Unpublished let-downs

[The Ancient Geek]

1000 feet should be fairly safe, much below that you can find oil rigs and wind turbines.
But are you sure of your QNH ?

[foxmoth]

Galaxy,
My point was not if you should observe these limitations or not but the definition of safety, and that safety is not a black and white issue but a variable. Good airmanship dictates that you select the least risk option, generally that will mean you do not descend below MSA, but there can be situations where that may not be the safest option!

[n5296s]

Two different animals here

You're quite right, but my point is that as far as the GPS is concerned, an approach is just a sequence of waypoints. Whether those form part of a published approached, or whether they're user-defined ones that you made up as part of your home-brew approach, it neither knows nor cares.

I'm not recommending home-brew approaches, just saying that it isn't too hard to figure the mechanics of how to fly one.

[rotarywise]

How low would you descend to over the sea??

Last time I did it, 125ft on the Rad Alt, but that was 50+ miles north of Iceland with no diversion. These days I would never descend below MSA without an approved IAP or radar vectors.

[27/09]

You're quite right, but my point is that as far as the GPS is concerned, an approach is just a sequence of waypoints. Whether those form part of a published approached, or whether they're user-defined ones that you made up as part of your home-brew approach, it neither knows nor cares.

Actually the GPS does know and care, very much.

With a published approach loaded the GPS will scale at the FAF from 1 mile to 0.3 mile full scale deflection and a TSO 146 GPS will scale to full scale deflection of 2 degrees inside the final fix down to 350 feet at the missed approach point.

A homebrew approach cobbled together using just a sequence of waypoints will be scaled to 1 mile at best and could be as much as 5 miles full scale.

I know what I'd want to use for an approach and it sure ain't some dodgy homebrew one.

[n5296s]

Actually the GPS does know and care, very much.

Good point, I'd forgotten about that (although of course it pops up on the GPS every time). It's another good argument against using a homebrew approach, as if any more were needed.

[bookworm]

A homebrew approach cobbled together using just a sequence of waypoints will be scaled to 1 mile at best and could be as much as 5 miles full scale.

It will be scaled to whatever you set it to. The more significant aspect is the integrity: the horizontal alerting limit may be significantly higher than for a procedure retrieved from the database

[compressor stall]

For those thinking of GPS and synthetic vision are infallible, have a read here.

https://www.caa.govt.nz/Accidents_an...-SML_Fatal.pdf

[n5296s]

I certainly don't think any of this stuff is infallible, but you can hardly lay this at the GPS. Yes, the terrain database was inaccurate, but presumably the aircraft had an altimeter. This is like truck drivers getting stuck under low bridges or people driving into rivers because they "followed the GPS".

[cessnapete]

Slightly off topic, but recently upgraded our G430 t0 430W. I have been amazed at the accuracy and stability of GPS approaches carried out. Even an LNAV/V with only advisory glideslope, (i.e. Shoreham) if flown accurately takes you to the Rwy numbers. Pity that unnecessary regulatory bulls..t prevents this great safety enhancing aid being stifled in CAA land.

[piperboy84]

Cessnapete

Slightly off topic, but recently upgraded our G430 t0 430W

I will be doing the same upgrade on my 430 later this year, what was the ballpark cost if you don't mind me asking?

[cessnapete]

Anything to do with aeroplanes, not cheap! C182Q
£2300 to Garmin UK to upgrade the internal hardware/software, quite a big mod apparently, new faster processor etc.
Then about another £2000 for avionics shop.
New GPS aerial and cable to G430 box.No new holes to cut as all new upgrade parts fit into present positions in aircraft. And nice new thick Garmin manual to teach you how to use it!
Includes a 'royalty' fee to GAMA Avionics for their time, expertise and paperwork for the mod in UK.
All done expeditiously and efficiently by RGV Glos.

[n5296s]

what was the ballpark cost

I just upgraded my 530 to a 530W, and replaced my 330 transponder with an ADS-B 345. Total cost including parts and labour was about $16K. Ouch.

I agree with pb84 - LPV approaches are a pleasure to fly.

[Council Van]

for example if you are sitting in a light single at 2,500' in icing conditions with an MSA of 2,400' and you get a pirep that the cloud base is 2,350' what is the safer option?

Hopefully you would be sat in your arm chair at home having carefully studied the weather forecast and realised that the forecast conditions were not suitable for your aircraft/qualifications.

1000 feet should be fairly safe, much below that you can find oil rigs and wind turbines.
But are you sure of your QNH ?

I flew maritime patrol for a living with a previous company. We would not decend below an absolute minimum of 1300ft on the forecast regional QNH if we had not become VMC as obstacles could be up to 299ft without being shown on a chart.

[foxmoth]

Hopefully you would be sat in your arm chair at home having carefully studied the weather forecast and realised that the forecast conditions were not suitable for your aircraft/qualifications.

Ideally yes, but if you have never been caught with an incorrect forecast you probably have not got too many hours under your belt, It is also very different operating commercially in light aircraft than someone who can choose to only fly in CAVOK conditions.

[Piltdown Man]

This thread is amazing! There are dead bodies and wreckage strew all over the place, well qualified professional pilots saying flying a DIY approach is a stupid thing to do and a bunch of plonkers saying it's OK. To those who think flying a home brewed approach is OK, may make one request please: Fill in a donor card. Your brain, although unused, will not be involved in any transplant.

PM

[alex90]

Fill in a donor card. Your brain, although unused, will not be involved in any transplant.

Shame they normally are beyond recovery by the time the ambulance gets to them...

This thread is making me feel as though there hasn't been enough lobbying to the UK CAA to allow GPS instrument approaches at uncontrolled airfields to be more widely accepted / cheaper (re: paperwork / CAA application fees).

Surely if the UK CAA had a duty of care, and had to ensure safety was paramount - all airfields in the UK would have GPS approaches.

[1800ed]

I've got a copy of a 'discrete procedure' for Wellesbourne - looks like it originates from 1995 and uses the HON VOR and DME. Is this the same as an unpublished approach? I've only ever used it during my IMCr training and I'm a bit unsure about what it is really!

[foxmoth]

My understanding is that this is a training procedure, only to be used in VMC, another interesting one is the VOR procedure at Goodwood - this USED to be a published procedure but got withdrawn, so how many would use that down to its (once) published minima?

[cessnapete]

Foxmoth
Flew the old GWC VOR/DME NPA and Hold on my last IR renewal. Worked a treat, and free!