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rkaplan
Administrator
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Posted: Fri Feb 10th, 2006 06:01 pm |
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If you do not have DME installed on your airplane and you want to display localizer DME, you can set your Garmin 430/530 waypoint to the localizer DME.
Suppose you want to identify your DME distance from the I-AFJ localizer. Garmin has created a "fake" intersection called IAFJ which is located at the I-AFJ localizer source.
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Richard Kaplan, CFII
rkaplan@flyimc.com
http://www.flyimc.com
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rps
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| Joined: | Thu Mar 9th, 2006 |
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Posted: Thu Mar 9th, 2006 04:33 pm |
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I'm not 100% sure of this, but I don't think you can legally rely on GPS-derived distance data as a substitute for DME distance. DME measures slant-range distance whereas GPS provides distance on the GPS plane. The higher the AGL, the more the difference will be between the two distance figures. That's probably why some charts say DME required - you can't use GPS distance instead when flying such approaches.
Can someone more knowledgeable confirm?
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rkaplan
Administrator
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Posted: Thu Mar 9th, 2006 04:51 pm |
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rps wrote: I'm not 100% sure of this, but I don't think you can legally rely on GPS-derived distance data as a substitute for DME distance. DME measures slant-range distance whereas GPS provides distance on the GPS plane.
Welcome to the IFR Forums.
AIM 1-1-21 states that an IFR GPS receiver is acceptable to substitute for DME -- even if the plate says "DME Required." An IFR GPS is also a substitute when a plate says "ADF Required." An IFR GPS is not approved, however, if the title of an approach says "NDB 5"; it would be approved for such an approach only if the title said "NDB or GPS 5".
Yes, there are some slant-range issues involved but at the altitudes at which approaches are flown slant-range error is not considered to be a safety factor.
____________________
Richard Kaplan, CFII
rkaplan@flyimc.com
http://www.flyimc.com
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