepp reference as well if anyone can provide one.

12th Jul 2006, 06:15
It's been a long time since I knew anything about the way procedures are designed in Oz but I think you'll find that the 360 ft value is included in the obstacle elevation assessment. Once the designer has assessed the elevation of the critical obstacle, the MOC (minimum obstacle clearance) value of 1,000 feet is added - or up to 2,000 feet in "mountainous" areas.

Thus, the minimum obstacle clearance altitude, in any segment of an approach procedure, is based on the elevation of the critical obstacle, plus the minimum value for obstacle clearance, known as MOC. There may or may not be an additional allowance for QNH error and it needs to be said, also, that the critical obstacle might not be in the primary protection area - in that event, a sliding scale of MOC is used. This is based on the full 1,000 feet at the boundary between primary and secondary area, reducing to ZERO at the outer edge of the secondary area.

That's a bit of a simplification, but I think it's enough to answer the question.


12th Jul 2006, 08:44
As defined with my former employer. Company specs may vary.

Minimum obstacle clearance altitude. (MOCA)

Is the sum of the maximum terrain or obstacle elevation whichever is highest plus 1000 feet for elevation up to and including 6000 feet or 2000 feet for elevation exceeding 6000 feet. MOCA in hundreds of feet is given in the RFC SID and STAR. The lowest MOCA to be indicated is 2000 feet. MOCA is valid for a corridor of variable width as indicated.