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IFR question

Asked by: 6207 views , , , , ,
Airspace, FAA Regulations, Instrument Rating

Today I was reading an article about the minimum IFR altitude. This is the link for it: ww1.jeppesen.com/download/aopa/dec-aopa.pdf

My question is about this paragraph in the mentioned article:

Obstruction Criteria: In order to provide one standard for the whole world, the minimum vertical distance between the MORA and the highest obstacle along the route was determined to be either 1,000 feet or 2,000 feet, depending on the elevation of the terrain and obstacles below. When flying over precipitous terrain and when flying at higher altitudes, the amount of error between indicated altitude and true altitude increases. As a result, 1,000 feet of obstacle clearance was provided for the lower altitudes. For all terrain and obstacles greater than 5,000 feet, it was decided to create an obstacle clearance of 2,000 feet. 

On Jeppesen charts, all MORA altitudes which are 6,000 feet or lower have an obstacle clearance of 1,000 feet. If the MORA altitudes are 7,000 feet or greater, the obstacle clearance is 2,000 feet. 

 Why he first connected the 1,000' / 2,000 feet obstacle clearance to terrain and non-terrain but later he connected the 1000 & 2000 to the 6000 & 7000? I thought Jep provides 1000 if the highest terrain is 5000 and 2000 if terrain is higher than 5000. 

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2 Answers



  1. Wes Beard on May 23, 2014

    The first time I read this statement, I was confused too. After reading it again the paragraph makes sense. The author adjusted the perspective from which he was talking.

    First off his perspective is based on the terrain. Any terrain greater than 5000′ MSL will have an obstacle clearance of 2000′ for the MORA. Any terrain below 5000′ MSL will have an obstacle clearance of 1000′.

    The author then changes perspectives and comes at the same information in relationship to what the pilot sees on the charts. For example, if the MORA is 6000′ or less we are guaranteed only 1000′ separation because terrain has to be 5000′ or less. if the MORA is 7000′ or above we are guaranteed 2000′ separation because terrain is at least 5001′.

    It also means we should never see MORA values between 6100′ and 6900′.

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  2. Mike Urban on May 23, 2014

    Wes Beard,

    Excellent explanation; it makes sense for me now. Thank you.

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