Judging Visibilty at minima MDA/DA?
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Judging Visibilty at minima MDA/DA?
Hello All,
Can someone point me in the direction of where I can find methods for establishing what the Vis is at the minima, ( I know its pilot judged)
is there a CAAP or something in the Jepps to help aid the pilot in this? cant seem to find any specific.
For E.g. I've picked up from a friend who showed me how the gradient on a SI 2d meets the MDA its usually close to the Vis req on the chart but not always. and try count runway lights and centre line markings. etc.
Hope any of this makes sense....
Can someone point me in the direction of where I can find methods for establishing what the Vis is at the minima, ( I know its pilot judged)
is there a CAAP or something in the Jepps to help aid the pilot in this? cant seem to find any specific.
For E.g. I've picked up from a friend who showed me how the gradient on a SI 2d meets the MDA its usually close to the Vis req on the chart but not always. and try count runway lights and centre line markings. etc.
Hope any of this makes sense....
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For precision approaches with approach lighting it is obvious to use these lights (that might be what you meant in the OP). As for NPAs to runways without approach lighting it depends on whether the approach is runway aligned or not, the former being much easier in my opinion to judging vis as you are used to judging distance from that angle to the runway.
As you mentioned about the SI minima usually matching the distance you will be at the MDA on descent profile, this usually works great (however check out the VOR R17 at Canberra, you get to MAPt further from the runway than the min vis required for SI approach)
Try considering the length of the runway and how many 'runways' you can see.
A thorough approach brief with reference to the vis info from the ATIS/AWS/observations is a must so that you can more accurately prepare for what you will see at the minima.
As you mentioned about the SI minima usually matching the distance you will be at the MDA on descent profile, this usually works great (however check out the VOR R17 at Canberra, you get to MAPt further from the runway than the min vis required for SI approach)
Try considering the length of the runway and how many 'runways' you can see.
A thorough approach brief with reference to the vis info from the ATIS/AWS/observations is a must so that you can more accurately prepare for what you will see at the minima.
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LeiYingLo
thanks for the thought.
I understand, its all up to pilot discretion what is indeed for e.g "4.2 km"
I get to the minima make my own decision as to wether it "is or is not" and go from there..
I can use the atis or awis to build a "mental picture" as what to expect but cannot use it as a hard and fast 'yes or no'
or put another way, other than RVR and pilot discretion. is there any other method that is 100% stand up in court??
Hope this makes sense.
thanks for the thought.
I understand, its all up to pilot discretion what is indeed for e.g "4.2 km"
I get to the minima make my own decision as to wether it "is or is not" and go from there..
I can use the atis or awis to build a "mental picture" as what to expect but cannot use it as a hard and fast 'yes or no'
or put another way, other than RVR and pilot discretion. is there any other method that is 100% stand up in court??
Hope this makes sense.
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A rule of thumb I was told for ILS approaches, at the DA you should see,
- For 800m vis, the start of the HIALs;
- For 1.2km vis, all the HIALs and at least the runway end lights;
- For 1.5km vis, runway end lights, and 'at least some' of the runway edge lighting.
Quick decision needed anyway!
- For 800m vis, the start of the HIALs;
- For 1.2km vis, all the HIALs and at least the runway end lights;
- For 1.5km vis, runway end lights, and 'at least some' of the runway edge lighting.
Quick decision needed anyway!
Last edited by wishiwasupthere; 18th Feb 2016 at 08:39.
Have a look in your Jeppesen/AIP at the runway approach lights and marking distances.
You will thence able to work out what your visibility is at the minima based on what airfield infrastructure you can see.
For instance there will be 5 cross bars spaced at 150m. It is 900m from the start of the HIAL to the green threshold lights.
On a standard cat 1 ILS at roughly 200 feet AGL (a typical ILS minima) on a 3 degree path, with 800m vis you will be above the 1st cross bar and should be able to see at least the other 4 cross bars and very shortly after the threshold lights.
You will certainly not be able to see the touchdown zone or papi at the minima with 800m vis.
Hope this helps.
You will thence able to work out what your visibility is at the minima based on what airfield infrastructure you can see.
For instance there will be 5 cross bars spaced at 150m. It is 900m from the start of the HIAL to the green threshold lights.
On a standard cat 1 ILS at roughly 200 feet AGL (a typical ILS minima) on a 3 degree path, with 800m vis you will be above the 1st cross bar and should be able to see at least the other 4 cross bars and very shortly after the threshold lights.
You will certainly not be able to see the touchdown zone or papi at the minima with 800m vis.
Hope this helps.
HAT at minima, convert @317ft/nm,convert to metres, add 160m (from memory check design criteria) will give vis .required to see runway end or app lights.Accounts for all the odd vis req for Non prec app.
Otherwise it's is the amazing pilot ability to judge vis of eg 3200m in rain.
It's all in the books!
Otherwise it's is the amazing pilot ability to judge vis of eg 3200m in rain.
It's all in the books!
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SI is straight in approach or runway aligned
No. And if there was how could anyone prove you otherwise? At the end of the day you are paid to be there at the pointy end to make an assessment of the weather and a safe decision as a result of that.
No. And if there was how could anyone prove you otherwise? At the end of the day you are paid to be there at the pointy end to make an assessment of the weather and a safe decision as a result of that.
HAT at minima, convert @317ft/nm,convert to metres, add 160m ... that's only approximate.
Wouldn't you be better using: HAT (on QNH) corrected for sea-level surface temperature, divide by 317, add 160m plus 18 * surface gradient of the HIAL; divide that total by the number of HIRLs you can see, add your birthday and then add the last 3 digits together ... that will give the day of the week for Christmas Day next year.
Of course, one of those little solar powered calculator makes this formula quicker - you'll have to be prompt, nimble of fingers, and well practised, you don't have much time from 200' AGL at 150k - but that the difference between IFR and VFR pilots.
On second thoughts, maybe a battery powered calculator would be better - gets dark at night.
Wouldn't you be better using: HAT (on QNH) corrected for sea-level surface temperature, divide by 317, add 160m plus 18 * surface gradient of the HIAL; divide that total by the number of HIRLs you can see, add your birthday and then add the last 3 digits together ... that will give the day of the week for Christmas Day next year.
Of course, one of those little solar powered calculator makes this formula quicker - you'll have to be prompt, nimble of fingers, and well practised, you don't have much time from 200' AGL at 150k - but that the difference between IFR and VFR pilots.
On second thoughts, maybe a battery powered calculator would be better - gets dark at night.
Avoid imitations
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In practice it just boils down to either a single word assessment, or a two word assessment.
One word assessment: "Aaaah!" =
Go.
Two word assessment: "Aaaah....sh!t!" =
No Go.
One word assessment: "Aaaah!" =
Go.Two word assessment: "Aaaah....sh!t!" =
No Go.
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Maybe we were too simplistic back in 1987
Long. long time ago....Sillly Bims and I, along with some flight ops and flight safety folk (a joint civil/RAAF team under the Air Coordinating Committee) looked at the "rules" for commencing an instrument approach. At the time RAAF aircraft could commence one but civil aircraft could not if the reported vis was below the minima. Mainly at Canberra, but it happened elsewhere, the accusation was that RAAF aircraft were "busting the minima".
Based on trust in the professional approach of pilots and after much discussion we decided that, having executed a prescribed instrument approach to place the aircraft on final near the runway and approaching the minimas the pilot was in the best position to look ahead and, if he/she, had the "runway environment" in sight decide to go ahead and land. We thought that controllers and met folk who were possibly several kilometers away and looking the "wrong" way and without the benefit of approach and runway lighting systems designed specifically to make the runway visible in low vis conditions were not the best placed to make operational landing decisions. As a result, AOI's etc were changed.
So, you have executed a prescribed instrument approach, you are approaching or at (but certainly not below!) the minima and you look ahead and see the "runway environment" surely you can go ahead and land. No need for maths formulas, slide rules, special equipment or worry.
Standing by for incoming.
MJG
Based on trust in the professional approach of pilots and after much discussion we decided that, having executed a prescribed instrument approach to place the aircraft on final near the runway and approaching the minimas the pilot was in the best position to look ahead and, if he/she, had the "runway environment" in sight decide to go ahead and land. We thought that controllers and met folk who were possibly several kilometers away and looking the "wrong" way and without the benefit of approach and runway lighting systems designed specifically to make the runway visible in low vis conditions were not the best placed to make operational landing decisions. As a result, AOI's etc were changed.
So, you have executed a prescribed instrument approach, you are approaching or at (but certainly not below!) the minima and you look ahead and see the "runway environment" surely you can go ahead and land. No need for maths formulas, slide rules, special equipment or worry.
Standing by for incoming.
MJG
Last edited by mgahan; 18th Feb 2016 at 14:16.
No. And if there was how could anyone prove you otherwise?
Some time ago, it didn't stop CASA prosecuting a pilot for taking of with less than the prescribed minima. The FOI who "assessed" the minima was not even on the airfield in question, but driving along a road near the airfield.
It took time, effort and cubic $$$$ to "beat the wrap", the general rules that (except for low weather minima operations) the only authority for assessing the operational viz. is the pilot in command was ignored by CASA said FOI., who was, of course, subsequently backed up by "the system".
There have been a number of instances, over the years, at YSBK, when early morning fog often clears from the south, but up around Marion St., there are still wisps of fog/low cloud ---- and FOIs start a flap when they hear an (IFR) aircraft take off, ignoring the fact that the viz. on the runways can be very different to the NE corner of the airfield --- or the second floor of Fort Fumble.
Tootle pip!!
