Please don’t misunderstand (as Dave loves to do, I am delighted he holds the position he does), of course I am not for a second suggesting going below minima on any procedure.
I am saying that once you have established that you have visual reference at 200’, in minimum visibility, the safest thing to do is to fly the needles to 100’. This is how I was taught, was the SOP in the four AOCs I used to fly for and has never given any kind of problem in 35 years of IFR flying.
However, what has repeatedly given me problems is people flying that first 100’ visually, where, on a regular basis, they drop below the slope. That is far more dangerous than any theoretical problem with the GS, which Dave may have read about in a book, but I bet he cannot demonstrate, anywhere.
In the days when I was flying single crew, there was no 800m single pilot minimum, and we were strongly discouraged (shall we say) from raising our personal minima. That meant that it was not uncommon to hold, waiting for the RVR to become 550m, and then shoot an approach. For that reason, I have flown a lot of such approaches in PA27, PA31, C404 and HS125, both single and two crew.
So, a lifetime of practical experience or an IRE reading a book. I guess that is the joy of individuals being able to make their own choices.
There are many little rules and ideas put in place because of bureaucrats reading books, like the switching off of the glideslope on LNAV/VNAV approaches, and ADF being preferred over the RNAV overlay, where the Type 2 risk greatly outweighs the Type 1, but the boffin cannot see past the Type 1.
Timothy wrote:
That is far more dangerous than any theoretical problem with the GS, which Dave may have read about in a book, but I bet he cannot demonstrate, anywhere.
You two should just do a flight together, no?
Noe wrote:
You two should just do a flight together, no?
Absolutely. The best thing would be for Dave to identify an ILS accessible from the London area which demonstrates this problem and then, provided its somewhere that a PA31 is allowed to go and play, we go there on a nice VMC day and watch what happens.
Less of the “personal” stuff please.
Dave_Phillips wrote:
Timothy, I can’t be bothered. My professional role is calibrating ILS. I’m also an IRE (of which you are not)
Why make statements if you can’t be bothered to elaborate or clarify them? Everyone on here would like to learn from this thread and while we accept your greater IRE+calibration experience, this statement in itself doesn’t allow us to improve our own individual knowledge of the subject.
I would be interested to know if the “junk” ILS info below 200 is a certainty in all circumstances, or a rare but genuine possibility, or something in between. And would also like to know how LPV stacks up here.
ortac wrote:
I would be interested to know if the “junk” ILS info below 200 is a certainty in all circumstances, or a rare but genuine possibility
I can assure you that it is not the case in any of the ones I listed. We hear of calibration flights there, but not that the GS wobbles between 200 and 100 ft at any of them.
So the most it could be would be “a rare but genuine possibility.”
I do suspect one ILS in the south of England, which is RAF Benson. That has a distinctly iffy GS, which I am told by a local pilot is something to do with the placement of a wire fence. But its dodginess is evident all the way down (you get a GS flag for more than half the time.) They compensate by making it a “monitored” approach where the controller gives you a sort of PAR along with the ILS. I cannot imagine it being certified for CAT use.
But that is quite different from a specific issue below 200’.
Dave’s comments were very helpful, so hopefully he is tempted to share more insight on glide slope reliability in relation to minima. The regulations are quite straightforward – if the ILS is a CAT 1 ILS the glideslope is not reliable below the system or published minima (200 feet), and the approach continues using visual references. Cat II I understood the glide slope was reliable down to 100 feet, but at 50 feet you get a fly up signal? Source FAA.
Timothy you mentioned Gatwick, Heathrow and Stansted – is the PA31 operating into these Cat III runways?
RobertL18C wrote:
Timothy you mentioned Gatwick, Heathrow and Stansted – is the PA31 operating into these Cat III runways?
This is historical. I was flying PA31, C404 and HS125 based at Gatwick and HS125 based at Heathrow. Stansted was a regular destination, mainly for freight.
I do suspect one ILS in the south of England, which is RAF Benson. That has a distinctly iffy GS, which I am told by a local pilot is something to do with the placement of a wire fence. But its dodginess is evident all the way down (you get a GS flag for more than half the time.) They compensate by making it a “monitored” approach where the controller gives you a sort of PAR along with the ILS. I cannot imagine it being certified for CAT use.
Don’t think you’re thinking about Benson. The ILS on 19 is fully operational down to 200’ QFE (410’QNH) minima and I flew it to that only a week or so ago in IMC. I know a number of military approaches that are / have been radar monitored but in my experience you would never get controller transmissions like a PAR when cleared for the ILS approach.
Balliol wrote:
Don’t think you’re thinking about Benson.
Yes, definitely Benson. 5/11/16. Maybe it was a temporary fault, hence the monitored approach, but the local RAF helicopter pilot I met in the Guardroom implied that it was an ongoing/permanent thing.
