Circling below circling MDA at night.
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Circling below circling MDA at night.
Circling approach at night where you can see the runway lights no problem, but due darkness you cannot see the ground ahead or below you. You have no idea the position of the controlling obstacle(s).
The AIP states you can commence descent on downwind leg (below the published circling MDA) in order to meet the desired descent profile for the aircraft type. Under the night conditions above, isn't that a bit dicey seeing as you cannot see the terrain below you and you are descending below the published MDA?
The AIP states you can commence descent on downwind leg (below the published circling MDA) in order to meet the desired descent profile for the aircraft type. Under the night conditions above, isn't that a bit dicey seeing as you cannot see the terrain below you and you are descending below the published MDA?
Circling below MDA at night
HSWL,
I'll think you'll find that it reads " cannot descend below MDA at night until you are in a position to establish the aircraft on a normal downwind, base or final position in a continous descent at rates of descent normal for aircraft category" . Assuming your circling off an approach, within the circling area and there are no circling restrictions, you should be in no immediate danger.
Tag
I'll think you'll find that it reads " cannot descend below MDA at night until you are in a position to establish the aircraft on a normal downwind, base or final position in a continous descent at rates of descent normal for aircraft category" . Assuming your circling off an approach, within the circling area and there are no circling restrictions, you should be in no immediate danger.
Tag
It shouldn't be dicey if you are flying a normal circuit pattern.
Otherwise the aerodrome wouldn't be there if you couldn't fly a normal circuit pattern there (day or night), otherwise there would be some type of restriction such as :
- right hand circuits on a particular runway
- no night operations ( Wyndham)
Otherwise the aerodrome wouldn't be there if you couldn't fly a normal circuit pattern there (day or night), otherwise there would be some type of restriction such as :
- right hand circuits on a particular runway
- no night operations ( Wyndham)
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HSWL,
How else will you get down below the circling minima then??
Seriously...
that is why there are "no circling areas", for night ops and less than VMC. To eliminate the areas that would not provide you with appropriate clearance on a "normal descent profile". You also need to study the spot-height obstacles on the approach chart (that's what they're on the chart for).
How else will you get down below the circling minima then??
Seriously...
that is why there are "no circling areas", for night ops and less than VMC. To eliminate the areas that would not provide you with appropriate clearance on a "normal descent profile". You also need to study the spot-height obstacles on the approach chart (that's what they're on the chart for).
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stay at circling minima until intercept of d/w,base or final using normal angles of bank and descent profiles.
This will, by design keep you clear of obstacles and normally have you descending from MDA once established on finals
This will, by design keep you clear of obstacles and normally have you descending from MDA once established on finals
WRT circling area, the old system was 3nm and now we have circling minima for different cat aircraft. Even tho the stipulation has the minima for your particular cat say catA. If the area has been surveyed for upto a catC, would you be safe using the higher cat area even tho it may not be "legal" to use it?
Regards
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RE: Higher Cat area.
Good point but as the MDA for Cat C is HIGHER than Cat B and the circling area is also LARGER wouldn't you be is a similar position re gradient of descent? Just a bit higher and further out? More limiting on cloud base and vis too...What is the advantage of it?
Good point but as the MDA for Cat C is HIGHER than Cat B and the circling area is also LARGER wouldn't you be is a similar position re gradient of descent? Just a bit higher and further out? More limiting on cloud base and vis too...What is the advantage of it?
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It's quite helpful sometimes....and perfectly legal. If you are in a cat b a/c you can maintain msa until you get to 4.2 nm then start your descent down to no lower than the cat c circling minima, then @2.66nm you will be closer to the cat b circling minima. It just means you don't have to dive from msa down to the cat b height when you get to 2.66. Safer this way, lower rates of descent when you are near the ground etc. Most of the time it works out for a normal profile. Correct me if I'm wrong. c ya.
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CJAM,
Can you please clarify this point for me?
Are you saying that you switch between Cat B and Cat C during the approach? If so, I would have to say that I don't agree with your method. You may choose to change categories, but once doing so, the approach must be completed in the newly elected category.
I would also recommend that a constant rate of descent from the applicable fix to the minima, will give you a more stabilised approach with no need to "dive down". All approaches are designed with a constant rate profile which is shown on the chart. (Although you can use the dive and drive method, in the interest of safety and passenger comfort the constant rate must be the best option IMHO)
Zhaadum,
You asked:
The one major advantage is SPEED!! and lots of it!!
Cheers, HH.
Can you please clarify this point for me?
If you are in a cat b a/c you can maintain msa until you get to 4.2 nm then start your descent down to no lower than the cat c circling minima, then @2.66nm you will be closer to the cat b circling minima.
I would also recommend that a constant rate of descent from the applicable fix to the minima, will give you a more stabilised approach with no need to "dive down". All approaches are designed with a constant rate profile which is shown on the chart. (Although you can use the dive and drive method, in the interest of safety and passenger comfort the constant rate must be the best option IMHO)
Zhaadum,
You asked:
More limiting on cloud base and vis too...What is the advantage of it?
Cheers, HH.
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heh heh, yeah tidy work HH....I was pretty tired when I wrote that and missed the fact that you guys were talking about an actual published approach. For some reason I was picturing in my mind a night visual approach and ensuring terrain clearance, just using the circling areas to gaurantee it. Does that make more sense to you now?
Zhaadum: like HH said, speed is the advantage. Most of the time you know around about what height you are going to get visual at anyway so if it is higher than the cat c circling minima you can smoke it on down at cat c speeds and spend more time eating pies before your next flight.
PS HH, your polite query was appreciated, I am now used to pruners jumping down each others throats before confirming what the other poster meant. Very refreshing!
Zhaadum: like HH said, speed is the advantage. Most of the time you know around about what height you are going to get visual at anyway so if it is higher than the cat c circling minima you can smoke it on down at cat c speeds and spend more time eating pies before your next flight.
PS HH, your polite query was appreciated, I am now used to pruners jumping down each others throats before confirming what the other poster meant. Very refreshing!
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I would have to agree with HH.
JEP/Terminal/2.1.2 does mention that an aircraft must fit into and be operated in accordance with the requirements of only one category. a) may not reduce category due to reduced operating weight & b) must increase category when actual handling speeds are in excess of those for category based on Vat.
Say you are a cat. B aircraft flying YPAD-ACTIN-W825-YLEC at night. LSALT is 5200, (if you have a TSO GPS for distance) within 25nm its 4700, within 10nm its 3500. I think the correct procedure from this point is to hold 3500 until you are 2.66nm from the field and then descend to the circling altitude of 1710 for a landing say 29.
cjam I dont think that, using the above example, one can hold at 3500 until 4.2nm for catC then descend to 1940 and when you are inside 2.66nm for catB keep on going down to 1710?
Please correct me if I am off the mark here.
JEP/Terminal/2.1.2 does mention that an aircraft must fit into and be operated in accordance with the requirements of only one category. a) may not reduce category due to reduced operating weight & b) must increase category when actual handling speeds are in excess of those for category based on Vat.
Say you are a cat. B aircraft flying YPAD-ACTIN-W825-YLEC at night. LSALT is 5200, (if you have a TSO GPS for distance) within 25nm its 4700, within 10nm its 3500. I think the correct procedure from this point is to hold 3500 until you are 2.66nm from the field and then descend to the circling altitude of 1710 for a landing say 29.
cjam I dont think that, using the above example, one can hold at 3500 until 4.2nm for catC then descend to 1940 and when you are inside 2.66nm for catB keep on going down to 1710?
Please correct me if I am off the mark here.
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Mango
A circling approach is conducted when visual at the end of an instrument approach proceedure, so if you were conducting a dme arrival at night then yes you could circle at the circleing mda within the circling area for your catagory but you cannot decend below the mda untill as mensioned before, that you meet the profile and decent rate requirements. If you have arrived visualy in the circleing area by decending to msa, then no you cannot decend to mda as you have not carried out an instrament approach and must maintain the mda/circuit alt (wichever is higher) untill you meet the decent and profile requirements. I think all this came about from the Young incident with the chieftan.
An operator who has a car217 check and training system can operate in a different catagory withe the approval of casa.
Hope this makes it as clear as mud for you and please excuse any spelling ect. as I now have a wopping headache and am off to find some panadol
Will.
A circling approach is conducted when visual at the end of an instrument approach proceedure, so if you were conducting a dme arrival at night then yes you could circle at the circleing mda within the circling area for your catagory but you cannot decend below the mda untill as mensioned before, that you meet the profile and decent rate requirements. If you have arrived visualy in the circleing area by decending to msa, then no you cannot decend to mda as you have not carried out an instrament approach and must maintain the mda/circuit alt (wichever is higher) untill you meet the decent and profile requirements. I think all this came about from the Young incident with the chieftan.
An operator who has a car217 check and training system can operate in a different catagory withe the approval of casa.
Hope this makes it as clear as mud for you and please excuse any spelling ect. as I now have a wopping headache and am off to find some panadol
Will.
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Mango:
Are you talking about a visual approach to an airport at night? (maybe you and I are the only ones that are...oops) . If you are then it is fine to use the circling minima of all the catagorys because all you are trying to do is gaurantee terrain clearance while you are visual on the airport.
Using the figures you gave, and doing it the way you suggest you will be at 3500ft until 2.66nm, in order to descend down to the cat b circling minima you will need to lose 672ft per nm (more than twice a standard descent profile), thats about 1350ft/min at 120kts, and even that is using the whole 2.66 and not reaching the minima as you enter the circuit, its to reach it overhead the dme. (I dont know the elevation of the fireld you are using).
If you start your descent from LSALT 3500 at 4.2 nm you need a ROD of 426ft/nm (much closer to the standard 300ft/nm), you will be about 2800ft at 2.66nm which is still well above your 1710 ft required and a lot better than still being at 3500ft.
For the record I agree you cannot change cat type half way through a 'published instrument approach' and should use only the minimas for that cat.
Will:
If you have arrived visually in the circling area by descending to msa, you can descend to the circling minima.If you are on a visual approach , all you are doing is maintaining terrain clearance by whatever method you see fit. Hope I haven't got the wrong end of the stick, cjam ps I think there may have been a headache induced typo "descend to mda" as opposed to "descend below mda"
Are you talking about a visual approach to an airport at night? (maybe you and I are the only ones that are...oops) . If you are then it is fine to use the circling minima of all the catagorys because all you are trying to do is gaurantee terrain clearance while you are visual on the airport.
Using the figures you gave, and doing it the way you suggest you will be at 3500ft until 2.66nm, in order to descend down to the cat b circling minima you will need to lose 672ft per nm (more than twice a standard descent profile), thats about 1350ft/min at 120kts, and even that is using the whole 2.66 and not reaching the minima as you enter the circuit, its to reach it overhead the dme. (I dont know the elevation of the fireld you are using).
If you start your descent from LSALT 3500 at 4.2 nm you need a ROD of 426ft/nm (much closer to the standard 300ft/nm), you will be about 2800ft at 2.66nm which is still well above your 1710 ft required and a lot better than still being at 3500ft.
For the record I agree you cannot change cat type half way through a 'published instrument approach' and should use only the minimas for that cat.
Will:
If you have arrived visually in the circling area by descending to msa, you can descend to the circling minima.If you are on a visual approach , all you are doing is maintaining terrain clearance by whatever method you see fit. Hope I haven't got the wrong end of the stick, cjam ps I think there may have been a headache induced typo "descend to mda" as opposed to "descend below mda"
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cjam & Will Robinson I should clarify that I am referring to visual approach at night and not instrument approaches.
At 2.66nm CAT B aircraft can descend from LSALT/MSA to the MDA=OCA.
During visual circling descent below MDA may occur when the aircraft is maintained within the circling area. Thus for a CAT B a/c that would be 2.66nm from the field and using the YLEC as an example 1710' is the circling altitude that will give you the 300' obstacal clearance required for CAT B or in other words the MDA. Because after leaving the MDA one has to do a continuous descent to the landing threshold using rates of descents and flight manouvers normal for that aircraft and during descent maintain an obstical clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the runway. Bit of a mouth full but I hope its clear
At 2.66nm CAT B aircraft can descend from LSALT/MSA to the MDA=OCA.
During visual circling descent below MDA may occur when the aircraft is maintained within the circling area. Thus for a CAT B a/c that would be 2.66nm from the field and using the YLEC as an example 1710' is the circling altitude that will give you the 300' obstacal clearance required for CAT B or in other words the MDA. Because after leaving the MDA one has to do a continuous descent to the landing threshold using rates of descents and flight manouvers normal for that aircraft and during descent maintain an obstical clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the runway. Bit of a mouth full but I hope its clear
Last edited by Mango; 19th Apr 2005 at 23:08.
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Mango and Cjam
Need just a little more info.
IFR or VFR plan.
I read the jepps as saying if you are flying at night VFR (no instrument proceedure has been commenced) then using the circling MDA is not an option. I only have jepps and a referance you can read is Terminal 3.16 Page AU23. Nice little drawing fig IAP 3.8 also dipicts the concept of circling and it is also described in 3.13.3. Effectivly in night VFR your MDA is your LSALT/MSA/circuit Alt within 3nm and your minimum terrain/ obstacle clearance is 500ft assertained from TOPOGRAPHIC charts of the area.
Will.
ps. . Also a notable warning is in 3.13.2 wich is the reason for not decending.
Need just a little more info.
IFR or VFR plan.
I read the jepps as saying if you are flying at night VFR (no instrument proceedure has been commenced) then using the circling MDA is not an option. I only have jepps and a referance you can read is Terminal 3.16 Page AU23. Nice little drawing fig IAP 3.8 also dipicts the concept of circling and it is also described in 3.13.3. Effectivly in night VFR your MDA is your LSALT/MSA/circuit Alt within 3nm and your minimum terrain/ obstacle clearance is 500ft assertained from TOPOGRAPHIC charts of the area.
Will.
ps. . Also a notable warning is in 3.13.2 wich is the reason for not decending.
Last edited by Will Robinson; 20th Apr 2005 at 04:35.
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Circling below the MDA
OR........ after you get to the MDA, start wearing your night vision goggles instead......... 
. and go straight to final....
I heard the US Army helo pilots wear these during night landings..... wonder if fixed wing pilots do as well ?
D6
. and go straight to final.... I heard the US Army helo pilots wear these during night landings..... wonder if fixed wing pilots do as well ?
D6
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Does that make more sense to you now?
HH, your polite query was appreciated, I am now used to pruners jumping down each others throats before confirming what the other poster meant. Very refreshing!
I think its time for a BIG group HUG!!
Cheers, HH.
PS: I want night vision goggles too...
Interesting points made by everyone. Take Canberra for example. Black night runway is clear as a bell, but no way can you see the hills or your height above individual hills because its night. AIP warns against using spot heights for obstacle clearance. Cat C circling MDA is 1684 ft above aerodrome reference point. That is a real high circling MDA because of hills surrounding the airport. It is misty and the viz is 4 kms.
Obviously to execute a stable three degree descent profile and keep within the 4 kms visibility in order to keep the runway in sight on downwind base and final, you would have to commence leaving the MDA on the downwind leg (just like AIP says you can).
As HSWL says its black and you cannot see the ground below you - only the runway lights.
Once you leave the protected altitude which is the published circling MDA, am I right in saying you become responsible for your own terrain clearance? Where is the most critical obstacle within 4.2 nm that gives you the required 400 ft obstacle clearance for Cat C circling? Have you got time to drag out a WAC or Military Survey chart to plot the position of the critical obstacle? Of course not.
The fact that you set up a three degree profile to the threshold plotted backwards up the intended flight path from downwind or early base certainly does not mean a thing when it comes to obstacle clearance. At night can you visually judge 400 ft above terrain on a pitch dark night with no celestial light meaning no horizon? Try it.
Even AIP states that the night azimuth splay is normally increased to 30 degrees to permit T-VASIS to be visible on base leg BUT that obstacle clearance IS NOT GUARANTEED (sorry about the capitals) until the aircraft is within the runway approach obstacle limitation surface. It also states that the T-VASIS should not be used for approach slope guidance until aligned with the runway.
So if Air Services say the VASIS will not guarantee a safe profile above obstacles until on final, what on earth is the aircraft doing descending below the MDA on downwind or base at night where obstacle clearance is not guaranteed below the MDA. Why have a MDA at all if your descent is predicated on a profile rather than height above an obstacle surface.
Clearly it is dangerous to commence descent below the circling MDA until you are established on final on the VASIS or as the AIP says - within the runway approach obstacle clearance surface.
Obviously to execute a stable three degree descent profile and keep within the 4 kms visibility in order to keep the runway in sight on downwind base and final, you would have to commence leaving the MDA on the downwind leg (just like AIP says you can).
As HSWL says its black and you cannot see the ground below you - only the runway lights.
Once you leave the protected altitude which is the published circling MDA, am I right in saying you become responsible for your own terrain clearance? Where is the most critical obstacle within 4.2 nm that gives you the required 400 ft obstacle clearance for Cat C circling? Have you got time to drag out a WAC or Military Survey chart to plot the position of the critical obstacle? Of course not.
The fact that you set up a three degree profile to the threshold plotted backwards up the intended flight path from downwind or early base certainly does not mean a thing when it comes to obstacle clearance. At night can you visually judge 400 ft above terrain on a pitch dark night with no celestial light meaning no horizon? Try it.
Even AIP states that the night azimuth splay is normally increased to 30 degrees to permit T-VASIS to be visible on base leg BUT that obstacle clearance IS NOT GUARANTEED (sorry about the capitals) until the aircraft is within the runway approach obstacle limitation surface. It also states that the T-VASIS should not be used for approach slope guidance until aligned with the runway.
So if Air Services say the VASIS will not guarantee a safe profile above obstacles until on final, what on earth is the aircraft doing descending below the MDA on downwind or base at night where obstacle clearance is not guaranteed below the MDA. Why have a MDA at all if your descent is predicated on a profile rather than height above an obstacle surface.
Clearly it is dangerous to commence descent below the circling MDA until you are established on final on the VASIS or as the AIP says - within the runway approach obstacle clearance surface.