FAA Cautions Pilots Against Unauthorized Procedures
- Thread starter RDoug
- Start date
ppragman
FLIPY FLAPS!
Hard to stop when it appears a large section of the aviation public doesn't understand the difference between vanilla GPS and RNP...
gotWXdagain
Polished Member
And the fact that if your GPS box was built post Y2K it can probably keep you on the path just as good as any RNP 0.3 system.
Dugie8
Well-Known Member
RNP .3 et al has more to do with fault earning and alerting than it does with accuracy levels.
RNP 10: your system doesn’t have to tell you that the system has degraded
RNP 4 and lower: there has to a warning that tells the pilot the box/system is no longer capable of the required RNP level.
So for shooting a RNP AR approach, you want the box to scream at you if the accuracy is degraded because that RNP number is what is keeping you away from the Cumulus Granite.
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RNP 10: your system doesn’t have to tell you that the system has degraded
RNP 4 and lower: there has to a warning that tells the pilot the box/system is no longer capable of the required RNP level.
So for shooting a RNP AR approach, you want the box to scream at you if the accuracy is degraded because that RNP number is what is keeping you away from the Cumulus Granite.
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gotWXdagain
Polished Member
Right, the needle sensitivities are the same and (at least all the Garmins) will throw up a flag pretty quick if it gets a fault. Functionally speaking you’re not getting anything different, it’s only legally speaking.
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Dugie8
Well-Known Member
Functionally it is very different. For a system to be RNP AR certified it has to have those fault detection features.
RNAV and RNP mean two very different things. RNP 10 is a misnomer it is RNAV 10.
If you were shooting a RNP AR approach with less than .3 accuracy and the signal or box degraded to .3 and the box wasn’t a RNP box you would never know and could end up very close if not hitting an obstacle.
There is a myriad of reasons those AR approached get you so much lower when an old fashion designer LNAV/VNAV won’t. Some of it is the missed approach course and some of it is the very tight approach path and the obstacles that get considered within that tight path.
Let me edit that a little bit.
The tight course tolerances are there. The RNP requirements are basically if the system thinks you are more than double the RNP standard, say RNP 4, if the system thinks there is. .0001% chance you are more than 8 miles off course you will get an alert.
Take that down to RNP .15 you see how tight those tolerances get and the chance for error.
Throw in the requirement for IRU/IRS for AR approaches and it starts to be real clear why you don’t wanna just go blasting off in a Garmin430 Cirrus trying to shoot these approaches. APPR mode with needle sensitivity of .3 is not the same as RNP .3
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RNAV and RNP mean two very different things. RNP 10 is a misnomer it is RNAV 10.
If you were shooting a RNP AR approach with less than .3 accuracy and the signal or box degraded to .3 and the box wasn’t a RNP box you would never know and could end up very close if not hitting an obstacle.
There is a myriad of reasons those AR approached get you so much lower when an old fashion designer LNAV/VNAV won’t. Some of it is the missed approach course and some of it is the very tight approach path and the obstacles that get considered within that tight path.
Let me edit that a little bit.
The tight course tolerances are there. The RNP requirements are basically if the system thinks you are more than double the RNP standard, say RNP 4, if the system thinks there is. .0001% chance you are more than 8 miles off course you will get an alert.
Take that down to RNP .15 you see how tight those tolerances get and the chance for error.
Throw in the requirement for IRU/IRS for AR approaches and it starts to be real clear why you don’t wanna just go blasting off in a Garmin430 Cirrus trying to shoot these approaches. APPR mode with needle sensitivity of .3 is not the same as RNP .3
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Last edited:
gotWXdagain
Polished Member
I get that inside the box of an RNP system there’s more going on, like comparing the GPS signal to IRU inputs.
But, a G430 on an LP or LPV approach is going to put you right down the runway center with a CDI sensitivity that starts at 0.3 and gets tighter as you get closer, and if it loses that capability the box will tell you. Would I trust it for .15? maybe not, but for 0.3 if it was authorized you bet I would.
...But only if it was authorized.
But, a G430 on an LP or LPV approach is going to put you right down the runway center with a CDI sensitivity that starts at 0.3 and gets tighter as you get closer, and if it loses that capability the box will tell you. Would I trust it for .15? maybe not, but for 0.3 if it was authorized you bet I would.
...But only if it was authorized.
Pilot Fighter
Well-Known Member
Is any effort made to enforce a carrier-specific procedure? I have heard that in Alaska if you are knowledgeable enough to ask for a special approach clearance you are likely to get it.
z987k
Well-Known Member
ATC has no idea what approaches you are or are not authorized for. If you ask for the LDA-Z or the RNP 33 that's what they'll clear you for.
Pilot Fighter
Well-Known Member
Yes, I understand that ATC has no responsibility to figure out what I'm authorized for.
What I'm trying to ask is how ATC will respond in the isolated case they know I'm not authorized.
RDoug
Well-Known Member
ATC does not have the authority to deny you an approach, even if we know you're not authorized to attempt it. For instance, an approach with weather below minimums; that's a pilot's call, not ours.
Pilot Fighter
Well-Known Member
Thanks for the clarification.
knot4u
Repeat Offender
Honest question, outside of 121, if an approach is in the data base is there anything that would alert the crew that they aren't authorized to use it? Is it something that's covered in 135 check ride training for each operator/aircraft? What about 91 guys with an FMS, how would they know?
NovemberEcho
Dergs favorite member
Afaik we don't know if it is a carrier specific approach or not. It's just an approach, who can use it or not is above our paygrade.
gotWXdagain
Polished Member
I thought you couldn’t clear a part 135 or 121 flight for an approach where visibility is below minimums?
RDoug
Well-Known Member
Not that I'm aware of.
Cptnchia
Dissatisfied Customer
Back in the day when ASAs E120s could only go down to 1800RVR, Delta would be flying CATIIs to 1600-1200 RVR in Atlanta. As we would be driving up to the final approach fix, RVR would suddenly be “reporting” 1800, then would be back down to 1600 for the following Delta.
Funny how that worked out. First 1600 RVR approach at SJI, the captain asked me what I thought of it. “Eh, looked like 1800 to me.”
NovemberEcho
Dergs favorite member
We still time RVR restricted arrivals to coincide with the departure blowing the sensor clear.