GPS Letdowns
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NigD, LAAS & WAAS are still vapor. Don't exist in the US. But the GPS approaches are still accurate. The only requirement for augmentation is for precision approaches, not non-precision. Even the fixed-wing folks are flying GPS approaches, & we're flying them to points-in-space in helicopters to 300/1 at heliports, & 200/.6NM offshore. I've never, ever been off course on a GPS approach if the CDI is centered, & at airports, with the needle centered, you're over the runway, close to centerline. GPS approaches are much more accurate than VOR, & about the same accuracy as localizers. Should be the same in the UK or anywhere else.
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Stan
Yep, GPS is very accurate for non precision approaches. It would just worry me coming into an unusual airfield with crap wx etc relying on GPS alone to fly the approach. You have obviously used it very succesfully in the past but I still have reservations about its reliability.
Maybe I should invest in a spanner to untighten the bolt up my ass.................. or apply to the CAA for a job.
Nigd
Yep, GPS is very accurate for non precision approaches. It would just worry me coming into an unusual airfield with crap wx etc relying on GPS alone to fly the approach. You have obviously used it very succesfully in the past but I still have reservations about its reliability.
Maybe I should invest in a spanner to untighten the bolt up my ass.................. or apply to the CAA for a job.
Nigd
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NigD,
The accuracy of GPS is a known thing, and wrapped into the approach geometries, so you are correct, but it is not a reason to prevent approval.
For example, the bottom of the FAA non-precision GPS approach lane is about .9 Nm wide, with the course in the center. This accounts for the maximum RAIM error at the worst place in the approach. Most GPS hits are within 100 meters, so most approaches can be kept within a 0.1 NM width. The extremely conservative airspace protection is a product of the safety built into the approvals.
LAAS and WAAS are about to be sprung. A commercial WAAS receiver will be sold next year (I know because I am on the FAA/Industry committee to determine the procedures - we are meeting again on Wed of this week!)
The FAA has been pretty good about getting this stuff approved.
The accuracy of GPS is a known thing, and wrapped into the approach geometries, so you are correct, but it is not a reason to prevent approval.
For example, the bottom of the FAA non-precision GPS approach lane is about .9 Nm wide, with the course in the center. This accounts for the maximum RAIM error at the worst place in the approach. Most GPS hits are within 100 meters, so most approaches can be kept within a 0.1 NM width. The extremely conservative airspace protection is a product of the safety built into the approvals.
LAAS and WAAS are about to be sprung. A commercial WAAS receiver will be sold next year (I know because I am on the FAA/Industry committee to determine the procedures - we are meeting again on Wed of this week!)
The FAA has been pretty good about getting this stuff approved.
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Nick hits it on the head; just because the procedures don't exist does not mean that they are not needed. I seem to recall the CAA have, or had, a "GPS Steering Group"; quite what they do or did is a bit of a mystery,
The CAA should have in place a sytem whereby operators can submit for approval a let down based on a predifined criterea. It should ideally be designed with VOR/DME crosscuts and if available an NDB beacon. When flown, use of a radar service should also be utilized. With all these and the acccuracy of GPS then accurate GPS approaches are very possible and safe.
If the CAA does not get it's act together, (there's a radical thought), then unapproved procedures will be flown with various outcomes; the Irish S76!
As to the original thread. Allowed to fly at 300 feet? Maybe on scene and with 100 feet cloud seperation, but in transit - I would think not. Check the POAM!
The CAA should have in place a sytem whereby operators can submit for approval a let down based on a predifined criterea. It should ideally be designed with VOR/DME crosscuts and if available an NDB beacon. When flown, use of a radar service should also be utilized. With all these and the acccuracy of GPS then accurate GPS approaches are very possible and safe.
If the CAA does not get it's act together, (there's a radical thought), then unapproved procedures will be flown with various outcomes; the Irish S76!
As to the original thread. Allowed to fly at 300 feet? Maybe on scene and with 100 feet cloud seperation, but in transit - I would think not. Check the POAM!
Just to reinforce the point the chaps made originally, whatever the legality or consequences for an aircraft making a GPS/VOR or suchlike approach without there being proper procedures, there is an elevated risk to the police or EMS operator of a mid-air when the police/EMs aircraft is operating legally in such poor weather.
Sorry, but if you see it being done, report it.
Sorry, but if you see it being done, report it.
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It seems that this thread has highlighted two issues.
1. The need for approved GPS approaches in the UK, or at least a method of persuading the CAA to start approving some of the unofficial ones more rapidly.
2. Some way in which an aircraft on an unofficial GPS letdown, can notify other aircraft in the vicinity of his intention to carry out such a letdown.
Now I appreciate that the sticklers will say that the simple answer is to stop those aircraft doing unofficial letdowns. That however is unrealistic for a number of further reasons.
1. The CAA don't seem that interested in doing it and have no real input into the private/corporate flight departments (as opposed to the AOC corporate flight departments).
2. The people utilising the services of these aircraft have paid serious money for the privilege and expect to get to their destination whatever the weather.
3. The guys/gals? flying those procedures are not going to make the customer/boss unhappy or risk losing their jobs.
4. It is in all our interests to ensure that helicopter aviation is successful. These guys may be pushing the legal boundaries, but if they succeed in making heli ops truly all-weather then that can only be good in the long run for the industry as a whole. If the legislators are turning a blind eye to it I don't see why fellow pilots should try and get it stopped, better to work out a practical system to co-exist with those guys safely.
1. The need for approved GPS approaches in the UK, or at least a method of persuading the CAA to start approving some of the unofficial ones more rapidly.
2. Some way in which an aircraft on an unofficial GPS letdown, can notify other aircraft in the vicinity of his intention to carry out such a letdown.
Now I appreciate that the sticklers will say that the simple answer is to stop those aircraft doing unofficial letdowns. That however is unrealistic for a number of further reasons.
1. The CAA don't seem that interested in doing it and have no real input into the private/corporate flight departments (as opposed to the AOC corporate flight departments).
2. The people utilising the services of these aircraft have paid serious money for the privilege and expect to get to their destination whatever the weather.
3. The guys/gals? flying those procedures are not going to make the customer/boss unhappy or risk losing their jobs.
4. It is in all our interests to ensure that helicopter aviation is successful. These guys may be pushing the legal boundaries, but if they succeed in making heli ops truly all-weather then that can only be good in the long run for the industry as a whole. If the legislators are turning a blind eye to it I don't see why fellow pilots should try and get it stopped, better to work out a practical system to co-exist with those guys safely.
Nick,
It is now apparant that graduates of Cobra Hall in Savannah must have been imprinted with liberalistic propaganda during a very vulnerable period in their life. Now, whereas, graduates from the Goldberg Stagefield of Cargo Helicopter dynamics and school of probability continium.....were imbued with conservative ideology early on......it is easy to see how you could take up for those bureaucratically burdened and freewill challenged sorts. Heheheheh!
It is now apparant that graduates of Cobra Hall in Savannah must have been imprinted with liberalistic propaganda during a very vulnerable period in their life. Now, whereas, graduates from the Goldberg Stagefield of Cargo Helicopter dynamics and school of probability continium.....were imbued with conservative ideology early on......it is easy to see how you could take up for those bureaucratically burdened and freewill challenged sorts. Heheheheh!
NigD2.....care to start your reasons for being worried about doing GPS based approaches and why you think they are more unreliable/less safe than current ground based approaches? Have some of your graybearded colleagues explain the Decca approaches we used to do on a routine basis at sunny places like Sumbrugh.....and then rethink your answers.....I think you too would become a convert to this SciFi American thing. I defy anyone to convince me that the old runway 27 Decca Approach at Sumbrugh was anything but an unmitigated disaster (remembering I was doing it single pilot....sometimes sas'ed helicopter) usually at night and always in rat s_ _ t weather.
That particular approach required both a map change and a key change for the final approach.....I can safely state that I not once ever got it all done when by myself when in bad weather. I did find religion there a couple of times trying however!
That particular approach required both a map change and a key change for the final approach.....I can safely state that I not once ever got it all done when by myself when in bad weather. I did find religion there a couple of times trying however!
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The issue with GPS approaches is to also make sure you have an IFR approved GPS. If you don't have RAIM, then it's like doing an ADF approach without monitoring the audio (what do you mean, you don't monitor the audio?).
Non-IFR approved GPS can wander off and not tell you. There is a whole different method (nearly said approach) to doing GPS instrument flying, and unless you know the whole thing, you are standing yourself and passengers into danger.
And a moving map GPS is far and away the best system to have.
Shawn
Non-IFR approved GPS can wander off and not tell you. There is a whole different method (nearly said approach) to doing GPS instrument flying, and unless you know the whole thing, you are standing yourself and passengers into danger.
And a moving map GPS is far and away the best system to have.
Shawn
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Moving map? What's a moving map? I've never seen a moving map. How does that thing work? 
I'd love to have one, but I thought it was great when I got a GPS with 2 lines of text. It's far better than the LORAN we used to use for approaches. It always (ALWAYS!) crapped out when the weather got bad. I trust GPS far more than VOR - the signal is far steadier & the indications are more precise, even at the VOR, never mind 30+ miles away.
I'd love to have one, but I thought it was great when I got a GPS with 2 lines of text. It's far better than the LORAN we used to use for approaches. It always (ALWAYS!) crapped out when the weather got bad. I trust GPS far more than VOR - the signal is far steadier & the indications are more precise, even at the VOR, never mind 30+ miles away.
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SASless
RAIM outages may occur due to an insufficient number of satellites or due to unsuitable satellite geometry which causes the error in the position solution to become too large. Loss of satellite reception and RAIM warnings may occur due to aircraft dynamics (changes in pitch or bank angle). Antenna location on the aircraft, satellite position relative to the horizon, and aircraft attitude may affect reception of one or more satellites. Since the relative positions of the satellites are constantly changing, prior experience with the airport does not guarantee reception at all times, and RAIM availability should always be checked. If RAIM is not available, another type of navigation and approach system must be used, another destination selected, or the trip delayed until RAIM is predicted to be available on arrival.
Not my quote but as in my last post I said I would have reservations about relying on GPS alone coming into an airfield with crap Wx and no alternative let down, as in the original posting of this thread
Hope this helps to show why I have my scaredy cat reservations
PS I have seen a GPS lose its signal on a flight test for an internally equipped GPS EGPWS....only once though.
RAIM outages may occur due to an insufficient number of satellites or due to unsuitable satellite geometry which causes the error in the position solution to become too large. Loss of satellite reception and RAIM warnings may occur due to aircraft dynamics (changes in pitch or bank angle). Antenna location on the aircraft, satellite position relative to the horizon, and aircraft attitude may affect reception of one or more satellites. Since the relative positions of the satellites are constantly changing, prior experience with the airport does not guarantee reception at all times, and RAIM availability should always be checked. If RAIM is not available, another type of navigation and approach system must be used, another destination selected, or the trip delayed until RAIM is predicted to be available on arrival.
Not my quote but as in my last post I said I would have reservations about relying on GPS alone coming into an airfield with crap Wx and no alternative let down, as in the original posting of this thread
Hope this helps to show why I have my scaredy cat reservations
PS I have seen a GPS lose its signal on a flight test for an internally equipped GPS EGPWS....only once though.
So Nig...if you have an IFR certified GPS, with RAIM alert, then shy of a complete loss of signal....you accept the GPS more than meets the requirements for making an approach.....that is what I read out of Nick's post which also reports new and finer coming attractions here in the USA.
Chaps, I think some peeps have missed the point of Mighty Gems thread - a published approach to an airfield is safe because a) everyone knows where the aircraft will be because the approach direction is widely promulgated and b) has a proper approach minima based on obstructions on the approach path. An ad hoc GPS approach has neither attribute and despite the accuracy of GPS, it is downright dangerous to fly this type of non published letdown in congested airspace.
In an emergency or if you have got completely caught out by the weather with no fuel to divert, then you might have a valid case - but if you plan to do this type of letdown on a routine basis you should hand in your license an IR and go and do something else for a job.
If anyone out there is doing this type of letdown in UK then I hope it is not me you kill when you either have a mid-air or collide with a mast that you didn't know about.
In an emergency or if you have got completely caught out by the weather with no fuel to divert, then you might have a valid case - but if you plan to do this type of letdown on a routine basis you should hand in your license an IR and go and do something else for a job.
If anyone out there is doing this type of letdown in UK then I hope it is not me you kill when you either have a mid-air or collide with a mast that you didn't know about.
