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#1
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Different WAAS altitude readings
My Garmin 296 indicates 330 MSL at KHKS, which is correct. My Echo Flight
GPS indicates 140 MSL. Both are locked on to WAAS. How can I have such a large discrepancy? Both units seem to be functioning properly other than this. |
#2
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Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS
altitudes. Doesn't say anything about WAAS...yet. Bob Gardner "Wyatt Emmerich" wrote in message ... My Garmin 296 indicates 330 MSL at KHKS, which is correct. My Echo Flight GPS indicates 140 MSL. Both are locked on to WAAS. How can I have such a large discrepancy? Both units seem to be functioning properly other than this. |
#3
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Given this discrepancy, I understand why.
"Bob Gardner" wrote in message ... Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS altitudes. Doesn't say anything about WAAS...yet. Bob Gardner "Wyatt Emmerich" wrote in message ... My Garmin 296 indicates 330 MSL at KHKS, which is correct. My Echo Flight GPS indicates 140 MSL. Both are locked on to WAAS. How can I have such a large discrepancy? Both units seem to be functioning properly other than this. |
#4
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"Bob Gardner" wrote in message ... Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS altitudes. Doesn't say anything about WAAS...yet. 1-1-20's title is "Wide Area Augmentation System (WAAS)." There is no 1-1-20(a)(8). 1-1-20(b) gives guidance and procedures for flying approaches with vertical guidance from WAAS and says that some installations of WAAS may be certified for precision approaches as having greater accuracy than barometric altimeters. |
#5
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I'm using the 2004 FAR-AIM as a convenience...guess I should have used my
Summit CD-ROM which is updated quarterly. Bob "C J Campbell" wrote in message ... "Bob Gardner" wrote in message ... Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS altitudes. Doesn't say anything about WAAS...yet. 1-1-20's title is "Wide Area Augmentation System (WAAS)." There is no 1-1-20(a)(8). 1-1-20(b) gives guidance and procedures for flying approaches with vertical guidance from WAAS and says that some installations of WAAS may be certified for precision approaches as having greater accuracy than barometric altimeters. |
#6
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I see that my reference should have been AIM 1-1-19(a)(8). Other than that,
the guidance remains the same. I note the phrase "will be" sprinkled through the discussion of WAAS. Has WAAS been approved for operational use? How many boxes have the functionality described in 1-1-20?...I think the CX-80 does. Bob Gardner "C J Campbell" wrote in message ... "Bob Gardner" wrote in message ... Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS altitudes. Doesn't say anything about WAAS...yet. 1-1-20's title is "Wide Area Augmentation System (WAAS)." There is no 1-1-20(a)(8). 1-1-20(b) gives guidance and procedures for flying approaches with vertical guidance from WAAS and says that some installations of WAAS may be certified for precision approaches as having greater accuracy than barometric altimeters. |
#7
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Right now, the CNX-80 does not give vertical guidance, but that is
promised in software version 2.0, hopefully to be approved by Q3/2004. That software v2.0 has been in flight test since Q4/2003. I'm unaware of any box nearer than the CNX-80 to LPV capability. ---JRC--- "Bob Gardner" wrote in message = ... I see that my reference should have been AIM 1-1-19(a)(8). Other than = that, the guidance remains the same. =20 I note the phrase "will be" sprinkled through the discussion of WAAS. = Has WAAS been approved for operational use? How many boxes have the functionality described in 1-1-20?...I think the CX-80 does. =20 Bob Gardner =20 "C J Campbell" wrote in = message ... "Bob Gardner" wrote in message ... Can't address your problem, but AIM 1-1-20(a)(8) tells us not to = use GPS altitudes. Doesn't say anything about WAAS...yet. 1-1-20's title is "Wide Area Augmentation System (WAAS)." There is = no 1-1-20(a)(8). 1-1-20(b) gives guidance and procedures for flying approaches with vertical guidance from WAAS and says that some installations of = WAAS may be certified for precision approaches as having greater accuracy = than barometric altimeters. |
#8
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"John R. Copeland" wrote: Right now, the CNX-80 does not give vertical guidance, but that is promised in software version 2.0, hopefully to be approved by Q3/2004. That software v2.0 has been in flight test since Q4/2003. I'm unaware of any box nearer than the CNX-80 to LPV capability. ---JRC--- Most of the modern iron has Baro VNAV which, in addition to being authorized in the final approach segment as primary vertical guidance where VNAV minimums are charted, is used extensively for flying constant angle descents in the segments of an IAP prior to the Baro VNAV P-FAF. That's different that LPV, which can only be used in the final approach segment where LPV minimums are charted, and you have LPV approval. If the CNX-80 will be able to do both Baro VNAV and LPV, that will be very advanced, indeed. Is that the plan? |
#9
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C J Campbell wrote: "Bob Gardner" wrote in message ... Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS altitudes. Doesn't say anything about WAAS...yet. 1-1-20's title is "Wide Area Augmentation System (WAAS)." There is no 1-1-20(a)(8). 1-1-20(b) gives guidance and procedures for flying approaches with vertical guidance from WAAS and says that some installations of WAAS may be certified for precision approaches as having greater accuracy than barometric altimeters. The sections were rearranged but Bob Garder is right; the prohibition still exists. What the language you cite refers to is LPV. If you have IFR certified LPV on your aircraft (which I doubt), then you can use LPV from the PFAF to Decision Altitude, only. There is no authorization to use LPV in any other manner to determine altitude, nor is there any other provision to use WAAS-augmented GPS in general to replace the barometric altitmeter for determining altitude under IFR. |
#10
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As a follow-up to the previous post: the new instrument PTS that goes into
effect in October requires students to be familiar with precision, non-precision, and approaches with vertical guidance. We need you to update your book! At the very least, turn what is written in 1-1-20 into plain English. |
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