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flying LPV with Garmin G1000 & King KAP140 WAAS



 
 
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  #1  
Old July 2nd 12, 05:01 PM posted to rec.aviation.ifr
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Default flying LPV with Garmin G1000 & King KAP140 WAAS

I'm a little new to this airplane and tried to fly an LPV approach on autopilot.

I had the approach activated and was outside the FAF at approx 30 degree intercept, when I pressed AP, then APR. It turned on course properly but never captured the glide path. What am I doing wrong?

thanks

Rick

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  #3  
Old November 26th 12, 12:46 AM posted to rec.aviation.ifr
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Default flying LPV with Garmin G1000 & King KAP140 WAAS

ILS intercepts from above is risky, due to the existence of false GS.
LPV by itself doesn't have this issue, because the GS is calculated instead of directly received.
That said, a GS intercept from above might pose energy issues (you might accelerate too much), and the autopilot might actually be designed not to do that (how to know how steep to descend until intercept, while an intercept from below is pretty simple=keep level until GS comes alive).

LPV approaches waste a lot of potential features that haven't been openly discussed to the usual "design for the dumbest possible IFR pilot" FAA/ICAO/EASA policy. LPV approaches should allow for 3.5 and 4 degree descents, depending only on the aircrafts capability to dissipate the extra energy with flaps/landing gear drag, or a slightly extended spoiler. In that sense you should never have an intercept from above, you should instead use a steeper descent angle all the way to the outter marker, and intercept that steeper GS from below. Most aircraft can descent at 4 degree profiles with full flaps, that would save time and fuel. The idea would be to consider the glide slope intercepted once bellow 4 degrees, but show the GS as very high, continue descending/bleeding energy to reach a 3 degree slope before DH.

LPV approaches could be way superior than CAT I ILS, if only FAA/ICAO/EASA decided to take full advantage of SBAS superiority over CAT I ILS.

1 - WAAS should support GLONASS like EGNOS does, it should also support GALILEO as soon as GALILEO have a half an operational constellation (12 healthy satellites). With a full GPS+full GLONASS+half GALILEO constellation, LPV approach availability would be 100%/100% for North America and Mexico all year round, including Alaska, compared to some significant daily outages in Alaska and Mexico, and small outages in the west coast of CONUS. It might also offer LPV support for Bermuda and Bahamas without extra SBAS stations.

2 - WAAS should fully support L2C when L2C ranging is healthy. It will take a LONG time before GPS reaches L5 FOC (and L5 is officially useable with SBAS). The FAA thinking that since L2C isn't on an ARNSS protected band it can't be used for Safety of Life is wrong. FAA ARNSS policy is based on non GNSS systems, where if one signal gets interference, the system is unreliable, while GNSS navigation can detect jamming very easily, can detect spoofing somewhat easily, and is capable of discarding bad GNSS signals (without depending on the ground segment to tell it so), adding extra GNSS signals on separate bands ADDS RELIABILITY. Receivers should only use L2C if a good L1 C/A / L1C or L5 signal is received from the same satellite (as a secondary frequency), and the signal delay between both is reasonable. Using GPS L1 C/A+L2C and GALILEO L1C + L5 (with a half Galileo constellation) would allow CAT II SBAS (LPV 100) approaches with the same safety margin as LPV200 today, as long as the Integrity feature is moved from the SBAS ground segment to the SBAS receivers (ARAIM) and SBAS is still available providing orbit/clock corrections to each satellite. SBAS was designed to be used with just 4 GPS satellites, but even with 2 and a half constellations, a minimum of 9 ranging sources will be visiable at ALL times (most times more than one dozen ranging sources will be visiable), use the extra ranging sources to cross validate each ranging source against all other satellites (simultaneously calculate position fix eliminating each ranging source, and compare all results to find bad satellites), current processor power for new SBAS receivers is about one thousand times what it was when first generation SBAS receivers were designed, take advantage of that extra processing power.

3 - Its actually easier to perform a tight intercept with LPV compared to ILS, due to moving maps+precise distance to FAF+precise instant ground track course (every LPV approach is better to fly than ILS/DME). Once the intercept is made, its easier to keep the lateral deviation centered since you don't need to think lateral winds, just keep the ground course +-1 degree from the final approach course, doing a single degree track correction is enough once your established.

Marcelo Pacheco

On Thursday, July 5, 2012 8:40:20 PM UTC-3, Sam Spade wrote:
wrote:

I'm a little new to this airplane and tried to fly an LPV approach on autopilot.




I had the approach activated and was outside the FAF at approx 30 degree intercept, when I pressed AP, then APR. It turned on course properly but never captured the glide path. What am I doing wrong?




thanks




Rick






Were you below the GS when it intercepted the lateral course? I can't

help much beyond that because I don't know the autopilot. But, most

autopilots with only intercept a GS from below.


  #4  
Old July 17th 13, 06:41 PM posted to rec.aviation.ifr
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Default flying LPV with Garmin G1000 & King KAP140 WAAS

L5 is not considered a Safety of Life service solely because of its reserved bandwidth. I'm given to understand that more crucial to this designation was the consideration that L1, L2P(Y) and L2C all share the same single point of failure on the GPS satellite: they all depend on the same Course Acquisition (C/A) chipset.

L5, on the other hand, has a completely independent data path, antenna, chipsets, power source, so that if the L1 or either of the L2 signals fail, the L5 signal will still remain operational.

I would also observe that, as of July 2013, while 11 current satellites have L2C, and only three have L5 operational, the current USAF schedule (which we know will change) has only a two year gap between FOC of L2C and FOC of L5. If either date slides to the right, both will, and probably by the same degree.
 




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